Oral Metronidazole Dosing for Adults
Yes, metronidazole is available in oral formulation, and the standard adult dose is 500 mg three times daily for most indications, though specific dosing varies by infection type. 1
Standard Oral Dosing by Indication
Clostridioides difficile Infection (CDI)
- Metronidazole 500 mg orally three times daily for 10 days is the recommended dose when vancomycin or fidaxomicin are unavailable 2, 3
- Important caveat: Metronidazole is now only recommended for initial episodes of nonsevere CDI when access to vancomycin (125 mg four times daily) or fidaxomicin (200 mg twice daily) is limited, as these agents are preferred due to superior efficacy 2
- Avoid repeated or prolonged courses due to risk of cumulative and potentially irreversible neurotoxicity 2, 3
Amebiasis
- Acute intestinal amebiasis: 750 mg orally three times daily for 5-10 days 1
- Amebic liver abscess: 500-750 mg orally three times daily for 5-10 days 1
Trichomoniasis
- Single-dose regimen: 2 grams as a single dose or divided into two 1-gram doses in the same day 1
- Seven-day regimen: 250 mg three times daily for 7 consecutive days 1
- The seven-day course may achieve higher cure rates and minimize reinfection compared to single-dose treatment 1
Anaerobic Bacterial Infections
- Standard dose: 7.5 mg/kg every 6 hours (approximately 500 mg for a 70 kg adult) 1
- Maximum: Do not exceed 4 grams in 24 hours 1
- Duration: Typically 7-10 days, though bone/joint, lower respiratory tract, and endocardial infections may require longer treatment 1
Alternative Dosing Schedules
Twice-Daily Dosing
- 400 mg twice daily has been shown to be as effective as three-times-daily dosing for certain indications, particularly surgical prophylaxis 4, 5
- This regimen achieves therapeutic serum concentrations (trough levels 3-11 mg/L) that exceed MICs for most obligate anaerobes 5
- Once-daily dosing (1 gram daily) has also demonstrated comparable efficacy to multiple-dose regimens for serious intraabdominal/pelvic infections, with pharmacokinetic and pharmacoeconomic advantages 6
Special Populations
Elderly Patients
- Metronidazole pharmacokinetics may be altered in elderly patients 1
- Monitoring of serum levels may be necessary to adjust dosage accordingly 1
Hepatic Impairment
- Patients with severe hepatic disease metabolize metronidazole slowly, resulting in drug and metabolite accumulation 1
- Administer doses below usual recommendations cautiously with close monitoring of plasma levels and toxicity 1
Renal Impairment
- Dose reduction is not specifically required in anuric patients since accumulated metabolites are rapidly removed by dialysis 1
Key Safety Considerations
- The half-life of metronidazole is 6-10 hours 7
- Metronidazole is well tolerated at doses less than 2 grams per day 7
- Drug interactions occur with alcohol, warfarin, and phenytoin 7
- When repeat courses are required, allow a 4-6 week interval between courses and reconfirm infection with appropriate laboratory measures 1