Objective:To evaluate the potential pharmacokinetic interactions of the anticancer agent gefitinib (Iressa(R)) and the oriental medications Guipi Decoction(归脾汤, GPD,Guibi-tang in Korean) and Bawu Decoction (八物汤, BWD,Palmul-tang in Korean).Methods:Methylcellulose (MC,control),GPD (1,200 mg/kg),or BWD (6,000 mg/kg) was orally administered to rats either as a single dose or multiple doses prior to gefitinib administration.To examine the effects of a single dose of the herbal medicines,gefitinib (10 mg/kg) was orally administered after 5 min or 1 h of MC or the herbal medicine pretreatments.To examine the effects of the multiple doses of the herbal medicines,gefitinib (10 mg/kg) was orally administered following 7 consecutive days of the administration of MC or each herbal medicine.The plasma concentrations of gefitinib were determined with liquid chromatography-tandem mass spectrometry assay.The plasma concentration-time profiles of gefitinib were analyzed with a noncompartmental analysis.Results:Gefitinib was rapidly absorbed and showed a monoexponential decline with an elimination half-life of 3.7-4.1 h.The pharmacokinetics of gefitinib was not affected by GPD pretreatment.However,a significantly lower maximum plasma concentration (Cmax,P＜0.05) and area under the curve (P＜0.05),and a delayed time to reach Cmax (Tmax,P＜0.01) were observed in both single-and multipledose BWD-pretreated rats compared with the control rats.Conclusions:BWD and not GPD might delay and interfere with gefitinib absorption.Further evaluations of the clinical significance of these findings are needed.