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Warfarin - Interactions and Warnings

Patients taking drugs with a narrow therapeutic index such as warfarin should be discouraged from using herbal products. All drugs with a narrow therapeutic index may either have increased adverse effects or be less effective when used in conjunction with herbal products.
- Crit Care Nurse 2002 Apr;22(2):22-8, 30, 32; quiz 34-5 -- Herbal remedies: drug-herb interactions. -- Kuhn MA.

Cimetidine is known to interfere with other drugs through hepatic metabolism, the concentration of co-committant drugs such as warfarin, benzodiazepine tend to be elevated. Cimetidine should be replaced by the other H2RAs which have no such effects.
- Nippon Rinsho 2002 Aug;60(8):1613-7 -- What is important in treating elderly with H2 receptor antagonists -- Kurosawa S.

St John's wort (Hypericum perforatum) lowers blood concentrations of warfarin. Ginkgo (Ginkgo biloba) interactions include bleeding when combined with warfarin. Ginseng (Panax ginseng) lowers blood concentrations of alcohol and warfarin. Garlic (Allium sativum) decreases blood concentrations of warfarin.
- Drugs 2001;61(15):2163-75 -- Interactions between herbal medicines and prescribed drugs: a systematic review. -- Izzo AA, Ernst E.

Potential interaction between vitamin C and warfarin.
- JAMA 1973 Jan 22;223(4):440 -- Ascorbic acid and warfarin. --Deckert FW.

Soy protein food-drug interactions with warfarin may be more common than the literature suggests, and further studies are needed to determine the exact mechanism. Healthcare professionals should be alerted to the potential implications of this food-drug interaction.
- Ann Pharmacother 2002 Dec;36(12):1893-6 -- Effect of soy milk on warfarin efficacy. -- Cambria-Kiely JA.

Consult with your physician before using herbs and supplements.

last update: November 2008

This information is not intended to be a substitute for professional medical advice. You should not use this material to diagnose or treat a health condition or disease without consulting with your healthcare provider.
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