<prompt> Active metabolite of azathioprine ?6-thioguanine6-thiouracil6-mercaptopurine6-mercaptoguanine  <response>: Ans. is c i.e., 6-mercaptopurine Azathioprine It is an analogue of mercaptopurine. It selectively affects T cells - cellular immunity is predominantly affected. It selectively affects defferentiation and formation of T cells. Azathioprine is conveed to active metabolite 6-mercaptopurine. It can inhibit the synthesis of both DNA RNA. Azathioprine and 6-MP are metabolize by xanthine oxidase -dose should be reduced if allopurinol a xanthine oxidase inhibitor is used concurrently. The most impoant action of azathioprine is prevention of renal and other graft rejection. 