Bioavailability refers to the extent and rate at which the active moiety (drug or metabolite) enters systemic circulation, thereby accessing the site of action. Bioavailability is one of the important terms in pharmacokinetics, When calculating dosages for non-intravenous routes of administration bioavailability should be measured.
Absolute bioavailability: Absolute bioavailability is a comparison of the bioavailability of the active drug in systemic circulation through non-intravenous administration (i.e., oral, sublingual administration, transdermal, rectal, subcutaneous, with the bioavailability of the same drug through intravenous administration. It is the comparison of the fraction of the drug absorbed through non-intravenous administration and corresponding intravenous administration of the same drug.
Factors affecting Bioavailability: Physical properties of the drug, drug formulation, Gastric emptying rate, Circadian differences, Interactions with other substances, Transporters, GI tract, Enzyme induction or inhibition by other substances, Individual variation such as Age, Sex Weight etc. & Disease state.
Last date updated on July, 2014