Doseextravascular

Doseextravascular is a pharmacokinetic term describing the administration of a drug by routes other than intravenous administration. Examples include oral, subcutaneous, intramuscular, transdermal, inhalational, and rectal dosing. The term is used to distinguish extravascular administration from intravenous dosing, which delivers the drug directly into the systemic circulation.

Extravascular dosing introduces an absorption process that shapes the concentration–time profile observed in plasma. Pharmacokinetic analyses of extravascular dosing focus on parameters such as bioavailability (F) and the absorption rate constant (ka). Bioavailability represents the fraction of the administered dose that reaches systemic circulation and is typically less than 1 due to incomplete absorption and first-pass metabolism, especially for oral routes.

A common approach to quantify bioavailability is to compare exposure after extravascular dosing with exposure after intravenous dosing, using the area under the concentration–time curve (AUC). A typical formula is F = (AUC_extravascular × Dose_IV) / (AUC_IV × Dose_extravascular). In practice, extravascular models may also incorporate lag times and various absorption models to fit the observed data.

Extravascular dosing is central to drug development and clinical practice because most therapeutic regimens are extravascular. It enables estimation of systemic exposure, informs dose selection, and aids in understanding variability in absorption among individuals. See also bioavailability, pharmacokinetics, intravenous dosing, and absorption (pharmacokinetics).