Severe. These medicines may interact and cause very harmful effects and are usually not taken together. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.
How the interaction occurs:
St. John's wort may speed up how quickly your liver processes irinotecan.
What might happen:
The amount of irinotecan in your blood may decrease and it may not work as well.
What you should do about this interaction:
Let your healthcare professionals (e.g. doctor or pharmacist) know right away if you have been taking St. John's wort. Your doctor may want you to stop taking St. John's wort for two weeks before and during your irinotecan therapy. Do not start taking St. John's wort during your irinotecan therapy. Do not stop taking St. John's wort while taking irinotecan without talking talking to your healthcare professionals.Your healthcare professionals may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.
1.Camptosar (irinotecan hydrochloride) US prescribing information. Pharmacia & Upjohn Company May, 2010.
2.Mathijssen RHJ, Verweij J, De Bruijn P, De Jonge MJA, Sparreboom A. Modulation of irinotecan (CPT-11) metabolism by st. john's wort cancer patients. 93rd Annual Meeting of the American Association for Cancer Research, San Francisco, CA 2002 Apr 8.
3.Mathijssen RH, Verweij J, de Bruijn P, Loos WJ, Sparreboom A. Effects of St. John's wort on irinotecan metabolism. J Natl Cancer Inst 2002 Aug 21; 94(16):1247-9.