Trichomoniasis

Clinical Snapshot

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]

Recognize the Condition

Typical Presentation

Ranges from asymptomatic to clearly symptomatic.

Vaginal discharge that is increased in volume, thin, and often frothy.
Vulvovaginal irritation, burning, or pruritus.
Dysuria or dyspareunia.
Cervical inflammation ("strawberry cervix") may be visible on examination.
In people with a penis: urethral irritation or discharge, though infection is frequently asymptomatic in this group.

Risk Factors

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.

Red Flags & Refer

Refer or escalate urgently for any of the following:

Severe lower abdominal or pelvic pain, fever, peritoneal signs, or hemodynamic instability — these suggest pelvic inflammatory disease rather than uncomplicated trichomoniasis, and need immediate assessment, not a course of metronidazole and reassessment later.
Infection that persists after a genuinely adequate treatment course with reinfection and nonadherence excluded — refer for specialist input.
True nitroimidazole hypersensitivity preventing standard treatment — effective non-nitroimidazole alternatives do not exist, so these patients need a specialist-directed desensitization protocol rather than a substitute drug.^[2]

Assessment & Diagnosis

Differentiating the 3 vaginal discharge infections

Parameter	Vulvovaginal candidiasis	Trichomoniasis	Bacterial vaginosis
Pruritus	Present	Present	Absent
Odour	Absent	Present	Present (fishy)
Discharge	White, clumpy and curdy	Off-white or yellow, frothy	Grey or milky, thin, copious
Inflammation	Present	Present	Absent
Vaginal pH	Under 4.5 (normal)	Over 4.5	Over 4.5
"Whiff" test (KOH)	Negative	Negative	Positive
Microscopy, specific finding	Budding yeast, pseudohyphae	Motile trichomonads	Clue cells; predominant gram-negative curved bacilli and coccobacilli
Microscopy, PMNs	Increased	Markedly increased	Not increased
Microscopy, lactobacilli	Present	Absent	Absent

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

Preferred testUse a vaginal NAAT for T. vaginalis wherever it is available — it is the most sensitive option. A wet mount showing motile trichomonads supports the diagnosis when positive, but a negative wet mount does not reliably rule out infection and should not be treated as a true negative when NAAT is available.^[1]

Treatment Targets

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.

Choose Initial Treatment

Direct treatment rule

Confirmed or strongly suspected trichomoniasis requires oral (systemic) metronidazole. Intravaginal metronidazole is not effective treatment for trichomoniasis and must not be used as the sole therapy.

For most patients, the preferred regimen is metronidazole 500 mg orally twice daily for 7 days; a 2 g single oral dose is an option, used particularly in men or where a multidose course is impractical.

Treat the current sexual partner(s) at the same time, regardless of their symptoms or test results.^[1]

Partner managementTreat every current sexual partner regardless of symptoms or testing status. Sexual partners from the current relationship should be tested and treated and treated empirically.

Non-Pharmacologic Treatment

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.

Pharmacologic Treatment Options

Drug / intervention	Role	Dose / use	Important adverse effects	Teaching points
Metronidazole, oral Preferred	Systemic trichomoniasis treatment	500 mg PO BID for 7 days	GI upset, metallic taste, urethral burning, dark urine	Preferred multidose approach. Treat current partner(s) regardless of symptoms. Avoid alcohol during treatment and for the interval stated in the product monograph.
Metronidazole, oral (single dose) Alternative	Systemic trichomoniasis treatment	2 g PO as a single dose	GI upset, metallic taste, urethral burning, dark urine	An option for male partners or when adherence to a 7-day course is a genuine concern. Avoid alcohol.

Not effective: intravaginal metronidazole gel is not adequate treatment for trichomoniasis (unlike bacterial vaginosis, where it works) — do not substitute it.^[1]

Special Populations

Pregnancy: treat symptomatic trichomoniasis in pregnancy with oral metronidazole regardless of trimester. For asymptomatic pregnant patients, treat as well — the historical concern that metronidazole increases preterm birth risk was based on a single 2005 study that is now considered methodologically flawed, and subsequent evidence has not reproduced that finding.^[3] Metronidazole is compatible with breastfeeding; some clinicians advise withholding breastfeeding for 12–24 hours after a single 2 g dose specifically, though continuing the multidose regimen requires no interruption.

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]

Monitoring & Follow-Up

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.

Treatment Failure / Next Step

Confirm the full prescribed regimen was actually taken, at the correct dose and duration.
Confirm the partner(s) were treated and ask specifically about any re-exposure since treatment.
Repeat diagnostic testing rather than treating empirically a second time.
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.

Common Errors to Avoid

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.

Clinical Decision Algorithm

Initial assessment and treatment

Vaginal discharge, vulvovaginal irritation, dysuria, or known trichomoniasis exposure

Assess for pelvic pain, fever, peritoneal signs, or hemodynamic instability

Red flags present

Manage as suspected PID — do not treat as uncomplicated vaginitis

No red flags

Obtain vaginal NAAT for T. vaginalis; assess for chlamydia/gonorrhea and other STBBIs as indicated

Positive, or strongly supported clinically

Metronidazole 500 mg PO BID x 7 days (preferred) or 2 g single dose

Treat current sexual partner(s) at the same time, regardless of symptoms

Avoid sexual contact until both patient and partner(s) are treated and asymptomatic

Alternative diagnosis more likely

Do not treat as trichomoniasis — evaluate for bacterial vaginosis, vulvovaginal candidiasis, or cervicitis

Persistent or recurrent symptoms

Symptoms persist or recur after completed treatment

Confirm adherence to the full regimen and confirm whether the partner(s) were treated

Re-exposure identified, or treatment incomplete

Retreat using metronidazole and ensure partner treatment this time

No re-exposure and treatment genuinely completed

Repeat testing; consider resistant infection or an alternative diagnosis; obtain expert guidance

Drug Tables

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.

Drug	Dosage	Adverse effects	Comments
Metronidazole (preferred multidose regimen) Flagyl, generics	500 mg PO BID x 7 days.	GI upset, metallic taste, urethral burning, dark or reddish-brown urine discolouration.	Preferred approach for most patients. Treat current partner(s) regardless of symptoms. Avoid alcohol during treatment and for the product-specific interval afterward — disulfiram-like reaction. Can be used in pregnancy and breastfeeding.
Metronidazole (single-dose regimen) Flagyl, generics	2 g PO as a single dose.	GI upset, metallic taste, urethral burning, dark or reddish-brown urine discolouration.	An option particularly for male partners or when a 7-day course is impractical; some clinicians advise withholding breastfeeding for 12-24 hours after this specific dose. Avoid alcohol.

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]

References

Sexually transmitted and blood-borne infections: Guides for health professionals — Public Health Agency of Canada. Canadian Guidelines on Sexually Transmitted Infections
Management of trichomonas vaginalis in women with suspected metronidazole hypersensitivity — American Journal of Obstetrics and Gynecology (Helms DJ, et al.). Am J Obstet Gynecol 2008;198(4):370.e1-e7
Trichomonas vaginalis as a cause of perinatal morbidity: a systematic review and meta-analysis — Sexually Transmitted Diseases (Silver BJ, et al.). Sex Transm Dis 2014;41(6):369-376

Professional reference only. Apply clinical judgment and verify patient-specific decisions against current authoritative guidance and product information.