All of following statements about 6-mercaptopurine are true EXCEPT:

All anticancer drugs can result in hyperuricemia by causing the destruction of excess cells. Azathioprine is an immunosuppressant drug that acts by generating 6-MP. 6-MP inhibits the formation of ribosyl-5-phosphate and it also inhibits the conversion of IMP to adenine and guanine nucleotides. When given orally the drug is subjected to first pass metabolism by enzyme Xanthine Oxidase which conves it into an inactive metabolite. So if allopurinol is given along with 6-MP, the metabolism of 6-MP will be reduced and it will lead to toxicity. Thus the dose of oral 6-MP is to be reduced by 75%.