Elimination | Bioavailability | Bioequivalence | Unit 2 Biopharmaceutics & Pharmacokinetics 6th Sem

This is a comprehensive lecture on Unit 2 of Biopharmaceutics and Pharmacokinetics. The instructor begins by explaining drug elimination, which consists of two main processes: metabolism and excretion. Metabolism, also called biotransformation, primarily occurs in the liver and involves converting lipid-soluble drugs to water-soluble forms for easier elimination. The lecture covers the Cytochrome P450 enzyme family in detail, explaining how it metabolizes approximately 80-90% of drugs, with specific focus on the CYP3A4 enzyme. Phase I reactions (oxidation, reduction, hydrolysis, cyclization, decyclization) and Phase II reactions (conjugation reactions like glucuronidation, acetylation, methylation) are thoroughly explained.

The second major topic is bioavailability, defined as the rate and extent to which an active ingredient is absorbed from a drug product and becomes available at the site of action. The instructor explains absolute vs. relative bioavailability, measurement methods including pharmacokinetic approaches (plasma drug concentration and urinary excretion) and pharmacodynamic responses. Area Under the Curve (AUC) calculations, Cmax, and Tmax parameters are detailed with graphical explanations.

The lecture also covers in-vitro drug dissolution methods using USP apparatus 1-4, in-vitro in-vivo correlation (IVIVC), bioequivalence studies, BCS classification system, and various methods for enhancing bioavailability including particle size reduction, solid dispersions, surfactants, salt formation, and pH modification.