MYELOSUPPRESSION ASSOCIATED WITH AZATHIOPRINE-ALLOPURINOL INTERACTIONAFTER HEART AND LUNG TRANSPLANTATION

It is widely recommended that, during concurrent therapy with allopuri nol, the azathioprine dosage should be decreased by at least two third s. We retrospectively studied compliance with this guideline in 24 pat ients who had commenced allopurinol at a median of 33 months (range, 2 -145 months) after heart and/or lung transplantation. The median reduc tion in azathioprine dose at initiation of allopurinol was 73.3% but r anged from 0% to 90% (>67% in 14 patients). Within 3 months, 11 (46%) of the patients became leukopenic (white blood cell count <4x10(9)/L), 7/23 (30%) became moderately anemic (hemoglobin <10 g/dl), and 5/23 ( 22%) became thrombocytopenic (platelets <150x10(9)/L). Decreasing the dose of azathioprine by two thirds or greater reduced but did not abol ish the risk of myelotoxicity. These data highlight the need for close hematological monitoring of patients treated with this drug combinati on. Agents other than allopurinol should be considered for treating hy peruricemia after thoracic organ transplantation.