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 the dosage for metronidazole, and how do I take it?

  • 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 or by injection every 6 hours for 7 to 10 days not to exceed 4 grams daily.
  • Bacterial vaginosis: 750 mg (extended release tablets) once daily for 7 days or 500 mg twice daily for 7 days or 2 g single dose or 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

Which drugs or supplements interact with this medication?

  • Alcohol should be avoided because metronidazole and alcohol together can cause severe nausea, vomiting, cramps, flushing, and headache.
  • Metronidazole can increase the blood thinning effects of warfarin (Coumadin, Jantoven) and increase the risk of bleeding probably by reducing the breakdown of warfarin.
  • Cimetidine (Tagamet) increases blood levels of metronidazole while cholestyramine (Questran, Questran Light) reduces blood levels of metronidazole by reducing its absorption.
  • Metronidazole should not be combined with amprenavir (Agenerase) for treating human immunodeficiency disease (infection with HIV) because amprenavir contains propylene glycol.
  • Metronidazole blocks the breakdown of propylene glycol in the liver leading to accumulation of propylene glycol in blood. Accumulation of propylene glycol could cause seizures, increased heart rate, and lead to kidney failure.
  • Metronidazole increases the blood levels of carbamazepine (Tegretol, Tegretol XR, Equetro, Carbatrol), lithium (Eskalith, Lithobid) and cyclosporine though unknown mechanisms. Serious reactions may occur if these drugs are taken with metronidazole.

Is this drug safe to use during pregnancy or while breastfeeding?

  • Metronidazole is not used in early pregnancy because of potential adverse effects on the fetus.
  • Metronidazole is excreted in breast milk. Females who are nursing, because of potential adverse effects on the newborn, should not use metronidazole.

What else should I know about Flagyl (metronidazole)?

What preparations of Flagyl (metronidazole) are available?
  • 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
How should I keep Flagyl (metronidazole) stored?
  • Metronidazole should be stored at room temperature and protected from light.
When was metronidazole approved by the FDA?
  • The FDA approved metronidazole tablets in July 1963.

Reference: FDA Prescribing Information

Medically Reviewed by a Doctor on 11/11/2016

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