The first-pass metabolism or the first-pass effect or presystemic metabolism is the phenomenon which occurs whenever the drug is administered orally, enters the liver, and suffers extensive biotransformation to such an extent that the bioavailability is drastically reduced, thus showing subtherapeutic action (Chordiya ...

Does metabolism influence bioavailability?

The liver is the site of first-pass metabolism. The bioavailability of a drug will be reduced proportionally to the fraction of the initial dose converted to inactive metabolites by liver enzymes. [14] Notably, hepatic cytochrome P450 metabolism can significantly alter drug bioavailability.

How is bioavailability determined?

Bioavailability of a drug is largely determined by the properties of the dosage form, which depend partly on its design and manufacture. Differences in bioavailability among formulations of a given drug can have clinical significance; thus, knowing whether drug formulations are equivalent is essential.