Ethnopharmacological relevance: The Dengzhan Shengmai capsule (DZSM) is known in China for its remarkable curative effect as a treatment of cardiovascular diseases, such as coronary heart disease and ischemic stroke. DZSM is a Chinese herbal compound preparation that consists of four ingredients, including Erigeron breviscapus (Vaniot) Hand.-Mazz., Panax ginseng C.A. Mey, Ophiopogon japonicas (Thunb.) Ker-Gawl. and Schisandra chinensis (Turcz.) Baill., and was indexed in the Chinese Pharmacopoeia 2010. DZSM and clopidogrel are often co-prescribed in the clinic to prevent the recurrence of stroke or other cardiovascular and cerebrovascular diseases. However, the effect of DZSM on the pharmacokinetics of clopidogrel remains unclear. Aim of the study: The purpose of the study is to explore the pharmacokinetics and potential interaction between DZSM and clopidogrel and the underlying mechanism. Materials and methods: Rats were used to investigate the effect of DZSM on the pharmacokinetics of clopidogrel and its active metabolite in vivo. The plasma concentrations were simultaneously determined using LC MS/MS. The effects of DZSM on the P-gp-mediated efflux transport and CYP450-mediated metabolism of clopidogrel were investigated using MDCKII-MDR1 cells and rat liver microsomes, respectively. Results: After pretreatment with DZSM, the C-max and AUC(0-infinity) of clopidogrel increased from 0.4 +/- 0.1 to 1.7 +/- 0.6 ng/mL and 0.9 +/- 0.4 to 2.0 +/- 0.2 ng/mL h, respectively. The C-max and AUC(0-infinity), of the derivatized active metabolite of clopidogrel decreased from 8.2 +/- 1.2 to 2.8 +/- 0.5 ng/mL and 18.2 +/- 5.6 to 6.4 +/- 3.7 ng h/mL, respectively. In MDCKII-MDR1 cells, the P-gp-mediated efflux transport of clopidogrel was significantly inhibited by the DZSM extract. In rat liver microsomes, DZSM inhibited clopidogrel metabolism with an IC50 of 0.02 mg/mL. Conclusions: DZSM significantly affects the pharmacokinetics of clopidogrel and its active metabolite by inhibiting the P-gp-mediated efflux transport and CYP450-mediated metabolism of clopidogrel. Thus, caution is needed when DZSM is co-administered with clopidogrel in the clinic because the interaction of these drugs may result in altered plasma concentrations of clopidogrel and its active metabolite. (C) 2016 Elsevier Ireland Ltd. All rights reserved.