There are four main patterns of drug metabolism.
The first three are often lumped together as phase I reactions, while the fourth process, conjugation, is called phase II metabolism. A common scheme in the overall metabolism of drugs is that metabolites are metabolized. In particular a drug maybe oxidized, reduced or hydrolyzed and then another group may be added in a conjugation step.A common cause of capacity limited metabolism is a limit in the amount of the conjugate added in the conjugation step.
Common reactions include :-
for example phenobarbitone
for example phenytoin
for example chlorpromazine
for example phenacetin
Outside the microsomes - in liver and brain
for example 5-hydroxytryptamine
Add a hydrogen or remove oxygen
azo (-N=N-) or nitro groups (-NO2) -----> amines (-NH2)
for example nitrazepam
Addition of water with breakdown of molecule. In blood plasma (esterases) and liver
for example aspirin to salicylic acid
for example procainamide
Copyright 2001 David W.A. Bourne