If an oral drug demonstrates unexpectedly low bioavailability despite excellent absorption from the small intestine, which pharmacokinetic process is most likely responsible?

💡 Explanation

Extensive first-pass metabolism in the liver significantly reduces bioavailability of orally administered drugs because a large fraction is metabolized before reaching systemic circulation. Therefore, if absorption is good, but bioavailability is low, first-pass metabolism is the dominant factor, rather than renal reabsorption, tissue binding, or biliary excretion.

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