Pharmaceutics
Pharmaceutics covers dosage-form design, formulation, manufacture and dispensing; the exam tests tablet and capsule excipients, dissolution, suspensions and emulsions, sterile products, isotonicity and incompatibilities.
Core rules
- The Biopharmaceutics Classification System groups drugs by solubility and permeability: Class I high/high, II low solubility/high permeability, III high solubility/low permeability, IV low/low.
- Tablets contain diluents, binders, disintegrants, lubricants and glidants; granulation improves flow and compressibility. Dissolution is often rate-limiting for absorption of Class II drugs.
- Suspensions are dispersed systems that must be shaken; emulsions can cream, flocculate or crack. Sterile products require validated filtration or autoclaving and an isotonic vehicle where appropriate.
Worked example
Prepare 100 mL of an isotonic solution containing 1 g of drug with sodium chloride equivalent E = 0.2. The drug contributes 1 × 0.2 = 0.2 g NaCl equivalent. An isotonic solution needs 0.9 g NaCl per 100 mL, so add 0.9 − 0.2 = 0.7 g NaCl, then make to volume.
Traps
0.9% w/v means 0.9 g per 100 mL. Do not confuse a suspension with a solution; shaking is essential. A sustained-release tablet must not be crushed unless the label permits. Check units, displacement volumes and whether the prescription asks for total dose or dose per kilogram.