Pharmaceutical Sciences: dosage forms, compounding and stability
What Pharmaceutical Sciences tests
This domain checks whether a D.Pharm candidate can apply pharmaceutics, physical pharmacy, pharmacognosy and basic microbiology to dosage-form design, preparation, stability and quality. NPC-level questions often ask about routes, excipients, sterilization, incompatibilities and compounding calculations rather than advanced research methods.
Core rules
- A dosage form must deliver the correct dose, remain stable and be acceptable to the patient; choice depends on drug properties, site of action and patient factors.
- In extemporaneous compounding, record the formula, source of ingredients, quantity, method, label and beyond-use date; use calibrated balances and graduated measures.
- For semisolid preparations, percentage strength is usually % w/w unless stated otherwise; for solutions, % w/v is common, so density matters.
- Sterilization by moist heat (autoclave) requires saturated steam, correct temperature-time combination and air removal; dry heat is for glassware and thermostable powders.
- Preservatives must partition into the aqueous phase to protect a cream or emulsion; oil-soluble preservatives may be ineffective.
Worked example
You must make 100 g of 2% w/w hydrocortisone cream from 1% w/w and 2.5% w/w creams. Alligation: parts of 1% = 2.5 - 2 = 0.5; parts of 2.5% = 2 - 1 = 1.0. Ratio 0.5:1.0 = 1:2. Total parts 3. For 100 g: 1% cream = 100 x 1/3 = 33.3 g; 2.5% cream = 66.7 g. Check: (33.3 x 1 + 66.7 x 2.5)/100 = 2.0%.
Traps
Using 2% of the final weight as drug instead of blending strengths; mixing w/w and w/v without density; assuming autoclave tape proves sterilization; and omitting a beyond-use date after repackaging.