The half-life provides a convenient summary measure of how long a drug persists in the body, integrating all the elimination processes that remove the drug from systemic circulation. After each half-life interval, approximately 50% of the remaining drug is eliminated, resulting in an exponential decay pattern. After five half-lives, approximately 97% of a drug has been eliminated, a principle relevant to both washout period design and achievement of steady-state concentrations with repeated dosing.

The elimination half-life is determined by two fundamental pharmacokinetic parameters: clearance and volume of distribution. Clearance represents the body's efficiency at removing drug, while volume of distribution reflects how extensively the drug distributes into tissues. A drug with extensive tissue distribution will have a longer half-life even if it is efficiently eliminated from the blood, because drug stored in tissues continues to re-enter the circulation. This relationship means that half-life alone does not fully characterize elimination but rather reflects the interplay of distribution and clearance.

Half-life has important clinical implications for dosing regimen design. Drugs with short half-lives may require frequent dosing or sustained-release formulations to maintain therapeutic concentrations throughout the dosing interval. Drugs with very long half-lives may require loading doses to achieve therapeutic concentrations promptly but also pose challenges if adverse effects occur, as the drug will persist for extended periods after discontinuation. Steady-state concentrations, where drug input equals elimination, are reached after approximately five half-lives of repeated dosing, informing expectations for the time to full therapeutic effect.

The half-life provides a convenient summary measure of how long a drug persists in the body, integrating all the elimination processes that remove the drug from systemic circulation. After each half-life interval, approximately 50% of the remaining drug is eliminated, resulting in an exponential decay pattern. After five half-lives, approximately 97% of a drug has been eliminated, a principle relevant to both washout period design and achievement of steady-state concentrations with repeated dosing.

The elimination half-life is determined by two fundamental pharmacokinetic parameters: clearance and volume of distribution. Clearance represents the body's efficiency at removing drug, while volume of distribution reflects how extensively the drug distributes into tissues. A drug with extensive tissue distribution will have a longer half-life even if it is efficiently eliminated from the blood, because drug stored in tissues continues to re-enter the circulation. This relationship means that half-life alone does not fully characterize elimination but rather reflects the interplay of distribution and clearance.

Half-life has important clinical implications for dosing regimen design. Drugs with short half-lives may require frequent dosing or sustained-release formulations to maintain therapeutic concentrations throughout the dosing interval. Drugs with very long half-lives may require loading doses to achieve therapeutic concentrations promptly but also pose challenges if adverse effects occur, as the drug will persist for extended periods after discontinuation. Steady-state concentrations, where drug input equals elimination, are reached after approximately five half-lives of repeated dosing, informing expectations for the time to full therapeutic effect.