Objective To discuss the role of therapeutic drug monitoring (TDM) in pharmaceutical care by successful intervention of severe drug-drug interaction in 3 patients with hematological disease treated with voriconazole and rifampin.Methods Three patients with hematological disease were monitored for the plasma concentration of voriconazole before,during,and after the concomitant use of rifampin.The severity of this drug interaction was revealed,risks for developing invasive fungal infection and tuberculosis dissemination after chemotherapy were evaluated based on the TDM results,and alternative regimens were recommended.Results Voriconazole plasma concentration was normal at baseline but significantly depressed after combination with rifampin in all 3 cases.Concomnitant use of rifampin leads to a rapid decline in plasma concentration of voriconazole in 2-3 days,and withdraw of this enzyme induction effect takes 8-10 days after discontinuation of rifampin.Conclusion TDM is a helpful tool for providing pharmaceutical care,it helps to objectively visualize the degree of clinically important drug-drug interactions.Clinical evidence together with TDM results suggests high risk for developing invasive fungal infection and tuberculosis dissemination in hematology patients while using this combination therapy.Discontinuation of rifampin was suggested and accepted.For these patients,combination of voriconazole and rifampin should be avoided.