Calculation of Doses I

1. Calculation of Doses I Dr. Osama A. A. Ahmed

2. Dose Definitions • Dose of a drug: the quantitative amount administered or taken by a patient for the intended medicinal effect • Single dose: the amount taken at one time • Total dose (Daily dose): the amount taken during the course of therapy (may be subdivided in divided doses) • Dosage regimen: the schedule of dosing (4 times per day for 10 days) Dr. Osama A. A. Ahmed

3. Usual adult dose: the amount that ordinarily produces the medicinal effect intended in the adult patient Usual pediatric dose: : the amount that ordinarily produces the medicinal effect intended in the infant or child patient Usual dosage range : the quantitative range or amounts of the drug that may be prescribed within the guidelines of usual medical practice Median effective dose: the amount that produces the desired intensity or effect in 50% of the individuals tested. Minimum effective concentration: the minimum concentration determined that can be expected to produce the drug’s desired effects in a patient. Minimum toxic concentration: The base level of blood serum concentration that produces dose-related toxic effects. Dose Definitions MTC Average serum conc. (mg/ml) MEC Time after drug administration (hours) Dr. Osama A. A. Ahmed

4. Dose Measurement • Doses are measured and administered by professional and paraprofessional personnel in case of institutional setting. • adults or child’s parents are generally measures and administers medication in the home setting. • Household measures Dr. Osama A. A. Ahmed

5. Household measures Calibrated droppers US Pharmacopeia, official medicinal dropper held vertically delivers approximately 20 drops water per millilitre. A drop (abbreviated gtt) doesn’t represent a definite quantity (few liquids have the same surface and flow characteristics as water). Dose Measurement Dr. Osama A. A. Ahmed

6. Case 1 A physician asks a pharmacist to calculate the dose of a cough syrup so that it may be safely administered dropwise to a child. The cough syrup contains the active ingredient dextromethorphan HBr, 30 mg/15 ml, in a 120- ml bottle. Based on the child’s weight and literature references, the pharmacist determines the dose of dextromethorphan HBr to be 1.5 mg for the child. The medicine dropper to be dispensed with the medication is calibrated by the pharmacist and shown to deliver 20 drops of the cough syrup per 1 ml. Calculate the dose in drops, for the child. Answer 30 mg dextromethorphan HBr 15 ml 1.5 mg dextromethorphan HBr X ml X = 15 * 1.5/30 = 0.75 ml Number of drops of cough syrup in 0.75 ml dose 1 ml 20 drops of cough syrup 0.75 ml X drops of cough syrup X = 0.75 * 20/1 = 15 drops of cough syrup Dose Measurement Dr. Osama A. A. Ahmed

7. Patient Parameters Geriatric medicine or geriatrics: is the field that encompasses the management of illness in the elderly Pediatrics: is the branch of medicine that deals with disease in children from birth through adolescence. Neonate (newborn): from birth to 1 month, neonate is considered premature if born less than 37 weeks‘ gestation Infant: 1 month to 1 year Early childhood: 1 year through 5 years Late childhood: 6 years through 12 years Adolescence: 13 years through 17 years of age Calculation of doses Dr. Osama A. A. Ahmed

8. Calculation of doses • Patient Parameters • According to age • Child and infant doses • Young’s rule • Cowling’s rule • Fried’s rule for infants Dr. Osama A. A. Ahmed

9. Patient Parameters According to body weight Clark’s rule According to body surface area (BSA) To determine patient’s BSA, use standard Nomogram or this equation Calculation of doses Dr. Osama A. A. Ahmed

10. If the adult dose of phenobarbital is 15 mg, what will be the dose for an 8 year-old child? Young’s rule = (8/8+12)X 15 = 6 mg Cowling’s rule = (9/24)X 15 = 5.625 Calculation of doses Dr. Osama A. A. Ahmed