Metronidazole Dosage for Bacterial Vaginosis
For non-pregnant women with bacterial vaginosis, take metronidazole 500 mg orally twice daily for 7 days, and completely avoid all alcohol during treatment and for at least 24 hours after the last dose. 1, 2
Standard Dosing Regimens
First-Line Treatment (Non-Pregnant Women)
- Metronidazole 500 mg orally twice daily for 7 days is the CDC-recommended standard treatment, achieving high cure rates (78-87%) with systemic coverage 1, 2, 3
- This 7-day oral regimen is more effective than single-dose alternatives and provides relief of symptoms with improvement in clinical course 2, 4
Alternative Oral Regimens
- Metronidazole 2g orally as a single dose can be used, but has lower efficacy compared to the 7-day course and higher relapse rates 2, 4
- Metronidazole extended-release (Flagyl ER) 750 mg once daily for 7 days is FDA-approved, though clinical equivalency data with other regimens is limited 2
Topical Alternatives
- Metronidazole gel 0.75%, one full applicator (5g) intravaginally once daily for 5 days achieves less than 2% of blood levels compared to oral medication, minimizing systemic side effects like gastrointestinal upset and metallic taste 1, 2
- The vaginal gel formulation is appropriate for patients who cannot tolerate systemic metronidazole due to gastrointestinal side effects 1
Pregnancy-Specific Dosing
Pregnant Women (All Trimesters After First)
- Metronidazole 250 mg orally three times daily for 7 days is the CDC-recommended regimen for pregnant women, using a lower dose to minimize fetal exposure while providing systemic coverage 1, 2, 5
- Metronidazole is safe during pregnancy after the first trimester, but metronidazole is contraindicated in the first trimester 1, 2
- Alternative regimens include metronidazole 2g single dose or clindamycin 300 mg orally twice daily for 7 days 1
- Avoid clindamycin vaginal cream in pregnancy as it may increase the risk of preterm deliveries 1
Critical Safety Warnings
Alcohol Interaction
- Patients must completely avoid all alcoholic beverages during treatment and for at least 24 hours after completing the last dose to prevent severe disulfiram-like reactions 1, 2
Common Side Effects
- Mild gastrointestinal upset and unpleasant metallic taste in mouth are common with oral metronidazole 1
- The vaginal gel formulation avoids the metallic taste associated with oral therapy 1
Special Populations
HIV-Infected Patients
- Use the same treatment regimens as for HIV-negative patients, including metronidazole 500 mg orally twice daily for 7 days or 250 mg three times daily for 7 days in pregnancy 1
Patients with Metronidazole Allergy
- Clindamycin 2% vaginal cream, one full applicator (5g) intravaginally at bedtime for 7 days is the preferred first-line alternative, with cure rates of 72% 2, 3
- Oral clindamycin 300 mg twice daily for 7 days achieves cure rates of 93.9%, comparable to metronidazole 2, 6
- Never use metronidazole gel vaginally in patients with true metronidazole allergy, as true allergy requires complete avoidance of all metronidazole formulations 2
Clinical Pitfalls to Avoid
Treatment Failure Considerations
- The bacterial vaginosis cure rate with standard metronidazole therapy is approximately 54-87%, with incomplete eradication of bacterial vaginosis-associated anaerobes in most women 3, 7
- High pretreatment concentrations of pathobionts and vaginal microbiota dominated by Gardnerella vaginalis (>50%) are associated with increased likelihood of treatment failure 7
- Recurrence rates approach 50% within one year of treatment, but no long-term maintenance regimen is currently recommended 1, 2
Partner Management
- Sexual partners do not need treatment, as multiple clinical trials demonstrate that treating partners does not improve cure rates or prevent recurrence 1, 2, 5
Follow-Up
- No follow-up visit is necessary if symptoms completely resolve 1, 2
- If symptoms return, contact your provider for retreatment with a recommended regimen rather than self-treating with over-the-counter products 1