The document discusses drug metabolism and biotransformation. It notes that the liver is the primary site of biotransformation, which converts non-polar compounds to polar ones for excretion. Biotransformation can inactivate drugs, produce active metabolites, or activate inactive prodrugs. It occurs in two phases: phase I involves oxidation, reduction, and hydrolysis; phase II involves conjugation. Cytochrome P450 enzymes, especially CYP3A4, are responsible for many phase I reactions. Drug metabolism determines a drug's half-life, clearance, and affects dosing. Therapeutic drug monitoring measures drug concentrations to optimize dosing for drugs with a narrow therapeutic index.