Introduction to Pharmacokinetics: ADME and Clinical Applications
Part of Pharmacology Fundamentals
Master the four pillars of pharmacokinetics — Absorption, Distribution, Metabolism, and Elimination — with clinical correlations and exam-focused key points.
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March 20, 2026
Introduction to Pharmacokinetics
Pharmacokinetics describes what the body does to a drug — how it is absorbed, distributed, metabolized, and eliminated. Understanding these four processes is essential for predicting drug concentration over time and optimizing therapeutic outcomes.
The ADME Framework
The ADME framework provides a systematic approach to understanding drug behavior in the body:
Absorption — The process by which a drug enters systemic circulation from its site of administration.
Distribution — The movement of drug from circulation to various tissues and organs.
Metabolism — The biochemical transformation of a drug, primarily in the liver.
Elimination — The removal of the drug and its metabolites from the body.
Bioavailability
Bioavailability (F) refers to the fraction of an administered dose that reaches systemic circulation in unchanged form. An intravenous drug has 100% bioavailability, while oral drugs must survive first-pass metabolism before reaching systemic circulation.
Clinical Pearl: Drugs with high first-pass metabolism (e.g., lidocaine, propranolol) cannot be effectively administered orally for systemic effects.
Half-Life and Steady State
The elimination half-life (t½) is the time required for drug concentration to decrease by 50%. Drugs reach steady-state after approximately 4-5 half-lives of repeated dosing. This concept is critical for planning dosing regimens.