Metronidazole Indications and Dosages
Metronidazole is indicated for trichomoniasis, bacterial vaginosis, amebiasis, giardiasis, and anaerobic bacterial infections, with specific dosing regimens for each condition. 1
Trichomoniasis Treatment
- First-line treatment: Metronidazole 500 mg orally twice daily for 7 days (90-95% cure rate) 1
- Alternative regimen: Metronidazole 2 g orally in a single dose 1
- For treatment failure: Re-treat with metronidazole 500 mg twice daily for 7 days 1
- For repeated failure: Metronidazole 2 g once daily for 3-5 days 1
Bacterial Vaginosis Treatment
- Metronidazole 500 mg orally twice daily for 7 days 1, 2
- Alternative: Metronidazole gel 0.75%, one full applicator (5 g) intravaginally, once daily for 5 days 1, 2
- Another alternative: Metronidazole 2 g orally in a single dose (note: lower efficacy) 1, 2
Amebiasis Treatment
- For acute intestinal amebiasis (acute amebic dysentery): 750 mg orally three times daily for 5 to 10 days 3
- For amebic liver abscess: 500 mg or 750 mg orally three times daily for 5 to 10 days 3
- Pediatric dosing: 35 to 50 mg/kg/24 hours, divided into three doses, orally for 10 days 3
Anaerobic Bacterial Infections
- Standard adult dosage: 7.5 mg/kg every six hours (approximately 500 mg for a 70 kg adult) 3
- Maximum daily dose: 4 g in a 24-hour period 3
- Duration: Usually 7 to 10 days; infections of bone, joint, lower respiratory tract, and endocardium may require longer treatment 3
- Metronidazole is the most active agent available against obligate anaerobes 4
Giardiasis
- Metronidazole is effective for giardiasis treatment 5
- Typically treated with similar dosing as amebiasis 5
Special Populations
Pregnancy
- Contraindicated during the first trimester of pregnancy 1, 6
- For trichomoniasis in second and third trimesters: 2 g orally in a single dose 1, 6
- For bacterial vaginosis after first trimester: Metronidazole 250 mg orally three times daily for 7 days 2
Elderly Patients
- Pharmacokinetics may be altered in elderly patients; monitoring of serum levels may be necessary to adjust dosage accordingly 3
Patients with Severe Hepatic Disease
- Doses below those usually recommended should be administered cautiously with close monitoring of plasma metronidazole levels and toxicity 3
Important Clinical Considerations
- Avoid alcohol during treatment and for 24 hours afterward due to disulfiram-like reaction 1, 2
- Metronidazole gel is NOT recommended for trichomoniasis treatment despite its approval for bacterial vaginosis (efficacy <50% compared to oral therapy) 1
- For patients with metronidazole allergy, options are limited; desensitization may be considered 1
- No dosage adjustment needed in anuric patients as accumulated metabolites can be rapidly removed by dialysis 3
Metronidazole remains a cost-effective agent with good tissue penetration, including into the central nervous system, making it particularly effective for anaerobic brain abscesses 5, 7.