4 known interactions • 2 major • 2 moderate • 0 minor
Always disclose all medications to your healthcare providers — prescription medicines, OTC medications, vitamins, and herbal supplements. This list may not include every possible interaction. Use our Medicine Interaction Checker to screen your complete medication list.
Potentially life-threatening or causing permanent damage. Avoid combination.
May worsen condition or require dose adjustment. Monitor closely.
Usually limited clinical effect. Manage with routine monitoring.
Alcohol (and propylene glycol)
Metronidazole inhibits aldehyde dehydrogenase, causing accumulation of acetaldehyde when alcohol is consumed. This produces a disulfiram-like reaction: flushing, nausea, vomiting, headache, palpitations, and hypotension. Can be severe.
Management: ABSOLUTELY AVOID ALCOHOL during treatment and for 48 hours after the last dose. Counsel emphatically. Also avoid products containing propylene glycol (some IV medications, topical products).
Warfarin
Metronidazole strongly inhibits CYP2C9, significantly increasing warfarin levels and anticoagulant effect. INR can increase dramatically.
Management: Monitor INR within 2–3 days of starting metronidazole. Reduce warfarin dose prophylactically (typically by 25–50%).
Lithium
Metronidazole reduces renal lithium clearance, increasing lithium levels and toxicity risk.
Management: Monitor lithium levels and for toxicity signs during metronidazole course.
Phenytoin / phenobarbital
These anticonvulsants induce metronidazole metabolism, reducing efficacy. Metronidazole also inhibits phenytoin metabolism.
Management: Monitor phenytoin levels; consider alternative antibiotic if possible.
Always ask your pharmacist about potential interactions with food, alcohol, and supplements specific to Metronidazole. Some medicines have significant interactions with grapefruit juice, high-fat meals, dairy products, or vitamin K-rich foods.