Drug Bioavailability By Jennifer Le, PharmD, MAS, BCPS-ID, FIDSA, FCCP, FCSHP, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego Reviewed / Revised Jun 2022 | Modified Sep 2022 View Patient Education Topic Resources Representative plasma concentrati... Bioavailability refers to the extent and rate at which the active moiety (drug or metabolite) enters systemic circulation, thereby accessing the site of action.