Pharmaceutics
Core concepts
Pharmaceutics is the science of turning a drug substance into a stable, effective product. You must understand preformulation (polymorphism, particle size, solubility, flow properties, hygroscopicity), the role of excipients (diluents, binders, disintegrants, lubricants, glidants, preservatives, antioxidants), and the principles of dissolution and bioavailability. Know the Biopharmaceutics Classification System (BCS) classes and their implications for formulation and biowaivers. Understand rheology, micromeritics, and the difference between content uniformity and dose uniformity. Stability testing concepts - shelf life, accelerated conditions, Arrhenius kinetics, zero- versus first-order degradation - are heavily examined. Also know the difference between pharmaceutical equivalence, bioequivalence, and therapeutic equivalence.
Traps in questions
- Assuming two products with the same active ingredient are interchangeable; bioavailability may differ.
- Mixing up zero-order (constant rate, concentration-independent) and first-order (rate proportional to concentration) kinetics.
- Confusing disintegrants (break the tablet) with diluents (add bulk).
- Believing accelerated stability data alone define shelf life without extrapolation rules.
Worked example / rule of thumb
A drug degrades by first-order kinetics with a rate constant of 0.05 per month. Using t90 = 0.105/k, the time to 90% potency is 0.105/0.05 ≈ 2.1 months - a useful shortcut for shelf-life estimation. Rule of thumb: t90 ≈ 0.105/k for first-order loss; for zero-order loss, t90 = 0.10 × initial concentration / k.