Does Flagyl (metronidazole) treat trichomoniasis, a sexually transmitted infection (STI)?

Does Flagyl Treat Trichomoniasis?

Yes, Flagyl (metronidazole) is the primary and FDA-approved treatment for trichomoniasis, achieving cure rates of 90-95% with oral regimens. 1, 2

Recommended Treatment Regimens

The CDC guidelines establish metronidazole as the only oral medication available in the United States for treating trichomoniasis. 1 The FDA has specifically approved metronidazole for both symptomatic and asymptomatic trichomoniasis. 2

First-Line Treatment Options:

• Preferred regimen: Metronidazole 2 g orally as a single dose 1
• Alternative regimen: Metronidazole 500 mg orally twice daily for 7 days 1

The 7-day regimen is more effective than single-dose therapy, with treatment failure rates of 11% versus 19% respectively (relative risk 0.55, p<0.0001). 3 This represents the highest quality recent evidence comparing these regimens directly.

Additional FDA-Approved Option:

• Flagyl 375 mg orally twice daily for 7 days (approved based on pharmacokinetic equivalency, though clinical equivalency data are lacking) 1

Critical Treatment Considerations

Partner Management:

• Sexual partners must be treated simultaneously to prevent reinfection, regardless of symptoms or culture results 1, 4
• Patients should abstain from sexual activity until both partners complete treatment and are asymptomatic 1, 4
• Reinfection from untreated partners is a major cause of apparent treatment failure 1

Why Topical Formulations Don't Work:

• Metronidazole vaginal gel achieves cure rates below 50% compared to 90-95% with oral therapy 4, 5
• Topical preparations fail to reach therapeutic levels in the urethra and perivaginal glands where trichomonads reside 1
• A pilot study confirmed only 44% cure rate with intravaginal metronidazole gel versus 100% with oral therapy 5

Managing Treatment Failures

If initial treatment fails, use this stepwise approach:

1. First failure: Re-treat with metronidazole 500 mg twice daily for 7 days 1
2. Repeated failure: Metronidazole 2 g orally once daily for 3-5 days 1
3. Persistent failure: Consult CDC for expert guidance and susceptibility testing 1

Most metronidazole-resistant strains respond to higher doses, though true resistance does occur. 1, 6 In refractory cases, intravenous metronidazole has shown success when oral regimens fail. 7

Special Populations

Pregnancy:

• Pregnant women can be treated with the 2 g single-dose regimen 1
• Treatment is important given associations with preterm delivery, premature rupture of membranes, and low birth weight 1, 6

HIV-Infected Patients:

• Use the same treatment regimens as HIV-negative patients 1
• Untreated trichomoniasis increases HIV transmission risk 4, 6

Metronidazole Allergy:

• Metronidazole desensitization is the recommended approach for documented allergies 4
• No effective alternative medications exist in the United States 1, 4
• Desensitization should be performed under medical supervision with appropriate monitoring 4

Common Pitfalls to Avoid

• Do not use metronidazole vaginal gel as monotherapy for trichomoniasis—it is only effective for bacterial vaginosis 1, 4, 5
• Do not assume treatment failure without excluding reinfection from untreated partners 1
• Do not skip partner treatment even if the partner is asymptomatic or has negative cultures, as the organism is difficult to isolate in men 1
• Follow-up is unnecessary for patients who become asymptomatic after treatment 1