Discussion on the Calculation of Absolute Bioavailability

• 1、Department of Pharmacology, Xi`an Jiaotong University College of Medicine
• 2、Department of Pharmacology, Xi`an Jiaotong University College of Medicine

Abstract：The absolute bioavailability (F) is defined as the ratio of drug amounts between being absorbed and the total amount of drug being administrated one after extravascular administration. It is calculated as the ratio of area under plasma drug concentration-time curve (AUC) between the extravascular administration and the intravenous injection. However, the distribution of a drug after intravenous administration does not reach balance in the body when the plasma drug concentration declines sharp at the distribution phase. Therefore, at this phase plasma drug concentration can't reflect the total drug amount in body. The goal of the present investigation was to analyze its insufficient and give a modification. The literatures about absolute bioavailability were searched by the keyword "absolute bioavailability" in "Pubmed" from 1983 to 2014. The data on plasma drug concentration were obtained from literatures directly or recovered from the concentration-time curve by Microsoft Paint. The plasma drug concentrations were calculated at each time point at the distribution phase according to the plasma drug concentration-time relationship at elimination phase, which represent the drug amount in body. The AUC basing on the drug concentrations in distribution balance after intravenous injection was 75%±11% of the one basing on actual measured drug concentrations in literatures. The absolute bioavailability from the literatures was 76%±12% of the actual one basing on the AUC from distribution balanced drug concentrations. Therefore, the present method underestimating absolute bioavailability should be corrected.

keywords： pharmacology absolute bioavailability distribution equilibrium intravenous injection oral administration

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