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.
It is the propoion (fraction) of unchanged drug that reaches the systemic circulation
Bioavailability of an orally administered drug can be calculated by comparing the Area Under Curve after oral and intravenous (iv) administration
Low oral bioavailability always and necessarily mean poor absorption
Bioavailability can be determined from plasma concentration or urinary excretion data