Busulfan (BU) is an alkylating drug frequently used to prepare patients for bone marrow transplantation (BMT). Several studies have documented that there is important interpatient variability in BU disposition and systemic exposure, and that other drugs with a common metabolic pathway are capable of influencing BU clearance. We compared the BU pharmacokinetics and pharmacodynamics of 13 patients given BMT and receiving BU and itraconazole, with those of 26 matched controls who did not receive any anti-fungal agent, and with those of 13 matched patients treated with fluconazole as prophylaxis against fungal infections. The effect of itraconazole was best reflected in BU clearance since the BU dose was modified in some patients. BU clearance was decreased by an average of 20% in patients receiving itraconazole as compared to control patients and patients receiving fluconazole (p < 0.01). Mean BU clearance was 7.653 +/- 1.871 l/hr.m2 in the itraconazole patients, 10.103 +/- 2.007 l/hr.m2 in the fluconazole group and 9.373 +/- 1.702 l/hr.m2 in the control group. In this study itraconazole, but not fluconazole, markedly affected the pharmacokinetics of BU as an increase of BU plasma concentrations was observed. The nature of this interaction has not yet been fully characterized. Itraconazole and its analogues are inhibitors of both cytochrome P450 and lipoxygenase and since itraconazole can modulate BU pharmacokinetics, oxidative catabolism is probably a determinant of BU metabolism. This hypothesis should be tested in human metabolic studies.