Flagyl (Metronidazole) 500 mg: Uses, Safety and Interactions

What this medicine treats

Flagyl contains metronidazole, a nitroimidazole antimicrobial. This overview concerns oral 500 mg tablets, using current UK and US generic tablet information. It does not describe vaginal products, skin gels or intravenous treatment. Metronidazole targets selected anaerobic bacteria and certain parasites; it does not treat ordinary viral colds.

Why the diagnosis matters

The UK label includes infections such as bacterial vaginosis, trichomoniasis, giardiasis, amoebiasis and specified anaerobic dental or other infections. Some infections require additional medicines, drainage or management of a sexual partner. Its role in Helicobacter pylori treatment is within a combination selected under current guidance, not single-drug self-treatment. Authorised uses differ by country, so the name and tablet strength do not establish a treatment schedule.

Adverse effects and warning signs

Nausea, abdominal discomfort and a metallic taste can occur. Metronidazole may darken urine, but yellow skin or eyes, severe abdominal symptoms or marked weakness need assessment for liver injury. New numbness, tingling, poor coordination, confusion, seizures or visual changes can signal neurological toxicity. Seek urgent help for breathing difficulty or an extensive blistering rash. Cockayne syndrome is especially important: serious, sometimes fatal liver injury has occurred, and the US label contraindicates use. Longer courses can require blood-count and neurological monitoring.

Alcohol, interactions and individual review

The reviewed labels advise avoiding alcohol during therapy and afterwards; the UK label specifies at least 48 hours, while the US label specifies at least three days and also warns about propylene glycol-containing products. Follow the applicable product leaflet and obtain advice if instructions conflict. Recent disulfiram use is an important US contraindication because psychotic reactions have occurred. Warfarin can require extra INR monitoring; lithium concentrations and toxicity can increase. Busulfan, phenytoin and other seizure medicines also need a professional interaction check. Pregnancy and breastfeeding recommendations depend on the infection, trimester and regimen; they should not be reduced to a blanket statement that all use is safe or prohibited. This summary is not an individual prescription.

Sources

• Metronidazole 500 mg film-coated tablets — UK SmPC, Zentiva — Text revision 21 July 2026; emc update 27 July 2026
• Metronidazole oral tablets — US prescribing information, DailyMed — DailyMed repackaged label update 5 August 2026; source NDC 23155-652

Source check: 30 October 2026. This date records verification of the cited sources, not a clinical review by a doctor or pharmacist. Use the current leaflet for your product and seek professional advice for personal treatment decisions.