bioavailable

Bioavailability is a pharmacokinetic term describing the proportion of a administered dose that reaches systemic circulation in an active form and is available to the site of action. It is a key determinant of the clinical efficacy of drugs and the nutritional usefulness of dietary components. Absolute bioavailability is the fraction of an administered dose that reaches systemic circulation relative to intravenous administration; relative bioavailability compares two formulations or routes against a reference.

Measurement often uses the area under the plasma concentration-time curve (AUC). Relative bioavailability = (AUC_non IV / dose_non IV) / (AUC_IV / dose_IV). A drug with intravenous administration has 100% bioavailability; other routes yield less, depending on absorption and first-pass metabolism.

Factors affecting bioavailability include the compound’s solubility, stability, and permeability; formulation; presence of food; first-pass hepatic and intestinal metabolism; transporter proteins; gastric pH; and patient factors (age, disease, genetics). In nutrition, bioavailability is influenced by food matrix, processing, and anti-nutrients that bind minerals or inhibit absorption, as well as interactions with other nutrients.

Bioavailability explains why intake alone does not guarantee sufficient systemic levels or clinical effect. Bioaccessibility is related but refers to the fraction released from the food matrix for absorption, while bioavailability encompasses absorption and utilization.