Antiprotozoals for giardiasis

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Antiprotozoals for giardiasis


Generic NameBrand Name

How It Works

This medicine kills Giardia lamblia in the digestive tract.

Metronidazole comes in tablet and liquid forms. It usually is taken in tablet form for 3 to 7 days for treatment of giardiasis.

Why It Is Used

This medicine is used to treat certain bacterial and parasite infections. It also is an effective treatment for giardiasis infection.

This medicine may be used if stool analysis or other testing shows giardiasis infection is present.

If your doctor thinks that your symptoms are caused by giardia, he or she may prescribe this medicine even before your test results are back.

If you are pregnant, talk with your doctor or pharmacist before taking this medicine.

How Well It Works

Metronidazole cures giardiasis in adults 80% to 95% of the time.1

Side Effects

The most common side effects of this medicine include:

  • A metallic taste in the mouth.
  • Nausea, vomiting.
  • Dizziness.
  • Headache.

A rare side effect is a low number of white blood cells (neutropenia, leukopenia). The white blood cell count returns to normal when you stop taking the drug.

Do not drink alcohol while you are taking metronidazole. Using alcohol while you are taking this medicine can cause headaches, nausea, reddening of the face, belly cramps, and vomiting. You should also avoid alcohol for at least 3 days after you finish your last dose of this medicine.

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

What To Think About

Metronidazole may be used with caution in pregnant women.

Do not use alcohol while you are taking either of this medicine or for 3 days after you finish your last dose.

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



  1. Hill DR (2005). Giardia lamblia. In GL Mandell et al., eds., Principles and Practice of Infectious Disease, 6th ed., vol. 2, pp. 3198–3205. Philadelphia: Elsevier.


By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
Last Revised November 9, 2009

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