How the dose is calculated
Metronidazole dosing depends heavily on the indication — anaerobic bacterial infection, invasive amoebiasis, and giardiasis all use different mg/kg/day targets and course lengths. Select the indication being treated to get the correct dose and frequency.
Typical dosing by indication
| Indication | Dose | Frequency | Max |
|---|---|---|---|
| Anaerobic infection | 30 mg/kg/day | every 8h (3×/day) | 1500 mg/day |
| Amoebiasis | 40 mg/kg/day | every 8h (3×/day) | 2250 mg/day |
| Giardiasis | 15 mg/kg/day | every 8h (3×/day) | 750 mg/day |
Clinical use
- Metronidazole is a key agent against anaerobic bacteria and protozoal infections (amoebiasis, giardiasis, trichomoniasis) — the correct indication must be selected since dosing and course length differ substantially between them.
- Course length varies by indication — anaerobic bacterial infections are typically 7–10 days, invasive amoebiasis 5–10 days, and giardiasis 5–7 days; confirm the specific course length against current guidance.
- Avoid alcohol during treatment and for at least 48 hours after the last dose — a disulfiram-like reaction (flushing, nausea, tachycardia) can occur.
- Metallic taste, nausea, and dark urine are common but harmless side effects worth counselling patients about in advance.
Frequently asked questions
Why does metronidazole dosing differ by indication?
Anaerobic bacterial infections, invasive amoebiasis, and giardiasis each need a different mg/kg/day target and course length to reliably clear the specific organism, so the indication must be selected correctly rather than using one flat dose for everything.
Can I drink alcohol while taking metronidazole?
No — alcohol should be avoided during treatment and for at least 48 hours after the last dose, as it can cause a disulfiram-like reaction with flushing, nausea, and a rapid heartbeat.
Is a metallic taste normal with metronidazole?
Yes — a metallic taste, along with nausea or darker urine, is a common and harmless side effect of metronidazole that resolves after finishing the course.
What is metronidazole used for in giardiasis?
It's one of the standard treatments for Giardia lamblia infection, dosed by weight for a shorter course (typically 5–7 days) than the doses used for bacterial or amoebic infections.
References
- World Health Organization. Model Formulary — Metronidazole.
- British National Formulary for Children (BNFc) — Metronidazole.
- Centers for Disease Control and Prevention. Giardiasis — Treatment Guidance.