Pharmaceutics: Physical Pharmacy and Manufacturing
Pharmaceutics covers physical pharmacy and manufacturing: how formulation, stability, and process control determine dose uniformity, dissolution, and shelf life. Philippine practice adds FDA GMP expectations and validated manufacturing.
Core rules
- Kinetics: zero-order means a constant amount per time; first-order means a constant fraction per time. For first-order, half-life = 0.693/k and t90 = 0.105/k.
- Stability: Arrhenius temperature dependence; protect from moisture and light; assign beyond-use dates.
- Physical pharmacy: solubility, partition coefficient, HLB, rheology (Newtonian vs non-Newtonian), particle size, and surface area.
- Dissolution: Noyes-Whitney principles; salt form, polymorph, particle size, and excipients affect rate.
- Manufacturing: GMP, process and cleaning validation, environmental monitoring, sterilization (autoclave typically 121°C, 15 psi, 15 min), and aseptic technique.
Worked example
A first-order degradation constant is 0.050 day^-1 at 25°C. t1/2 = 0.693/0.050 = 13.9 days. t90 = 0.105/0.050 = 2.1 days, so only about 2 days are available before 10% loss. A 24-month label claim is therefore unacceptable; reformulate or use a lower temperature.
Traps
Using first-order equations for zero-order drugs; confusing t90 with half-life; applying Arrhenius without valid data; ignoring salt or polymorph effects; treating HLB as universal; assuming sterilization destroys pyrogens.