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