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Pharmacy Author: Omudhome Ogbru, PharmD
Medical and Pharmacy Editor: Jay W. Marks, MD

GENERIC NAME: metronidazole

BRAND NAME: Flagyl

DRUG CLASS AND MECHANISM: Metronidazole is an antibiotic effective against anaerobic bacteria and certain parasites. Anaerobic bacteria are single-celled, living organisms that thrive in environments in which there is little oxygen (anaerobic environments) and can cause disease in the abdomen (bacterial peritonitis), liver (liver abscess), and pelvis (abscess of the ovaries and the Fallopian tubes). Giardia lamblia and ameba are intestinal parasites that can cause abdominal pain and diarrhea in infected individuals. Trichomonas is a vaginal parasite that causes inflammation of the vagina (vaginitis). Metronidazole selectively blocks some of the functions within the bacterial cells and the parasites resulting in their death.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes

PREPARATIONS: Tablets: 250 and 500 mg. Tablets, extended release: 750 mg. Capsule: 375 mg. Cream: 0.75% and 1%. Lotion: 0.75%. Gel: 0.75% and 1%. Injection: 5 mg/ml

STORAGE: Metronidazole should be stored at room temperature and protected from light.

PRESCRIBED FOR: Metronidazole is used to treat parasitic infections including Giardia infections of the small intestine, amebic liver abscess and amebic dysentery (infection of the colon causing bloody diarrhea), bacterial vaginosis, trichomonas vaginal infections, and carriers of trichomonas (both sexual partners) who do not have symptoms of infection. Metronidazole is also used alone or in combination with other antibiotics in treating abscesses in the liver, pelvis, abdomen and brain caused by susceptible anaerobic bacteria. Metronidazole is also used in treating infection of the colon caused by a bacterium called C. difficile. (Many commonly-used antibiotics can alter the type of bacteria that inhabit the colon. C. difficile is an anaerobic bacterium that can infect the colon when the normal types of bacteria in the colon are inhibited by common antibiotics. This leads to inflammation of the colon (pseudomembranous colitis) with severe diarrhea and abdominal pain.) Metronidazole also is used in combination with other drugs to treat Helicobacter pylori (H. pylori) that causes stomach or intestinal ulcers. Metronidazole topical gel is used for treating acne rosacea, and the vaginal gel is used for treating bacterial vaginosis.

DOSING: Metronidazole may be taken orally with or without food. In the hospital, metronidazole can be administered intravenously to treat serious infections. The liver is primarily responsible for eliminating metronidazole from the body, and doses may need to be reduced in patients with liver disease and abnormal liver function.

Various metronidazole regimens are used. Some examples are listed below.

• Amebic dysentery: 750 mg orally 3 times daily for 5-10 days
  
  
• Amebic liver abscess: 500-750 mg orally three times daily for 5-10 days
  
  
• Anaerobic infections: 7.5 mg/kg orally every 6 hours not to exceed 4 grams daily
  
  
• Bacterial Vaginosis: 750 mg (extended release tablets) once daily for 7 days. One applicator-full of 0.75% vaginal gel, once or twice daily for 5 days.
  
  
• Clostridium difficile infection: 250-500 mg orally 4 times daily or 500-750 orally 3 times daily
  
  
• Giardia: 250 mg orally three times daily for 5 days
  
  
• Helicobacter pylori: 800-1500 mg orally daily for several days in combination with other drugs.
  
  
• Pelvic inflammatory disease (PID): 500 mg orally twice daily for 14 days in combination with other drugs.
  
  
• Trichomoniasis: 2 g single dose or 1 g twice
  
  
• Rosacea: apply topical gel 0.75-1% once daily