Herb-drug interactions

Herb-drug interactions are drug interactions that occur between herbal medicines and conventional drugs.^[1] These types of interactions may be more common than drug-drug interactions because herbal medicines often contain multiple pharmacologically active ingredients, while conventional drugs typically contain only one.^[1] Some such interactions are clinically significant,^[2] although most herbal remedies are not associated with drug interactions causing serious consequences.^[3] Most herb-drug interactions are moderate in severity.^[4] The most commonly implicated conventional drugs in herb-drug interactions are warfarin, insulin, aspirin, digoxin, and ticlopidine, due to their narrow therapeutic indices.^[4][5] The most commonly implicated herbs involved in such interactions are those containing St. John’s Wort, magnesium, calcium, iron, or ginkgo.^[4]

Examples

Examples of herb-drug interactions include, but are not limited to:

• St. John's wort affects the clearance of numerous drugs, including cyclosporin, SSRI antidepressants, digoxin, indinavir, and phenprocoumon.^[1] It may also interact with the anti-cancer drugs irinotecan and imatinib.^[6]
• Salvia miltiorrhiza may enhance anticoagulation and bleeding among people taking warfarin.^[2]
• Allium sativum has been found to decrease the plasma concentration of saquinavir, and may cause hypoglycemia when taken with chlorpropamide.^[2]
• Ginkgo biloba can cause bleeding when combined with warfarin or aspirin.^[2]
• Concomitant ephedra and caffeine use has been reported to, in rare cases, cause fatalities.^[7]

Mechanisms

The mechanisms underlying most herb-drug interactions are not fully understood.^[8] Interactions between herbal medicines and anticancer drugs typically involve enzymes that metabolize cytochrome P450.^[6] For example, St. John's Wort has been shown to induce CYP3A4 and P-glycoprotein in vitro and in vivo.^[6]

References

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