Calculation of Doses I Dr Osama A A

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

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 2

Dose Definitions • 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. • • Average serum conc. (mg/ml) • • MTC MEC Time after drug administration (hours) Minimum toxic concentration: The base level of blood serum concentration that produces dose-related toxic effects. Dr. Osama A. A. Ahmed 3

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 Household measure (Abbreviation) ounce Metric system 1 teaspoonful (tsp) 1 tablespoonful (tbsp) 1/6 fluidounce 1/2 fluidounce 5 ml 15 ml Dr. Osama A. A. Ahmed f f ss 4

Dose Measurement Household measures Signa Label dose f One teaspoonful 5 ml One dessertspoonful 10 ml One tablespoonful 15 ml f One coffee cupful 30 m One drop i f ii f ss • 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). Dr. Osama A. A. Ahmed 5

Dose Measurement • 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 Dr. Osama A. A. Ahmed 6

Calculation of doses • 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 Dr. Osama A. A. Ahmed 7

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 8

Calculation of doses • 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 Dr. Osama A. A. Ahmed 9

Calculation of doses • 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 • Dr. Osama A. A. Ahmed = (9/24)X 15 = 5. 625 10