metronidazole at a glance
Medicine class
Nitroimidazole antibacterial and antiprotozoal agent
Alcohol
Avoid alcohol with systemic metronidazole and for two days after finishing it
Available routes
Selected products include tablets, intravenous infusion, skin cream and skin gel
What is metronidazole used for?
Selected UK products are licensed for:
Treatment and prevention of susceptible anaerobic infections, including abdominal, pelvic, respiratory, bone and postoperative infections.
Prevention of anaerobic infection associated with relevant surgery.
Protozoal infections, including trichomoniasis, amoebiasis and giardiasis.
Bacterial vaginosis, acute ulcerative gingivitis, dental infections and selected infected wounds or ulcers.
Combination treatment for Helicobacter pylori infection.
Topical treatment of rosacea-related inflammatory spots and redness.
How does metronidazole work?
In susceptible anaerobic organisms and protozoa, metronidazole is converted into reactive compounds that damage DNA and inhibit nucleic-acid synthesis. Its precise action in rosacea is uncertain.
metronidazole preparations and strengths
Cream
Route: Cutaneous
Strengths: 0.75% w/w
Gel
Route: Cutaneous
Strengths: 0.75% w/w
Solution for infusion
Route: Intravenous
Strengths: 500 mg/100 mL
Tablet
Route: Oral
Strengths: 200 mg, 400 mg, 500 mg
How to take metronidazole
Follow the label and product leaflet; administration differs by formulation.
Swallow tablets whole; taking them during or after food may help if stomach upset occurs.
For skin cream or gel, wash and dry the affected area, apply a thin layer, avoid the eyes and wash hands afterwards.
Intravenous formulations are prepared and administered by healthcare professionals.
Complete the prescribed course unless a clinician tells you to stop or a serious reaction occurs.
metronidazole side effects
Common or expected effects
- Nausea, vomiting, diarrhoea or stomach discomfort with systemic formulations
- Metallic or unpleasant taste
- Headache or reduced appetite
- Dryness, redness, itching, burning, stinging or irritation with skin formulations
- Temporary worsening of rosacea
Get urgent medical advice
- Severe allergic reaction
- Jaundice or other evidence of liver injury
- New numbness, tingling, poor coordination, seizures, confusion or other neurological symptoms
- Severe skin reaction with blistering or peeling
- Unexpected bruising, bleeding, mouth ulcers or recurrent infection
- Severe abdominal pain suggesting pancreatitis
- Blurred or double vision
metronidazole in pregnancy
Metronidazole may be used in pregnancy when treatment is clinically necessary and expected benefit outweighs possible risk. Available human evidence does not show increased risks of birth defects, stillbirth, low birth weight or premature delivery.
metronidazole while breastfeeding
Most usual short systemic courses are compatible with breastfeeding in a healthy, full-term infant, with observation for poor feeding, gastrointestinal upset, oral thrush, rash or irritability. Topical use is also acceptable; prevent infant contact with treated skin and wash hands after application. Seek specialist advice for prolonged treatment, premature infants or unwell infants.
metronidazole interactions
Interactions are generally more important with systemic formulations because absorption from skin products is low.
Alcohol and alcohol-containing products
May cause nausea, flushing, abdominal pain, headache, breathlessness or palpitations; avoid during systemic treatment and for two days afterwards.
Warfarin and related anticoagulants
Anticoagulant effects can increase, so clotting tests and anticoagulant management may need review.
Lithium
Lithium concentrations and toxicity may increase; specialist review and laboratory monitoring may be required.
Common questions about metronidazole
Answers are fully visible for fast scanning and source review.
Why must alcohol be avoided with metronidazole?
Systemic metronidazole can react with alcohol and cause nausea, vomiting, flushing, abdominal pain, headache, breathlessness or palpitations.
Can metronidazole make urine darker?
Yes. Systemic metronidazole can darken urine; this is usually harmless, but jaundice or pale stools require medical assessment.
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.