Potentiation of myelosuppression from cancer chemotherapy and thiazide diuretics.

Fourteen patients with metastatic breast cancer and concomitant essential hypertension received treatment with combination chemotherapy (cyclophosphamide, methotrexate, and 5-fluorouracil) and thiazide diuretics. Significant augmentation of granulocytopenia during thiazide-chemotherapy combination, as compared with chemotherapy without thiazides, was observed in all patients. The most consistent changes in the neutrophil count were observed during the period of maximal myelosuppression from the antitumor drugs. An interaction between the thiazide diuretic and one or more of the cytotoxic agents is a possible explanation for the findings. The implications of this phenomenon are discussed.