All of the following statements regarding bioavailability of a drug are true except -
Ans. is 'c' i.e., Low oral bioavailability always and necessarily means poor absorption o Bioavailability of a drug is frequently lower after oral ingestion because of two factors (not poor absorption alone): 1. Extent of absorption 2. First pass metabolism in intestinal wall, poal blood or liver (most common). About other options o Bioavailability of a drug is a measure of fraction of administered dose of a drug that reaches the systemic circulation in unchanged form. o Biovailability is determined by the area under the plasma concentration - time curve. Area under the curve of an orally administered drug when compared to the area under the curve for an I.V. administered drug (100%) can ceainly give an idea of its bioavailability. o The systemic bioavailability of a drug can be predicted from the extent of absorption (function of concentration in plasma) and extraction ratio. o Bioavailability can also be calculated by comparing the excretion in urine.