( azathioprine ), ( 6-mercaptopurine )
50 mg yellow to off-white, scored, overlapping circle-shaped tablet
Severe systemic lupus
erythematosus, rheumatoid arthritis, psoriatic arthritis, steroid-resistant
polymyositis or dermatomyositis.
100 to 150 mg ( two or three
tablets ) daily is the usual dose.
Azathioprine and 6-mercaptopurine
are closely related drugs with almost identical actions. Azathioprine is the
more frequently used. Side effects include opportunistic infections and
possibility of late development of cancer, so far rare to absent in humans.
Gastrointestinal ( stomach ) distress is occasionally noted. Hair loss is
unusual, and there appears to be little effect on the sperm or the eggs.
There are no bladder problems. Although liver damage has been reported, the
drug is usually well tolerated.
Regular blood tests are required.
Patients taking these drugs should never take allopurinol ( Zyloprim ) at
the same time since the combination of drugs can be fatal. Once the patient
responds to this drug, it is often possible to reduce the dose.
Theoretically, this decreases the risk of late side effects. Azathioprine
has been shown to slow down the progression of rheumatoid arthritis and is
very effective in some patients. Most people seem not to have any side
effects but there is still concern about what might happen over the long