Warfarin, herb interactions

Tea Tree (Melaleuca alternifolia) Uses Rx of superficial wounds (bacterial, viral, fungal, insect bites, minor burns, cold sores, acne Action Broad-spectrum antibiotic activity against E. coli, S. aureus, C. albicans Available forms Topical creams, lotions, oint, oil apply topically PRN Notes/SE Ataxia, contact dermatitis, D, drowsiness, GI mucosal irritation Interactions Effects OF drugs that affect histamine release EMS effects of Benadryl Valerian (Valeriana officinalis) Uses Anxiolytic, antispasmodic, dys-menorrheal, restlessness, sedative Action Inhibits uptake stimulates release of GABA, which T GABA concentration extracellularly causes sedation Available forms Ext 400-900 mg PO 30 min < hs, tea 2-3 g (1 tsp of crude herb) qid, PRN, tine 3-5 mL (1/2-1 tsp) (1 5 ratio) PO qid, PRN Efficacy Probably effective sedative (reduces sleep latency) Notes/SE GI upset, HA, insomnia, N/V, palpitations, restlessness, vision changes Interactions T Effects OF barbiturates, benzodiazepines, opiates, EtOH, catnip, hops, kavakava, passion flower, skullcap effects OF MAOIs, phenytoin, warfarin EMS T Effects of benzodiazepines and opiates abruptly D/C may cause withdrawal symptoms... 

St John s wort is the most well established example of a herb that can induce the metabolism of drugs, principally by the cytochrome P450 isoenzyme CYP3A4. This herb appears to have a modest effect on warfarin , (p.418), which might be clinically important. Danshen , (p.415) might interact by increasing the bioavailability of warfarin. No other herbs appear to have an established effect on the metabolism of warfarin. 

There are many reviews of the effect of various herhal medicines on warfarin. Most of these include interactions based on theoretical data, based on the knowledge that a plant has been shown to contain antiplatelet substances or coumarins. The problem with these lists is that a suggested interaction might never be clinically relevant if, for example, the coumarins present are found not to be anticoagulants, or the substances are found in such small quantities and the herb cannot be ingested in sufficient amounts to cause an interaction. With natural substances, there is also the problem of chemical variations between batches of product if they are not standard-... 

These appear to be the only reports of ginger as a probable cause of overanticoagulation, despite the fact that prior to these Ginger Zingiber officinale ) has been sometimes listed as a herb that interacts with warfarin. on the basis that in vitro it inhibits platelet aggregation. However, this antiplatelet effect has not been demonstrated in clinical studies (which have been the subject of a review ), see also Coumarins + Herbal medicines , p.414. 

Chamomile has been indicated as an herb with the theoretical potential for interacting with warfarin due to the coumarin content of the herb (Heck et al. 2000). The cou-marin content, however, consists of the coumarin derivatives herniarin and umbelliferone. Herniarin has been shown to have hemostatic activity (Ahmad and Misra 1997) and umbelliferone has shown no evidence of anticoagulant activity (Egan et al. 1990 Feuer 1974 Pelkonen et al. 1997). The flavonoid apigenin has been shown to inhibit platelet aggregation in vitro (Landolfi et al. 1984 Teng et al. 1985). 

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