Drug-enzyme interactions allopurinol

Drug Interactions Allopurinol Agents affecting myelopoiesis Angiotensin converting enzyme inhibitors... 

Drug interactions 5-HT3 antagonists are CYP450 substrates. Enzyme inducers (i.e., rifampin, phenytoin) may iixrease S-HTj antagonist clearance, and enzyme inhibitors (i.e, cimetidine, allopurinol) may increase toxichy. Metoclopramide and promethazine are CYP450 substrates. Drug clearance may be altered with concomitant use of enzyme inducers and inhibitors. 

Drug Interactions Xanthine oxidase, a key enzyme in the catabolism of azathioprine metabolites, is blocked by aUopurinol. If azathioprine and allopurinol are used concurrently, the azathioprine dose must be decreased to 25-33% of the usual dose it is best not to use these two drugs together. Adverse effects resulting from coadministration of azathioprine with other myelosuppres-sive agents or angiotensin-converting enzyme inhibitors include leukopenia, thrombocytopenia, and anemia as a result of myelosuppression. 

Allopurinol, a xanthine oxidase inhibitor used for the treatment of gout, inhibits metabolism of 6-mercaptopurine and other drugs metabolized by this enzyme. A serious drug interaction results from the concurrent use of allopurinol for gout and 6-mercaptopurine to block the immune response from a tissue transplant or as antimetabolite in neoplastic diseases. In some cases, however, allopurinol is used in conjunction with 6-mercaptopurine to control the increase in uric acid elimination from 6-mercaptopurine metabolism. The patient should be supervised closely, because when given in large doses, allopurinol, an inhibitor of purine metabolism, may have serious effects on bone marrow. 

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