Effects of Excipients on Metoprolol Tertrate Delivery from Biodegradable Polymeric In Situ Implants 1.1. Advanced Drug Delivery System The term â€œDrug Delivery Systemâ€? refers to the technology utilized to present the drug to the desired body site for drug release and absorption. The first drug delivery system developed was the syringe, invented in 1855, used to deliver medicine by injection. The modern transdermal patch is an example of advanced drug delivery system. The goal of any drug delivery system is to provide a therapeutic amount of drug to the proper site in the body to promptly achieve and then maintain the desired drug concentration. This idealized objective points to the two aspects most important to the drug delivery, namely: # Spatial placement: relates to targeting of a drug to a specific organ or tissue. # Temporal delivery of a drug: refers to controlling the rate of drug delivery to controlling the rate of drug delivery to the target tissue. The drug delivery technology landscape is highly competitive and rapidly evolving. The market involves both numerous startups and major players in the medical device, pharmaceutical and biotechnology industries. This is a market with intensive intellectual property protection. Products that have been brought to market or that are in clinical trials often involve combinations of technologies from multiple players, with complex licensing and strategic partnering relationships. New classes of pharmaceuticals and biologics (peptides, proteins and DNA-based therapeutics) are fueling the rapid evolution of drug delivery technology. These new drugs typically cannot be effectively delivered by conventional means. Additionally, it has been determined that, for many conventional pharmaceutical therapies, the efficacy may be improved and the side effects reduced if the therapy is administered continuously (although potentially variable rate), rather than through conventional burst release techniques (oral ingestion, injection, etc). The benefits from targeted, localized delivery of certain therapeutic agents are another driving force in this market. Additional drivers include the desire to eliminate or minimize the danger of needle stick injuries (and blood-born pathogens) to healthcare workers, increase patient compliance by simplified or reduced stigma delivery methods, reduced healthcare worker involvement and reduced health care costs. Increasingly, delivery devices and drugs will be more tightly coupled. In some cases, device development is beginning as early as the discovery phase of the pharmaceutical development process. To compete in this arena companies must be able to demonstrate the value that their combination of drugs and delivery devices and/or systems brings to the market. To improve the odds of a successful product introduction, companies must be implementing advanced development and technology portfolio plans that define the technologies and delivery devices that will be funded. Because drug development can be a 10-year undertaking, advanced development and technology portfolio plans need to be concerned with market requirements and value propositions more than a decade into the future. Short-sightedness in focusing only on nearterm shareholder needs in the face of The challenge of identifying and managing complex technology and intellectual property (IP) portfolios, such as those found in the drug delivery arena, and successfully leveraging these assets to create new opportunities is a critical element in the success of the modern, technology and IP driven firm. In todayâ€™s hypercompetitive environment, it is not enough for firms to focus only on short-term technology development based on existing core competencies and IP; they must be able to place long-
term technology bets, based on the convergence of trends in the stakeholder value chain, user base and technology development. A structured methodology for the integration and infusion of trend mining and convergence analysis (from emerging technology development, market dynamics, and user and stakeholder needs) into the technology portfolio planning process allows organizations to more effectively leverage their investments in innovation while increasing the probability of major opportunity creation – ultimately translating these discrete wins into overall firm success. 1.2. Challenges Historically, drug delivery has taken the form of injection, infusion, ingestion, and inhalation, with additional variations of each category. For example ingestion may be in tablet, capsule or liquid form; inhalation may be via use of a dry powder inhaler, an MDI, or a nebulizer. The challenge for both drug and drug delivery companies is to deliver both existing and emerging drug technologies in a manner that improves the benefits to the patients, healthcare workers and the healthcare system. Areas that are being targeted for improvements through device development include: • Improved efficacy • Reduced side effects • Continuous dosing (sustained release) • Reduced pain from administration • Increased ease of use • Increased use compliance • Improved mobility • Decreased involvement of healthcare workers • Improved safety for healthcare workers • Reduced environmental impact (elimination of CFC’s) To provide these benefits, a number of approaches are being (or in some cases have been) developed. The common thread running through the approaches is the concept of selfadministered, targeted, sustained release with increased bioavailability. Determining which of the emerging approaches best meets stakeholder needs is a complex, multifaceted problem. Although ingestion is probably the most widely accepted form of delivery it presents difficulties for a number of important classes of drugs. Many drug delivery scientists view oral delivery as the ideal drug delivery method. In the case of proteins and peptides, historical oral delivery mechanisms can only delivery bioavailabities of a few percent. In some cases, dose limiting toxicity levels are caused by lack of selectivity. Although oral delivery meets the need for self-administered drugs, targeted, sustained release and increased bioavailability present the areas of difficulty in meeting the emerging value proposition. To address this difficulty, companies are developing micro-fabricated drug delivery systems. Technologies such as nano-pore membranes and micro-particles enable the drug to survive stomach acids and be released at specific targeted areas of the gastrointestinal tract. These technologies are being developed to provide more efficient drug absorption and enhanced bioavailability. Pulmonary delivery provides a number of benefits particularly with regard to absorption area and avoidance of first pass metabolism in the liver. However, meeting the sustained-release goal is somewhat problematic. The lungs tend to expel materials that are introduced and it is
therefore difficult to keep the drug in the lung long enough for the sustained release to be effective. Additional challenges revolve around elimination of excipient (enabling delivery of a neat drug), elimination of CFC propellants (in the case of MDI), reduction of the stigma associated with inhalers, and ease of use. A number of companies are working in this arena with technologies varying from ultrasonic de-aggregation, to heat vaporization of the drug. Transdermal patches have been used for a number of years. To improve their effectiveness for a broader range of drugs, devices are being developed that disrupt the skin barrier to allow drug transfer to the interstitial fluid. Technologies are being developed that range from ultrasonic disruption of the skin, to microprojections, to using electro-transport to drive molecules though the skin barrier. These technologies are being developed individually and in various combinations. Although from a patient standpoint the elimination of injections is ideal, indications are that injection will remain a necessary means of drug delivery. To minimize the pain, biohazard, cost and inconvenience associated with injections, companies are working to reduce the negative aspects of this delivery method. Along these lines, advances in needle-free injection, micro needle injection and MEMS syringes are under development. To minimize the number of injections required new implants and time release approaches are in development. Meeting the need for better bioavailability and reduced side effects is not being left only to the mechanical delivery systems; methods are being developed to better target the drug once it is introduced into the body. Ultrasound or other energy sources are being used to activate the drug once it reaches the targeted location. Receptors are being used to target specific cells, and in the event that a targeted cell does not have a required receptor, methods for adding receptors for a specific drug are being developed. 1.3. Competitive Landscape A top-level view of the competitive landscape and some of the companies involved in various areas has been developed as follows: Sustained Release Technology • Injectable: MacroMed (Oligosphere); Alkermes (ProLease, Medisorb) • Oral: (MacroMed (SQ2Gel); Altus Biologics (Crystalized proteins); Alkermes (PLG microspheres); Spherics (sticky spheres); DepoMed (GR System) • Ocular: InSite Vision (Durasite polymer eye drops) • Pulmonary: Acusphere (microspheres); Alkermes (AIR microparticles) Targeted Delivery Technology • Ultrasound activated: Point Medical (biSpheres); ImaRx (NanoInjection) • RF activated: Scintipharma (Intelesite capsule) Enhanced Absorption/Transport Technology • Enhanced transmucosal absorption: Generex Biotechnology (oral mucosa target); Anesta Corp. (OTS oral mucosa target) • Enhanced transdermal absorption: Sontra (ultrasonic); Antares (CombiGel -- transdermal gel); Altea (micropore technology); TransPharma Medical; Norwood Abbey (laser) Implantable Technology • Constant release: Alza (DUROS Implant); Guilford Pharmaceuticals (polymer wafers)
• Controllable release: MicroCHIPS (programmable MEMS implant) Pulmonary Systemic Delivery • Dry Powder: Nektar Therapeutics (formerly Inhale Therapeutic Systems (inhance, PulmoSpheres)); Alkermes (AIR); Meridica (Xcelovair); GlaxoSmithKline (Diskus, Advair) • Liquid Aerosol: Aradigm (AERx); Evit Labs (Sonik, LDI); Meridica (Xcelovent); Chrysalis Technologies ; GlaxoSmithKline (non CFC MDI’s) Transdermal/Intramuscular Technology • Bolus injection: Becton Dickenson etc. • Gas-based injection: Bioject (Biojector 2000); PowderJect (powder-based injection) • Mechanical injection: Bioject (Vitajet 3); antares/Medi-Ject (Vision -- Insulin injector, ZomaJet, SciToJet); Norwood Abbey • Micro needles: Altea/Elan (MEDIPAD); BioValve; Alza (Macroflux); MEMS Syringe (Berkeley); Norwood Abbey • Electrotransport (Iontophoresis): Alza (E-Trans); Hisamitu Pharma; Iomed Clinical Systems; Vyteris; 3M Drug Delivery Systems • Ambulatory “Wearable/Reusable” Infusion: Abbott (AIM); Medtronic (MiniMed); PROMED (Smart Dose); Electronic Infusion Systems (I-Flow, VIVUS 4000); I-Flow (Homepump Eclipse and C Series, Paragon); Animas (IR 1200 insulin pump) • Ambulatory “Disposable” Infusion: Insulet (Insulin, basal and bolus) 1.4. Meeting the Challenge Meeting the challenges that are presented by emerging drug technologies and the requirement for improved stakeholder benefits, including the impact of the aging population, will require some combination of drugs, delivery devices and mechanisms currently underdevelopment, as well as the identification and integration of new yet to be defined technologies. Complicating the need for self-administered, targeted, sustained release with increased bioavailability, is the need to improve patient compliance. To achieve improved compliance will require further simplification of the user experience. The next step can easily be envisioned as involving further integration of devices and drugs to provide means to deliver multiple therapies in a simple, pain free, unobtrusive, and targeted sustained release device. The proper combination of technology portfolios, intellectual property, market and stakeholder understanding required achieve this next step is the challenge on the horizon. Making sense of this complex interaction of competing companies, intellectual property, core competencies, stakeholder needs, and technology trends, in a manner that will meet the corporate goals requires a structured methodology, such as the Innovation Genesis framework, to drive corporate planning and decision-making. Based on the corporate strategies, portfolio investments can be managed to meet the appropriate mix of high and low risk activities for the company. By establishing a deep understanding of convergent trend (and the conditions and drivers underlying the trends), and by maintaining knowledge of emerging technologies outside the core competencies of the firm, IP and technology portfolio strategies can be optimized. Visibility of long range evolution scenarios enables actionable short and mid range activities and decisions that are aligned with the long term goals. In short, this structured methodology enables Strategic Innovation. The approach enables informed technology investments that deliver meaningful business consequences, and the development of new ideas that fundamentally change the basis of competition within the drug delivery industry.
1.5. Biodegradable Implants The biodegradable implant technology is a platform for parenteral delivery of drugs for periods of weeks to six months or more. The technology is based on the use of biodegradable polyester excipients, which have a proven record of safety and effectiveness in approved drug delivery and medical device products. 1.5.1. Overview of the Technology The biodegradable implant technology is based on the use of biodegradable polyesters as excipients for implantable drug formulations. This family of materials, which is used extensively in medical devices and drug delivery applications, includes the polymers and copolymers prepared from glycolide, DL-lactide, L-lactide, and e-caprolactone. These thermoplastic materials are stable when dry but degrade by simple hydrolysis of the polymer backbone when exposed to an aqueous environment. The degradation times and physical properties of the biodegradable excipient can be engineered to achieve a wide variety of drug delivery goals by adjusting monomer composition and distribution, polymer molecular weight, and endgroup chemistry. In addition to polymer engineering, the physical structure of implants is designed to achieve the desired therapeutic outcome. The overall form of the implant is typically a small rod or pellet that can be placed by means of a needle or trochar. The composition of the rod or pellet can be monolithic, where the drug is uniformly dispersed throughout the excipient. Alternatively, reservoir-type designs are also possible in which the rod or pellet is composed of a drug-rich core surrounded by a rate-controlling membrane. Depending on drug chemistry and desired kinetics, the membrane may or may not contain drug. Typically, the drug and excipient are mixed together, and the mixture is formed into a fiber, rod, tablet, or pellet by an extrusion or molding process. The ratecontrolling membrane, if required, may be applied during or subsequent to the core-forming process. The release of the drug from the implant can occur by degradation of the excipient, diffusion of the drug through the excipient or pores in the excipient, or a combination of degradation and diffusion. The relative contributions of these processes and the overall release profile are controlled by a number of variables including drug content, excipient composition, and implant design. As a result, a variety of drug delivery profiles including first-order, zero-order, delayed, and biphasic drug release can all be achieved with the implant technology.
Durin implant can be formulated with drug loading as high as 80 wt %. Thus very small implants are able to provide prolonged therapy. 1.5.2. Peptides
Peptides are not typically permeable through dense biodegradable polymeric membranes; hence they are difficult to deliver with polymer implants. We have done a great deal of work with LHRH analogs such as leuprolide and goserelin, and have found that excipient properties can be modified so that these larger, water-soluble compounds can be delivered in a near zero-order manner. The release of a peptide from biodegradable implants compared to conventionally design hydrophobic DL-PLG implants. The implant demonstrates near zeroorder release with no initial burst. These implants were later used in Phase I human clinical trials. 1.5.3. Safety and Toxicology The biodegradable polyester excipients used in implants have been approved in over 30 medical devices and drug delivery systems since the first suture based on poly-glycolide was approved by the FDA in the 1970â€˜s. One notable example of a commercially successful biodegradable implant formulation is ZoladexÂŽ, which delivers goserelin acetate for the treatment of prostate cancer. These excipients and the products based on them have a long history of use and acceptance by the FDA and other regulatory agencies. 1.5.4. Manufacturing Typically, use melt extrusion at modest temperatures to produce biodegradable implants for drug delivery. The active and excipients are combined and fed to a melt extruder to produce a bulk rod, which is then cut to produce the unit dose. For coaxial, membrane-controlled implants, two extruders are operated to simultaneously produce the core and membrane in a continuous process. For particularly heat labile compounds, the technology is also compatible with proprietary manufacturing methods other than extrusion that ensure drug stability. Because implants are produced using continuous manufacturing processes, batch size is determined by the length of the extrusion run. 1.6. Non Biodegradable Implants Non Biodegradable implants are available as monolithic systems or reservoir systems. The release kinetics of drugs from such system depends on both the solubility and diffusion coefficient of the drug in the polymer. In case of non biodegradable polymeric implant, a mini surgery is needed to remove the polymer from the body. 1.7. Polymer: Poly Lactic Acid The disposal problem due to non-degradable petroleum based plastics has raised the demand for biodegradable polymers as means of reducing the environmental impact. Several aliphatic polyesters having similar material properties comparable to conventional plastics have been developed such as: poly (lactide) (PLA), polyhydroxyalkanoates (PHAs), poly (caprolactone) (PCL), and poly (butylene succinate) (PBS). Among these biodegradable polymers, PLA has received the most attention because its raw material, L-lactic acid can be efficiently produced by fermentation from renewable resources such as starchy materials and sugars. Moreover, it has good properties such as high melting point (175 Â°C), high degree of transparency, and ease of fabrication. PLA can be synthesized either by condensation polymerization of lactic acid or by ring opening polymerization of lactide (the cyclic dimer of lactic acid). This polymer exists in three stereoforms: poly (Llactide) (L-PLA), poly (D-lactide) (D-PLA), and poly (DL-lactide) (DL-PLA). L-PLA and D-
PLA are semicrystalline and exhibit high tensile strength and low elongation. On the other hand, DL-PLA is more amorphous exhibiting a random distribution of both isomeric forms of lactic acid depending on the amount of D or L. 1.7.1. Medical Applications of PLA Currently, PLA is primarily used for medical applications such as drug delivery devices, absorbable sutures, and as a material for medical implants and other related applications. The mechanical properties of PLA, which are comparable to polystyrene and polyethylene, have also stimulated interest in its application as packaging materials. Hence, it would be of interest to study the biodegradation mechanisms and biological treatment of PLA. The degradation of PLA has been studied several years ago, but understanding on this subject is still inadequate. This is clearly evidenced by lack of information on the mechanisms involved and the microorganisms associated with the degradation. Majority of reports concluded that PLA degradation occurred strictly through hydrolysis with no enzymatic involvement. Other reports suggest that enzymes have a significant role in the degradation of PLA 1.7.2. Factors influencing the biodegradation behavior of PLA In general, polymer degradation takes place through the scission of the main chains or side chains of polymers. Different degradation mechanisms whether chemical or biological can be involved in the degradation of biodegradable polyesters. A combination of these mechanisms can also happen at some stage of degradation. There are several important factors that affect the biodegradability of polymers. These are: (1) Factors associated with the first-order structure (chemical structure, molecular weight and molecular weight distribution); (2) Factors associated with the higher order structure [glass transition temperature (Tg), melting temperature (Tm), crystallinity, crystal structure and modulus of elasticity]; and (3) Factors related to surface conditions (surface area, hydrophilic, and hydrophobic properties) (Nishida and Tokiwa 1992). 1.7.3. Biodegradation of PLA Poly (lactide) (PLA) has been developed and made commercially available in recent years. One of the major tasks to be taken before the widespread application of PLA is the fundamental understanding of its biodegradation mechanisms. Most of the PLA-degrading microorganisms phylogenetically belong to the family of Pseudonocardiaceae and related genera such as Amycolatopsis, Lentzea, Kibdelosporangium, Streptoalloteichus, and Saccharothrix. Several proteinous materials such as silk fibroin, elastin, gelatin, and some peptides and amino acids were found to stimulate the production of enzymes from PLA-degrading microorganisms. In addition to proteinase K from Tritirachium album, subtilisin, a microbial serine protease and some mammalian serine proteases such as Îą-chymotrypsin, trypsin, and elastase could also degrade PLA. 1.8. Drug: Metoprolol Tartrate
Metoprolol tartrate USP, is a selective beta1-adrenoreceptor blocking agent, available as 50and 100-mg tablets for oral administration and in 5-mL ampoules for ministration. Each ampul contains a sterile solution of metoprolol tartrate USP, 5 mg, and sodium chloride USP, 45 mg, and water for injection USP. Metoprolol tartrate USP is (Âą)-1-v (Isopropylamino)-3[p-(2-methoxyethyl) phenoxy]-2-propanol L-(+)-tartrate (2:1) salt. Metoprolol tartrate USP is a white, practically odorless, crystalline powder with a molecular weight of 684.82. It is very soluble in water; freely soluble in methylene chloride, in chloroform, and in alcohol; slightly soluble in acetone; and insoluble in ether.
Pic: Chemical structure of Metoprolol Tartrate 1.8.1. Physical Data Melt Point: 1200 c (2480 F) 1.8.2. Pharmacokinetic Data Bioavailability: Metabolism: Half life: Excretion:
12% Hepatic 3-7 hours Renal
1.8.3. Inactive Ingredients Tablets contain cellulose compounds, colloidal silicon dioxide, D&C Red No. 30 aluminum lake (50-mg tablets), FD&C Blue No. 2 aluminum lake (100-mg tablets), lactose, magnesium stearate, polyethylene glycol, propylene glycol, povidone, sodium starch glycolate, talc, and titanium dioxide. 1.8.4. CLINICAL PHARMACOLOGY Metoprolol is a beta-adrenergic receptor blocking agent. In vitro and in vivo animal studies have shown that it has a preferential effect on beta1 adrenoreceptors, chiefly located in cardiac muscle. This preferential effect is not absolute, however, and at higher doses, Metoprolol also inhibits beta2 adrenoreceptors, chiefly located in the bronchial and vascular musculature. Clinical pharmacology studies have confirmed the beta-blocking activity of metoprolol in man, as shown by (1) reduction in heart rate and cardiac output at rest and upon exercise, (2) reduction of systolic blood pressure upon exercise, (3) inhibition of isoproterenol-induced tachycardia, and (4) reduction of reflex orthostatic tachycardia.
Relative beta1 selectivity has been confirmed by the following: (1) In normal subjects, Metoprolol is unable to reverse the beta2-mediated vasodilating effects of epinephrine. This contrasts with the effect of nonselective (beta1 plus beta2) beta blockers, which completely reverse the vasodilating effects of epinephrine. (2) In asthmatic patients, Metoprolol reduces FEV1 and FVC significantly less than a nonselective beta blocker, propranolol, at equivalent beta1-receptor blocking doses. Metoprolol has no intrinsic sympathomimetic activity, and membrane-stabilizing activity is detectable only at doses much greater than required for beta blockade. Metoprolol crosses the blood-brain barrier and has been reported in the CSF in a concentration 78% of the simultaneous plasma concentration. Animal and human experiments indicate that Metoprolol slows the sinus rate and decreases AV nodal conduction. In controlled clinical studies, Metoprolol has been shown to be an effective antihypertensive agent when used alone or as concomitant therapy with thiazide-type diuretics, at dosages of 100- 450 mg daily. In controlled, comparative, clinical studies, Metoprolol has been shown to be as effective an antihypertensive agent as propranolol, methyldopa, and thiazide-type diuretics, and to be equally effective in supine and standing positions. The mechanism of the antihypertensive effects of beta-blocking agents has not been elucidated. However, several possible mechanisms have been proposed: (1) competitive antagonism of catecholamines at peripheral (especially cardiac) adrenergic neuron sites, leading to decreased cardiac output; (2) a central effect leading to reduced sympathetic outflow to the periphery; and (3) suppression of renin activity. By blocking catecholamine-induced increases in heart rate, in velocity and extent of myocardial contraction, and in blood pressure, Metoprolol reduces the oxygen requirements of the heart at any given level of effort, thus making it useful in the long-term management of angina pectoris. However, in patients with heart failure, beta-adrenergic blockade may increase oxygen requirements by increasing left ventricular fiber length and end-diastolic pressure. Although beta-adrenergic receptor blockade is useful in the treatment of angina and hypertension, there are situations in which sympathetic stimulation is vital. In patients with severely damaged hearts, adequate ventricular function may depend on sympathetic drive. In the presence of AV block, beta blockade may prevent the necessary facilitating effect of sympathetic activity on conduction. Beta2-adrenergic blockade results in passive bronchial constriction by interfering with endogenous adrenergic bronchodilator activity in patients subject to bronchospasm and may also interfere with exogenous bronchodilators in such patients. In controlled clinical trials, Metoprolol, administered two or four times daily, has been shown to be an effective antianginal agent, reducing the number of angina attacks and increasing exercise tolerance. The dosage used in these studies ranged from 100-400 mg daily. A controlled, comparative, clinical trial showed that Metoprolol was indistinguishable from propranolol in the treatment of angina pectoris. In a large (1,395 patients randomized), double-blind, placebo-controlled clinical study, Metoprolol was shown to reduce 3-month mortality by 36% in patients with suspected or
definite myocardial infarction. Patients were randomized and treated as soon as possible after their arrival in the hospital, once their clinical condition had stabilized and their hemodynamic status had been carefully evaluated. Subjects were ineligible if they had hypotension, bradycardia, peripheral signs of shock, and/or more than minimal basal rales as signs of congestive heart failure. Initial treatment consisted of intravenous followed by oral administration of Metoprolol or placebo, given in a coronary care or comparable unit. Oral maintenance therapy with Metoprolol or placebo was then continued for 3 months. After this double-blind period, all patients were given Metoprolol and followed up to 1 year. The median delay from the onset of symptoms to the initiation of therapy was 8 hours in both the Metoprolol- and placebo-treatment groups. Among patients treated with Metoprolol, there were comparable reductions in 3-month mortality for those treated early (â‰¤8 hours) and those in whom treatment was started later. Significant reductions in the incidence of ventricular fibrillation and in chest pain following initial intravenous therapy were also observed with Metoprolol and were independent of the interval between onset of symptoms and initiation of therapy. The precise mechanism of action of Metoprolol in patients with suspected or definite myocardial infarction is not known. In this study, patients treated with metoprolol received the drug both very early (intravenously) and during a subsequent 3-month period, while placebo patients received no betablocker treatment for this period. The study thus was able to show a benefit from the overall metoprolol regimen but cannot separate the benefit of very early intravenous treatment from the benefit of later beta-blocker therapy. Nonetheless, because the overall regimen showed a clear beneficial effect on survival without evidence of an early adverse effect on survival, one acceptable dosage regimen is the precise regimen used in the trial. Because the specific benefit of very early treatment remains to be defined however, it is also reasonable to administer the drug orally to patients at a later time as is recommended for certain other beta blockers. 1.8.5. Pharmacokinetics In man, absorption of Metoprolol is rapid and complete. Plasma levels following oral administration, however, approximate 50% of levels following intravenous administration, indicating about 50% first-pass metabolism. Plasma levels achieved are highly variable after oral administration. Only a small fraction of the drug (about 12%) is bound to human serum albumin. Metoprolol is a racemic mixture of R- and S-enantiomers. Less than 5% of an oral dose of Metoprolol is recovered unchanged in the urine; the rest is excreted by the kidneys as metabolites that appear to have no clinical significance. The systemic availability and halflife of Metoprolol in patients with renal failure do not differ to a clinically significant degree from those in normal subjects. Consequently, no reduction in dosage is usually needed in patients with chronic renal failure. Metoprolol is extensively metabolized by the cytochrome P450 enzyme system in the liver. The oxidative metabolism of Metoprolol is under genetic control with a major contribution of the polymorphic cytochrome P450 isoform 2D6 (CYP2D6). There are marked ethnic
differences in the prevalence of the poor metabolizers (PM) phenotype. Approximately 7% of Caucasians and less than 1% Asian are poor metabolizers. Poor CYP2D6 metabolizers exhibit several-fold higher plasma concentrations of Metoprolol than extensive metabolizers with normal CYP2D6 activity. The elimination half-life of metoprolol is about 7.5 hours in poor metabolizers and 2.8 hours in extensive metabolizers. However, the CYP2D6 dependent metabolism of metoprolol seems to have little or no effect on safety or tolerability of the drug. None of the metabolites of metoprolol contribute significantly to its betablocking effect. Significant beta-blocking effect (as measured by reduction of exercise heart rate) occurs within 1 hour after oral administration, and its duration is dose-related. For example, a 50% reduction of the maximum registered effect after single oral doses of 20, 50, and 100 mg occurred at 3.3, 5.0, and 6.4 hours, respectively, in normal subjects. After repeated oral dosages of 100 mg twice daily, a significant reduction in exercise systolic blood pressure was evident at 12 hours. Following intravenous administration of metoprolol, the urinary recovery of unchanged drug is approximately 10%. When the drug was infused over a 10-minute period, in normal volunteers, maximum beta blockade was achieved at approximately 20 minutes. Doses of 5 mg and 15 mg yielded a maximal reduction in exercise-induced heart rate of approximately 10% and 15%, respectively. The effect on exercise heart rate decreased linearly with time at the same rate for both doses, and disappeared at approximately 5 hours and 8 hours for the 5mg and 15-mg doses, respectively. Equivalent maximal beta-blocking effect is achieved with oral and intravenous doses in the ratio of approximately 2.5:1. There is a linear relationship between the log of plasma levels and reduction of exercise heart rate. However, antihypertensive activity does not appear to be related to plasma levels. Because of variable plasma levels attained with a given dose and lack of a consistent relationship of antihypertensive activity to dose, selection of proper dosage requires individual titration. In several studies of patients with acute myocardial infarction, intravenous followed by oral administration of metoprolol caused a reduction in heart rate, systolic blood pressure, and cardiac output. Stroke volume, diastolic blood pressure, and pulmonary artery end diastolic pressure remained unchanged. In patients with angina pectoris, plasma concentration measured at 1 hour is linearly related to the oral dose within the range of 50-400 mg. Exercise heart rate and systolic blood pressure are reduced in relation to the logarithm of the oral dose of metoprolol. The increase in exercise capacity and the reduction in left ventricular ischemia are also significantly related to the logarithm of the oral dose. In elderly subjects with clinically normal renal and hepatic function, there are no significant differences in metoprolol pharmacokinetics compared to young subjects. 1.8.6. INDICATIONS AND USAGE Hypertension Metoprolol tablets are indicated for the treatment of hypertension. They may be used alone or in combination with other antihypertensive agents. Angina Pectoris
Metoprolol is indicated in the long-term treatment of angina pectoris. Myocardial Infarction Metoprolol ampuls and tablets are indicated in the treatment of hemodynamically stable patients with definite or suspected acute myocardial infarction to reduce cardiovascular mortality. Treatment with intravenous Metoprolol can be initiated as soon as the patient’s clinical condition allows (see DOSAGE AND ADMINISTRATION, CONTRAINDICATIONS, and WARNINGS). Alternatively, treatment can begin within 3 to 10 days of the acute event (see DOSAGE AND ADMINISTRATION). 1.8.7. CONTRAINDICATIONS Hypertension and Angina Metoprolol is contraindicated in sinus bradycardia, heart block greater than first degree, cardiogenic shock, and overt cardiac failure (see WARNINGS). Hypersensitivity to Metoprolol and related derivatives, or to any of the excipients; hypersensitivity to other beta blockers (cross sensitivity between beta blockers can occur), Sick-sinus syndrome, Severe peripheral arterial circulatory disorders. Myocardial Infarction Metoprolol is contraindicated in patients with a heart rate <45 beats/min; second- and thirddegree heart block; significant first-degree heart block (P-R interval ≥0.24 sec); systolic blood pressure <100 mmHg; or moderate-to-severe cardiac failure (see WARNINGS). 1.8.8. WARNINGS 18.104.22.168. Hypertension and Angina Cardiac Failure: Sympathetic stimulation is a vital component supporting circulatory function in congestive heart failure, and beta blockade carries the potential hazard of further depressing myocardial contractility and precipitating more severe failure. In hypertensive and angina patients who have congestive heart failure controlled by digitalis and diuretics, Metoprolol should be administered cautiously. In Patients without a History of Cardiac Failure: Continued depression of the myocardium with beta-blocking agents over a period of time can, in some cases, lead to cardiac failure. At the first sign or symptom of impending cardiac failure, patients should be fully digitalized and/or given a diuretic. The response should be observed closely. If cardiac failure continues, despite adequate digitalization and diuretic therapy, Metoprolol should be withdrawn. Ischemic Heart Disease: Following abrupt cessation of therapy with certain beta-blocking agents, exacerbations of angina pectoris and, in some cases, myocardial infarction have occurred. When discontinuing chronically administered Metoprolol, particularly in patients with ischemic heart disease, the dosage should be gradually reduced over a period of 1-2 weeks and the patient should be carefully monitored. If angina markedly worsens or acute coronary insufficiency develops, Metoprolol administration should be reinstated promptly, at least temporarily, and other measures appropriate for the management of unstable angina should be taken. Patients should be warned against interruption or discontinuation of therapy without the physician’s advice. Because coronary artery disease is common and may be unrecognized, it may be prudent not to discontinue Metoprolol therapy abruptly even in patients treated only for hypertension.
Bronchospastic Diseases: PATIENTS WITH BRONCHOSPASTIC DISEASES SHOULD, IN GENERAL, NOT RECEIVE BETA BLOCKERS, including Metoprolol. Because of its relative beta1 selectivity, however, Metoprolol may be used with caution in patients with bronchospastic disease who do not respond to, or cannot tolerate, other antihypertensive treatment. Since beta1 selectivity is not absolute, a beta2-stimulating agent should be administered concomitantly, and the lowest possible dose of Metoprolol should be used. In these circumstances it would be prudent initially to administer Metoprolol in smaller doses three times daily, instead of larger doses two times daily, to avoid the higher plasma levels associated with the longer dosing interval (see DOSAGE AND ADMINISTRATION). Major Surgery: Chronically administered beta-blocking therapy should not be routinely withdrawn prior to major surgery; however, the impaired ability of the heart to respond to reflex adrenergic stimuli may augment the risks of general anesthesia and surgical procedures. Diabetes and Hypoglycemia: Metoprolol should be used with caution in diabetic patients if a betablocking agent is required. Beta blockers may mask tachycardia occurring with hypoglycemia, but other manifestations such as dizziness and sweating may not be significantly affected. Pheochromocytoma: If Metoprolol is used in the setting of pheochromocytoma, it should be given in combination with an alpha blocker, and only after the alpha blocker has been initiated. Administration of beta blockers alone in the setting of pheochromocytoma has been associated with a paradoxical increase in blood pressure due to the attenuation of betamediated vasodilatation in skeletal muscle. Thyrotoxicosis: Beta-adrenergic blockade may mask certain clinical signs (e.g., tachycardia) of hyperthyroidism. Patients suspected of developing thyrotoxicosis should be managed carefully to avoid abrupt withdrawal of beta blockade, which might precipitate a thyroid storm. 22.214.171.124. Myocardial Infarction Cardiac Failure: Sympathetic stimulation is a vital component supporting circulatory function, and beta blockade carries the potential hazard of depressing myocardial contractility and precipitating or exacerbating minimal cardiac failure. During treatment with Metoprolol, the hemodynamic status of the patient should be carefully monitored. If heart failure occurs or persists despite appropriate treatment, Metoprolol should be discontinued. Bradycardia: Metoprolol produces a decrease in sinus heart rate in most patients; this decrease is greatest among patients with high initial heart rates and least among patients with low initial heart rates. Acute myocardial infarction (particularly inferior infarction) may in itself produce significant lowering of the sinus rate. If the sinus rate decreases to <40 beats/min, particularly if associated with evidence of lowered cardiac output, atropine (0.250.5 mg) should be administered intravenously. If treatment with atropine is not successful, Metoprolol should be discontinued, and cautious administration of isoproterenol or installation of a cardiac pacemaker should be considered.
AV Block: Metoprolol slows AV conduction and may produce significant first- (P-R interval ≥0.26 sec), second-, or third-degree heart block. Acute myocardial infarction also produces heart block. If heart block occurs, Metoprolol should be discontinued and atropine (0.25-0.5 mg) should be administered intravenously. If treatment with atropine is not successful, cautious administration of isoproterenol or installation of a cardiac pacemaker should be considered. Hypotension: If hypotension (systolic blood pressure ≤90 mmHg) occurs, Metoprolol should be discontinued, and the hemodynamic status of the patient and the extent of myocardial damage carefully assessed. Invasive monitoring of central venous, pulmonary capillary wedge, and arterial pressures may be required. Appropriate therapy with fluids, positive inotropic agents, balloon counterpulsation, or other treatment modalities should be instituted. If hypotension is associated with sinus bradycardia or AV block, treatment should be directed at reversing these (see above). Bronchospastic Diseases: PATIENTS WITH BRONCHOSPASTIC DISEASES SHOULD, IN GENERAL, NOT RECEIVE BETA BLOCKERS, including Metoprolol. Because of its relative beta1 selectivity, Metoprolol may be used with extreme caution in patients with bronchospastic disease. Because it is unknown to what extent beta2-stimulating agents may exacerbate myocardial ischemia and the extent of infarction, these agents should not be used prophylactically. If bronchospasm not related to congestive heart failure occurs, Metoprolol should be discontinued. A theophylline derivative or a beta2 agonist may be administered cautiously, depending on the clinical condition of the patient. Both theophylline derivatives and beta2 agonists may produce serious cardiac arrhythmias. 1.9. PRECAUTIONS General Metoprolol should be used with caution in patients with impaired hepatic function. Information for Patients Patients should be advised to take Metoprolol regularly and continuously, as directed, with or immediately following meals. If a dose should be missed, the patient should take only the next scheduled dose (without doubling it). Patients should not discontinue Metoprolol without consulting the physician. Patients should be advised (1) To avoid operating automobiles and machinery or engaging in other tasks requiring alertness until the patient’s response to therapy with Metoprolol has been determined; (2) To contact the physician if any difficulty in breathing occurs; (3) To inform the physician or dentist before any type of surgery that he or she is taking Metoprolol. Drug Interactions Catecholamine-depleting drugs (e.g., reserpine) may have an additive effect when given with beta-blocking agents. Patients treated with Metoprolol plus a catecholamine depletor should therefore be closely observed for evidence of hypotension or marked bradycardia, which may produce vertigo, syncope, or postural hypotension. Both digitalis glycosides and beta blockers slow atrioventricular conduction and decrease heart rate. Concomitant use can increase the risk of bradycardia.
Risk of Anaphylactic Reaction: While taking beta blockers, patients with a history of severe anaphylactic reaction to a variety of allergens may be more reactive to repeated challenge, either accidental, diagnostic, or therapeutic. Such patients may be unresponsive to the usual doses of epinephrine used to treat allergic reaction. General Anesthetics Some inhalation anesthetics may enhance the cardiodepressant effect of beta blockers (see WARNINGS, Major Surgery). CYP2D6 Inhibitors Potent inhibitors of the CYP2D6 enzyme may increase the plasma concentration of Metoprolol. Strong inhibition of CYP2D6 would mimic the pharmacokinetics of CYP2D6 poor metabolizer (see Pharmacokinetics section). Caution should therefore be exercised when coadministering potent CYP2D6 inhibitors with Metoprolol. Known clinically significant potent inhibitors of CYP2D6 are antidepressants such as fluoxetine, paroxetine or bupropion, antipsychotics such as thioridazine, antiarrhythmics such as quinidine or propafenone, antiretrovirals such as ritonavir, antihistamines such as diphenhydramine, antimalarials such as hydroxychloroquine or quinidine, antifungals such as terbinafine and medications for stomach ulcers such as cimetidine. Clonidine If a patient is treated with clonidine and Metoprolol concurrently, and clonidine treatment is to be discontinued, Metoprolol should be stopped several days before clonidine is withdrawn. Rebound hypertension that can follow withdrawal of clonidine may be increased in patients receiving concurrent beta-blocker treatment. Carcinogenesis, Mutagenesis, Impairment of Fertility Long-term studies in animals have been conducted to evaluate carcinogenic potential. In a 2year study in rats at three oral dosage levels of up to 800 mg/kg per day, there was no increase in the development of spontaneously occurring benign or malignant neoplasms of any type. The onlyhistologic changes that appeared to be drug related were an increased incidence of generally mild focal accumulation of foamy macrophages in pulmonary alveoli and a slight increase in biliary hyperplasia. In a 21-month study in Swiss albino mice at three oral dosage levels of up to 750 mg/kg per day, benign lung tumors (small adenomas) occurred more frequently in female mice receiving the highest dose than in untreated control animals. There was no increase in malignant or total (benign plus malignant) lung tumors, or in the overall incidence of tumors or malignant tumors. This 21-month study was repeated in CD-1 mice, and no statistically or biologically significant differences were observed between treated and control mice of either sex for any type of tumor. All mutagenicity tests performed (a dominant lethal study in mice, chromosome studies in somatic cells, a Salmonella/mammalian-microsome mutagenicity test, and a nucleus anomaly test in somatic interphase nuclei) were negative. No evidence of impaired fertility due to Metoprolol was observed in a study performed in rats at doses up to 55.5 times the maximum daily human dose of 450 mg. Pregnancy Category C
Metoprolol has been shown to increase postimplantation loss and decrease neonatal survival in rats at doses up to 55.5 times the maximum daily human dose of 450 mg. Distribution studies in mice confirm exposure of the fetus when Metoprolol is administered to the pregnant animal. These studies have revealed no evidence of impaired fertility or teratogenicity. There are no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed. Nursing Mothers Metoprolol is excreted in breast milk in a very small quantity. An infant consuming 1 liter of breast milk daily would receive a dose of less than 1 mg of the drug. Caution should be exercised when Metoprolol is administered to a nursing woman. Pediatric Use Safety and effectiveness in pediatric patients have not been established. Geriatric Use Clinical trials of Metoprolol in hypertension did not include sufficient numbers of elderly patients to determine whether patients over 65 years of age differ from younger subjects in their response to Metoprolol. Other reported clinical experience in elderly hypertensive patients has not identified any difference in response from younger patients. In worldwide clinical trials of Metoprolol in myocardial infarction, where approximately 478 patients were over 65 years of age (0 over 75 years of age), no age-related differences in safety and effectiveness were found. Other reported clinical experience in myocardial infarction has not identified differences in response between the elderly and younger patients. However, greater sensitivity of some elderly individuals taking Metoprolol cannot be categorically ruled out. Therefore, in general, it is recommended that dosing proceed with caution in this population. 1.10. ADVERSE REACTIONS Hypertension and Angina Most adverse effects have been mild and transient. Central Nervous System: Tiredness and dizziness have occurred in about 10 of 100 patients. Depression has been reported in about 5 of 100 patients. Mental confusion and short-term memory loss have been reported. Headache, nightmares, and insomnia have also been reported. Cardiovascular: Shortness of breath and bradycardia have occurred in approximately 3 of 100 patients. Cold extremities; arterial insufficiency, usually of the Raynaud type; palpitations; congestive heart failure; peripheral edema; and hypotension have been reported in about 1 of 100 patients. Gangrene in patients with pre-existing severe peripheral circulatory disorders has also been reported very rarely. (See CONTRAINDICATIONS, WARNINGS, and PRECAUTIONS.) Respiratory: Wheezing (bronchospasm) and dyspnea have been reported in about 1 of 100 patients (see WARNINGS). Rhinitis has also been reported.
Gastrointestinal: Diarrhea has occurred in about 5 of 100 patients. Nausea, dry mouth, gastric pain, constipation, flatulence, and heartburn have been reported in about 1 of 100 patients. Vomiting was a common occurrence. Postmarketing experience reveals very rare reports of hepatitis, jaundice and non-specific hepatic dysfunction. Isolated cases of transaminase, alkaline phosphatase, and lactic dehydrogenase elevations have also been reported. Hypersensitive Reactions: Pruritus or rashes have occurred in about 5 of 100 patients. Very rarely, photosensitivity and worsening of psoriasis has been reported. Miscellaneous: Peyronie’s disease has been reported in fewer than 1 of 100,000 patients. Musculoskeletal pain, blurred vision, and tinnitus have also been reported. There have been rare reports of reversible alopecia, agranulocytosis, and dry eyes. Discontinuation of the drug should be considered if any such reaction is not otherwise explicable. There have been very rare reports of weight gain, arthritis, and retroperitoneal fibrosis (relationship to Metoprolol has not been definitely established). The oculomucocutaneous syndrome associated with the beta blocker practolol has not been reported with Metoprolol. Myocardial Infarction Central Nervous System: Tiredness has been reported in about 1 of 100 patients. Vertigo, sleep disturbances, hallucinations, headache, dizziness, visual disturbances, confusion, and reduced libido have also been reported, but a drug relationship is not clear. Cardiovascular: In the randomized comparison of Metoprolol and placebo described in the CLINICAL PHARMACOLOGY section, the following adverse reactions were reported: a) Metoprolol (Lopressor®) Placebo Hypotension (systolic BP <90 mmHg) 27.4% 23.2% Bradycardia (heart rate <40 beats/min) 15.9% 6.7% Second- or third-degree heart block 4.7% 4.7% First-degree heart block (P-R ≥0.26 sec) 5.3% 1.9% Heart failure 27.5% 29.6% b) Respiratory: Dyspnea of pulmonary origin has been reported in fewer than 1 of 100 patients. c) Gastrointestinal: Nausea and abdominal pain have been reported in fewer than 1 of 100 patients. d) Dermatologic: Rash and worsened psoriasis have been reported, but a drug relationship is not clear. e) Miscellaneous: Unstable diabetes and claudication have been reported, but a drug relationship is not clear. Potential Adverse Reactions A variety of adverse reactions not listed above have been reported with other beta-adrenergic blocking agents and should be considered potential adverse reactions to Metoprolol.
Central Nervous System: Reversible mental depression progressing to catatonia; an acute reversible syndrome characterized by disorientation for time and place, short-term memory loss, emotional lability, slightly clouded sensorium, and decreased performance on neuropsychometrics. Cardiovascular: Intensification of AV block (see CONTRAINDICATIONS). Hematologic: Agranulocytosis, nonthrombocytopenic purpura, thrombocytopenic purpura. Hypersensitive Reactions: Fever combined with aching and sore throat, laryngospasm, and respiratory distress. Postmarketing Experience The following adverse reactions have been reported during postapproval use of Metoprolol: confusional state, an increase in blood triglycerides and a decrease in High Density Lipoprotein (HDL). Because these reports are from a population of uncertain size and are subject to confounding factors, it is not possible to reliably estimate their frequency. 1.11. OVERDOSAGE Acute Toxicity Several cases of overdosage have been reported, some leading to death. Oral LD 50â€™s (mg/kg): mice, 1158-2460; rats, 3090-4670. 1.12. Signs and Symptoms Potential signs and symptoms associated with overdosage with Metoprolol are bradycardia, hypotension, bronchospasm, and cardiac failure. 1.13. Treatment There is no specific antidote. In general, patients with acute or recent myocardial infarction may be more hemodynamically unstable than other patients and should be treated accordingly (see WARNINGS, Myocardial Infarction). On the basis of the pharmacologic actions of Metoprolol, the following general measures should be employed: Elimination of the Drug: Gastric lavage should be performed. Bradycardia: Atropine should be administered. If there is no response to vagal blockade, isoproterenol should be administered cautiously. Hypotension: A vasopressor should be administered, e.g., levarterenol or dopamine. Bronchospasm: A beta2-stimulating agent and/or a theophylline derivative should be administered. Cardiac Failure: A digitalis glycoside and diuretic should be administered. In shock resulting from inadequate cardiac contractility, administration of dobutamine, isoproterenol, or glucagon may be considered. 1.14. DOSAGE AND ADMINISTRATION
Hypertension The dosage of Metoprolol tablets should be individualized. Metoprolol tablets should be taken with or immediately following meals. The usual initial dosage of Metoprolol tablets is 100 mg daily in single or divided doses, whether used alone or added to a diuretic. The dosage may be increased at weekly (or longer) intervals until optimum blood pressure reduction is achieved. In general, the maximum effect of any given dosage level will be apparent after 1 week of therapy. The effective dosage range of Metoprolol tablets is 100-450 mg per day. Dosages above 450 mg per day have not been studied. While once daily dosing is effective and can maintain a reduction in blood pressure throughout the day, lower doses (especially 100 mg) may not maintain a full effect at the end of the 24-hour period, and larger or more frequent daily doses may be required. This can be evaluated by measuring blood pressure near the end of the dosing interval to determine whether satisfactory control is being maintained throughout the day. Beta1 selectivity diminishes as the dose of Metoprolol is increased. Angina Pectoris The dosage of Metoprolol tablets should be individualized. Metoprolol tablets should be taken with or immediately following meals. The usual initial dosage of Metoprolol tablets is 100 mg daily, given in two divided doses. The dosage may be gradually increased at weekly intervals until optimum clinical response has been obtained or there is pronounced slowing of the heart rate. The effective dosage range of Metoprolol tablets is 100-400 mg per day. Dosages above 400 mg per day have not been studied. If treatment is to be discontinued, the dosage should be reduced gradually over a period of 1-2 weeks (see WARNINGS). Myocardial Infarction Early Treatment: During the early phase of definite or suspected acute myocardial infarction, treatment with Metoprolol can be initiated as soon as possible after the patientâ€™s arrival in the hospital. Such treatment should be initiated in a coronary care or similar unit immediately after the patientâ€™s hemodynamic condition has stabilized. Treatment in this early phase should begin with the intravenous administration of three bolus injections of 5 mg of Metoprolol each; the injections should be given at approximately 2minute intervals. During the intravenous administration of Metoprolol, blood pressure, heart rate, and electrocardiogram should be carefully monitored. In patients who tolerate the full intravenous dose (15 mg), Metoprolol tablets, 50 mg every 6 hours, should be initiated 15 minutes after the last intravenous dose and continued for 48 hours. Thereafter, patients should receive a maintenance dosage of 100 mg twice daily (see Late Treatment below). Patients who appear not to tolerate the full intravenous dose should be started on Metoprolol tablets either 25 mg or 50 mg every 6 hours (depending on the degree of intolerance) 15 minutes after the last intravenous dose or as soon as their clinical condition allows. In patients with severe intolerance, treatment with Metoprolol should be discontinued (see WARNINGS). Late Treatment: Patients with contraindications to treatment during the early phase of suspected or definite myocardial infarction, patients who appear not to tolerate the full early treatment, and patients in whom the physician wishes to delay therapy for any other reason should be started on Metoprolol tablets, 100 mg twice daily, as soon as their clinical condition allows. Therapy should be continued for at least 3 months. Although the efficacy of
Metoprolol beyond 3 months has not been conclusively established, data from studies with other beta blockers suggest that treatment should be continued for 1-3 years. Note: Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit. 1.15. Dimethyl sulfoxide (DMSO) Dimethyl Sulfoxide is the organo sulfur compound with the formula (CH3)2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water. It penetrates the skin very readily, giving it the unusual property of being secreted onto the surface of the tongue after contact with the skin and causing a garlic-like taste in the mouth. 1.15.1. Synthesis and production It was first synthesized in 1866 by the Russian scientist Alexander Zaytsev, who reported his findings in 1867. Dimethyl sulfoxide is a by-product of kraft pulping, which produces dimethyl sulfide as a side product. Oxidation of dimethyl sulfide with oxygen or nitrogen dioxide gives DMSO. 1.15.2. Applications Solvent
Distillation of DMSO requires a partial vacuum to achieve a lower boiling point. DMSO is a polar aprotic solvent and is less toxic than other members of this class, such as dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, and HMPA. DMSO is frequently used as a solvent for chemical reactions involving salts, most notably Finkelstein reactions and other nucleophilic substitutions. It is also extensively used as an extractant in biochemistry and cell biology. Because DMSO is only weakly acidic, it tolerates relatively strong bases and as such has been extensively used in the study of carbanions. A set of nonaqueous pKa values (C-H, O-H, S-H and N-H acidities) for thousands of organic compounds have been determined in DMSO solution. Because of its high boiling point (189 째C; 462 K), DMSO evaporates slowly at normal atmospheric pressure. Samples dissolved in DMSO cannot be as easily recovered compared to other solvents, as it is very difficult to remove all traces of DMSO by conventional rotary evaporation. Reactions conducted in DMSO are often diluted with water to precipitate or phase-separate products. The relatively high freezing point (18.5 째C; 292 K) of DMSO means that at, or just below, room temperature it is a solid, which can limit its utility in some chemical processes (e.g. crystallization with cooling). In its deuterated form (DMSO-d6), it is a useful but expensive solvent for NMR spectroscopy, again due to its ability to dissolve a wide range of analytes, its own simple spectrum, and its suitability for high-temperature NMR spectroscopic studies. Disadvantages to the use of DMSO-d6 are its high viscosity, which broadens signals, and its hygroscopicity,
which leads to an overwhelming H2O resonance in the 1H NMR spectrum. It is often mixed with CDCl3 or CD2Cl2 for lower viscosity and melting points. DMSO is finding increased use in manufacturing processes to produce microelectronic devices. It is widely used to strip photoresist in TFT-LCD 'flat panel' displays and advanced packaging applications (such as wafer-level packaging / solder bump patterning). It also used in biopreservation especially stem cell banking. DMSO is an effective paint stripper, being safer than many of the others such as nitromethane and dichloromethane. Because of its ability to dissolve many kinds of compounds, DMSO plays a role in sample management and high-throughput screening operations in drug design. 1.15.3. Reactions The sulfur center in DMSO is nucleophilic toward soft electrophiles and the oxygen is nucleophilic toward hard electrophiles. The methyl groups of DMSO are somewhat acidic in character (pKa=35) due to the stabilization of the resultant carbanion by the S(O)R group, and so are deprotonated with strong bases like lithium diisopropylamide and sodium hydride. The sodium salt of DMSO formed in this way (sometimes referred to as "dimsyl sodium") is a useful base, e.g. it is often used for the deprotonation of ketones to form sodium enolates, phosphonium salts to form Wittig reagents, and formamidinium salts to form diaminocarbenes. DMSO reacts with methyl iodide to form trimethylsulfoxonium iodide, [(CH3)3SO]I, which can be deprotonated with sodium hydride to form the sulfur ylide: (CH3)2SO + CH3I → [(CH3)3SO]I [(CH3)3SO]I + NaH → [(CH3)2CH2SO + NaI + H2 In organic synthesis, DMSO is used as a mild oxidant, as illustrated by the PfitznerMoffatt oxidation and the Swern oxidation. DMSO is a common ligand in coordination chemistry. The complex dichlorotetrakis(dimethyl sulfoxide)ruthenium(II), RuCl2(dmso)4, features DMSO bonded to ruthenium through sulfur and through oxygen. 1.15.4. Biology DMSO is used in PCR to inhibit secondary structures in the DNA template or the DNA primers. It is added to the PCR mix before reacting, where it interferes with the selfcomplementarity of the DNA, minimizing interfering reactions. DMSO may also be used as a cryoprotectant, added to cell media to prevent cell death during the freezing process. Approximately 10% may be used with a slow-freeze method, and the cells may be frozen at -80°C or stored in liquid nitrogen safely. 1.15.5. Medicine Use of DMSO in medicine dates from around 1963, when a Oregon Health & Science University Medical School team, headed by Stanley Jacob, discovered it could penetrate the skin and other membranes without damaging them and could carry other compounds into a biological system. In medicine, DMSO is predominantly used as a topical analgesic, a vehicle for topical application of pharmaceuticals, as an anti-inflammatory, and an antioxidant. . Because DMSO increases the rate of absorption of some compounds through organic tissues including skin, it can be used as a drug delivery system. It is frequently compounded with antifungal medications, enabling them to penetrate not just skin but also toe and fingernails. In cryobiology DMSO has been used as a cryoprotectant and is still an important constituent of cryoprotectant vitrification mixtures used to preserve organs, tissues, and cell suspensions. Without it, up to 90 percent of frozen cells will become inactive. It is particularly important
in the freezing and long-term storage of embryonic stem cells and hematopoietic stem cells, which are often frozen in a mixture of 10% DMSO , Media and 30% fetal bovine serum. In the cryogenic freezing of heteroploid cell lines (MDCK, VERO, etc.) a mixture of 10% DMSO with 90% EMEM (70% EMEM + 30% fetal bovine serum + antibiotic mixture) is used. As part of an autologous bone marrow transplant the DMSO is re-infused along with the patient's own hematopoietic stem cells. In a 1978 study at the Cleveland Clinic Foundation in Cleveland, Ohio, researchers concluded that DMSO brought significant relief to the majority of the 213 patients with inflammatory genitourinary disorders that were studied. They recommended DMSO for all inflammatory conditions not caused by infection or tumor in which symptoms were severe or patients failed to respond to conventional therapy. DMSO has been examined for the treatment of numerous conditions and ailments, but the U.S. Food and Drug Administration (FDA) has only approved its use for the symptomatic relief of patients with interstitial cystitis. Animal studies have indicated that treatment with DMSO within one hour of spinal cord injury can prevent total paralysis. 1.15.6. Veterinary medicine DMSO is commonly used in veterinary medicine as a liniment for horses, alone or in combination with other ingredients. In the latter case, often, the intended function of the DMSO is as a solvent, to carry the other ingredients across the skin. Also in horses, DMSO is used intravenously, again alone or in combination with other drugs. It is used alone for the treatment of increased intracranial pressure and/or cerebral edema in horses. 1.15.7. Safety DMSO by itself has low toxicity. On September 9, 1965, the Wall Street Journal reported the death of an Irish woman after undergoing DMSO treatment for a sprained wrist although no autopsy was done nor was a causal relationship established. Clinical research using DMSO halted and did not begin again until the National Academy of Sciences (NAS) published findings in favor of DMSO in 1972. In 1978, the U.S. FDA approved DMSO for treating interstitial cystitis. In 1980, the U.S. Congress held hearings on claims that the FDA was slow in approving DMSO for other medical uses. In 2007, the U.S. FDA granted "fast track" designation on clinical studies of DMSO's use in reducing brain tissue swelling following traumatic brain injury. DMSO exposure to developing mouse brains can produce brain degeneration. This neurotoxicity could be detected at doses as low as 0.3 mL/kg, a level exceeded in children exposed to DMSO during certain medical treatments. Glove selection is important when working with DMSO. Thick rubber gloves are recommended. Nitrile gloves, which are very commonly used in chemical laboratories, have been found to dissolve rapidly with exposure to DMSO. Because DMSO easily penetrates the skin, substances dissolved in DMSO may be quickly absorbed. For instance, a solution of sodium cyanide in DMSO can cause cyanide poisoning through skin contact.  Dimethyl sulfoxide can produce an explosive reaction when exposed to acid chlorides; at a low temperature, this reaction produces the oxidant for Swern oxidation. Recently, DMSO disposed into sewers caused odor problems in cities: waste water bacteria transform DMSO under hypoxic (anoxic) conditions into dimethyl sulfide (DMS) that has a strong disagreeable odor, similar to rotten cabbage. 1.16. Objective of this Study
The objective of this study was to develop sustained release Metoprolol Tartrate delivery from biodegradable polymeric in situ implants for parenteral administration. Metoprolol Tartrate, which is used in a wide variety of indications including hypertension, angina, tachycardia, coronary heart disease, heart falure etc, is a highly water soluble drug. Therefore, entrapping it in sustained release in situ implant would be a piece of work with great challenge. Moreover, although a vast number of studies on controlled release drug delivery with Metoprolol Tartrate have been carried out. The prospect of in situ formed metoprolol Tartrate preparation and drug release relation for prolonged period was explored in this research work. This work would hopefully generate interest in further studies with this drug using this delivery device. Two: MATERIALS AND METHODS 2.1. Materials In these analytical study different machineries, instruments, glass equipments, reagents and chemicals were use. 2.1.1. Machineries and Instruments Digital Weight Balance (AY Shimadzu Corporation) Vortex Mixer (VM2000, Digisystem Laboratory Instruments INC) UV Spectroscopy (UV- 1601, SI-TIMADZIJ Corporation) Incubator Centrifuge Machine (Model-800, China) 6. Magnetic Stirrer Ultrasonic Machine (Power sonic 505, 1-IWASHIN) pH Meter (Cyber scan 500, Eutech Instrumwnts) 1ml disposable syringe (100 unit) 5ml disposable syringe Butterfly needles 2.1.2. Glass Equipments Volumetric Flask (10ml, 100ml, 500ml) Beaker ( 50ml, 100ml, 500ml, 1000ml) Measureing Cylinder (100ml) Petri Dish Funnel Screw Capped Test Tube Test Tube 100 ml Glass Vial Formulation Bottle Pipette (1ml, 5ml, 10ml) 2.1.3. Reagents Acetonitrile Acetone Distilled Water
2.1.4. Chemicals A. Active Ingredient: Metoprolol Tartrateb B. Polymer: DL-PLA C. Excipients Glyceryl Mono Stearate (GSM) Magnesium Stearate Stearyl Alcohol Ceto Stearyl Alcohol Arachis Oil Stearic Acid Cetyl Alcohol D. Solvent: Di Methyl Sulfoxide (DMSO) E. Media: Phosphate Buffer (pH 7.4) 2.1.5. Other Materials Wax Paper Filter Paper Tissue Paper Seizer Tape 2.2. Methods 2.2.1. Perparation of Phosphate Buffer with pH 7.4 Firstly, measured required amount of KH2PO4 and NaOH. Then kept it into two different beakers and added required amount of distilled water. Both KH2PO4 and NaOH were dissolved in the distilled water with constant stirring. After complete dissolution both solution were mixed each other in a volumetric flask and distilled water were added to make the required volume. Then the buffer solution was kept in a beaker and measures the pH using pH meter and then pH was adjusted to 7.40 with adding either by KH2PO4 or NaOH. Finally the buffer solution was filtered with filter paper. 2.2.2. Preparation of the Standard Curve Metoprolol Tartrate solution was prepared in concentration range of 0mg/L to 180mg/Lin phosphate buffer. Firstly 20mg of metoprolol tartrate was accurately weighedand dissolved in phosphate buffer and it was made 100ml solution by adding phosphate buffer in a100 ml volumetric flask. Then a serial dilution was carried out by taking 1, 2, 3, 4, 5, 6, 7, 8, 9 ml solution from the drugâ€™s stock solution in different 10 ml volumetric flasks. Then phosphate buffer were added in each volumetric flask to make the final volume 10 ml. This serial dilution was carried out to get different metoprolol tartrate concentration. The absorbance of that standard solution of different concentration was observed in the single beam UV Spectrophotometer at 273.5 nm. From the observed absorbance calibration curve was made
for the assay of Metoprolol Tartrate. The standard curve of metoprolol tartrate was drawn based on the data of drug concentration and UV absorbance of the respective concentration of drug. 2.2.3. Preparation of Biodegradable Polymeric In Situ Implants Biodegradable polymeric in situ implants were prepared by the required amount of Metoprolol tartrate and polymer with required amount of solvent (DMSO). Formulation was prepared with 2% drug loading. Excipient incorporated implants were also prepared with 2% drug load. 2.2.4. Drug (Metoprolol Tartrate) loaded polymer (PLA) Implants Preparation Firstly required amount of Dimethyl Sulfoxide (DMSO) was measured by pipette into formulation bottle. Then required amount of polymer was measured and incrementally added to DMSO and dissolved over a period of time by means of heating at 500c with a heating magnetic stirrer. After complete dissolution of the polymer, the solution was cooled under ambient condition. Then required amount of drug was added and again mixed the drug with the polymer solution by using vortex mixer. Though the polymer-solvent-drug system had a viscous consistency but it is sufficiently syringeable and easily injected in the phosphate buffer by conventional syringe and needle. When formulation was injected, it came into contact with phosphate buffer and as a result the polymer precipitated and formed an implant entrapping the drug. 2.2.5. Implant Preparation with different Excipients Excipient incorporated implants of Matoprolol tartrate was prepared in respect of 2% drug load by the same procedure as describe in 2.2.4. The only different was that the excipient was mixed with the polymer solution before drug; otherwise excipient load was the same as the drug load.
Fig: 2.1. Standard Curve of Metoprolol Tartrate 2.2.6. Characterization of Implants
126.96.36.199. Photographic Imaging Photographs of drug loaded in situ implants were taken using digital camera before and after the drug release studies. 188.8.131.52. Implant Analysis The actual amount of drug that was loaded in implants during fabrication process was determined by spectrophotometric analysis. For determining the drug content of Metoprolol Tartrate loaded implants, the following procedure was followed: The weight of the implant was measured with electronic balance and recorded. After that the implant was crushed with mortar and pestle and again weighed with electric balance and was recorded. Then the implant’s powder was put into screw capped test tube. Added 1ml Acetonitrile in the screw capped test tube and was shaken with vortex mixer for 2-3 minutes. Added 9ml phosphate buffer in the screw capped test tube and again shaken with vortex mixer for 5-6 minutes. The solution was then centrifuged at 3000 RPM for 15 minutes 5ml of supernatant solution was taken and filtered the solution. Then it was analyzed at 273.5 nm with UV Spectrophotometer. Absorbance was recorded. Most of the time dilution was needed. So 1ml solution was collected and placed into a 100ml volumetric flask Then Phosphate buffer was added to make the final volume 100ml Then UV absorbance was taken and recorded. Second part of Implant Analysis was done after 30 days and the procedure of Implant Analysis was same as first part. 2.2.7. In vitro Drug Release Studies After formation of implants, in vitro dissolution studies of implants were carried out in static condition at 370 C in an incubator in order to observe the drug release profile. Implants were prepared spontaneously upon injection of drug containing liquid polymeric solution inside rubber capped glass vessels containing 100 ml phosphate buffer (pH – 7.40) and incubated at 370 C without agitation. At predetermined time interval 5 ml of solution was withdrawn using syringe after shaking the dissolution vessels for 10 seconds and it was replaced with fresh 5 ml of phosphate buffer (pH – 7.40) at the same to sink condition. The withdrawn sample was analyzed for release by UV spectrophotometer at 273.5 nm. The dissolution study was carried out for over a period of 30 days for implants containing only Metoprolol Tartrate with different excipients respectively. Chapter Three: RESULT AND DISCUSSION 3.1. Morphological Depiction of In Situ Implants Surface morphology greatly influences the release kinetics of implants. The shape and structure of implants have profound influence on drug release (Dunn et. al., 1994). The drug release kinetics is strongly related with morphological characters of implants. Therefore implant shapes were investigated for thorough characterization. Among all implants most
were found round, some were found semi spherical or spherical shaped. Figure 3.1 represents some randomly selected digital images of in situ implants. 3.2. Drug Loading Efficiency of In Situ DL-PLA Implants The loading efficiency of implant is dependent on a number of factors related to the drug, polymer and solvent properties. The lipophilicity / hydrophilicity of the drug and the polymer, the solubility of the drug and polymer in the solvent and the non solvent (physiological fluid / aqueous buffer) and the physicochemical properties of the solvent like log partition co efficient, miscibility with the aqueous outer media and viscosity are the determining factors for the implant forming process and corresponding drug loading (Swarnali Islam, 2008). In this study, in situ DL-PLA implants were analyzed for actual Metoprolol Tartrate content against the theoretical drug content. Implants were formulated for one drug loadings 2% respectively. The percentage of loading efficiency (% LE) of implant was calculated with the following formula based on experimentally determined drug load. % LE = (AD/LD) X 100 Here AD is the actual drug content which was loaded in the implant and LD is the theoretical drug content which is to be loaded in the implant. The implant forming process is mainly dependent on the solvent movement out of the implant formulation during the precipitation of the polymer. Directly after the injection into dissolution apparatus the solvent diffuse from the formulation into the aqueous dissolution media, dragging the solved drug with it (Swarnali Islam, 2008). 3.2.1. Loading Efficiency of In Situ DL-PLA Implants: Effect of Drug Loading In situ DL-PLA implant was prepared with 2% drug loading respectively. The data for actual Metoprolol Tartrate for 2% drug loading efficiency was 105.93. 3.2.2. Loading Efficiency of In Situ DL-PLA Implants: Effect of Excipients The effect of incorporation of different excipients on drug loading efficiency of Metoprolol Tartrate was studied for 2% drug load. The excipient load was same as the drug load. The changes which were observed in the loading efficiency probably caused due to the respective excipients only. The data for different excipients with 2% load of Metoprolol Tartrate are represented in the Table 3.1. In case of excipients incorporated implants the highest drug loading efficiency was found with Arachis Oil (87.25%) and the lowest drug loading efficiency was found with Cetyl Alcohol (60.78%) with 2% drug load. Figure 3.1 represents the effect of drug loading efficiency on different excipient incorporated implants. 184.108.40.206. Justification of Effects of Excipients on Metoprolol Tartrate Loading Efficiency Gleceryl Mono Stearate (GMS) The drug loading efficiency was found 70.09 % when GMS was incorporated in the implant with 2% drug as compared to 70.31% for drug only implants. GMS has a HLB value 3.8 (Raymond C Rowe et. al., 2003), which indicate itâ€™s hydrophobic nature (Michael E. Aulton, 2004) and also GMS is practically insoluble in water (Raymond C Rowe et. al., 2003). So for its such property, it probably decreased the dispersibility of the drug in DMSO, consequently lowering the passage of drug of aqueous buffer increasing its load (Swarnali Islam, 2008). Magnesium Stearate
The drug loading efficiency was found 71.07 % when Mg Stearate was incorporated in the implant with 2% drug as compared to 70.31% for drug only implants. As Mg Stearate is practically insoluble in both DMSO and aqueous buffer, therefore it probably increases the loading efficiency of the drug. Stearyl Alcohol The drug loading efficiency was found 61.76% when Stearyl Alcohol was incorporated in the implant with 2% drug as compared to 70.31 % for drug only implants. Stearyl Alcohol has been used in controlled release tablets (Prasad C M et. al., 1971 and Kumar K et. al., 1975). Stearyl Alcohol is practically insoluble in water (Raymond C Rowe et. al., 2003). Therefore it should probably increase the loading efficiency. So, further investigation is needed for this respect. Ceto Stearyl Alcohol The drug loading efficiency was found 72.55 % when Ceto Stearyl Alcohol was incorporated in the implant with 2% drug as compared to 70.31% for drug only implants. Ceto Stearyl Alcohol is practically insoluble in water (Raymond C Rowe et. al., p.125, 2003) and for its hydrophobicity it should increase drug loading efficiency. Not only have that different research articles been published in which it has been used to slow the dissolution of water soluble drugs (Al-Kassas et. al., 1993; Lashmar UT et. al., 1993; Wong LP et. al., 1992 and Ahmed M et. al., 1981). But the loading efficiency remains the same. So, further investigation is needed in this respect. Arachis Oil The drug loading efficiency was found 87.25 % which is highest among all the used excipients when Arachis Oil was incorporated in the implant with 2% drug as compared to. 70.31% for drug only implants. Most recently Arachis Oil is used as a part of controlled release injectables (Matsubara K et. al., 1994). As Arachis Oil is an organic material (Peanut Oil From Wikipedia) it is insoluble in aqueous media. There for it may arrests the drug particles and help to entrap them in the polymer which may result in decrease drug loss in aqueous buffer and thus increase drug loading efficiency. As this excipient is oily in nature it involves in phase separation. Any condition leading to rapid phase separation is likely to increase drug loading by decreasing drug loss in non solvent. Moreover, it may have reduced the solubility of Metoprolol Tartrate in DMSO which led to further decrease in drug movement to aqueous buffer resulting in increased drug load (Swarnali Islam, 2008). Stearic Acid The drug loading efficiency was also found 81.86 % when Stearic Acid was incorporated in the implant with 2% drug as compared to 70.31% for drug only implants. Stearic Acidâ€™s has a lower acid value: 200-212 (Raymond C Rowe et. al., 2003), indicates its hydrophobic nature (P K Puranik, 1991). Stearic Acid is also practically insoluble in water (Raymond C Rowe et. al., 2003) for which it may dissolved in DMSO and decreased the passage for hydrophilic drug which may result in increased drug loading efficiency. Cetyl Alcohol The drug loading efficiency was found 60.78% when Cetyl Alcohol was incorporated in the implant with 2% drug as compared to 70.31% for drug only implants. Here Cetyl Alcohol decreased the Metoprolol Tartrate loading efficiency. Cetyl Alcohol is insoluble in both DMSO and aqueous buffer. Cetyl Alcohol is widely used in modified release dosage form. Cetyl alcohol is used for its water absorption properties (Raymond C Rowe et. al., 2003). The percentage of Cetyl alcohol that is used in this formulation may act as a water absorptive
agent. For which it may reduce drug loading efficiency. Though, further investigation is needed in this respect. Table 3.2: Effects of different excipients on Metoprolol Tartrate loading efficiency (%) of in situ implants Excipients with 2% Drug Load
Loading Efficiency (%)
Drug without excipients Arachis oil Stearic Acid Ceto Stearyl Alcohol Mg Stearate Glyseryl Mono Stearate Stearyl Alcohol Cetyl Alcohol
70.31 87.25 81.86 72.55 71.07 70.09 61.76 60.78
Figure 3.1: Effects of excipients variation on Metoprolol Tartrate loading efficiency 3.3. Kinetics of Release Study The regression analysis of release data was done to determine the proper order of in-vitro release of Metoprolol Tartrate from the investigated in situ implants. Zero order, First order, Higuchi and Korsmeyer-Peppas model equations were applied to all in-vitro release studies. The drug releasing mechanism from the matrix is a consequence of concomitant process such as solidification kinetics of the polymers, precipitation kinetics of the active ingredient, diffusion of the active ingredient through the polymer matrix along a concentration gradient, dynamic of solvents and water flows, erosion of biodegradable polymers by hydrolysis, bulk water uptake, swelling of polymers as well as release through pores formed in the matrix. The drug release rate from a polymeric matrix may also depend on interactions between active ingredient and polymer. High interactions resulting from e.g. hydrogen bonds between drug and polymer would lead reduced release rate of the drug substance from the matrix. These parameters affect the solubility properties and dissolution kinetics and therefore influence the drug release rate of substances from a polymeric matrix (Bolton et al., 1984; Taylor et al., 1997 and Broman et al., 2001).
Zero order kinetic model A zero order kinetic model has a rate which is independent of the concentration of the drug(s). Increasing the concentration of the reacting species will not speed up the rate of the reaction. Zero-order reactions are typically found when a material that is required for the reaction to proceed, such as the drug, is saturated by the reactants. The rate law for a zeroorder reaction isWhere r is the reaction rate and k is the reaction rate coefficient with units of concentration/time (Kenneth A. Connors, 1991). If a time versus cumulative amount of drug released yields a straight line and the slope is 1 or more than 1, then the release pattern follows zero order kinetics. First order kinetic model A first order kinetic depends on the concentration of only one reactant (e.g. drug). Other reactants (polymer, DMSO, excipient) can be present, but each will be zero-order. The rate law for an elementary reaction that is first order with respect to a reactant A is-
Where k is the first order rate constant, which has units of 1/time (Kenneth A. Connors, 1991). When the release pattern goes for time versus logarithm of cumulative percent remain to be released then the kinetics termed as first order. Higuchi kinetic model Higuchi developed several theoretical models to study release of high and low water soluble drugs incorporated in semisolid and/or solid matrices. Scientific method as envisaged by eminent scientists is fundamental to the investigation of new knowledge based upon evidence. Scientists use hypothesis and logic to prepare explanations for physical phenomenon in the form of equations. One of the most important controlled release equations is called "Higuchi equation". The Higuchi equation has helped define the mathematical perspective of controlled release drug delivery systems since the era of development of sustained release dosage forms. The release of a drug from a drug delivery system (DDS) involves both dissolution and diffusion. Several mathematical equations models describe drug dissolution and/or release from DDS. In the modern era of controlled-release oral formulations, 'Higuchi equation' has become influential kinetic equation in its own right, as evidenced by employing drug dissolution studies that are recognized as an important element in drug delivery development. Today the Higuchi equation is considered one of the widely used and the most well-known controlled-release equation (Subal C Basak, 2006). According to this model, drug release was described as a square root time dependent diffusion process based on Fickâ€™s law. This relation can be used to describe drug dissolution from several types of modified release pharmaceutical dosage forms. Q = KHt1/2 Where Q is the amount of drug released at time t and KH is the Higuchiâ€™s release rate constant. If a plot of square root time versus cumulative amount of drug released yields a straight line and the slope is 1 or more than 1, then the particular dosage form is considered to follow Higuchi kinetics of drug release. Korsmeyer-Peppas kinetic model Korsmeyer-Peppas kinetics model is applied when the release mechanism deviates from Fickâ€™s equation.
Korsmeyer et. al. (1983) derived a simple relationship which described drug release from a polymeric system (following equation). To find out the mechanism of drug release, first 60% drug release data was fitted in Korsmeyer–Peppas model: Mt / M∞ = ktn Where Mt / M∞ is fraction of drug released at time‘t’ and ‘k’ is the rate constant. Here ‘n’ is the release exponent (M Harris Shoaib et. al., 2006). It is shown that this equation can adequately describe the release mechanism of drugs or other solutes from slabs, spheres, cylinders and discs (tablets), regardless of the release mechanism. It is shown that in case of pure fickian release the exponent ‘n’ have the limiting values of 0.50, 0.45 and 0.43 for release from slabs, cylinders and spheres respectively. For tablets and depending on the aspect ratio i.e., the ration of diameter to thickness, the Fickian diffusion mechanism is described by 0.43 < n < 0.50. For drug release from spherical polymer matrix of a wide distribution, the value of the exponent n for Fickian diffusion depends on the width of the distribution (Ritger and Peppas, 1986). When the release pattern goes for log time versus logarithm of cumulative fraction released then the kinetics termed as KorsmeyerPeppas. 3.3.1. Metoprolol Tartrate Release Kinetics from DL-PLA In Situ Implants: Effect of Excipients Pharmaceutical Dosage Forms contain both pharmacologically active compounds and excipients added to aid the formulation and manufacture of the subsequent dosage form for administration to patients (Raymond C Rowe et. al., 2003). Excipients have various effects on drug release profile. The rate and extent of drug release from in situ implants can be controlled by the use of excipients in the formulation. These agents can act as rate modifier by increasing or retarding the rate of release depending upon the nature of the agent. They probably extent their effects by influencing the way of formulation coagulate after injection into the aqueous medium and therefore on the release characteristics of the sustained release injectables formed in situ (Swarnali Islam, 2008). Metoprolol Tartrate release was studied for 30 days for all excipients with 2% drug load. Result of in vitro release profile parameters are summarized in the Table 3.2 and also graphically represented in the Figure 3.16-3.19 as compared to drug only implant. Table 3.2: Overview of parameters describing the in vitro Metoprolol Tartrate release profiles from in situ DL-PLA implants to see the effects of excipients. Excipients Calculated Drug release Calculated Calculated with 5% Drug time (Day) for during initial time interval time (Day) Load Initial Burst Burst Phase (%) (Day) for for 100 % Linear Phase drug release Gleceryl Mono Stearate Mg Stearate Stearyl Alcohol Ceto Stearyl Alcohol Arachis Oil Stearic Acid Cetyl Alcohol Drug without Excipient
0.042 0.042 0.042 0.042
55.29 63.55 79.74 62.341
0.042-7 0.042-7 0.042-3 0.042-5
7 7 3 5
Figure 3.2.: Graphical representation of % release during burst phase for different excipient incorporated implant as compared to drug only implant
Figure 3.3: Metoprolol Tartrate release from DL-PLA implants with two different excipients (GMS & Mg Stearate) 2% drug load in phosphate buffer (pH 7.4) at 37oC
Figure 3.4: Metoprolol Tartrate release from DL-PLA implants with two different excipients (Ceto Stearyl Alcohol & Stearyl Alcohol) with 5% drug load in phosphate buffer (pH 7.4) at 37oC
Figure 3.5: Metoprolol Tartrate release from DL-PLA implants with two different excipients (Arachis Oil, Searic Acid & Cetyl Alcohol) with 2% drug load in phosphate buffer (pH 7.4) at 37oC 220.127.116.11. Burst State Release Kinetics: Effect of Excipients The burst release data were analyzed using Zero order, First order, Higuchi and KorsmeyerPeppas model to identify burst release characteristics for implants with different excipients. The respective data are presented in the Table 3.3. The burst release phase of most of the implants with excipients best fitted to Higuchi kinetic model and regression analysis was performed on the fitted curves. The Higuchi Kinetic release rate constant therefore is plotted in the Figure 3.6 and the fitting data are given in Table 3.4. All excipients best fitted to Higuchi kinetic model (Table 3.4) except Gleceryl Mono Stearate with R2 value 0.947. Stearic Acid best fitted to Higuchi model with R2 value 0.994. Figure 3.6-3.22 exhibit the burst release of drug for excipient incorporated in situ implants compared to drug only implant. In the burst phase, all excipients were best fitted to Higuchi Kinetic model (Table 3.3.). Stearic acid with R2 value 0.994 was found to be best fitted in the Higuchi Kinetic model. But in the same burst phase Mg Stearate with R2 was found to be best fitted in the Korsmeyer-Peppas model. Table 3.3: Fitting comparison of equation of Zero order, First order, Higuchi and KorsmeyerPeppas for describing burst release of Metoprolol Tartrate from DL-PLA in situ implants with different excipients. Kinetic Model Drug Glecery Steari Ceto Cetyl Arachi Mg Stearyl without l Mono c Stearyl Alcoho s oil Stearat Alcoho excipien Stearate Acid Alcoho l e l t l Zero Order Rate 1484 1432 1513 1474 1898 1316 1514 1615 Constant (Cumulative % release/Days) R2 Value 0.828 0.798 0.907 0.820 0.835 0.824 0.816 0.802 First Order Rate -10.09 Constant (Cumulative % to be released/Day s) R2 Value 0.870
Rate Constant (Cumulative % release/Days 1/2) R2 Value Korsmeyer Rate -Peppas Constant
(Log of Cumulative fraction released / Log Day) R2 Value 0.948
Table 3.4: Fitting comparison of equation of Higuchi Kinetic Model for describing burst release of Metoprolol Tartrate from DL-PLA in situ implants with different excipients. Excipient Higuchi Kinetic Model Rate Constant (Cumulative % release/Days) without 319
Drug excipient Gleceryl Mono Stearate (GMS) Stearic Acid Ceto Stearyl Alcohol Cetyl Alcohol Arachis oil Mg Stearate Stearyl Alcohol
R2 Value 0.963
315.7 317.8 407.1 283.3 326.8 350
0.994 0.959 0.966 0.961 0.957 0.949
Figure 3.6: Graphical representation of release rate constant (Burst Phase) of implants with different excipients in the Higuchi kinetic models
Figure 3.7: Zero Order plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (GMS & Mg Stearate)
Figure 3.8: First order plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (GMS & Mg Stearate)
Figure 3.9: Higuchi Kinetic plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (GMS & Mg Stearate)
Figure 3.10: Korsmeyer- Peppas plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (GMS & Mg Stearate)
Figure 3.11: Zero Order plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (Stearyl Alcohol & Ceto Stearyl Alcohol)
Figure 3.12: First Order plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (Stearyl Alcohol & Ceto Stearyl Alcohol)
Figure 3.13: Higuchi Kinetic plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (Stearyl Alcohol & Ceto Stearyl Alcohol)
Figure 3.14: Korsmeyer- Peppas plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (Stearyl Alcohol & Ceto Stearyl Alcohol)
Figure 3.15: Zero Order plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (Arachis Oil & Stearic Aid)
Figure 3.16: First Order plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (Arachis Oil & Stearic Aid)
Figure 3.17: Higuchi Kinetic plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (Arachis Oil & Stearic Aid)
Figure 3.18: Korsmeyer-Peppas Kinetic plot of Metoprolol Tartrate burst release from DLPLA in situ implants with different excipients (Arachis Oil & Stearic Aid)
Figure 3.19: Zero Order plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (Cety Alcohol)
Figure 3.20: First Order plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (Cety Alcohol)
Figure 3.21: Higuchi Kinetics plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (Cety Alcohol)
Figure 3.22: Korsmeyer-Peppas plot of Metoprolol Tartrate burst release from DL-PLA in situ implants with different excipients (Cety Alcohol) 18.104.22.168. Steady State Release Kinetics: Effect of Excipients The kinetics of steady state Metoprolol Tartrate release from implants with different excipients was determined by finding the best fit of the linear potion of the release data to Zero order, First order, Higuchi and Korsmeyer-Peppas model. Release rate constants and R2
values, used to evaluate the accuracy of the fit are listed in Table 3.5. The Higuchi release rate constant is plotted in the Figure 3.23 and the fitting data are given in Table 3.6. In the steady state rlelease kinetics, Cetyl alcohol (R2= 0.997) was found to bebest fitted to Higuchi Kinetic model.GMS (R2=0.999) was found to be best fitted to Korsmeyer-Peppas model. Figure 3.23-3.39 exhibit the steady state release of drug for excipient incorporated in situ implants compared to drug only implant. In case of Steady State phase, all the excipients were best fitted in the Higuchi Kinetic model except Mg Stearate (R2 value 0.680). CetylAlcohol (R2= 0.997) and Arachis oil (R2= 0.995) were found to be best fitted in the Higuchi Kinetic Model. Table 3.5: Fitting comparison of equation of Zero order, First order, Higuchi and KorsmeyerPeppas for describing steady state release of Metoprolol Tartrate from DL-PLA in situ implants with different excipients. Kinetic Model
Cetyl Arachi Alcoho s oil l
Mg Stearat e
Stearyl Alcoho l
Ceto Stearyl Alcoho l 5.036
First Order Rate -0165 Constant (Cumulative % to be released/Day s) R2 Value 0.907
Zero Order Rate Constant (Cumulative % release/Days) R2 Value
Rate Constant (Cumulative % release/Days 1/2) R2 Value Korsmeyer Rate -Peppas Constant (Log of Cumulative fraction released / Log Day) R2 Value
Drug without excipien t 7.866
Glecery Steari l Mono c Stearate Acid 4.792
Table 3.6: Fitting comparison of equation of Higuchi for describing steady state release of Metoprolol Tartrate from DL-PLA in situ implants with different excipients. Excipient
Higuchi Kinetic Model Rate Constant (Cumulative % release/Days R2 Value 1/2) without 17.18 0.940
Drug excipient Gleceryl Mono Stearate (GMS) Stearic Acid Ceto Stearyl Alcohol Cetyl Alcohol Arachis oil Mg Stearate Stearyl Alcohol
13.95 14.75 10.29 16.93 11.60 15.89
0.993 0.991 0.997 0.995 0.680 0.956
Figure 3.23: Graphical representation of release rate constant (Steady State Phase) of implants with different excipients in the Higuchi kinetic model
Figure 3.24: Zero order plot of Metoprolol Tartrate steady state release from DL-PLA in situ implants with different excipients (GMS & Mg Stearate)
Figure 3.25: First Order plot of Metoprolol Tartrate steady state release from DL-PLA in situ implants with different excipients (GMS & Mg Stearate).
Figure 3.26: Higuchi Kinetic plot of Metoprolol Tartrate steady state release from DL-PLA in situ implants with different excipients (GMS & Mg Stearate).
Figure 3.27: Korsmeyer-Peppas plot of Metoprolol Tartrate steady state release from DLPLA in situ implants with different excipients (GMS & Mg Stearate)
Figure 3.28: Zero Order plot of Metoprolol Tartrate steady state release from DL-PLA in situ implants with different excipients (Stearyl Alcohol & Ceto Stearyl Alcohol).
Figure 3.29: First Order plot of Metoprolol Tartrate steady state release from DL-PLA in situ implants with different excipients (Stearyl Alcohol & Ceto Stearyl Alcohol).
Figure 3.30: Higuchi Kinetic plot of Metoprolol Tartrate steady state release from DL-PLA in situ implants with different excipients (Stearyl Alcohol & Ceto Stearyl Alcohol).
Figure 3.31: Korsmeyer-Peppas plot of Metoprolol Tartrate steady state release from DLPLA in situ implants with different excipients (Stearyl Alcohol & Ceto Stearyl Alcohol).
Figure 3.32: Zero Order plot of Metoprolol Tartrate steady state release from DL-PLA in situ implants with different excipients (Arachis Oil & Stearic Acid).
Figure 3.33: First Order plot of Metoprolol Tartrate steady state release from DL-PLA in situ implants with different excipients (Arachis Oil & Stearic Acid)
Figure 3.34: Higuchi Kinetic plot of Metoprolol Tartrate steady state release from DL-PLA in situ implants with different excipients (Arachis Oil & Stearic Acid)
Figure 3.35: Korsmeyer-Peppas Kinetic plot of Metoprolol Tartrate steady state release from DL-PLA in situ implants with different excipients (Arachis Oil & Stearic Acid)
Figure 3.36: Zero Order Kinetic plot of Metoprolol Tartrate steady state release from DLPLA in situ implants with different excipients (Cetyl Alcohol)
Figure 3.37: First Order Kinetic plot of Metoprolol Tartrate steady state release from DLPLA in situ implants with different excipients (Cetyl Alcohol)
Figure 3.38: Higuchi Kinetic plot of Metoprolol Tartrate steady state release from DL-PLA in situ implants with different excipients (Cetyl Alcohol)
Figure 3.39: Korsmeyer-Papper plot of Metoprolol Tartrate steady state release from DLPLA in situ implants with different excipients (Cetyl Alcohol) Chapter Four: Summary 4.1. Summary The field of in situ forming implants has grown exponentially in recent years. Liquid formulations generating a semi solid depot after subcutaneous injection, also designated as implants, are attractive delivery system for parenteral application because they are less invasive and less painful compared to conventional implants (Building Biotechnology, 2008). Therefore the aim of this study is to develop sustained release Metoprolol Tartrate delivery from biodegradable polymeric (DL-PLA) in situ implants for parenteral administration. Metoprolol Tartrate was chosen for its high water solubility property and entrapping it in implant would be a piece of innovative work. In this study a biodegradable polymer (DL-PLA) was combined with a biocompatible aprotic solvent (DMSO) and then the active ingredient (Metoprolol Tartrate) was dissolved in it. Then it was injected into phosphate buffer (pH 7.4) and kept in static condition at 37oC in an incubator in order to observe the drug release profile. Effect of 2% drug loadings was observed. The drug release profile was also studied for seven different excipients (GMS, Stearic Acid, Ceto Stearyl Alcohol, Cetyl Alcohol, Arachis Oil, Mg Stearate, Stearyl Alcohol) incorporated implants with 2% drug load. Among all implants most were found round, sphericaland some were found semi spherical shaped. Figure 3.1 represents some randomly selected digital images of in situ implants. The implants structures were investigated for thorough characterization, because kinetics of drug release is greatly influenced by morphological characteristics of implants. The effect of incorporation of different excipients on loading efficiency of Metoprolol Tartrate in situ implants was studied for 2% drug load. The excipient load was same as the drug load. In case of excipient incorporated implants the highest drug loading efficiency was found with Arachis oil (87.25%) and the lowest drug loading efficiency was found with Cetyl Alcohol (60.78%) as compared to the loading efficiency of 70.13% for drug without excipient. The loading efficiency was found to decrease in the following sequence:
Arachis Oil > Stearic Acid > Ceto Stearyl Alcohol > Mg Stearate > Drug without excipient > GMS > Stearyl Alcohol > Cetyl Alcohol. Here Arachis Oil (87.25%), Stearic Acid (81.86%), Ceto Stearyl Alcohol (72.55), Mg Stearate (71.07%) increased drug loading efficiency as compared to drug without excipient (70.31%). This may be due to the hydrophobic property of these excipients. On the other hand Stearyl Alcohol (61.76%) and Cetyl Alcohol (60.78%) showed decrease in drug loading efficiency as compared to drug without excipient. The percentage of Cetyl alcohol that is used in the formulation may act as a water absorptive agent for which it probably reduced the drug loading efficiency. In this study in vitro drug release was studied for 30 days in phosphate buffer with pH 7.4 from biodegradable in situ implants. Composition of the investigated formulations varied with respect to drug loading and addition of different excipients. The kinetics of steady state Metoprolol Tartrate release and burst release from implants with different drug loading and with different excipients was determined by finding the best fit of the linear potion of the release data to Zero order, First order, Higuchi and Korsmeyer-Peppas model. The initial burst release was found on the 0.042th day (one hour) in case of all excipients with 2% drug load. The drugâ€™s burst releases were found 60.16 %, 63.55%, 61.93%, 79.74 %, 55.29%, 63.58%, 67.84% for Gleceryl Mono Stearate (GMS), Stearic Acid, Ceto Stearyl Alcohol, Cetyl Alcohol, Arachis oil, Mg Stearate, Stearyl Alcohol with 2% drug load respectively. But in case of drug only in the implants it was found to be 62.34 %. The calculated time interval for linear phase was found 0.042-7, 0.042-7, 0.042-7, 0.042-7, 0.042-5, 0.042-3, 0.042-3 days for Gleceryl Mono Stearate (GMS), Stearic Acid, Ceto Stearyl Alcohol, Arachis oil, Mg Stearate, Stearyl Alcohol and Cetyl Alcohol 2% drug load, respectively. But in case of only drug without excipient in the implant it was found 0.042-5 days. So GMS, Stearic Acid, Ceto Stearyl Alcohol and Arachis oil reduced the drug release from the implant as compared to drug without excipients. In the burst phase all excipients best fitted to Higuchi kinetic model except Gleceryl Mono Stearate with R2 value 0.947. Gleceryl Mono Stearate best fitted to Korsmeyer- Peppas model with R2 value 0.989. As the release profile exhibited biphasic behavior the kinetics was evaluated for the both phases, the initial burst release phase and the steady state release phase. In the burst phase, all excipients were best fitted to Higuchi Kinetic model (Table 3.3.). Stearic acid with R2 value 0.994 was found to be best fitted in the Higuchi Kinetic model. But in the same burst phase Mg Stearate with R2 was found to be best fitted in the Korsmeyer-Peppas model. In case of Steady State phase, all the excipients were best fitted in the Higuchi Kinetic model except Mg Stearate (R2 value 0.680). CetylAlcohol (R2= 0.997) and Arachis oil (R2= 0.995) were found to be best fitted in the Higuchi Kinetic Model. The DL-PLA in situ implant of Metoprolol Tertrate delayed the drug release up to a period of 5 to 7 days though it is a highly water soluble drug. Moreover decreasing drug content and increasing polymer content in the implant exhibited increasing loading efficiency as well as decreasing drug release. Inclusion of suitable excipient also increased loading efficiency with retarding the drug release more than that of the drug only implant. As no surgery is needed for this type of drug delivery system, it may be a very attractive candidate for further future development with this drug. So, this piece of work is expected to encourage researchers to develop Metoprolol Tartrate in situ implants.