Metronidazole — NZ Medication Guide
📋 Reviewed by a Registered Pharmacist NZ — This information is for general educational purposes only and does not replace professional medical advice. Always consult your doctor or pharmacist before starting, stopping, or changing any medication.
What is Metronidazole?
Metronidazole is a nitroimidazole antibiotic and antiprotozoal medicine used for a wide range of bacterial and parasitic infections. This medication is funded by Pharmac for anaerobic infections, bacterial vaginosis, and H. pylori eradication.
What is Metronidazole Used For?
Metronidazole is used for anaerobic bacterial infections (intra-abdominal, pelvic, dental), bacterial vaginosis, Helicobacter pylori eradication (as part of triple or quadruple therapy), Clostridium difficile infection, Trichomonas vaginalis, Giardia lamblia, and protozoal infections.
How Does Metronidazole Work?
Metronidazole is reduced to reactive intermediates by anaerobic (or microaerophilic) organisms, which then damage microbial DNA strands — causing strand breakage and impaired DNA synthesis. This selective toxicity to anaerobes and protozoa is the basis for its clinical utility.
How to Take Metronidazole
For most infections: 400 mg three times daily or 500 mg twice daily for 5–7 days. For Clostridium difficile: 400–500 mg three times daily for 10–14 days. For Helicobacter pylori: as part of triple therapy (e.g., PPI + amoxicillin + metronidazole) for 7–14 days. Take with food to reduce nausea. Avoid alcohol completely during treatment and for 48 hours after completing the course.
Common Side Effects of Metronidazole
- Nausea and vomiting
- Metallic taste in the mouth (very common)
- Headache
- Dizziness
- Dark urine (harmless — due to metabolites)
- Dry mouth
Serious Side Effects — Seek Medical Attention
Contact your doctor or call 111 immediately if you experience any of the following:
- Disulfiram-like reaction with alcohol (severe nausea, vomiting, flushing, tachycardia — avoid all alcohol including alcohol in medicines)
- Peripheral neuropathy (with prolonged high-dose use)
- Encephalopathy and seizures (high dose or severe renal/hepatic impairment)
- Severe skin reactions (rare)
Drug Interactions
Metronidazole may interact with other medicines. Always inform your doctor and pharmacist of all medications you are taking. Key interactions include:
- Alcohol (severe — disulfiram-like reaction — MUST avoid during treatment and 48 hours after)
- Warfarin (metronidazole significantly increases warfarin levels — INR check required)
- Lithium (increased lithium levels)
- Phenytoin (increased phenytoin levels)
- Ciclosporin (increased levels)
New Zealand Prescribing Information
Metronidazole (200 mg, 400 mg tablets; 500 mg/100 mL IV infusion; 0.75% topical gel) is funded by Pharmac. Metronidazole resistance in H. pylori is increasing in NZ — treatment regimens are reviewed periodically by BPAC NZ. The absolute prohibition on alcohol during and 48 hours after metronidazole treatment must be clearly communicated to patients.
Frequently Asked Questions
Why can’t I drink alcohol with metronidazole?
Metronidazole inhibits acetaldehyde dehydrogenase, causing acetaldehyde to accumulate when alcohol is consumed. This causes a severe disulfiram-like reaction: intense flushing, nausea, vomiting, headache, and rapid heart rate. The reaction can occur with any amount of alcohol, including that in medicines, mouthwash, and food.
Will metronidazole affect my contraception?
Unlike some antibiotics, metronidazole does not affect hormonal contraceptives (combined pill, progestogen-only pill, injection, implant, IUD). Additional contraceptive precautions are not required specifically for metronidazole.
⚠️ Disclaimer: This page is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your doctor or a qualified health provider. In New Zealand, medication availability and funding may vary — check with Pharmac or your pharmacist for current information.
Reviewed by a Registered Pharmacist NZ
References & Further Information
The following New Zealand and international resources were used to inform this page: