Garlic Enhances Anticoagulant Effects and Reduces Protease Inhibitor Levels

Garlic (known scientifically as Allium sativum L.) is both a food and a dietary supplement, and its effects are well documented because of its beneficial effects on health [3, 4]. Garlic contains phytochemicals that may influence the pharmacokinetic and pharmacodynamic behaviors of prescription drugs. However, the compounds contained in garlic have shown inconsistent effects on the cytochrome P450 isoenzymes. Clinical reports show a possible interaction with garlic (primarily as a dietary supplement) and warfarin. Some case reports show that the ingestion of garlic with warfarin may increase the INR, but other reports showed no effect. However, since garlic decreases platelet aggregation, there may be a chance of bleeding with warfarin [3]. In addition, garlic is well known to have antimicrobial activities and may prevent intestinal flora from producing vitamin K, thus potentiating the effects of anticoagulants. Synergistic pharmacodynamics effects have been observed after the ingestion of garlic or garlic-containing supplements with fluindione, chlorpropamide, and NSAIDs, and pharmacokinetic interactions have been observed with both acetaminophen and lisino- pril [3, 4]. In addition, garlic and garlic supplements have a significant impact on the efficacy of protease inhibitors used to treat human immunodeficiency virus (HIV). For example, there is a significant decrease in maximal plasma levels and the mean area under the curve (AUC) of saquinavir after coadministration of a garlic product for 3 weeks. However, no changes in the single-dose ritonavir pharmacokinetics were observed after 4 days [4].

Soy Reduces Anticoagulant Effects

Soy beans (Glycine max) are fermented and then used as part of a wide array of Asian cuisine and soy-based products. These fermented products are well known to contain high levels of vitamin K that may interact with anticoagulants. Clinical reports and studies have shown that the administration of warfarin along with soy protein, soymilk, or other soy products may decrease the INR in patients [2].

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