Azathioprine Imuran was developed as a longer lasting and less toxic replacement for 5 mercapto pruine, by Dr George Hitchings at the Burroughs-Wellcome company. This doctor collaborated with Roy Calne in doing transplants in a dog model of renal transplantation. Mercapto purine was able to prolong the graft survival and Azathioprine was better. From 1962 on Azathioprine became used routinely in patients post renal transplantation.
Azathioprine is metabolised to mercaptopurine in the body.
Azathioprine is contraindicated in patients on Allopurinol which is used for gout due to the inhibition of xanthine oxidase.