Azathioprine is metabolised to the active compound mercaptopurine, a purine analogue that inhibits purine synthesis. A thiopurine methyltransferase (TPMT) test may be needed to look for individuals prone to azathioprine toxicity.

Adverse effects

Adverse effects include
  • Bone marrow depression
  • Nausea/vomiting
  • Pancreatitis
  • Increased risk of non-melanoma skin cancer


A significant interaction may occur with allopurinol and hence lower doses of azathioprine should be used.