hi paul,
i can only give you the evidence of what happend to me, but i also know some people are fine on azathioprine, i have been diganoised with crohns of the termial illeum, recently, i have a very high immune system with my white blood count at 9.7 excellent if you havent got crohns.
at first they put me on steriods for 12 weeks, which held the disease, reducing visits to the loo to 4/5 times a day, but as soon as i came of them the crohns returned. So the next solution was azathioprine with 100g taken aday, i did not understand about taken them and read the instruction as take 1 four times a day, but i should have taken them together. I intially felt very sick, but 10 days into them i was sick, i telephoned the nurse , she said i should take them together maybe at night, and sleep through the sickness, The next day i took 4 tablets, at 10pm at 1.00 i was being violently sick, with diahorrea , nearly passing out, this lasted for 6 hours, i can honestly say i have never felt so ill, in all my life. I then the next day had a rash that was red and big bruishing blotches on my legs and torso.
Previously to all this i had mouth ulcers, felt athough i had flu, aching joints and often had to have a few hours sleep through the day. After test it was found i had a very bad reaction to this drug, but some people are fine.
At present i am having metrotaxate injection which i will have for 16 weeks, and then hopefully go onto tablet form, this drug seems to lower the immune system, but in a gentler way, it still has side affects similiar to azathioprine , i still feel sick a few times a week, and tired aching joints, mouth ulcers, but the crohns seems at bay at the moment Hope you find the right treatments