Trichomoniasis

Trichomoniasis is a sexually transmitted infection caused by the protozoan parasite Trichomonas vaginalis. It can be symptomatic or entirely asymptomatic, so a patient without symptoms cannot be assumed to be uninfected on clinical grounds alone. When symptomatic, it typically produces vaginal discharge and vulvovaginal irritation in people with a vagina, and urethral irritation in people with a penis. The single most important management principle is that the current sexual partner(s) must be treated at the same time as the patient — this is not optional counselling advice, it is part of the treatment itself, because an untreated partner is the most common cause of apparent treatment failure.^[1]

• Sexual exposure to a partner with trichomoniasis, known or unrecognized.
• New or multiple sexual partners.
• Inconsistent or absent barrier protection.
• A current sexual partner who has not been treated.
• Other concurrent or recent STI exposure — trichomoniasis frequently coexists with other STIs.

Differentiating the 3 vaginal discharge infections

Nonsexually transmitted causes of vaginitis are also common and include atrophic vaginitis, trauma, contact or irritant dermatitis (detergents, contraceptive chemicals), foreign bodies, and allergy (e.g., latex condoms). Candidiasis and bacterial vaginosis are not generally considered sexually transmitted; trichomoniasis is.

History

• Characterize the discharge (colour, consistency, odour), and ask directly about pruritus, dysuria, dyspareunia, and pelvic pain.
• Ask about pregnancy status, recent antimicrobial use, previous similar episodes, and whether a partner has symptoms or a known diagnosis.
• Identify all exposure sites (vaginal, anal, oral) and assess the need for concurrent chlamydia, gonorrhea, syphilis, and HIV testing — trichomoniasis is a marker of ongoing sexual exposure risk, not an isolated event.

Testing

• Eradicate T. vaginalis in the patient.
• Eradicate infection in the current sexual partner(s) at the same time.
• Resolve discharge, irritation, and urinary symptoms.
• Identify and treat any coexisting STI found during the same assessment.

• Avoid sexual contact until the patient and partner(s) have both completed treatment and are asymptomatic.
• Use barrier protection consistently after treatment to reduce reinfection risk going forward.
• Offer testing for other STBBIs (chlamydia, gonorrhea, syphilis, HIV) at the same visit, since trichomoniasis is a marker of ongoing exposure risk.

Metronidazole hypersensitivity

Because no effective non-nitroimidazole alternative exists, true hypersensitivity to metronidazole is managed with specialist-directed graded oral or intravenous desensitization, not a substitute drug — refer rather than attempting an alternative regimen.^[2]

• Confirm symptom resolution in the patient and confirm the partner(s) completed treatment.
• Routine test-of-cure is not required in an asymptomatic, successfully treated patient.
• Repeat testing when reinfection risk is ongoing, per current local public-health guidance.
• If symptoms persist or recur, reassess for bacterial vaginosis, vulvovaginal candidiasis, cervicitis, or pelvic inflammatory disease rather than assuming the same diagnosis has simply failed to respond.

1. Confirm the full prescribed regimen was actually taken, at the correct dose and duration.
2. Confirm the partner(s) were treated and ask specifically about any re-exposure since treatment.
3. Repeat diagnostic testing rather than treating empirically a second time.
4. If infection persists despite confirmed adherence, confirmed partner treatment, and no re-exposure, obtain expert guidance — this pattern suggests resistant infection and may require an alternative nitroimidazole dosing strategy under specialist direction.

• Using intravaginal metronidazole gel as the sole treatment — it does not work for trichomoniasis.
• Treating the patient but not the current sexual partner(s).
• Assuming recurrent symptoms automatically mean drug failure without first checking for re-exposure or nonadherence.
• Missing pelvic inflammatory disease in a patient who actually has pelvic pain or systemic symptoms rather than uncomplicated vaginitis.
• Relying on a negative wet mount to exclude infection when NAAT is available and has not been done.

How to use this table: Doses are adult doses and require patient-specific confirmation, including renal/hepatic adjustment. Select any drug name to open its complete Pharmasist Drug Database page.

Systemic Therapy

Nitroimidazoles

The only effective treatment class; no effective alternative exists for genuinely hypersensitive patients.

Not effective: intravaginal metronidazole gel is not adequate treatment for trichomoniasis despite being effective for bacterial vaginosis — do not substitute it.

Evidence note: Drug inventory, dosing, adverse effects, and comments reflect standard Canadian practice, cross-checked against current PHAC guidance.^[1]