August 21, 2002
It has been previously reported that St. John’s wort increases the liver’s ability to metabolize numerous medications, including immunosuppressants, protease inhibitors, and calcium channel blockers. New data suggest that administration of St. John’s wort may also reduce blood levels of SN-38, the active metabolite of irinotecan, by as much as 40%. The effects of St. John’s wort on metabolism may persist for 3 weeks or longer following discontinuation of the herb. Dr. Ron Mathijssen, of the Laboratory of Experimental Chemotherapy and Pharmacology, Department of Medical Oncology, Rotterdam Cancer Institute in The Netherlands, presented this data at the American Association for Cancer Research 93rd Annual Meeting. A more detail report was published in the August 21, 2002 Brief Communications of the Journal of the National Cancer Institude. Reduced levels of SN-38 may result in decreased efficacy of this chemotherapy. Based on this new information, it may be advisable for patients to discontinue St. John’s wort at least a month before beginning treatment with irinotecan or any chemotherapy.