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Interactions Between Herbal Medicines and Prescribed Drugs: An Updated Systematic Review

Izzo AA, Ernst E.


Department of Experimental Pharmacology, University of Naples Federico II, via D Montesano 49, Naples 80131, Italy.


The concomitant use of herbal medicines and pharmacotherapy is wide spread. We have reviewed the literature to determine the possible interactions between seven popular herbal medicines (ginkgo, St John’s wort, ginseng, garlic, echinacea, saw palmetto and kava) and conventional drugs. Literature searches were performed using MEDLINE, Cochrane Library and EMBASE and we identified 128 case reports or case series, and 80 clinical trials.


Clinical trials indicate that St John’s wort (Hypericum perforatum), via cytochrome P450 (CYP) and/or P-glycoprotein induction, reduces the plasma concentrations (and/or increases the clearance) of alprazolam, amitriptyline, atorvastatin, chlorzoxazone, ciclosporin, debrisoquine, digoxin, erythromycin, fexofenadine, gliclazide, imatinib, indinavir, irinotecan, ivabradine, mephenytoin, methadone, midazolam, nifedipine, omeprazole, oral contraceptives, quazepam, simvastatin, tacrolimus, talinolol, verapamil, voriconazole and warfarin.


Case reports or case series suggest interactions of St John’s wort with adrenergic vasopressors, anaesthetics, bupropion, buspirone, ciclosporin, eletriptan, loperamide, nefazodone, nevirapine, oral contraceptives, paroxetine, phenprocoumon, prednisone, sertraline, tacrolimus, theophylline, tibolone, tryptophan, venlafaxine and warfarin.


Ginkgo (Ginkgo biloba) decreases the plasma concentrations of omeprazole, ritonavir and tolbutamide. Clinical cases indicate interactions of ginkgo with antiepileptics, aspirin (acetylsalicylic acid), diuretics, ibuprofen, risperidone, rofecoxib, trazodone and warfarin.


Ginseng (Panax ginseng) may interact with phenelzine and warfarin.


Kava (Piper methysticum) increases the clearance of chlorzoxazone (a CYP2E1 substrate) and may interact with alprazolam, levodopa and paroxetine.


Garlic (Allium sativum) interacts with chlorpropamide, fluindione, ritonavir and warfarin; it also reduces plasma concentrations of chlorzoxazone (a CYP2E1 probe).


Echinacea might affect the clearance of caffeine (a CYP1A2 probe) and midazolam (a CYP3A4 probe). No interactions have been reported for saw palmetto (Serenoa repens).


Numerous interactions between herbal medicines and conventional drugs have been documented. While the significance of many interactions is uncertain, several interactions, particularly those with St John’s wort, may have serious clinical consequences.


Source…

Copyright © 2009 All rights reserved.


Natural Herbal Supplements Aren’t Always Safe


Thursday, August 13, 2009


ROCHESTER, Minn. — Natural doesn’t always mean safe when it comes to herbal supplements, according to the August issue of Mayo Clinic Health Letter.


When used properly, many herbal supplements may be safe and possibly beneficial to health. However, a few supplements can cause life-threatening problems or dangerous interactions with medications.


Mayo Clinic Health Letter covers some of the known interactions between herbal supplements and medications:


St. John’s wort: This supplement can greatly increase or decrease the potency of many medications and cause serious side effects. Patients who take antidepressants, anti-blood-clotting drugs, certain asthma drugs, immune-suppressing medications or steroids should probably avoid St. John’s wort.


S-adenosylmethionine (SAM-e): This can cause serious side effects when taken with antidepressant medications that affect serotonin.


Garlic, ginseng, ginger and feverfew: Patients who take anti-clotting medications such as aspirin, warfarin (Coumadin) and clopidogrel (Plavix) should avoid these supplements. They may increase the risk of bleeding. Supplements chondroitin and glucosamine also may interfere with warfarin.


Ginkgo: Ginkgo may increase the risk of bleeding in patients taking anti-clotting medications. Ginkgo can counteract the blood pressure-lowering benefits of thiazide diuretic drugs. It also can interfere with anti-seizure medications.


Kava: Kava is a sedative herb and is associated with serious liver problems, even when taken for a short time. Many medications, such as cholesterol-lowering drugs, pose a risk of liver damage. Taking kava may increase the risk of liver problems even more.


It’s always best to keep health care providers informed about supplement use, especially when starting a new medication or preparing for a medical procedure. Some supplements need to be discontinued two to three weeks before certain surgical procedures, because they affect blood clotting, response to sedation and blood pressure control.


Mayo Clinic Health Letter is an eight-page monthly newsletter of reliable, accurate and practical information on today’s health and medical news. To subscribe, please call 800-333-9037 (toll-free), extension 9771, or visit www.healthletter.mayoclinic.com.


http://www.mayoclinic.org/news2009-mchi/5375.html?rss-feedid=4



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