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Mohammad M. Kamal Nawar Steward of Clinical Pharmacy Department & Drug Information Center ERMED Minstry of Transport 2011 – 2013


Drug Dose Calculation

System Internationale ( S. I )

Imperial System

There are 3 types of measurements you will encounter ‫ تواجهها‬when dealing with medications : Type Household ً‫منزل‬

Number Whole numbers & fractions ‫ الكسور‬before unit . e.x. 11/2 T

Apothecary ً‫صٌدالن‬

Whole numbers fractions roman numerals after unit , e.x. gr 151/2 , or dr iss Whole Grams ( g ) numbers & Meter ( m ) decimals ‫األرقام‬ ‫ العشرٌة‬before unit . e.x. 0.15 ml ‫ البد من‬: ‫مالحظة‬ ‫كتابة الرقم صفر‬ ‫قبل العالمة‬ ‫العشرٌة‬

Metric ‫المتري‬

Solids Liquids Teaspoons ( Drop ( gtt ) tsp , t ) Ounce ( oz ) Tablespoons ( ‫ أوقٌة‬، ‫أونص‬ Cup ( c ) Tbs , T ) Pounds ( lb ) Pint ( pt ) ‫نصف‬ ‫لتر‬ ‫ رطل‬، ‫باوند‬ Quart ( qt ) ‫ربع‬ ‫جالون‬ Glass Grains ( gr ) Minum ( m ) , Drams ( dr ) Fluid drams ( & ‫دراخمة‬ dr )

Liters ( L )

2 By : Dr. Mohammad M. Kamal Nawar


Common conversion factors 1 cc ( cubic centimeter ) = 1 mL = 15 gtt = m 15 dr 1 = 4 mL 1 T = 3 t = 15 mL 1 oz = 30 mL = dr 8 gr 1 = 60 mg 1 gr = gr 15 1 in ( inch ) = 2.54 cm 1 kg = 2.2 lb

Roman numerals 1

/2 = iss

1 = I or i , 2 = II or ii , 3 = III or iii 4 = IV or iv ( i before v = 5-1 ) 5 = V , 6 = VI , .... 9 = ix , 10 = x , 11 = xi , .... 19 = xix ( = 10 + ( 10-1 ) ), 20 = xx Kilo Kilogram Kiloliter Kilometer 1

Unit Gram Liter Meter 1000

Milli Milligram Milliliter Millimeter 1000000

Micro Microgram Microliter Micrometer 1000000000

3 By : Dr. Mohammad M. Kamal Nawar


‫) ‪Body Surface Area ( BSA ) ( m2‬‬ ‫تأتً أهمٌته فً حساب ‪ renal clearance‬و ) ‪. glomerular filtration rate ( GFR‬‬ ‫𝑚𝑐 𝑋 𝑔𝑘‬ ‫‪3600‬‬

‫=‬

‫𝑛𝑖 𝑋 𝑏𝑙‬ ‫‪3131‬‬

‫= ‪BSA‬‬

‫‪Calculating a child's dose using an adult dose‬‬ ‫𝑒𝑔𝑎𝑠𝑜𝑑 𝑡𝑙𝑢𝑑𝑎 𝑋‬

‫𝐴𝑆𝐵 𝑠 ‪𝐶𝑕𝑖𝑙 𝑑 ′‬‬ ‫‪1.7 𝑚 2‬‬

‫= ‪Child's dosage‬‬

‫‪Calculations of intravenous drips‬‬ ‫‪Flow rate ( mL / hr. ) :‬‬ ‫𝑑𝑒𝑟𝑒𝑑𝑟𝑜 𝐿𝑚 𝑙𝑎𝑡𝑜𝑡‬ ‫𝑑𝑒𝑟𝑒𝑑𝑟𝑜 ‪𝑡𝑜𝑡𝑎𝑙 𝑕𝑟.‬‬

‫= ‪Flow rate‬‬

‫فمثال ‪ ،‬ما هو معدل التدفق المطلوب لمرٌض ٌتناول ‪ 500‬مللٌلٌتر ‪IVI ( Intravenous‬‬ ‫) ‪ infusion‬لمدة ‪ 12‬ساعة ؟؟ سٌكون ‪ 41.66‬مللٌلٌتر ‪ /‬ساعة ‪ .‬و ٌقرب ألقرب رقم صحٌح‬ ‫فٌكون ‪. 42‬‬ ‫‪Drip rate ( gtt / min. ) :‬‬ ‫) ‪𝑋 𝑑𝑟𝑜𝑝 𝑓𝑎𝑐𝑡𝑜𝑟 ( gtt / mL‬‬

‫𝑑𝑒𝑟𝑒𝑑𝑟𝑜 𝐿𝑚 𝑙𝑎𝑡𝑜𝑡‬ ‫𝑑𝑒𝑟𝑒𝑑𝑟𝑜 ‪𝑡𝑜𝑡𝑎𝑙 𝑚𝑖𝑛 .‬‬

‫= ‪Drip rate‬‬

‫‪" Drop factor : is the number of drops which make up every millilitre of‬‬ ‫و هو رقم ثابت ٌعطى مع جهاز منظم معدل التدفق و غالبا ما ٌكون ‪fluid delivered " 20 :‬‬ ‫نقطة‪/‬مللٌلٌتر أو ‪ 15‬نقطة‪/‬مللٌلٌتر و أحٌانا ‪ 60‬نقطة‪/‬مللٌلٌتر مع بعض حاالت االطفال ‪.‬‬ ‫مثال ‪ :‬ما هو معدل التنقٌط لكل دقٌقة لمرٌض ٌتناول ‪ 500‬مللٌلٌتر من محلول دكستروز ‪%5‬‬ ‫ورٌدٌا على مدار ‪ 12‬ساعة ؟ مع العلم بأن معامل التنقٌط هو ‪ 20‬نقطة ‪/‬مللٌلٌتر ؟ فاالجابة‬ ‫ستكون ‪ 13.89‬نقطة‪/‬دقٌقة = ‪ 14‬نقطة ‪ /‬دقٌقة ( بعد تقرٌب الرقم ألقرب رقم صحٌح ) ‪.‬‬ ‫ملحوظة ‪ :‬الناتج البد و أن ٌكون رقم صحٌح أو ٌتم تقرٌبه الى أقرب رقم صحٌح ‪.‬‬

‫‪4‬‬ ‫‪By : Dr. Mohammad M. Kamal Nawar‬‬


‫) ‪Converting between oC ( Celsius ) & oF ( Fahrenheit‬‬ ‫‪F = 1.8 (oC ) + 32‬‬

‫‪o‬‬

‫=‪C‬‬

‫‪o‬‬

‫‪o F−32‬‬ ‫‪1.8‬‬

‫ملحوظة ‪ :‬فً حالة كتابة اختصار وحدة اللتر ‪ٌ Liter‬كن بحرف ‪ L‬و لٌس ‪lower case L ( l‬‬ ‫) نظرا للشبه بٌن حرف " ‪ " l‬و رقم " ‪ " 1‬عند القراءة ‪ .‬كما ٌفضل كتابة ‪ microgram‬كاملة‬ ‫للتعبٌر عنها بدال من استخدام الرمز الالتٌنً الخاص بها و هو ‪ µ‬اذ قد تتم قراءته خطأ كـ ‪( m‬‬ ‫= ‪ milli‬مللً ) ‪.‬‬

‫‪Dosage calculations‬‬ ‫‪For tablet dosage form :‬‬ ‫𝑑𝑒𝑏𝑖𝑟𝑐𝑠𝑒𝑟𝑝 𝑡𝑛𝑢𝑜𝑚𝑎‬ ‫𝑡𝑒𝑙𝑏𝑎𝑡 𝑕 𝑐𝑎𝑒 𝑛𝑖 𝑡𝑛𝑢𝑜𝑚𝑎‬

‫= ‪Number of tablets‬‬

‫فلو وصف لمرٌض عقار فٌرابامٌل و بجرعة ‪ 120‬ملجم و األقراص المتاحة هً ‪ 40‬ملجم ‪،‬‬ ‫اذا عدد األقراص سٌكون ثالثة ‪.‬‬ ‫‪For liquid dosage form :‬‬ ‫𝑒𝑚𝑢𝑙𝑜𝑣 𝑡𝑖𝑛𝑢 𝑋 𝑑𝑒𝑏𝑖𝑟𝑐𝑠𝑒𝑟𝑝 𝑡𝑛𝑢𝑜𝑚𝑎‬ ‫𝑡𝑖𝑛𝑢 𝑟𝑒𝑝 𝑡𝑛𝑢𝑜𝑚𝑎‬

‫= ‪Volume to be given‬‬

‫فمثال ‪ ،‬ما هو الحجم المطلوب ( مللٌلٌتر ) العطاء مرٌض ‪ 75‬مللجم من عقار تركٌزه ( ‪25‬‬ ‫ملجم‪/‬مللً ) ؟ بالتأكٌد ‪ 3‬مللٌلٌتر‬

‫‪5‬‬ ‫‪By : Dr. Mohammad M. Kamal Nawar‬‬


Body mass index ( BMI )

‫عادة ما ٌستخدم لقٌاس معدل السمنة‬

6 By : Dr. Mohammad M. Kamal Nawar


Drug Timing Because food can interact with drugs in different ways, perhaps making the drugs more or less effective, it can be very important to take the drugs as recommended - before, after or with food. Always follow the instructions on drugs labels, and if in doubt, talk to a doctor or pharmacist. Taking Drugs Before Food Some drugs need to be absorbed quickly to have an effect, such as nitrates in angina, drugs to help sleep (hypnotics), drugs to reduce agitation (sedatives), and painkillers (analgesics). As food can slow the absorption of these drugs , they need to be taken on an empty stomach. Taking Drugs With or After Food Some foods can delay the emptying of the stomach into the small intestine, where most drugs and nutrients are absorbed. This means that the stomach contents, including the drug, are exposed to stomach acid for longer, which can have different effects on different drugs. The acid in the stomach breaks down some drugs, so delayed emptying will mean that more of the drug is broken down, and less of the drug is available, so it will be less effective. The acid in the stomach also changes some drugs, making them more soluble and so more easily absorbed. This means that the drug will be more effective, but could potentially also cause more side effects. NSAIDs (non-steroidal anti-inflammatory drugs – used in pain and inflammation), diuretics (used in high blood pressure), some antibiotics, and corticosteroids (used in inflammation and allergy) can cause stomach upsets. Taking these drugs, such as ibuprofen, with food (or milk) can reduce the irritation to the stomach lining. According to a study carried out in the USA in 2007, taking lapatinib (a drug used in the treatment of breast cancer) with food, especially fatty 7 By : Dr. Mohammad M. Kamal Nawar


food , could reduce the side effect of diarrhea and lower the dose needed, which may potentially save money on treatment. According to the researchers, following up the meal and tablets with a glass of grapefruit juice (which changes the way the body breaks down the drug) could make one tablet have the same effect as five tablets taken on an empty stomach. Patients should only change their pattern of taking drugs after discussion with a doctor or pharmacist. Some drugs have to be taken during or after meals to be effective – for example, obesity drugs is designed to block the absorption of some of the fat in food as a treatment for obesity. However, if it is taken with a high fat meal this can cause unpleasant side effects. Taking the right number of doses of the drug at the right times (known as ‘adherence’), is very important for the effectiveness of treatment. Taking drugs with or after meals can help people establish a routine and remember their treatments. Some people take drugs at bedtime or when they first get up for a similar reason.

8 By : Dr. Mohammad M. Kamal Nawar


Drug Dose Calculations & Timing