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Drug Profile

The information on this site is intended to supplement and enhance, not replace, the advice of a physician who is familiar with your medical history. Decisions about your health should always be made ONLY after detailed conversation with your doctor.

Limited Use [what does this mean?]
Generic drug name: metronidazole (me troe NI da zole)
Brand name(s): FLAGYL, FLAGYL ER
GENERIC: available FAMILY: Other Drugs for Bacterial Infection
Find the drug label by searching at DailyMed.

Pregnancy and Breast-feeding Warnings [top]

Breast-feeding Warning

Metronidazole is excreted in human milk. Because of the potential for serious adverse effects in nursing infants, you should not take this drug while nursing.

Pregnancy Warning

Metronidazole crosses the placenta and rapidly enters the fetal blood system. Because the drug causes cancer and has the potential for causing serious adverse effects in the fetus, it should not be used by pregnant women.

Safety Warnings For This Drug [top]

FDA BLACK BOX WARNING

Metronidazole has been shown to be carcinogenic in mice and rats. Unnecessary use of the drug should be avoided. Its use should be reserved for the conditions described in the Indications and Usage section below [of the professional product labeling].[1]

Facts About This Drug [top]

Metronidazole is used to treat some serious infections caused by bacteria or protozoa, including trichomonas, amoebiasis, giardiasis, and pseudomembranous colitis caused by clostridia from taking other antibiotics. This drug will not help in the treatment of a cold or the flu.

Metronidazole is sometimes used in combination with other drugs to treat ulcers caused by Helicobacter pylori (See Combination Treatments for Helicobacter Pylori Infection).

Metronidazole has been shown to cause...

Metronidazole is used to treat some serious infections caused by bacteria or protozoa, including trichomonas, amoebiasis, giardiasis, and pseudomembranous colitis caused by clostridia from taking other antibiotics. This drug will not help in the treatment of a cold or the flu.

Metronidazole is sometimes used in combination with other drugs to treat ulcers caused by Helicobacter pylori (See Combination Treatments for Helicobacter Pylori Infection).

Metronidazole has been shown to cause cancer in mice and rats. It can cause genetic damage in human cells.[2] Because of this connection, you should only be using metronidazole if you have a serious infection. Doctors sometimes prescribe metronidazole for a vaginal infection called trichomonas (“trich”), but you should not be using this drug for this kind of infection until you have tried other treatments, such as taking a tub bath twice a day, wearing cotton underwear and not wearing panty hose. If you have tried these treatments and you still have symptoms of a trichomonas infection, then metronidazole may be prescribed.[3]

If you are taking metronidazole for a vaginal trichomonas infection, it is best to use the form that must be taken for one day only. If you are taking metronidazole for any reason and you have kidney or severe liver impairment, you may need to take less than the usual adult dose.[4]

Metronidazole may cause encephalopathy (brain disease), peripheral neuropathy (nerve injury) and seizures.

The dose of metronidazole should be reduced in patients with severe liver disease.

Interactions

In October 2014, JAMA Internal Medicine published a study showing that older patients taking one of two commonly used oral sulfonylurea diabetes drugs — glipizide (GLUCOTROL, GLUCOTROL XL) or glyburide (DIABETA, GLUCOVANCE, GLYNASE) — in combination with metronidazole had an increased risk of developing dangerously low blood sugar levels, a condition known as hypoglycemia.[5]

Metronidazolecan cause psychotic reactions when taken concomitantly with disulfiram (ANTABUSE) (a drug used in the treatment of alcoholism).[6]

Before You Use This Drug [top]

Tell your doctor if you have or have had:

  • allergies to drugs
  • an unusual reaction to metronidazole
  • disease of the central nervous system
  • epilepsy or seizures
  • severe liver disease
  • blood problems
  • heart problems
  • pregnancy or are breast-feeding
  • known or previously unrecognized candidiasis

Tell your doctor about any other drugs you take, especially an anticoagulant such as warfarin or heparin, and including aspirin, herbs, vitamins, and other nonprescription products.

When You Use This Drug [top]

  • Do not drink alcohol while taking this drug or for at least three days after stopping the drug, because it can have a serious interaction with alcohol.
  • If you plan to have any surgery, including dental, tell your doctor that you take this drug.
  • If dry mouth occurs, use sugarless gum or sucking candy; check with your dentist if dry mouth continues for more than two weeks.
  • For treatment of giardiasis: Have a follow-up visit with your doctor.
  • For treatment for trichomonas: Male sexual partner may also need treatment and should use a condom while female partner is being treated.
  • Until you know how you react to this drug, do not drive or perform other activities requiring alertness.
  • Metronidazole may cause your urine to get darker. This is normal and not dangerous.
  • Check with your doctor if there is no improvement within a few days.

How to Use This Drug [top]

  • Take this drug for the prescribed length of time. If you stop too soon, your symptoms could come back.
  • If you miss a dose, take it as soon as you remember, but skip it if it is almost time for the next dose. Do not take double doses.
  • Do not share your medication with others.
  • Take the drug at the same time(s) each day.
  • For regular tablets: Take with food or milk.
  • For extended-release tablets: Take with water only. Do not eat or drink for about an hour before taking this medication.
  • For tablets and capsules: Store at room temperature with lid on tightly. Do not store in the bathroom. Do not expose to heat, moisture, or strong light. Keep out of reach of children.

Interactions with Other Drugs [top]

The following drugs, biologics (e.g., vaccines, therapeutic antibodies), or foods are listed in Evaluations of Drug Interactions 2003 as causing “highly clinically significant” or “clinically significant” interactions when used together with any of the drugs in this section. In some sections with multiple drugs, the interaction may have been reported for one but not all drugs in this section, but we include the interaction because the drugs in this section are similar to one another. We have also included potentially serious interactions listed in the drug’s FDA-approved professional package insert or in published medical journal articles. There may be other drugs, especially those in the families of drugs listed below, that also will react with this drug to cause severe adverse effects. Make sure to tell your doctor and pharmacist the drugs you are taking and tell them if you are taking any of these interacting drugs:

alcohol, ANTABUSE, ARALEN, carbamazepine, chloroquine, cimetidine, COUMADIN, DILANTIN, disulfiram, EFUDEX, ESKALITH, fluorouracil, lithium, LITHOBID, LITHONATE, LUMINAL, phenobarbital, phenytoin, SOLFOTON, TAGAMET, TEGRETOL, warfarin.

Adverse Effects [top]

Call your doctor immediately if you experience:

  • numbness, tingling, pain, or weakness in hands or feet
  • unusual bleeding or bruising
  • clumsiness or unsteadiness
  • seizures
  • confusion, irritability, depression, weakness, or trouble sleeping
  • mood or mental changes
  • frequent or painful urination
  • inability to control urine flow
  • skin rash, redness, hives, or itching
  • sore throat or fever
  • new vaginal dryness, discharge, or irritation
  • pain, tenderness, redness, or swelling over skin after injection
  • severe abdominal or back pain
  • anorexia
  • nausea or vomiting
  • black, tarry stools
  • blood in urine
  • pinpoint red spots on skin

Call your doctor if these symptoms continue:

  • nausea or vomiting
  • diarrhea (even if you stopped taking the drug a month ago)
  • dizziness or lightheadedness
  • headache
  • loss of appetite
  • stomach cramps or pain
  • sore mouth or tongue
  • problems urinating
  • dry mouth
  • bad taste in mouth
  • dark urine

Signs of overdose:

  • nausea or vomiting
  • seizures
  • clumsiness or unsteadiness
  • numbness, tingling, pain, or weakness in hands or feet

If you suspect an overdose, call this number to contact your poison control center: (800) 222-1222.

Periodic Tests[top]

Ask your doctor which of these tests should be done periodically while you are taking this drug:

  • stool examinations (for giardiasis)

last reviewed April 30, 2021