Which of the following statements about drug bioavailability is INCORRECT?

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It represents the fraction of the unchanged drug that enters the systemic circulation.Bioavailability of an orally given drug can be assessed by comparing the area under the curve (AUC) after oral and intravenous administration.A low oral bioavailability always indicates poor absorption of the drug.Bioavailability can be measured using data from plasma drug levels or urinary excretion.Bioavailability reflects the rate and extent to which the active drug reaches systemic circulation.

Explanation

Bioavailability refers to the fraction of an unchanged drug that reaches systemic circulation. It is commonly calculated by comparing the AUC following oral and intravenous administration. While bioavailability can be estimated from plasma concentrations or urine data, a low oral bioavailability does not necessarily mean poor absorption; it may also result from first-pass metabolism or other factors.