In a crossover study, a healthy volunteer receives 100 mg of a drug intravenously (AUC = 200 mg.h/L) and then 100 mg orally (AUC = 100 mg.h/L). The oral bioavailability of this drug is:
- A 25%
- B 50% ✓
- C 75%
- D 100%
Correct answer: B. 50%
Explanation
Absolute bioavailability F = (AUC oral / AUC IV) x (Dose IV / Dose oral). With equal doses, F = 100/200 = 0.5, that is 50%. Bioavailability reflects the fraction of administered dose reaching systemic circulation intact, reduced here by incomplete absorption or first-pass metabolism. The distractor of 75% tempts students who average the two AUCs rather than taking their ratio, a common computational error in pharmacokinetics questions.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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