Coadministration of rifampin and itraconazole leads to undetectable levels of serum itraconazole

SIR-Drugs that induce hepatic drug-metabolizing enzymes accelerate the metabolism of the triazole itraconazole. One prospective study has shown that coadministration of rifampin and itraconazole may lead to undetectable levels of serum itraconazole [I]. This coadministration was associated with therapeutic failures in two patients with coccidioidomycosis. We measured levels ofitraconazole after therapy with rifampin was discontinued for a patient with disseminated histoplasmosis and pulmonary tuberculosis who had received both medications. After rifampin was discontinued, the levels of itraconazole in the serum were measurable and clinical improvement occurred.