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Oral Availability

Oral Availability

Oral availability (F) is the fraction of drug that reaches the systemic circulation after oral ingestion. It is determined by 'absorption' and 'first-pass' metabolism.

Absorption refers to the ability of a drug to cross the gut wall into the portal vein.

First-pass metabolism describes presystemic drug elimination and can occur in the gut wall, portal vein or liver. The liver is usually the most important contributor.

Adjust the sliders for drug absorption and first-pass metabolism to see how these affect oral availability.

Main Arrows
Main Arrows
Intestine Arrows Intestine Arrows Stomach Arrows



Oral Availability



Portal Vein

Small Intestine

Large Intestine

Systemic Blood Stream (Vena Cava)

Poor Good
Low High