Bioavailability (BA) is a measurement of the rate and extent to which the active ingredient or active moiety of a drug is absorbed, reaches the systemic circulation and becomes available at the site of action. BA assessment is an important component of new drug development. Absolute bioavailability (ABA) in humans is increasingly requested by the EMEA, the US FDA and Japanese regulatory agencies for new chemical entities and is required for new drug application submission to Australian Therapeutic Goods Administration since 2006.