Evaluation of the drug interaction between intravenous high-dose fluconazole and cyclosporine or tacrolimus in bone marrow transplant patients.

The purpose of this open-label, prospective study was to compare steady state concentrations and clearances of intravenously administered cyclosporine or tacrolimus with and without concomitant high-dose (400 mg/day) fluconazole in allogeneic BMT patients. Twenty-one patients were evaluable. The mean steady state cyclosporine and tacrolimus concentrations without fluconazole were 320.3 and 18.2 ng/ml and increased to 389.2 and 21.2 ng/ml, respectively, after the addition of fluconazole, corresponding to a 21% (P=0.031) and 16% (P=0.125) increase. The mean steady state clearance of cyclosporine and tacrolimus without fluconazole was 6.82 and 1.28 ml/min/kg, which decreased to 5.57 and 1.10 ml/min/kg with fluconazole, corresponding to a 21% (P=0.031) and 16% (P=0.125) decrease, respectively. The 21% difference in the cyclosporine concentration and clearance was not thought to be clinically significant. These results suggest that fluconazole's interaction with cyclosporine or tacrolimus may be a result of fluconazole's inhibition of gut metabolism, resulting in a greater extent of absorption.