Hyperforin in St. John's wort drug interactions

Eur J Clin Pharmacol (2006) 62: 225–233 DOI 10.1007/s00228-006-0096-0

PH ARMA COK INETICS AND DISPOSITION

Rajanikanth Madabushi . Bruno Frank .

Bernd Drewelow . Hartmut Derendorf .

Veronika Butterweck

Hyperforin in St. John’s wort drug interactions

Received: 16 September 2005 / Accepted: 6 January 2006 / Published online: 14 February 2006 # Springer-Verlag 2006

Abstract Recently, interactions of herbal medicines with synthetic drugs came into focus of particular interest. In the past 3 years, more than 50 papers were published regarding interactions between St. John’s wort (Hypericum perforatum L.; SJW) and prescription drugs. Co-medication with SJW resulted in decreased plasma concentrations of a number of drugs including amitriptyline, cyclosporine, digoxin, indinavir, irinotecan, warfarin, phenprocoumon, alprazolam, dextrometorphane, simvastatin, and oral contraceptives. Sufficient evidence from interaction studies and case reports indicate that SJW is a potent inducer of cytochrome P450 enzymes (particularly CYP3A4) and/or P-glycoprotein. Recent studies could show that the degree of enzyme induction by SJW correlates strongly with the amount of hyperforin found in the product. Products that do not contain substantial amounts of hyperforin (<1%) have not been shown to produce clinically relevant enzyme induction. On the other hand, some evidence suggests that hyperforin may also contribute to the antidepressant activity of SJW. However, clinical studies using SJW preparations with a low hyperforin amount (<1%) clearly demonstrated the superiority of this plant extract over placebo and its equivalence to imipramine and fluoxetine in the treatment of mild to moderate forms of depression. In the present paper clinical significant SJW interactions are critically evaluated against the background of hyperforin.

R. Madabushi . H. Derendorf . V. Butterweck (*) Department of Pharmaceutics, College of Pharmacy, University of Florida, P.O. 100494 Gainesville, FL 32610, USA e-mail: butterwk@cop.ufl.edu Tel.: +1-352-8462470 Fax: +1-352-3924447 B. Frank Kneipp Werke Würzburg, Germany, Würzburg B. Drewelow Institute of Clinical Pharmacology, University of Rostock, Germany, Rostock

Keywords Drug interactions . Hypericum perforatum .

Herbal medicine . St. John’s wort

Introduction St John’s wort (Hypericum perforatum L, Clusiaceae) is a plant that has been used as a medicinal herb since ancient times. Today, Hypericum is used in many countries for the treatment of mild to moderate forms of depression. Several clinical trials have demonstrated mood enhancement with efficacy that is comparable to widely prescribed synthetic antidepressants such as fluoxetine [1–3], sertraline [4, 5], and imipramine [6, 7]. SJW is usually well-tolerated. In a review of SJW preparations and adverse drug reactions, the author noted that this incidence was approximately ten times less than with synthetic antidepressants [8].

The extracts of SJW contain different groups of compounds such as hypericin, hyperforin and flavonoids (for review see [9]). The majority of hydroalcoholic SJW extracts is standardized on a hypericin content of 0.2–0.3% and a variable amount of hyperforin (0.2–5%). A German study that analyzed 33 different St. John’s wort products showed that the hyperforin content varied from <0.5 mg per unit (<0.02% of extract) to 24.87 mg per unit (5.85% of extract) [10].

For example, the extract ZE 117, marketed as Remotive, contains hypericin in an amount of 0.2% and negligible amounts of hyperforin (0.2%) [11]. In the past, this was also most likely the case for extract LI 160, marketed as Jarsin, or a similar extract, marketed as Neuroplant, before the extraction process was modified [12, 13]. With the modified method, a hyperforin content of 4–5% has been reported for products containing LI 160 [10]. This is equivalent of a daily dose of approximately 50 mg of hyperforin, based on a 300-mg extract administered three times daily. The widely differing amounts of hyperforin in SJW preparations should be taken into account when drug interactions with SJW are discussed. Most of the current cases which report a specific product involved SJW products that are rich in hyperforin (up to 5%). No drug

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interaction has been reported with products that have low contents of hyperforin [11, 14, 15]. Furthermore, it is interesting to note that reports of drug interactions with St. John’s wort were not reported before 1998, when a modified extraction method was introduced that led to products with higher content of hyperforin [12, 13]. The present review discusses the possible role of hyperforin in clinical significant drug interactions with SJW. However, the most documented drug interactions of St. John’s wort are only discussed in brief, since these have been extensively reviewed in recently published articles [16, 17]. The second focus of this review is therefore on reported drug interactions where the literature is inconsistent. The literature has been searched systematically without language restrictions using the databases Medline and Embase up to August 2005. The following search terms were used: “St. John’s wort”, “hypericum”, “hypericin”, “hyperforin”, “flavonoids”, “CYP”, “P-glycoprotein”, “interaction”, “induction”, “inhibition”.

Influence of SJW on P-glycoprotein and several cytochrome P-450 enzyme activities in humans CYP3A4, the most abundant cytochrome P450 (CYP450) isoenzyme, is responsible for the metabolism of more than 73 medications and numerous endogenous compounds [18–20]. Substrates for this isoenzyme include protease inhibitors, non-sedating antihistamines, calcium channel blockers, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, benzodiazepines, estrogens, macrolide antibiotics, cyclosporine, carbamazepine, ketoconazole, and corticosterone. [18–20]. One method to determine the in vivo effect of medications on CYP3A4 activity is through the evaluation of the urinary 6-β-hydroxycortisol/ cortisol ratio. 6-β-hydroxycortisol has been shown to be a non-specific marker of CYP3A4 activity [21–23]. Roby et al. [24] could show that reagent grade SJW taken for 14 days (Hypericum Byers Club, Lot 180632, 0.3% hypericin, 3×300 mg/d, hyperforin amount not provided) at the dose recommended for the treatment of mild to moderate depression was associated with a significant increase in the mean urinary 6-β-hydroxycortisol/cortisol ratio. The ratio increased from 7.1 to 13.0 suggesting a CYP3A4 induction after intake of SJW at the recommended dosage.

Besides an induction of CYP3A4 enzyme activities in the liver and small intestine, the involvement of the Pglycoprotein/MDR1 system in the intestine was also discussed. P-glycoprotein (P-gp), an ATP-dependent primary active transporter belonging to the ABC transporter superfamily, occurs in plasma membranes of many tissues, where is serves as an efflux transporter of xenobiotics [25].

In the intestine, P-gp is located at the apical surface of epithelial cells and interferes with drug absorption by pumping out a variety of orally administered drugs, such as cyclosporine, into the intestinal lumen [26]. After uptake by the enterocyte, many lipophilic drugs are either

metabolized by CYP3A4 or pumped back into the lumen by the P-gp transporter. Therefore, CYP3A4 and P-gp may act in tandem as a barrier to oral delivery of many drugs.

This hypothesis could be confirmed in animal experiments as well as in clinical studies [27]. The administration of SJW extract to rats during 14 days resulted in a 3.8-fold increase of intestinal P-glycoprotein/MdR1 expression and in a 2.5-fold increase in hepatic CYP3As expression [27].

In a clinical study, the administration of SJW extract resulted in a 1.4- and 1.5-fold increased expressions of duodenal P-glycoprotein/MDR and CYP3A4, respectively [27]. These results indicate direct inducing effects of SJW on intestinal P-glycoprotein/MDR1 and intestinal and hepatic CYP3A4. In both studies, the extract LI 160 (80% methanol v/v, 0.3% hypericin, batch 99100400, 3×300 mg/d, unknown amount of hyperforin) was used.

In contrast to short-term administration (1×900 mg SJW in 24 h), long-term SJW administration (3×300 mg/d for 14 days) resulted in a significant and selective induction of CYP3A4 (midazolam) activity in the intestinal wall [28].

There was no change in CYP2C9 (tolbutamide), CYP1A2 (caffeine), or CYP2D6 (dextrometorphan) activities as a result of SJW administration. In contrast to the >50% decrease in the area under the plasma-concentration time curve (AUC) when midazolam was administered orally, long-term SJW administration caused a 20% decrease in AUC when midazolam was given intravenously. This result confirms the involvement of intestinal as well as hepatic CYP3A4. In this study, a SJW extract from Rexall Sundown Pharmaceuticals was used (0.3% hypericin, unknown hyperforin content, 3×300 mg) [28]. The authors concluded that the reduced therapeutic efficacy of drugs metabolized by CYP3A4 should be anticipated during long-term administration of SJW. Several reports have documented clinically relevant drug interactions between SJW and coadministered drugs such as indinavir, cyclosporine and digoxin [29–31], attributing induction of hepatic CYP3A4 as the likely mechanism [24, 32]. However, interactions with digoxin and indinavir are unlikely to be fully explained by this mechanism, as they are not only a CYP3A4 substrate but also a substrate for Pgp. Hennessy and coworkers [33] could show that SJW increased expression and enhanced the drug efflux function of P-gp in peripheral blood lymphocytes of healthy volunteers. P-gp expression increased 4.2-fold from baseline in subjects treated with SJW (Good n’ Natural, 0.15% hypericin, 600 mg extract 3× daily) over a period of 16 days; there was no effect observed in patients receiving placebo.

In another pharmacokinetic study in healthy volunteers, changes in plasma pharmacokinetics of alprazolam as a probe for CYP3A4 activity and the ratio of dextrometorphan to its metabolite dextrorphan were measured after 14 days of co-medication with SJW extract (LI 160, 2×300 mg/day; each tablet contained 1,398 μg hyperforin, 151 μg hypericin, 279 μg pseudohypericin). [34]. A 2-fold decrease in the area under the curve for alprazolam plasma

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concentration versus time and a 2-fold increase in alprazolam clearance were observed following St. John’s wort administration. Alprazolam elimination half-life was shortened from a mean (±SD) of 12.4±3.9 h to 6.0±2.4 h.

The mean (±SD) urinary ratio of dextrometorphan to its metabolite was 0.006 at baseline and 0.014 after St. John’s wort administration [34]. These findings indicate that longterm administration of St. John’s wort may result in diminished clinical efficacy or increased dosage requirements for CYP3A4 substrates.

Recently, Rengelshausen et al. [35] investigated the short-term and long-term effects of SJW on the pharmacokinetics of voriconazole. The metabolism of this new antifungal triazole is mediated by CYP2C19 and CYP3A4, as well as by CYP2C9 to a lesser extent. These authors could show that coadministration of the hyperforin-rich methanolic extract LI160 with voriconazole increased the plasma AUC of the antifungal drug (by 22%) during the first initial 10 h of the first day of SJW administration when compared to the control. After 15 days of SJW intake, the AUC from hour 0 to infinity was reduced by 59% compared with control with a corresponding increase in oral voriconazole clearance. Thus, it is reasonable that SJW might induce the metabolism of voriconazole, depending on both CYP3A4 and CYP2C19.

Based on the studies listed above it can be concluded that SJW induces hepatic and intestinal CYP3A4 and intestinal P-gp. Thus, it is likely that SJW will interact with drugs that are metabolized via CYP3A4 or P-gp. Interactions (until 2004) of SJW and synthetic drugs have been systematically reviewed [16, 17, 36, 37]. These reviews clearly show that interactions between xenobiotics and the plant extract particularly occur with drugs that are metabolized and eliminated by both CYP3A4 and P-gp.

It also becomes evident that not all drugs have the potential to interact with SJW. Table 1 gives an overview about drugs where an interaction with SJW is likely to occur.

Whereas pharmacokinetic interactions between SJW and

imatinib, irinotecan, indinavir, nevirapine, cyclosporine, tacrolimus, warfarin, phenprocoumon, digoxin and methadone can be taken for granted, interactions with oral contraceptives, carbamazepine, theophylline and HMGCoA reductase inhibitors (Table 1) need to be critically evaluated and will be discussed in greater detail in this review.

Altered drug pharmacokinetics Oral contraceptives The first cases describing breakthrough bleeding in women taking ethinyl estradiol (EE) and desogestrel concomitantly with SJW were reported in 1999. The breakthrough bleeding was presumed to be due to lowered concentrations of ethinyl estradiol from an interaction with SJW [38]. This was followed by two cases of pregnancies reported in women using SJW simultaneously with oral contraceptives by the Adverse Reactions Database of the Swedish Medical Products Agency, which described the cases “due to decrease in the effect of oral contraceptives when they were concurrently taken with products containing St John’s Wort” [39]. Authorities in the United Kingdom have had seven reports of women becoming pregnant while using contraceptives along with SJW. Five cases of ineffective contraception coincident with St John’s wort consumption have been reported to the German Federal Institute for Drugs and Medical Devices, Drug Commission of the German Medical Profession [40]. To date, there have been no confirmed reports of pregnancy due to contraceptive failures clearly associated with the use of SJW reported to the U.S. Federal Drug Administration (FDA). It is important to note that the number of reported cases worldwide is small, and the number of women actually taking both, oral contraceptives and SJW, is unknown.

However, the occurrence of irregular bleeding during

Table 1 Reported drug interactions with St. John’s wort (Hypericum perforatum) preparations Reported pharmacokinetic interactions Drug category Cystostatic drugs HIV drugs Immunosuppressants Anticoagulants Cardiovascular drugs Opiates Oral contraceptives Antiepileptic drugs Anti-Asthma drugs HMG-CoA reductase inhibitors

Drug(s) Imatinib, Irinotecan Indinavir, Nevirapine Cyclosporine, Tacrolimus Warfarin, Phenprocoumon Digoxin Methadone Ethinylestradiol (EE)/Desogestrel, EE/Norethisterone, Levonorgestrel, Norethisterone* Carbamazepine* Theophylline* Simvastatin, Atorvastatin*

Possible mechanism of interaction CYP 3A4 induction CYP 3A4 and MDR1 induction CYP3A4 and MDR1 induction CYP2C9 induction MDR1 efflux activity induced CYP3A4 induction CYP3A4 induction CYP3A4 induction CYP1A2 induction Intestinal CYP3A4 induction

Drug category and drugs that are highlighted with an asterisk (*) are discussed in greater detail in the text

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concomitant intake of SJW and oral contraceptives seems to be verified by several reports to drug authorities and three interaction studies [41–43].

The main mechanism of contraceptive action of lowdose oral contraceptives is prevention of ovulation through inhibition of gonadotropin release from the pituitary, which interferes with the normal cascade of events that leads to ovulation. The EE component of the pill mainly inhibits release of follicle-stimulating hormone (FSH), and the progestin component inhibits release of luteinizing hormone (LH). The major route of inactivation of EE is via hydroxylation by CYP3A4 [44]. Progestins are also CYP3A4 substrates, and progestin-only contraceptives may also be vulnerable to induction of CYP3A4 by comedication [45]. Although not as well documented as EE drug interactions, contraceptive failure of levonorgestrel has been reported in women who received phenobarbital [46] and phenytoin [47, 48]. Any drug that could induce the metabolism of EE and progestins increases the risk of contraceptive failure and unwanted pregnancies.

In 2002, a first pharmacokinetic interaction study (n=16) was performed using the SJW extract ZE117 (0.2% hypericin, 0.2% hyperforin, 500 mg/day) and a low dose oral contraceptive (0.02 mg ethinyl estradiol, 0.15 mg desogestrel) [11]. There was no significant change in estradiol and 3-ketodesogestrel (active metabolite of desogestrel) levels when SJW was given concomitantly with SJW. Furthermore, intracyclic bleedings during SJW comedication were not reported. CYP-3A4, -2D6 and 2C19 activities were also unchanged on days 7 and 21 of the cycle. These enzymes are involved in the bioactivation of desogestrel to its active metabolite 3-ketodesogestrel [49]. In another pharmacokinetic study, 12 healthy premenopausal women who were using oral contraception (>3 months) received a combination oral contraceptive pill (Ortho-Novum 1/35) for 3 consecutive 28-day menstrual cycles [41]. During the second and third cycles, the participants received 300 mg SJW three times daily (Rexall Sundown Pharmaceuticals, each capsule contained 1.1 mg hypericin and 8.9 mg hyperforin). Concomitant use of SJW resulted in modest but significant changes in EE and norethindrone pharmacokinetics. The clearance of norethindrone increased form 8.2±2.7 L/h to 9.5±3.4 L/h. and the half-life of ethinyl estradiol decreased from 23.4±19.5 h to 12.2±7.1 h. The oral clearance of midazolam (CYP3A4 model substrate) was significantly increased (109.2±47.9 l/ h to 166.7±81.3) during SJW co-administration, but the systemic clearance of midazolam was unchanged [41].

Serum concentrations of FSH, LH and progesterone were not significantly affected by SJW. Breakthrough bleeding occurred in 2 of 12 women in the control phase and in 7 of 12 women in the SJW phase. In a third study, 18 women were treated with a low-dose contraceptive (0.02 mg ethinyl estradiol, 0.15 mg desogestel) alone or combined with 600 mg or 900 mg SJW (LI 160, 80% methanolic extract, 0.3% hypericin, no information about the hyperforin amount provided), respectively, on two consecutive cycles [43]. During co-medication of low-oral contraceptive and SJW, there was no significant change in follicle

maturation, serum estradiol or progesterone concentrations when compared with the oral contraceptive treatment alone. Thirteen and 15 women reported intracyclic bleeding under the two SJW dosages if compared with 6 women of the oral contraceptive treatment group alone. The AUC and Cmax of EE remained unchanged during all study cycles, whereas the AUC and Cmax of 3-ketodesogestrel decreased significantly during both cycles. The authors conclude that the decreased formation of 3-ketodesogestrel from the prodrug desogestrel might be due to an inhibition of CYP2C9/CYP2C19 or an induction of CYP3A4 [43]. In a recent study, 16 women were treated with a low-dose oral contraceptive (Loestrin 1/20, 0.02 mg ethinyl estradiol, 1 mg norethindrone) and a placebo for two consecutive 28day cycles in a single-blind sequential trial [42]. Treatment with SJW 900 mg/d (Hypericum Buyers Club, alcoholic extract, 0.3% hypericin, 3.7% hyperforin) was then added for two additional 28-day cycles. Treatment with SJW was associated with a significant 13–15% reduction in the dose exposure from the contraceptive. Breakthrough bleeding increased in the treatment cycles, as did evidence of follicle growth and probable ovulation. Based on the “FDA Guidance for Industry: In vivo drug metabolism/drug interaction studies” a reduction of oral contraceptive levels of 13–15% are not considered as clinically relevant, since the confidence interval is within the equivalence range of 80–125% (document available at: http://www.fda.gov/ cber/cberftp.html). Only if the ratio falls beyond this equivalence range standard Agency practice is to conclude that there are clinically significant differences present.

In conclusion, a significant impact of SJW co-medication on contraceptive efficacy appears to be unlikely. In all studies, no significant change in follicle maturations, serum estradiol or progesterone concentrations were detected on SJW co-medication with oral contraceptives. Bioavailability of ethinyl estradiol remained unchanged whereas the pharmacokinetics of desogestrel [43] and norethindrone [42] appeared to be slightly decreased. Those decreases were achieved with SJW extracts that contained hyperforin amounts between 3–5%, whereas no changes in desogestrel pharmacokinetics were observed with an SJW extract containing low amounts of hyperforin (<0.2%) [11].

Carbamazepine A 2-week open study of eight healthy volunteers did not find a significant difference in carbamazepine and carbamazepine-10,11-epoxide concentrations with concomitant therapy with SJW [50]. Subjects received 100 mg of carbamazepine twice daily for 3 days, 200 mg twice daily for 3 days, and then 400 mg once daily for 14 days. Blood samples at different times points were collected on day 21.

The subjects then took 300 mg of SJW (Hypericum Buyers Club, Lot 91021, 0.3% hypericin, no information about hyperforin amount provided) 3 times daily with carbamazepine for 14 days. Since carbamazepine is a potent inducer of CYP3A4 itself the authors concluded that after auto-induction of CYP3A4 by carbamazepine itself SJW

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could not further induce this enzymes activity [50]. Thus, concomitant use of SJW and carbamazepine apparently does not result into a loss of anti-epileptic activity of the drug.

Theophylline Theophylline is mainly metabolized by CYP1A2 and to a lesser extent also by CYP2E1 and CYP3A4 [51]. Several papers have listed theophylline as one of the drugs of concern that interacts with SJW [36, 52–54]. In the case report cited by those review articles, withdrawal of SJW doubled theophylline plasma levels [55]. However, the patient was a smoker taking 11 other medications, some of them are also known to interact with theophylline. A follow-up study in healthy volunteers could not detect changes in the pharmacokinetics of theophylline after intake of SJW [56]. The subjects took SJW (300 mg, 3× daily, Tru Nature, bulk No1EA0316, 0.3% hypericin, no information about hyperforin amount provided) for 15 days. On day 14, they received a single oral dose of theophylline (400 mg) without SJW treatment on another occasion. Plasma and urine samples were obtained during a 48-h period after theophylline administration. SJW did not cause significant changes in theophylline pharmacokinetics. In a recent study, Komoroski et al. [57] used primary cultures of human hepatocytes to characterize the effect of hyperforin and hypericin on CYP1A2, CYP2C9, CYP2D6, and CYP3A4 enzyme activity. Hyperforin did not significantly change CYP1A2 or CYP2D6 activity when compared to the control group. The same result was observed for hypericin. The authors conclude that it is unlikely that hyperforin as well as hypericin will result in any clinically significant drug interaction in vivo with substrates of CYP1A2 and CYP2D6. In conclusion, since SJW is a potent inducer of CYP 3A4, 2C9, and 2C19 and considering that theophylline mainly is metabolized by CYP 1A2, a clinical significant interaction between theophylline and SJW can therefore be excluded regardless of the amount of hyperforin.

HMG-CoA Reductase Inhibitors Simvastatin and pravastatin are widely used 3-hydroxy-3methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, and they have beneficial effects on coronary disease and mortality rates in patients with hypercholoesterolaemia [58]. The metabolic profiles of simvastatin are remarkably different from those of pravastatin. Simvastatin is primarily metabolized by CYP3A4 in the gut wall and in the liver [59, 60]. Pravastatin is metabolized by CYPindependent pathways such as degradation and phase II reactions [59, 60]. Thus, co-medication with SJW would more likely cause a pharmacokinetic interaction with simvastatin than with pravastatin. The pharmacokinetic

profiles of both substances were determined after repeated administration of SJW in a double-blind, crossover study [61]. Eight healthy volunteers received SJW (300 mg, 3× daily, Tru Nature, bulk No. N481103948, 0.3% hypericin, unknowm hyperforin amount) over a period of 14 days. On day 14, a single oral dose of 10 mg simvastatin and 20 mg pravastatin and blood samples were obtained during a 24-h period after the administration of each drug. SJW significantly lowered plasma concentrations of simvastatin but not of pravastatin. Based on this study, it is not justified to list the whole group of HMG-CoA reductase inhibitors as compounds that interact with SJW, since physicians can switch to the prescription of pravastatin instead if the patient wants to continue taking SJW.

Role of hyperforin in SJW drug interactions Pharmacological evaluation The mechanism for the apparent increase in drug metabolism by St. John’s wort extracts was examined by Moore and collaborators [62]. They showed that hyperforin, a constituent of St. John’s wort, is a potent ligand (K(i)= 27 nM) for the pregnane X receptor, an orphan nuclear receptor that regulates expression of the cytochrome P450 (CYP) 3A4 monooxygenase. Treatment of primary human hepatocytes with Hypericum extracts or hyperforin resulted in a marked induction of CYP3A4 expression. The authors cautioned that because CYP3A4 is involved in the oxidative metabolism of >50% of all drugs, their findings provide a molecular mechanism for the interaction of St. John’s wort with drugs and suggest that Hypericum extracts would be likely to interact with numerous drugs [62].

Interestingly, a study using alcoholic extracts of St. John’s wort prepared with methods that did not stabilize hyperforin reported CYP3A4 inhibition [32].

A study in mice investigated the role of components of Hypericum extracts on CYP3A induction [63]. This study explored whether hyperforin accounts for the inductive effects on CYP3A enzymes of St. John’s wort extracts. A hydroalcoholic extract containing 4.5% hyperforin was given at a dose of 300 mg/kg twice daily for 4 and 12 days.

Hyperforin was given as dicyclohexylammonium (DCHA) salt (18.1 mg/kg) on the basis of its content in the extract, to ensure comparable exposure to hyperforin. The extract increased hepatic erythromycin-N-demethylase (ERND) activity, which is cytochrome P450 enzyme (CYP) 3Adependent, about 2.2-fold after 4 days of dosing, with only slightly greater effect after 12 days (2.8 times controls).

Hyperforin similarly increased ERND activity within 4 days, to 1.8 times the activity of controls, suggesting that hyperforin behaves qualitatively and quantitatively like the extract as regards induction of CYP3A activity. This effect was confirmed by Western blot analysis of hepatic CYP3A expression. Exposure to hyperforin at the end of the 4-day treatment was still similar to that with SJW extract,

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although it was variable and lower than after the first dose in both cases, further suggesting that hyperforin plays a key role in CYP3A induction by the SJW extract in the mouse.

The authors proposed standardizing the extracts based on the hyperforin content in addition to hypericin content.

Clinical Evaluation of Hyperforin A recently completed 4-period study in 10 stable kidney transplant patients examined the influence of two St. John’s Wort preparations with different hyperforin content on cyclosporine pharmacokinetic parameters [15]. Test periods included: baseline with cyclosporine alone, 14 days treatment with low-hyperforin St. John’s Wort co-medication (<1 mg hyperforin/day), 4 weeks washout with cyclosporine doses alone, and 14 days treatment with high-hyperforin St. John’s Wort co-medication (>40 mg hyperforin/day). Cyclosporine kinetic parameters (AUC, Cmax, and tmax) were determined at the end of each period.

Pharmacokinetic parameters were adjusted for cyclosporine dose and plasma creatinine was monitored for safety. As shown in Table 2, there was no significant effect of low hyperforin on cyclosporine. However, high-hyperforin St. John’s wort decreased dose adjusted exposure to cyclosporine and increased doses of the immunosuppressant were required to maintain plasma creatinine. Serum creatinine was not different among treatment periods.

The results are consistent with a role for hyperforin in decreasing cyclosporine exposure. Induction of the intestinal drug transporter, P-glycoprotein as well as induction of CYP3A4 could explain decreased bioavailability of cyclosporine in the presence of hyperforin-rich St. John’s wort preparations. The increased mean cyclosporine daily dose from 225 to 362 mg, when patients were co-medicated with the high hyperforin preparation, indicates that the change in cyclosporine levels were considered clinically significant by the medical investigator and required a dose increase. Thus, the dose adjusted decrease in cyclosporine exposure of approximately 50% that is reflected by AUC and Cmax values should be considered clinically significant.

Another study compared effects of different St. John’s wort preparations containing different amounts of hyperforin on CYP3A4 activity using a midazolam probe (Study Table 2 Influence of different preparations of St. John’s wort on cyclosporine dose corrected pharmacokinetic parameters in 10 renal transplant patients [15] Parameter

Dose (mg/ day) AUC (ng×h/ mL) Cmax (ng/ mL)

Baseline

216±58

Lowhyperforin 223±54

3,663±678 3,109±527 995±284

Washout

225±54*

Highhyperforin 362±63**

3,442±741 1,671±313**

894±187

*p<0.05 vs baseline, **p<0.01 vs baseline

986±201

532±117**

No. 786, Pilotstudie1: Midazolam-Interaktion). The approach provides a means to evaluate whether drugs affect CYP3A enzymes and thus would be likely to alter the clearance of other substances metabolized by this important isoenzyme. Hydroxylation of the benzodiazepine, midazolam, to 1-OH-midazolam is mediated almost exclusively by CYP3A isoenzymes. Midazolam plasma clearance that is reflected from plasma profiles of the benzodiazepine can be used as a marker for CYP3A activitiy. Drugs that are substrates, inducers or inhibitors of CYP3A enzymes would be expected to alter the plasma profiles of midazolam.

The study included 42 healthy subjects randomized to 6 groups of 7 subjects each. Midazolam plasma profiles were characterized following a 7.5 mg oral dose on day 1 prior to St. John’s wort exposure and 14 days later after repeated daily dosing with one of six St. John’s wort preparations.

The test groups included the following different SJW preparations: extract LI160 (drug-extract ratio 4–7:1; hyperforin content 4.6%, Lichtwer Berlin, Germany), Hypericum herb powder A which was used to explore dose-response relationship with hyperforin (hyperforin content 0.4%, Kneipp-Werke, Wuerzburg, Germany) and Hypericum herb powder B with a very low hyperforin content (<0.1%, Kneipp-Werke, Wuerzburg, Germany).

Results are summarized in Table 3 for the percent change in midazolam AUC on day 14 compared to baseline. The decrease in midazolam AUC was highest in the LI160 treated group exposed to the highest hyperforin concentrations with a mean decrease of 79%, indicating induction of CYP3A enzymes. Using the herb powder A, the highest concentration (2,700 mg/day, hyperforin amount 12.1 mg/ day) showed the strongest decrease on midazolam AUC (−47.9%), when compared to the further dilutions of the powdered herb. A limited effect was noted after 14 days of dosing with the SJW herb powder B with a mean decrease in midazolam AUC values of 20.4% compared to baseline.

Interestingly, the upper limit of the calculated 95% confidence intervals approached 0 for the two lowest hyperforin preparations, indicating little clinical significance. The results indicate induction of CYP3A4 varies between SJW products. SJW products with low hyperforin content induce CYP3A4 significantly less than those preparations with a high hyperforin amount. The degree of induction depends on the hyperforin dose.

The question arises, if hyperforin is necessary for the antidepressant activity of SJW. Data from in vitro or animal studies are either pro or contra hyperforin and are not helpful to answer the question appropriately. Interestingly, a recent study showed that step by step elimination of hyperforin and hypericin from a hydroalcoholic SJW extract did not result in a loss of pharmacological activity [64]. An extract free of hyperforin and hypericin, but enriched in flavonoids (∼12%), showed antidepressant activity in valid animal models. The results indicate that flavonoids are also involved in the therapeutic efficacy of SJW. In order to bring more light into the hyperforin discussion, clinical studies investigating this question are needed. One approach in this direction was performed by

231 Table 3 Effect of 14 days of different St. John’s wort preparations on percent change in Midazolam AUC0–12h compared to baseline [67] SJW preparation LI 160 extract Hypericum powder A Hypericum powder A Hypericum powder A Hypericum powder A Hypericum powder B

Extract dose Hyperforin Mean % 95%-CI (mg/day) dose (mg/day) change 900

41.25

−79.4

−88.6; −70.1

2,700

12.06

−47.9

−59.7; −36.2

1,800

8.04

−37.0

−58.2; −15.8

1,200

5.36

−31.3

−45.3; −17.3

600

2.68

−20.4

−40.0; −0.8

2,700

0.13

−21.1

−33.9; −8.3

Laakman et al [65]. The authors compared two different extracts of SJW. It showed a statistically significant difference between an extract with 5% hyperforin in reducing the Hamilton depression score towards placebo, and an extract with 0.5% hyperforin. This finding suggested that hyperforin may be of relevance for the clinical efficacy of the extract. Although studies which compare different Hypericum preparations are necessary, the study of Laakmann et al. [65] is not convincing because quantitative data for additional constituents (such as flavonoids, hypericins, biflavones) in the two extracts are not presented. Thus, it cannot be excluded that constituents other than hyperforin may have caused the small differences in efficacy of both extracts. Therefore, the outcome does not give convincing proof for the activity of hyperforin, but indicates that there are extracts that show clinical efficacy, and others which are inactive.

However, until now, three clinical trials were performed using a SJW extract with a low hyperforin amount (<0.2%).

The studies showed that the efficacy of SJW extract was superior to placebo and as effective as imipramine and fluoxetine [3, 7, 66].

Conclusions Considerable differences exist in the composition of biologically active constituents among various commercially available preparations of St. John’s wort. Although several reports unfortunately fail to rigorously define the specific herbal product used in clinical studies, investigators are increasingly aware that significant differences in outcome are likely to be product specific. However, a major change took place from 1998, when the quite unstable component of SJW, hyperforin, became stabilized in many products leading to a 10–20-fold increased amount of hyperforin into the product. Moreover, the first reports of clinically significant drug interactions of St. John’s wort coincided with the availability of hyperforin enriched

products. Further laboratory investigations demonstrated that CYP3A4 induction with SJW preparations was associated with hyperforin content, suggesting that this component plays a major role in clinically significant drug interactions. Clinical studies with traditional SJW extracts and products with low hyperforin content found low enzyme induction using midazolam probes that consistently had AUC decreases that were less than 50% compared to baseline. Since “hyperforin-free” extracts have been proven to be effective in clinical therapy it is recommended to set an upper limit (1%) for the amount of hyperforin in SJW extracts in order to prevent clinical significant interactions with other co-medicated drugs. It is further suggested that products used for interaction studies should be characterized by the extraction solvent, drugextract ratio and the amount of hyperfoin, hypericin and total flavonoids. This information would allow a more substantial discussion of the data and would help to better explain discrepancies between studies.

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