Pharmacy: Dosage Calculations, Legal Schedules and Core Pharmaceutics
The Pharmacy paper covers pharmaceutics, pharmacology, pharmacognosy, pharmaceutical chemistry, hospital and clinical pharmacy, drug store management and pharmaceutical jurisprudence under the Drugs and Cosmetics Act 1940 and Rules 1945. Questions are definitional and numerical, so knowing exact schedules and formulations matters more than broad theory.
Paediatric dose calculations
Young's rule uses age in years: child dose = age divided by (age + 12), multiplied by the adult dose. Clark's rule uses body weight in pounds: weight divided by 150, multiplied by the adult dose. Dilling's rule uses age divided by 20. Fried's rule, for infants under one year, uses age in months divided by 150.
Pharmacokinetic formulas
Volume of distribution = amount of drug in the body divided by plasma concentration. Half-life = 0.693 divided by the elimination rate constant. Loading dose = volume of distribution times target concentration divided by bioavailability.
Legal schedules you must know
Schedule H drugs are prescription-only; Schedule H1 is a list of about 46 drugs, mainly third-generation cephalosporins and anti-tubercular drugs, requiring a separate register with details kept for three years; Schedule X requires two copies of the prescription, one retained for two years, with no refills. Schedule G carries the warning that the drug should be taken under medical supervision; Schedule M sets good manufacturing practice; Schedule P gives the life period of drugs; Schedule P1 fixes pack sizes.
Worked example: an adult dose is 500 mg. For a child aged 4 years, Young's rule gives 4 divided by (4 + 12) = 0.25, so the dose is 500 times 0.25 = 125 mg.
Traps that cost marks
Using weight in kilograms in Clark's rule, which needs pounds; using age in months in Young's rule; confusing the H1 register retention period (three years) with the Schedule X prescription retention period (two years); reporting a volume of distribution as a concentration.