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Also indexed as: Flagyl, MetroCream, MetroGel, MetroLotion, Noritate, Protostat
Combination drug: Helidac
Metronidazole is an antibiotic used to treat a variety of bacterial and parasitic infections, such as amebiasis, trichomoniasis, and giardiasis. It is also used as a component of multidrug antibiotic combinations to heal stomach and duodenal ulcers caused by Helicobacter pylori infections. Metronidazole is available alone and in a combination product.
Summary of Interactions with Vitamins, Herbs, and Foods
In some cases, an herb or supplement may appear in more than one category, which may seem contradictory. For clarification, read the full article for details about the summarized interactions.
 May Be Beneficial: Side effect reduction/prevention—Taking these supplements may help reduce the likelihood and/or severity of a potential side effect caused by the medication. | Saccharomyces boulardii (for Clostridium difficile only) |
| May Be Beneficial: Supportive interaction—Taking these supplements may support or otherwise help your medication work better. | Saccharomyces boulardii (for Clostridium difficile only) |
 Check: Other—Before taking any of these supplements or eating any of these foods with your medication, read this article in full for details. | Diosmin Milk thistle |
| Depletion or interference | None known |
| Reduced drug absorption/bioavailability | None known |
| Adverse interaction | None known |
An asterisk (*) next to an item in the summary indicates that the interaction is supported only by weak, fragmentary, and/or contradictory scientific evidence.
Diosmin
Diosmin is a flavonoid used to treat hemorrhoids and vein disorders. In a study of healthy male volunteers who took 800 mg of metronidazole, pretreatment with 500 mg of diosmin per day for nine days increased blood levels of metronidazole by 24%.1 Diosmin appears to increase the availability of metronidazole by inhibiting the enzyme that normally breaks it down. The results of this study suggest that taking diosmin may increase both the effectiveness and toxicity of metronidazole.
Saccharomyces boulardii
The yeast Saccharomyces boulardii may help restore microbial balance in the intestines and prevent pseudomembranous colitis (PMC), an intestinal disorder caused by infection with Clostridium difficile. Even when Clostridium difficile is successfully treated with antibiotics, symptoms recur in about 20% of cases. Saccharomyces boulardii has been shown in controlled trials to reduce recurrences when given as an adjunct to antibiotic therapy.2 3 4
Milk thistle (Silybum marianum)
Milk thistle has been reported to protect the liver from harm caused by some prescription drugs.5 While milk thistle has not yet been studied directly for protecting people against the known potentially liver-damaging actions of metronidazole, it is often used for this purpose.
Food
Metronidazole should be taken with food to avoid stomach upset.
Alcohol
Alcohol may interact with metronidazole, causing facial flushing, headache, light-headedness, nausea, breathlessness, and other symptoms.6 Vinegar typically contains small amounts of alcohol and should be avoided during metronidazole therapy. People should read all product labels carefully for alcohol content and should avoid alcohol-containing products during metronidazole therapy.
1. Rajnarayana K, Reddy MS, Krishna DR. Diosmin pretreatment affects bioavailability of metronidazole. Eur J Clin Pharmacol 2003;58:803–7.
2. Surawicz CM, McFarland LV. Pseudomembranous colitis: causes and cures. Digestion 1999;60:91–100 [review].
3. Eddy JT, Stamatakis MK, Makela EH. Saccharomyces boulardii for the treatment of Clostridium difficile-associated colitis. Ann Pharmacother 1997;31:919–21.
4. McFarland LV, Surawicz CM, Greenberg RN, et al. A randomized placebo-controlled trial of Saccharomyces boulardii in combination with standard antibiotics for Clostridium difficile disease. JAMA 1994;271:1913–8 [published erratum appears in JAMA 1994;272:518].
5. Morazzoni P, Bombardelli E. Silybum marianum (Carduus marianus). Fitoterapia 1995;66:3–42 [review].
6. Threlkeld DS, ed. Systemic Anti-Infectives, Metronidazole. In Facts and Comparisons Drug Information. St. Louis, MO: Facts and Comparisons, Nov 1992, 353a–3e.
Copyright © 2007 Healthnotes, Inc. All rights reserved. www.healthnotes.com
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The information presented in Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires September 2008.
