Metronidazole

Antibiotic / Antiprotozoal — Nitroimidazole

Nigerian brand names:FlagylMetrozolMetridRozexEmzor Metronidazole

Reviewed by the PMC Medical Team · Promise Medical Centre

Overview

Metronidazole is an antibiotic and antiprotozoal medication used to treat a wide range of infections caused by bacteria and parasites, particularly anaerobic bacteria (organisms that grow without oxygen) and certain protozoa. It is one of the most commonly prescribed medications in Nigeria and is available as tablets, suspensions, vaginal gel, and intravenous infusion. Metronidazole is the drug of choice for amoebiasis (amoebiasis is very common in Nigeria), giardiasis, bacterial vaginosis, Trichomonas infections, and is a key component of H. pylori eradication regimens. It has been on the WHO Essential Medicines List for decades.

Uses

• Amoebiasis (intestinal and hepatic) — caused by Entamoeba histolytica; very common in Nigeria • Giardiasis — intestinal parasite infection • Bacterial vaginosis • Trichomonas vaginitis (sexually transmitted infection) • H. pylori eradication — in combination with a PPI and another antibiotic • Pelvic inflammatory disease (PID) — in combination • Dental infections — particularly periapical abscesses and acute necrotising ulcerative gingivitis (ANUG) • Intra-abdominal infections — peritonitis, appendicitis • Clostridium difficile infections • Prevention and treatment of anaerobic bacterial infections in surgery • Skin infections involving anaerobic organisms

How to Use

Adults: • Amoebiasis: 800 mg three times daily for 5 days (then a luminal agent like diloxanide furoate) • Bacterial vaginosis: 400–500 mg twice daily for 7 days, OR 2 g as a single dose • H. pylori eradication: 400 mg twice or three times daily for 7–14 days (in combination) • Dental infections: 200–400 mg three times daily for 3–7 days • Giardiasis: 400 mg three times daily for 5 days OR 2 g once daily for 3 days Children: weight-based dosing; consult a doctor or pharmacist for the correct dose. IMPORTANT — Alcohol interaction: • Do not drink alcohol during treatment and for at least 48 hours after completing metronidazole — causes a severe reaction (see warnings) • Take with food or milk to reduce stomach upset • Complete the full prescribed course

Side Effects

Common: • Nausea and vomiting (take with food to reduce) • Metallic or bitter taste in the mouth • Headache • Loss of appetite • Diarrhoea or stomach cramps • Dark or reddish-brown urine (harmless — from a breakdown product of the drug) Less common: • Dizziness • Dry mouth • Furry tongue or oral thrush Rare but serious: • Peripheral neuropathy — tingling, numbness, or burning in hands and feet (with prolonged use; stop if this occurs) • Seizures and encephalopathy — with high doses or liver disease • Severe skin reactions (Stevens-Johnson syndrome) — rare • Optic neuropathy — rare

Warnings & Precautions

ALCOHOL — The most important warning: • NEVER drink alcohol while taking metronidazole and for 48 hours after the last dose. The combination causes a severe disulfiram-like reaction: intense flushing, rapid heartbeat, nausea, vomiting, headache, and difficulty breathing. This is a toxic reaction and is very distressing. Even alcohol-containing mouthwashes and cough medicines should be avoided. Other warnings: • Pregnancy: avoid in the first trimester if possible; use with caution in second and third trimesters — consult doctor • Breastfeeding: avoid single high doses (2 g); if used, interrupt breastfeeding for 12–24 hours • Liver disease: reduce dose for severe liver impairment; metronidazole is metabolised by the liver • Epilepsy or seizure disorder: use with caution; may lower seizure threshold • Blood disorders: metronidazole may affect blood cell production with very prolonged use

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Drug Interactions

• Alcohol: disulfiram-like reaction (severe flushing, vomiting, tachycardia) — avoid completely during treatment and 48 hours after • Warfarin: metronidazole significantly increases warfarin anticoagulant effect — risk of serious bleeding; reduce warfarin dose and monitor INR closely • Lithium: metronidazole can increase lithium toxicity • Phenytoin and phenobarbital: may increase metronidazole metabolism, reducing its effectiveness • Disulfiram: avoid combination — risk of acute psychosis and confusion • Fluorouracil (cancer drug): metronidazole reduces its metabolism, increasing toxicity

Storage

• Store at room temperature (below 25°C) away from light and moisture • Metronidazole vaginal gel: store in a cool place, do not freeze • Keep out of reach of children

Buy only NAFDAC-registered medications

Nigeria has a significant problem with counterfeit and substandard drugs. Always purchase medications from a licensed pharmacy and check the NAFDAC registration number on the package — verify at nafdac.gov.ng.