Azathioprine and 6-mercaptopurine are effective drugs in the management of
steroid dependent and chronic active inflammatory bowel diseases. They are
also well tolerated on the long term. However, their use is still hampered
by some drawbacks including delay before efficacy, 20-35% of non responders
, relapse at withdrawal of the drugs, possible bone marrow toxicity and oth
er side effects. During the last few years, these drawbacks have been chall
enged by important studies showing that a better knowledge of the metabolis
m of these drugs may help to improve their use.