First pass effect

The first-pass effect (or first-pass metabolism) is a phenomenon of drug metabolism.

After a drugis swallowed, it is absorbed by the digestive systemand enters the portal circulation. The absorbed drug is carried through the portal vein into the liver.

The liver is responsible for metabolizingmany drugs. Some drugs are so extensively metabolized by the liver that only a small amount of unchanged drug may enter the systemic circulation, so the bioavailabilityof the drug is reduced.

Alternative routes of administration(e.g., intravenous, intramuscular) avoid the first-pass effect.

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/First+pass+effect Wikipedia article First pass effect.