first (1st) pass metabolism
Last reviewed 01/2018
First pass metabolism of drugs can occur in the gut and the liver. Examples include:
- gut - benzylpenicillin, insulin
- liver - propanolol, lignocaine, chloromethiasole, GTN
The first pass effect of the liver is much reduced if there is shunting; this is much more important than damage to the liver in that it only requires a relatively small amount of functional liver to achieve adequate first pass metabolism. However, cirrhotic patients are apparently more sensitive to some drugs, and this appears to be a systematic effect of the disturbed liver function.