PHAR 4634 - Chapter 5 Page 4

Metabolism and Excretion - Parallel Pathways

So far we have considered elimination by excretion into urine only. Usually drugs are eliminated by excretion AND metabolism, with possibly more than one metabolite involved.

Scheme or diagram

Schematically this can be represented as:-

Diagram V-2. Schematic for drug eliminated by excretion and metabolism

ke is the excretion rate constant and km is the metabolism rate constant. Here we have two parallel pathways for elimination (with others as a shadow). We can write the differential equations for the three components shown in this diagram. There could be more pathways. It may be appropriate to specify excretion by exhalation, in sweat, or as is commonly the case, more than one metabolite.


This page was last modified: 12 February 2001

Copyright 2001 David W.A. Bourne