What is the recommended treatment regimen for Trichomonas vaginalis infection, including first‑line therapy, alternative dosing, options for pregnant patients, partner management, and alcohol precautions?

Trichomonas Vaginalis Treatment

First-Line Therapy

Metronidazole 500 mg orally twice daily for 7 days is the preferred first-line treatment for trichomoniasis in non-pregnant women, achieving superior cure rates (89-95%) compared to single-dose therapy (81%). 1, 2

• The 7-day regimen outperforms the single 2-gram dose in the highest-quality randomized controlled trial, with an 8% absolute improvement in cure rates. 2
• The single 2-gram dose remains an acceptable alternative when adherence to multi-day therapy is unreliable or cost is a significant barrier. 3, 4
• Both regimens should be taken with food to minimize gastrointestinal side effects. 5

Alternative Regimen

• Metronidazole 2 grams orally as a single dose may be used when directly observed therapy can be provided or when the 7-day regimen is not feasible. 3, 4
• For men, either the single 2-gram dose or the 7-day regimen (500 mg twice daily) is acceptable, with cure rates of 90-95% when partners are treated simultaneously. 6

Pregnancy-Specific Management

Metronidazole is contraindicated during the first trimester of pregnancy; defer treatment until after 12 weeks gestation. 3, 1

• After the first trimester, treat with metronidazole 2 grams orally as a single dose (not the 7-day regimen) to minimize total fetal drug exposure. 3, 1
• Treatment after the first trimester is essential because trichomoniasis is associated with premature rupture of membranes, preterm delivery, and low birth weight. 3, 6
• If a pregnant woman presents with symptomatic trichomoniasis during the first trimester, treatment must be delayed until the second trimester begins. 3

Partner Management (Critical for Success)

All sexual partners must be treated simultaneously with the same metronidazole regimen, regardless of symptoms or test results, because untreated partners are the primary cause of treatment failure. 3, 6, 1

• Most infected men are asymptomatic carriers, making them unknowing vectors of transmission. 3
• Patients must abstain from sexual intercourse until both partners complete treatment and are asymptomatic. 3, 6, 1
• Failure to treat partners is the most common cause of apparent treatment failure and reinfection. 3, 6

Treatment Failure Algorithm

First failure: Re-treat with metronidazole 500 mg orally twice daily for 7 days. 3, 6

Second failure: Administer metronidazole 2 grams orally once daily for 3-5 days. 3, 6

Persistent failure: After confirming that reinfection from untreated partners has been excluded, consult an infectious disease specialist for susceptibility testing. 3, 6, 1

• Most treatment failures are due to reinfection from untreated partners rather than drug resistance. 1
• Even strains with reduced susceptibility generally respond to higher metronidazole doses. 3

Metronidazole Allergy

Metronidazole desensitization is the recommended first-line approach for patients with confirmed metronidazole hypersensitivity, because no equally effective oral alternatives exist. 6

• Desensitization should be performed in collaboration with an allergist or infectious disease specialist. 6
• Tinidazole 2 grams orally as a single dose is an alternative nitroimidazole with comparable efficacy (95% cure rate), but cross-reactivity may occur in truly allergic patients. 5, 7

Special Populations

• HIV-infected patients should receive the same metronidazole regimens as HIV-negative patients. 6, 1
• Untreated trichomoniasis increases HIV transmission risk, making effective treatment crucial. 6
• In elderly patients, monitoring of serum levels may be necessary due to altered pharmacokinetics. 4
• Patients with severe hepatic disease metabolize metronidazole slowly; doses below those usually recommended should be administered cautiously with close monitoring. 4

Alcohol Precautions

Patients must avoid all alcohol during treatment and for at least 24 hours after the last metronidazole dose (or 3 days after tinidazole) to prevent severe disulfiram-like reactions. 3, 1, 5

Follow-Up Recommendations

• Routine follow-up testing is unnecessary for patients who become asymptomatic after treatment. 3, 6, 1
• Rescreening at 3 months is advised when partner treatment cannot be verified, because reinfection rates are high. 6

Critical Pitfalls to Avoid

Do not use metronidazole vaginal gel for trichomoniasis—it achieves cure rates below 50% and is only effective for bacterial vaginosis. 3, 6, 1

• Topical preparations fail to attain therapeutic concentrations in the urethra or perivaginal glands. 6
• Do not skip partner treatment, even if the partner is asymptomatic or has negative test results. 6
• Do not treat pregnant women during the first trimester; defer therapy until the second trimester. 3, 1
• Do not rely on single-dose therapy as first-line in non-pregnant women when adherence to a 7-day regimen is feasible, since the longer course provides superior cure rates. 3, 2