Month: January 2026

Introduction Definition and Overview Enzyme induction and inhibition refer to the modulation of drug-metabolizing enzymes, most notably those of the cytochrome P450 (CYP) superfamily, by exogenous or endogenous agents. Induction enhances enzyme expression or activity, accelerating drug clearance, whereas inhibition reduces enzyme function, prolonging systemic exposure. These interactions are pivotal in determining the pharmacokinetic profile…

Introduction Biotransformation refers to the enzymatic modification of xenobiotics within the body to enhance solubility and facilitate excretion. Two sequential stages, traditionally termed Phase I and Phase II reactions, constitute the core of drug metabolism. Phase I reactions typically introduce or expose functional groups through oxidation, reduction, or hydrolysis, whereas Phase II reactions conjugate these functional groups with endogenous…

Introduction Definition and Overview Volume of distribution (Vd) and plasma protein binding (PPB) are foundational parameters that shape the disposition of drugs within the human body. Vd serves as a theoretical construct that relates the total amount of drug in the body to the concentration observed in plasma. PPB, on the other hand, quantifies the…

Introduction Definition and Overview Pharmacokinetics encompasses the quantitative description of drug absorption, distribution, metabolism, and excretion (ADME). Within this field, bioavailability, first-pass metabolism, and extraction ratio constitute pivotal concepts that influence the systemic availability of therapeutic agents following non‑intravenous administration. Bioavailability refers to the fraction of an administered dose that reaches the systemic circulation unchanged,…

Introduction Drug absorption represents the first and often most critical step in the journey from administration to therapeutic effect. It encompasses the processes by which a pharmaceutical compound traverses biological barriers, enters systemic circulation, and becomes available for interaction with target tissues. In the context of pharmacokinetics, absorption is frequently described by the equation F…

Introduction Definition and Overview Routes of drug administration refer to the anatomical or physiological pathways by which a therapeutic agent is delivered into the body to achieve its intended pharmacological effect. The selection of a specific route influences the rate and extent of drug absorption, distribution, metabolism, and elimination, thereby shaping the overall pharmacokinetic profile….

Introduction Definition and Overview Membrane transport refers to the regulated movement of molecules across biological membranes, a fundamental determinant of drug disposition. This process governs absorption into the bloodstream, distribution to tissues, and elimination via renal or biliary routes. Membrane transport mechanisms encompass passive diffusion, facilitated diffusion, active transport, and efflux processes, each contributing distinct…