ADME

ADME stands for absorption, distribution, metabolism, and excretion, and it describes the fate of a drug within the body. Together, these processes determine the systemic exposure of a compound and its potential duration of action.

Absorption is the process by which a drug enters the bloodstream from the site of administration. Route of administration, drug solubility, permeability, and transporter proteins, as well as first-pass metabolism, influence this step. Bioavailability is the fraction of the dose that reaches systemic circulation.

Distribution refers to the dispersion of the drug throughout body fluids and tissues. Distribution is influenced by blood flow, tissue binding, and plasma protein binding; highly lipophilic drugs may accumulate in fatty tissues. The apparent volume of distribution is a pharmacokinetic parameter describing this distribution.

Metabolism transforms drugs, primarily in the liver, via enzymes such as the cytochrome P450 family. Metabolic pathways form more polar compounds (phase I and phase II reactions) that can be either inactive, active, or toxic. Excretion eliminates unchanged drug or metabolites, mainly through the kidneys (renal clearance) or through biliary/fecal routes.

Applications of ADME knowledge support dosing decisions, efficacy and safety assessment, and overall drug development. ADME data inform formulation, route selection, and potential drug interactions. In regulatory science, ADME studies are part of preclinical and clinical evaluation, and modeling approaches such as physiologically based pharmacokinetic models integrate ADME information to predict tissue concentrations.

Variability in ADME between individuals and species can affect drug response and risk assessment, highlighting the importance of translational studies in pharmacology.