Antiprotozoals for Trichomoniasis

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Antiprotozoals for Trichomoniasis


Generic NameBrand Name

How It Works

Antiprotozoals kill the tiny parasite (a one-celled protozoan organism) that causes trichomoniasis (trich).

Why It Is Used

This medicine is used to cure trichomoniasis by destroying the parasite that causes the condition.

Oral metronidazole can be taken either as a single dose or as multiple doses. A single oral dose of metronidazole can be taken by a pregnant woman if needed.1 Women who are breast-feeding will be instructed by their doctors on the use of metronidazole.

How Well It Works

The cure rate in treating trichomoniasis using metronidazole is 90% to 95%.2

Sex partners should be treated at the same time. Sexual intercourse should be avoided until symptoms are gone. Men may not have any symptoms but still need treatment.

People who are infected with HIV receive the same treatment for trich as those who are HIV-negative.


  • No follow-up is needed if symptoms go away.
  • If symptoms do not go away, you may need to take the medicine again.
  • If treatment fails after this and you have not been reinfected, further testing may be done to find out the cause of your symptoms. It is possible to have a strain of trich that is resistant to metronidazole. If this is the case, you may need to take a large dose of metronidazole. This will usually cure the infection.1

Metronidazole vaginal suppositories or creams are not recommended, because oral metronidazole is much more effective. Vaginal medicines cure trich in less than 50% of cases.2 Metronidazole vaginal gel, which is used to treat bacterial vaginosis, is not recommended by the Public Health Agency of Canada (PHAC) for treatment of trich.1

Side Effects

Common and expected side effects include:

  • Metallic taste in the mouth.
  • Dark urine colour.
  • Nausea and vomiting with the higher dose of metronidazole or with use of alcohol or products that contain alcohol during treatment.

These side effects will go away after the medicine is stopped.

In rare cases, metronidazole may cause pancreatitis, an inflammation of the pancreas, in some people. Also, metronidazole may not cure trich in some people. When treatment resistance or severe side effects occur, another type of treatment will be needed.

Caution: Do not use alcohol or products that contain alcohol (such as non-prescription nighttime cold medicines) while taking metronidazole. You should not use alcohol for at least 3 days after your last dose of this medicine. Alcohol interacts with this medicine, and the combination can cause nausea, abdominal cramps, headaches, reddening of the face, and vomiting.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

The oral form of this medicine is the most effective treatment for trichomoniasis.

Oral metronidazole can be taken by pregnant women at any time during pregnancy.

While you are taking this medicine and for at least 3 days after your last dose, do not use alcohol or products that contain alcohol.

Trich during pregnancy raises the risk of premature rupture of membranes (PROM) and premature delivery. Treating the infection does not appear to reduce this risk.3 If you are pregnant and have trich, talk to your doctor about the pros and cons of treatment.

Complete the new medication information form (PDF) (What is a PDF document?) to help you understand this medication.



  1. Public Health Agency of Canada (2006, updated 2008). Vaginal discharge (bacterial vaginosis, vulvovaginal candidiasis, trichomoniasis). Canadian Guidelines on Sexually Transmitted Infections. Available online:
  2. U.S. Department of Health and Human Services (2006). Sexually Transmitted Diseases Treatment Guidelines, 2006 (CDC Publication Vol. 55, No. RR-11), pp. 52–54. Atlanta: U.S. Department of Health and Human Services. Also available online:
  3. American College of Obstetricians and Gynecologists (2006, reaffirmed 2008). Vaginitis. ACOG Practice Bulletin No. 72. Obstetrics and Gynecology, 107(5): 1195–1206.


By Healthwise Staff
Primary Medical Reviewer Kathleen Romito, MD - Family Medicine
Primary Medical Reviewer Brian D. O'Brien, MD - Internal Medicine
Specialist Medical Reviewer Jeanne Marrazzo, MD, MPH - Infectious Disease
Last Revised September 3, 2010

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information.