metronidazole (Flagyl) Side Effects and Adverse Effects

  • 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.

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What is metronidazole (Flagyl, Flagyl ER)?

Brand name(s): Flagyl, Flagyl ER

Metronidazole (Flagyl, Flagyl ER) is a prescription antibiotic medication prescribed for the treatment of a variety of parasitic and bacterial infections of the vagina, gynecological area, skin, intra-abdominal cavity, blood, bone, joint, nervous system, and heart. For example:

Research has shown that Flagyl causes cancer in mice and rats. Only take this drug as your doctor prescribes it. This medicine is an antibacterial drug and is susceptible to antibiotic resistance; a healthcare provider should only prescribe it for treatment if the infection is proven or strongly thought to be caused by bacteria.

Common side effects of Flagyl are loss of appetite, headaches, and nausea. Serious side effects are encephalopathy, seizures, and aseptic meningitis. You can take metronidazole taken with or without food. Avoid drinking alcohol while taking this drug because the combination can cause severe nausea, vomiting, headache, flushing, and cramps.

Flagyl is available in doses for adults as tablets of 250 mg, 500 mg, and 750 mg. The dose for pediatric patients is available as tablets of 35 to 50 mg/kg/24 hours. Patient dosage administration depends upon the severity of infection caused by parasites or bacteria, and any other existing medical conditions, particularly if they are severe. There are several drug interactions with Flagyl. Interactions, for example, like warfarin (Coumadin, Jantoven), cimetidine (Tagamet), cholestyramine (Questran, Questran Light), amprenavir (Agenerase), lithium (Eskalith, Lithobid), and cyclosporine. This medicine may cause increased heart rate, which can lead to seizures. Ask your doctor, pharmacist, or other medical professional if you have questions about Flagyl.

Metronidazole also is available as a capsule (375 mg), cream (0.75% and 1 mg), Lotion (0.75%), gel (0.75% and 1%), and injection (5mg/ml).

If you notice other effects not listed above, contact your doctor or pharmacist. In the US -Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Read the entire consumer metronidazole (Flagyl) drug information >>

What are the side effects of metronidazole (Flagyl)?

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:

  • Seizures
  • Damage of nerves resulting in numbness and tingling of extremities
  • Peripheral neuropathy
  • Encephalopathy
  • Aseptic meningitis
  • Colon cancer in people with Crohn's disease

If you notice other effects not listed above, contact your doctor or pharmacist. In the US -Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Read the entire consumer metronidazole (Flagyl) drug information >>

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Other consumer metronidazole (Flagyl) side effects*

SIDE EFFECTS:

If any of these effects persist or worsen, notify your doctor or pharmacist promptly.T his drug may cause urine to darken in color. This is harmless.Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects.

Many people using this medication do not have serious side effects.

Tell your doctor immediately if any of these unlikely but serious side effects occur:

Tell your doctor immediately if any of these rare but very serious side effects occur:

Use of this medication for prolonged or repeated periods may result in oral thrush or a new vaginal yeast infection (oral or vaginal fungal infection).

Contact your doctor if you notice white patches in your mouth, a change in vaginal discharge, or other new symptoms.

A very serious allergic reaction to this drug is unlikely, but seek immediate medical attention if it occurs.

Symptoms of a serious allergic reaction may include:

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.In the US -Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088. In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Read the entire metronidazole - oral, Flagyl side effects, uses, interaction, overdose and precautions >>

REFERENCES:

FDA metronidazole (Flagyl) Prescribing Information

FDB. "metronidazole - oral."

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Report Problems to the Food and Drug Administration

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

Reviewed on 6/13/2017
References
REFERENCES:

FDA metronidazole (Flagyl) Prescribing Information

FDB. "metronidazole - oral."

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