Metronidazole Patient Tips

Medically reviewed by Carmen Pope, BPharm. Last updated on Sep 9, 2025.

1. How it works

• Metronidazole is used to treat trichomoniasis, amebiasis, and serious anaerobic bacterial infections including abdominal, skin, gynecologic, and CNS infections.
• Once absorbed, metronidazole diffuses into susceptible organisms, where it becomes active and detrimentally affects DNA synthesis and degradation in the organism, causing cell death. However, the exact way metronidazole works is unknown.
• Metronidazole belongs to the drug class called nitroimidazole antibiotics.

2. Upsides

• Used to treat symptomatic and asymptomatic T. vaginalis infections. Male sexual partners of people with Trichomoniasis infections should be treated simultaneously. Isolating the organism from asymptomatic males can be difficult and negative smears or cultures cannot be relied upon. Treating asymptomatic male partners also reduces the reinfection rate in women.
• Also used to treat acute intestinal amebiasis (amebic dysentery) and amebic liver abscess (in conjunction with pus drainage).
• Has good penetration into tissue and is an important antibiotic for the treatment of serious anaerobic bacterial infections, including intra-abdominal infections (peritonitis, abscesses), skin and skin structure infections, gynecologic infections (endometritis, tubo-ovarian abscess), bacterial septicemia, bone and joint infections (as adjunctive therapy), central nervous system infections (meningitis, brain abscess), lower respiratory tract infections (pneumonia, lung abscess), and endocarditis.
• Active against the following types of bacteria: gram-positive anaerobes (Clostridium species, Eubacterium species, Peptococcus species, Peptostreptococcus species); gram-negative anaerobes (some Bacteroides fragilis group organisms, Fusobacterium species, Protozoal parasites, Entamoeba histolytica, Trichomonas vaginalis).
• Metronidazole should only be used for proven or suspected susceptible bacterial infections and culture and susceptibility testing is recommended when available. May require combination with other antimicrobials for mixed infections
• No dosage adjustment is required in mild-to-moderate kidney or liver disease.
• Available as tablets (250 mg, 500 mg), capsules, extended-release tablets, an oral solution, and in an injectable form.
• Generic metronidazole is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

• A headache, nausea, diarrhea, an unpleasant metallic taste, peripheral neuropathy (nerve damage to fingers and toes), or a rash are common side effects. Rarely, seizures. Elderly people may be more sensitive to the side effects of metronidazole.
• Metronidazole interacts with alcohol and propylene glycol (a food additive). Symptoms include abdominal cramps, nausea, vomiting, headaches, and flushing. Avoid alcohol and products containing propylene glycol while taking metronidazole.
• The dosage of metronidazole may need to be reduced in severe hepatic impairment (Child-Pugh C) and end-stage kidney disease. No dosage adjustment is needed for mild-to-moderate kidney or liver disease.
• May not be suitable for some people including those with a history of certain blood disorders, Cockayne syndrome, Crohn's disease, or seizure or nerve disorders. Metronidazole will not treat a vaginal yeast infection. Not recommended during pregnancy or while breastfeeding.
• May interact with several other medicines including disulfiram, warfarin and other anticoagulants, lithium, busulfan, and other drugs metabolized by hepatic enzymes such as CYP2C9. May also cause erroneous results on some laboratory tests, such as aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, and triglycerides.
• Is carcinogenic in mice and rats; unnecessary use should be avoided.
• Metronidazole should not be given to women during the first trimester of pregnancy. Weigh up the risks versus benefits of giving metronidazole during other trimesters. Metronidazole passes into breast milk; however, most studies have reported no adverse effects in infants who were breastfeeding.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Metronidazole treats T. vaginalis infections (both partners should be treated simultaneously) and amebic infections. It is also effective against serious anaerobic bacterial infections affecting the abdomen, skin, reproductive organs, bones, CNS, and lungs. Common side effects include headache, nausea, metallic taste, and peripheral neuropathy. Avoid alcohol during treatment and for 3 days afterwards due to dangerous interactions.

5. Tips

• May be taken with or without food.
• Take exactly as directed and for the duration intended. For some infections, metronidazole may be given as a single dose. For other types of infections, it may need to be taken for seven to ten days, or even longer. Do not use metronidazole to treat infections other than the one you have been prescribed it for. Metronidazole has no activity against viruses (such as those that cause a cold or flu).
• Do not crush, break, or chew extended-release metronidazole tablets. Swallow them whole.
• Likmez is a ready-to-use liquid suspension of metronidazole, which is an antibiotic that may be used to treat certain bacterial infections. Likmez does not need refrigeration and the suspension is a strawberry-peppermint flavor. The strength is 500mg/5ml.
• Avoid alcohol or products containing propylene glycol (found in some flavored iced teas, frostings, and salad dressings) while taking metronidazole, and for three days after the course of metronidazole has finished.
• Seek medical advice if numbness, pain, or sensitivity occurs in your fingers or toes, or if you notice any skin color changes in these areas. Also, talk to your doctor if you develop a furry-feeling tongue or an inflamed or sore mouth as this may be a sign of Candida overgrowth (a yeast infection).
• Seek urgent medical advice if you develop a rash, diarrhea that is watery or bloody, vision problems, pain when you urinate, or seizures.
• Talk to your doctor or pharmacist before taking any other medication, including that bought over the counter, because it may not be compatible with metronidazole. Do not take metronidazole if you have taken disulfiram (Antabuse) within the past two weeks.
• Tell your doctor if you are pregnant or intending to become pregnant because metronidazole tablets may not be suitable for you, and they should not be used during the first trimester of pregnancy. Metronidazole is excreted into breast milk so talk to your doctor about breastfeeding while taking metronidazole.

6. Response and effectiveness

• Peak concentrations are reached within one to two hours after dosing; however, it may take up to 48 hours before infection-related symptoms start to abate.

7. Interactions

Medicines that interact with metronidazole may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with metronidazole. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with metronidazole include:

• alcohol
• anticoagulants, such as warfarin
• astemizole
• busulfan
• cimetidine
• disulfiram
• lithium
• medications that inhibit cytochrome p450 enzymes (CYP2C9 and possibly others), such as phenytoin or phenobarbital.

Note that this list is not all-inclusive and includes only common medications that may interact with metronidazole You should refer to the prescribing information for metronidazole for a complete list of interactions.

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Frequently asked questions

• What happens if you drink alcohol with metronidazole?
• How long does it take for metronidazole to work?
• What are the most common skin conditions? (with photos)
• Is metronidazole safe for dogs? Uses, dosage, side effects?
• What can I do about the metallic taste of Flagyl?
• Can metronidazole cause a yeast infection?
• Does metronidazole treat chlamydia?
• Can you have sex while taking metronidazole?
• Does Flagyl cause diarrhea?

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use metronidazole only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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