Metronidazole (Flagyl)

• Generic name: Metronidazole
• Brand/Trade names: Flagyl
• Pharmacologic category: Antiprotozoal, antibacterial agent
• FDA approved: July 18, 1963
• Pregnancy risk factor: B

Metronidazole is classified as a nitroimidazole antiprotozoal and antibacterial agent used to treat protozoal infections and anaerobic bacterial infections.

• Amebiasis
• Trichomoniasis (caused by Trichomonas vaginalis)
• Skin and skin structure infections
• CNS infections
• Intra-abdominal infections (as part of combination regimen)
• Antibiotic-associated pseudomembranous colitis (AAPC)
• Bacterial vaginosis

The most common side effects are gastrointestinal, particularly nausea reported by about 12% of patients, headache, vomiting, diarrhea, metallic taste, and abdominal discomfort.

• Elimination half-life: 8 h in healthy adults, and the hydroxy-metabolite half-life is 15 h.
• Metabolism: metabolized in the liver with the formation of metabolites (2–hydroxymethyl, acid metabolite, glucuronide conjugation)
• Excretion: Main route of elimination is by kidney but it is also secreted in bile and breast milk. 77% is recovered from urine and 14% from stool.

• Low cost.

• Alcohol interaction. Drinking alcohol while taking metronidazole can cause severe nausea, vomiting, flushing and rapid heart rate. A disulfiram-like reaction may occur if alcohol is ingested within 7 days of use.
• Possible carcinogenic potential. Metronidazole is carcinogenic to animals. It has shown to have tumorigenic activity in mice and rats, the most prominent being pulmonary lesions in the mouse. Unnecessary use of the drug should be avoided.

• Clostridium Difficile Colitis. Metronidazole may be helpful as a first-line therapy for antibiotic-associated colitis (C. difficile-associated diarrhea).
• Crohn's disease. Studies3 have shown that metronidazole can be effective in keeping symptoms of Crohn's disease from coming back after surgery. Other studies2 have shown that metronidazole relieved symptoms of Crohn's disease, especially in the colon.
  Metronidazole may be used to treat infections that develop because of Crohn's disease, especially when abscesses, abnormal connections (fistulas) between two parts of the intestines; treat active disease and may help with symptoms when aminosalicylates do not; keep symptoms of Crohn's disease from coming back after surgery.
• Hepatic encephalopathy. Hepatic encephalopathy is a brain dysfunction that occurs when toxins are not removed from the blood because of impaired liver function. Hepatic encephalopathy is an acute condition that may become a medical emergency. Metronidazole4 is used to reduce the colonic concentration of ammoniagenic bacteria, and has shown to be as effective as neomycin.
• Giardiasis. Giardiasis is diarrheal disease caused by a microscopic parasite Giardia lamblia. Metronidazole5 is usually is taken in tablet form for 3 to 7 days for treatment of giardiasis.
• Helicobacter Pylori. Helicobacter Pylori is capable of surviving in the harsh acidic environment of the stomach. The bacteria can directly damage the stomach's protective mucous lining, decrease the body's ability to defend itself and cause an increase in acid production leading to the development of an ulcer, or sore. Some of the treatment regimens use metronidazole6.

Metronidazole is an anti-pathogen with selective toxicity to microaerophilic, anaerobic, and anoxic or hypoxic cells. It enters bacterial or protozoal cell and inhibits DNA synthesis, resulting in cell death.

However the mechanisms by which topical preparation works in reducing inflammatory lesions of rosacea are unknown. Possible mechanisms of action include antibacterial and/or anti-inflammatory effects.

• Metronidazole ratings for giardiasis, diverticulitis, tooth abscess in the Askapatient database
• Flagyl reviews, ratings by patients on DrugLib.com
• Metronidazole user reviews for bacterial vaginitis, infections, diverticulitis on Drugs.com
• Flagyl user reviews on DailyStrength.org

• 1. Metronidazole Prescribing Information (PDF format)
• 2. Bernstein LH, Frank MS, Brandt LJ, Boley SJ. Healing of perineal Crohn's disease with metronidazole. Gastroenterology. 1980 Aug;79(2):357-65. PubMed
• 3. Froehlich F, Juillerat P, Felley C, Mottet C, Vader JP, Burnand B, Michetti P, Gonvers JJ. Treatment of postoperative Crohn's disease. Digestion. 2005;71(1):49-53.
• 4. Morgan MH, Read AE, Speller DC. Treatment of hepatic encephalopathy with metronidazole. Gut. 1982 Jan;23(1):1-7
• 5. Alizadeh A, Ranjbar M, Kashani KM, Taheri MM, Bodaghi M. Albendazole versus metronidazole in the treatment of patients with giardiasis in the Islamic Republic of Iran. East Mediterr Health J. 2006 Sep;12(5):548-54. PubMed
• 6. Matsuhisa T, Kawai T, Masaoka T, Suzuki H, Ito M, Kawamura Y, Tokunaga K, Suzuki M, Mine T, Takahashi S, Sakaki N. Efficacy of metronidazole as second-line drug for the treatment of Helicobacter pylori Infection in the Japanese population: a multicenter study in the Tokyo Metropolitan Area. Helicobacter. 2006 Jun;11(3):152-8. PubMed

Last modified: March 11, 2011