metronidazole (Flagyl, Flagyl ER) Antibiotic

  • Pharmacy Author:
    Omudhome Ogbru, PharmD

    Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

  • Medical and Pharmacy Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

What is metronidazole (Flagyl, Flagyl ER), and how does it work?

Flagyl 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). Anaerobic bacteria 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.

What brand names are available for metronidazole?

  • Flagyl and Flagyl ER are the available brand names for metronidazole in the US.
    • Metro IV, Metromidol, Protostat, and Satric are brands names for metronidazole that have been discontinued in the US.

    Is this drug available as a generic?


    Do I need a prescription for this drug?


    Why is metronidazole prescribed to patients?

    • Flagyl 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.
    • Flagyl 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.
    • Flagyl 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.)
    • Flagyl also is used in combination with other drugs to treat Helicobacter pylori (H. pylori) that causes stomach or intestinal ulcers.
    • Flagyl topical gel is used for treating acne rosacea.
    • Flagyl vaginal gel is used for treating bacterial vaginosis.

    What are the side effects of metronidazole?

    Flagyl is a useful antibiotic and is generally well tolerated with appropriate use.

    The most common and minor side effects include:

    Side effects that are uncomfortable, but may become serious include:

    • Brain disease
    • Fevers
    • Mouth sores
    • Pain with urination
    • Prickling or tingling sensations that may become permanent
    • Cystitis
    • Pelvic pain or pressure
    • Decrease of libido
    • Proctitis
    • Stomitis
    • Glossitis

    Serious side effects of Flagyl are rare and the drug should be stopped if these symptoms appear:

    Medically Reviewed by a Doctor on 11/11/2016

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