Bioavailability
In pharmacology, bioavailability is a term used to describe a pharmacokinetic property of drugs, namely, the fraction of a dose which reaches the systemic circulation. It is an essential tool in pharmacokinetics, as bioavailability must be considered when calculating dosages for administration routes other than intravenous.
Definition
Bioavailability is a measurement of the rate and extent of therapeutically active drug that reaches the systemic circulation and is available at the site of action. (Shargel & Yu, 1999)
It is expressed as the letter F.
Absolute bioavailability
Absolute bioavailability measures the availability of the active drug in systemic circulation after non-intravenous administration (i.e. after oral, rectal, transdermal, subcutaneous, etc administration).
In order to determine absolute bioavailability of a drug, a pharmacokinetic study must be done to obtain a plasma drug concentration vs time plot for the drug after both intravenous and ADME-Tox, Lipinski's Rule of 5
