Effects of herbal products on the metabolism and transport of anticancer agents.

IMPORTANCE OF THE FIELD: Cancer patients on chemotherapy treatment often seek herbal therapies and this may alter the clearance of anticancer drugs. AREAS COVERED IN THIS REVIEW: Many anticancer drugs are metabolized by CYPs and are substrates of P-glycoprotein, breast cancer resistance protein and multi-drug resistance proteins. CYPs and drug transporters are subject to inhibition and/or induction by the herbal medicines used by cancer patients and the metabolism and pharmacokinetics of anticancer agents may be altered by herbal products. There are increased reports on the interaction of herbal medicines with anticancer agents. A clinical study in cancer patients reported that treatment of St John's wort at 900 mg/day orally for 18 days decreased the plasma levels of the active metabolite of irinotecan, SN-38, by 42%. In healthy subjects, treatment with St John's wort for 2 weeks significantly decreased the systemic exposure of imatinib by 32%. Induction and/or inhibition of CYPs and transporters is considered an important mechanism for these interactions. WHAT THE READER WILL GAIN: Potential interactions of herbal medicines with anticancer agents have become a safety concern in cancer chemotherapy. TAKE HOME MESSAGE: Further studies are warranted to investigate the efficacy and safety profiles of herbal medicines commonly used by cancer patients.