Metronidazole

Pronunciation: meh-troh-NYE-dah-zole.

Generic name
metronidazole
Drug class
Nitroimidazole antibiotic/antiprotozoal
Form
Tablets, capsules, oral suspension, IV infusion, vaginal cream/gel, topical cream/gel, suppositories
Route
Oral, intravenous, topical, or vaginal (formulation-dependent)
Legal status
Prescription-only

Availability and supply rules vary by country

Trade names by country: United States · United Kingdom · Canada · Australia · New Zealand

Australia: Flagyl (5) · Full directory

What metronidazole is and how it works

Metronidazole is a prescription antibiotic and antiprotozoal medicine used to treat certain bacterial and parasitic infections, including some infections in the abdomen, skin, gynecologic tract, and central nervous system, as well as trichomoniasis and amebiasis. (1)

Take metronidazole exactly as your prescriber directs and complete the full course, even if you feel better before finishing it. Avoid alcohol while taking this medicine and for a period afterward, since it can cause an unpleasant, disulfiram-like reaction (flushing, nausea, vomiting, headache, abdominal cramps).

Mechanism of action: how metronidazole works

Metronidazole is a nitroimidazole that is selectively taken up by anaerobic bacteria and susceptible protozoa, where it is reduced intracellularly to reactive intermediates that damage microbial DNA, leading to cell death. Carcinogenicity has been demonstrated in mice and rat studies, the basis for the current FDA boxed warning; this has not been definitively established in humans, but is the reason unnecessary use should be avoided. (1) (2)

What metronidazole is used for

Trichomoniasis

Used to treat symptomatic and asymptomatic trichomoniasis, a sexually transmitted parasitic infection. (1)

Amebiasis

Used to treat intestinal amebiasis and amebic liver abscess. (1)

Serious anaerobic bacterial infections

Used to treat serious infections caused by susceptible anaerobic bacteria, including intra-abdominal, skin and skin-structure, gynecologic, central nervous system, and respiratory tract infections, and to prevent post-operative infections due to anaerobic bacteria. (1) (2)

Before taking metronidazole

Do not take / not appropriate for

  • Do not take metronidazole if you have had a hypersensitivity (allergic) reaction to metronidazole or other nitroimidazole medicines. (all countries) (1)
  • Metronidazole is contraindicated for treating trichomoniasis during the first trimester of pregnancy. (first trimester of pregnancy (trichomoniasis indication)) (1)

Tell your clinician about

  • Any history of blood disorders, active neurological disease, or peripheral neuropathy.
  • Cockayne syndrome, given real reports of severe, sometimes irreversible liver injury in this specific patient group.
  • Whether you take disulfiram, warfarin or other blood thinners, or lithium, because of real, clinically important interactions.
  • Whether you drink alcohol, since alcohol should be avoided during treatment and for a period afterward.
  • Pregnancy, plans for pregnancy, or breastfeeding.
  • Any liver problems, since dose adjustment may be needed.
(1) (2)

How to take metronidazole

  • Take exactly as prescribed and complete the full course, even if symptoms improve before you finish it.
  • Avoid alcohol during treatment and for a period afterward -- the current US label specifies at least 1 day after the last dose, while UK NHS/BNF guidance advises 48 hours; follow your prescriber's or pharmacist's specific instruction.
  • Vaginal and topical formulations should be used as directed and not taken orally.
  • Tell your prescriber promptly about any numbness, tingling, or other new neurological symptoms, especially with a longer course of treatment.
(1) (7)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6) (7) (8)

Missed dose

Take the missed dose as soon as you remember, unless it is almost time for your next dose -- in that case, skip the missed dose and continue your regular schedule. Do not take a double dose. Contact your prescriber or pharmacist if you are unsure.

Overdose

Seek urgent medical attention or contact a poison control centre if you think too much metronidazole has been taken. Reported overdoses (including single doses up to 15 g) have caused nausea, vomiting, and unsteady movements (ataxia). There is no specific antidote; treatment is supportive. (1)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Metallic taste in the mouth.

What to notice: Metallic taste in the mouth.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Nausea, vomiting, or loss of appetite.

What to notice: Nausea, vomiting, or loss of appetite.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Headache.

What to notice: Headache.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Diarrhoea, abdominal cramping, or a furry/coated tongue.

What to notice: Diarrhoea, abdominal cramping, or a furry/coated tongue.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Serious warnings

Signs of nerve problems (peripheral neuropathy) or central nervous system effects — high caution

Symptoms: Numbness, tingling, or pain in the hands or feet; seizures; confusion; unsteady movements; visual changes.

Action: Contact your prescriber promptly if any of these develop, especially during a prolonged course -- a clinician will assess whether treatment needs to be adjusted or stopped. These effects are more common with prolonged or high-dose use and can occasionally persist. (1)

Disulfiram-like reaction with alcohol — high caution

Symptoms: Flushing, throbbing headache, nausea, vomiting, and abdominal cramps after drinking alcohol.

Action: Avoid alcohol during treatment and for the period afterward advised by your prescriber or pharmacist (guidance ranges from at least 1 day per the current US label to 48 hours per UK NHS/BNF guidance). (1) (7)

Severe liver injury (particularly in Cockayne syndrome) — emergency

Symptoms: Yellowing of the skin or eyes (jaundice), dark urine, severe fatigue, or abdominal pain.

Action: Seek prompt medical attention. Cases of severe, sometimes irreversible liver failure have been reported specifically in patients with Cockayne syndrome; tell your prescriber if you or your child has this condition before starting treatment. (2)

Interactions

  • Disulfiram: concurrent use has been associated with psychotic reactions. Avoid metronidazole within 2 weeks of taking disulfiram. (1)
  • Warfarin and other oral anticoagulants: metronidazole can potentiate their anticoagulant effect, prolonging clotting times. Your prescriber may need to adjust your dose and monitor you more closely. (1)
  • Lithium: short courses of metronidazole have been linked to raised lithium levels and toxicity. Lithium levels may need closer monitoring. (1)
  • Alcohol and propylene-glycol-containing products: can cause a disulfiram-like reaction (flushing, nausea, vomiting, headache, cramps). Avoid during treatment and for the period afterward advised by your prescriber. (1)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

Metronidazole is contraindicated for treating trichomoniasis during the first trimester of pregnancy per the US label. It is an older FDA Pregnancy Category B medicine (animal studies have not shown fetal harm, though adequate controlled human studies are limited); a separate literature review found no clear teratogenic signal overall, but this does not override the specific first-trimester contraindication for trichomoniasis. Discuss any use in pregnancy with your prescriber. (1) (2) (3) (4) (5) (6) (7) (8)

Breastfeeding

Metronidazole passes into breast milk at concentrations similar to blood plasma levels. Discuss with your prescriber; some sources suggest a nursing parent may choose to pump and discard milk during therapy and for a period afterward because of the carcinogenicity signal seen in animal studies. (1) (2) (3) (4) (5) (6) (7) (8)

Children

Used in children for specific indications under a prescriber's guidance; dosing is individualised by weight and indication. (1) (2) (3) (4) (5) (6) (7) (8)

Elderly

No specific dose adjustment based on age alone is described in the source reviewed, but older adults may be more susceptible to neurological side effects and should be monitored accordingly. (1) (2) (3) (4) (5) (6) (7) (8)

Hepatic_impairment

Dose adjustment may be needed in significant liver impairment; discuss with your prescriber. Severe hepatotoxicity has specifically been reported in patients with Cockayne syndrome. (1) (2) (3) (4) (5) (6) (7) (8)

Renal_impairment

Not specifically addressed in the source reviewed for this dossier; kidney problems should be discussed with your prescriber. (1) (2) (3) (4) (5) (6) (7) (8)

Source_ids

US-DAILYMED-METRONIDAZOLE-2026,SECONDARY-METRONIDAZOLE-PREGNANCY-TERATOGENICITY-REVIEW,UK-EMC-METRONIDAZOLE-2026 (1) (2) (3) (4) (5) (6) (7) (8)

Monitoring

Before starting

  • Review of alcohol use and other medicines (especially disulfiram, warfarin, lithium)
  • Baseline liver function where relevant
  • Screening for Cockayne syndrome history if relevant

During treatment

  • Watch for numbness, tingling, or other new neurological symptoms, especially with prolonged courses.
  • Watch for signs of liver problems (jaundice, dark urine, severe fatigue).
  • Monitor INR more closely if taking warfarin, and lithium levels if taking lithium.
  • Avoid alcohol throughout treatment and for the period afterward advised by your prescriber.
(1)

Storage

Store at room temperature, away from excess heat and moisture, as directed on the product label. Follow specific storage instructions for liquid suspensions or reconstituted products.

Study the drug class: Metronidazole & the Nitroimidazoles

Professional information

Clinician-facing context only, sourced from the current US FDA prescribing information; verify against the current full label before prescribing.

United States

Indication: Trichomoniasis, amebiasis, serious anaerobic bacterial infections

Dose summary: Dosing is indication-specific (e.g. single-dose or multi-day regimens for trichomoniasis; weight-based, multi-day courses for amebiasis and anaerobic infections). Not diluted or combined outside labelled formulations. Boxed warning against unnecessary use applies to all indications.

Renal context: Not established in the source reviewed for this dossier. (1)

Mechanism of action

Hepatic guidance

Dose adjustment may be needed in significant hepatic impairment. Severe, sometimes irreversible hepatotoxicity/acute liver failure has been specifically reported in patients with Cockayne syndrome, who require close monitoring and prompt discontinuation if liver injury is suspected.

Overdose note

Reported overdoses (single doses up to 15 g) have produced nausea, vomiting, and ataxia. No specific antidote exists; manage with supportive care and monitoring, including for neurological symptoms. (1) (2)

Frequently asked questions

Why does metronidazole have a warning about cancer risk?

Metronidazole has been shown to be carcinogenic in mice and rat studies, which is why the US label carries a boxed warning advising against unnecessary use -- it should be reserved for the specific infections it is approved to treat. This has not been definitively established as a cancer risk in humans, but the precaution remains in the current label. (1)

How long do I need to avoid alcohol after taking metronidazole?

This varies by source. The current US FDA label advises avoiding alcohol during treatment and for at least 1 day after the last dose. UK NHS and British National Formulary guidance advises 48 hours. Follow the specific guidance given by your prescriber or pharmacist, since combining metronidazole with alcohol can cause a disulfiram-like reaction (flushing, nausea, vomiting, headache, cramps). (1) (7)

Why does metronidazole cause a metallic taste?

A metallic taste is one of the most common side effects of metronidazole, though the exact mechanism is not fully established. It is generally harmless and resolves after finishing the course. (1)

Is metronidazole available in the US, UK, Europe, Canada, Australia, and New Zealand?

Yes, it is an authorised, widely available generic antibiotic/antiprotozoal medicine in all of these regions, sold as Flagyl and numerous generic equivalents. (1) (2) (3) (4) (5) (6)

What is the mechanism of action of metronidazole?

Metronidazole is a nitroimidazole that is selectively taken up by anaerobic bacteria and susceptible protozoa, where it is reduced intracellularly to reactive intermediates that damage microbial DNA, leading to cell death. Carcinogenicity has been demonstrated in mice and rat studies, the basis for the current FDA boxed warning; this has not been definitively established in humans, but is the reason unnecessary use should be avoided. (1) (2)

What is the generic name of Metronidazole?

The generic name is metronidazole. (1)

What class of drug is metronidazole?

Metronidazole is classed as: Nitroimidazole antibiotic/antiprotozoal. (1)

References

  1. METRONIDAZOLE tablet -- full prescribing informationU.S. Food and Drug Administration / DailyMed (NIH), full prescribing information · United States · accessed 2026-07-29 · source 1
  2. Metronidazole 400 mg Film-Coated Tablets -- Summary of Product Characteristics (SmPC)electronic medicines compendium (emc), United Kingdom · United Kingdom · accessed 2026-07-29 · source 2
  3. Metronidazole -- nationally authorised medicinal product across EU member states (PSUSA/00010199)European Medicines Agency (EMA) -- periodic safety update report single assessment (PSUSA) framework confirming nationally authorised status across EU member states · European Union · accessed 2026-07-29 · source 3
  4. FLAGYL (metronidazole) Product MonographHealth Canada product monograph, Sanofi-Aventis Canada Inc. · Canada · accessed 2026-07-29 · source 4
  5. FLAGYL metronidazole 400 mg tablet blister pack -- ARTG registrationTherapeutic Goods Administration (TGA), Australia · Australia · accessed 2026-07-29 · source 5
  6. New Zealand Data Sheet -- Metronidazole (multiple registered formulations including Flagyl, Metrogyl, Metronidamed)Medsafe (New Zealand regulator) · New Zealand · accessed 2026-07-29 · source 6
  7. Metronidazole and alcohol -- comparison of current US label vs UK NHS/BNF guidance on avoidance durationSecondary clinical/regulatory reporting cross-referencing the UK NHS and British National Formulary (BNF) alongside the US FDA label · Not country-specific (comparative guidance) · accessed 2026-07-29 · source 7
  8. Metronidazole Appears Not to Be a Human Teratogen: Review of the LiteraturePeer-reviewed literature review, hosted on PubMed Central (NIH/NCBI) · Not country-specific · accessed 2026-07-29 · source 8

Brand names by country

Single-ingredient metronidazole names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

United States

  • LIKMEZ100 mg/mL · kesin pharma corporation
  • Nuvessa65 mg/5g · exeltis usa, inc.
  • Vagizole7.5 mg/g · inutrition llc
  • Noritate10 mg/60g · bausch health us, llc
  • Firming antibacterial1 g · jiangxi he-oumei health industry co., ltd.
  • Flagyl375 mg · pfizer laboratories div pfizer inc
  • Vandazole7.5 mg/g · upsher-smith laboratories, llc

United Kingdom

  • Metronidazole (generic; multiple licensed manufacturers) (2)MHRA licensed emc smpc confirmed · 200 mg, 400 mg, 500 mg · Multiple UK-licensed manufacturers

Canada

  • FLAGYL
  • METROGEL
  • NIDAGEL
  • NORITATE
  • METROCREAM - CRM
  • NOVO-NIDAZOL

Australia

  • Flagyl (5)TGA ARTG registered 2009-06-22 confirmed · 400 mg (tablet), 500 mg (suppository) · Vitalion Pty Ltd

New Zealand

  • Flagyl, Metrogyl, Metronidamed (multiple registered brands) (6)Medsafe approved confirmed · 200 mg, 400 mg, 500 mg (suppository) · Multiple NZ-registered suppliers
View brands in additional countries.

European Union

Metronidazole (generic; nationally authorised, e.g. TERGYNAN combination in France) (3)

This page provides general reference information about metronidazole and is not a substitute for advice from the prescriber managing your treatment. All dosing and treatment decisions should be made with your prescriber.

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