[PSCI-04] Biopharmaceutics, BCS Classification, Dissolution Kinetics & Bioequivalence

PSCI-04 • 4. Pharmaceutics

Learning Objectives

Classify drugs across Amidon's Biopharmaceutics Classification System (BCS Classes I–IV) and identify rate-limiting steps and CDSCO biowaiver eligibility.; Apply the Noyes–Whitney dissolution rate equation and Hixson–Crowell cube-root law to solubility enhancement strategies.; Evaluate absolute vs relative bioavailability and CDSCO / US-FDA bioequivalence acceptance criteria (90% CI of AUC and Cmax within 80.00%–125.00%).

Chapter Overview & Core Explanation

Biopharmaceutics explains how a drug's physical form (crystal structure, particle size, salt form, tablet excipients) controls how fast it dissolves in gut fluids and crosses the intestinal wall to reach the bloodstream.

Key Exam & Clinical Takeaways

• BCS Class II drugs have low solubility but high permeability—formulation techniques like micronization, solid dispersion, cyclodextrin complexation, or salt formation dramatically improve their oral bioavailability.
• In a randomized 2×2 crossover bioequivalence trial, the washout period between Period 1 and Period 2 must be at least 5 to 10 elimination half-lives (≥ 5 t1/2) to eliminate carryover.

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