Warfarin: An evidence-based review of interactions with drugs and food
DOI:
https://doi.org/10.32385/rpmgf.v24i4.10527Keywords:
Warfarin, Drug interactions, Food-drug interactions, Herb-drug interactionsAbstract
Introduction:Warfarin has been the mainstay of oral anticoagulant therapy. Its effectiveness has been established in various contexts in clinical practice. Objectives: Review the interactions of warfarin with food, drugs and natural substances/herbs. Methods: British Medical Journal (BMJ) Clinical Evidence, Evidence Based Medicine online, National Guideline Clearinghouse,National Library of Guidelines, The Cochrane Library, DARE, Bandolier and MEDLINE were searched using the following key words (MeSH terms):warfarin, drug interactions, food interactions and herbal interactions. The search was limited to articles written in English, French, Spanish and Portuguese, published between January 2003 and present. The Index of Portuguese Medical Journals (Índex de Revistas Médicas Portuguesas) was also searched using the following key words: varfarina, interacções alimentares and interacções medicamentosas. To evaluate the Level of Evidence, the rating system of the American Family Physician (Strength Of Recommendation Taxonomy - SORT) was used: level A (randomized controlled trials/meta-analysis); level B (other evidence) and level C (consensus/expert opinion). Results and Discussion: Food-Drug Interactions: Foods with a high content of vitamin K interact with warfarin. Their absolute eviction is not recommended but a stable and moderate ingestion is advised. Drug Interactions:These are numerous and involve different mechanisms: (1) Reduced warfarin absorption; (2) Potentiation/Inhibition of cytochrome P450 in the liver; (3) Reduction of endogenous vitamin K synthesis by the intestinal flora; (4) Inhibition of platelet aggregation; (5) Increase of the catabolism of vitamin K-dependent coagulation factors; (6) Induction of coagulant factors; (7) Unknown mechanisms. Herbal drug interactions: St Johns wort (hypericum), in healthy subjects, induces warfarin clearance, which in turn inhibits its anticoagulant effect. Conclusion: Studies with a good level of evidence, concerning an issue of this importance, are scarce. More high quality and long-term controlled and randomized studies about warfarin interactions with foods, drugs and herbs are needed.Downloads
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