How Effective Is Metronidazole for Giardiasis?

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  • Written By: C.B. Fox
  • Edited By: Susan Barwick
  • Last Modified Date: 03 November 2019
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For the majority of patients, the use of metronidazole for giardiasis will quickly and effectively treat infections by this microorganism. In most cases, infections are cured after one course of treatment, though some patients may require a few courses to completely get rid of the parasite. There are some strains of giardiasis that have grown resistant to this medication, however, and for patients with these varieties of giardiasis, using metronidazole for giardiasis may not be an effective treatment. Though metronidazole is considered to be an effective treatment, other medications with higher success rates and fewer side effects are used in most of the world.

Between 85 and 90 percent of patients who are prescribed metronidazole for giardiasis completely recover after taking one course of this antibiotic. In most cases, patients are given three 250 milligram tablets to take for five days. A liquid suspension of this medication may be given to children or to patients who cannot swallow pills. After this course of medication is completed, a doctor must examine the patient's stool to determine whether any giardiasis are present.

Patients who do not clear a giardiasis infection after the first course of medication may be asked to attempt the treatment again. The dosage and time duration are usually the same for subsequent treatments. Some patients may continue to test positive for giardiasis, in which case the use of metronidazole for giardiasis will be considered ineffective for that patient.


Though using metronidazole for giardiasis is considered an effective cure and is still the most widely used medication to treat giardiasis in some parts of the world, including the United States, other treatments are more effective. Tinidazole, a drug related to metronidazole, reports a consistent 90 percent cure rate with only a single pill. Another medication that is not available worldwide, quinacrine, may cure between 90 and 95 percent of patients. The side effects many patients experience with the use of metronidazole are often more severe than those caused by more recent medications.

The treatment of giardiasis requires strong medications such as metronidazole because the infection is caused by a protozoan, rather than a bacterium or fungus. Though using metronidazole for giardiasis is not as effective as other giardiasis treatments on the market, it still remains a valuable and relatively inexpensive treatment for this condition. It is very effective against most strains of giardiasis, though some mutations in these organisms have made them resistant to this drug.


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Post 3

I had to take two courses of metronidazole to treat my giardiasis. It worked but such a long treatment made me sick. It took a while for my digestive system and intestines to recover.

Post 2

@anamur-- It's true that parasites are increasingly becoming resistant to metronidazole. But this applies to any treatment that is commonly used. Parasites, bacteria and fungi all start becoming resistant after some point.

I had giardiasis after a trip to the tropics three years ago. I was given one course of metronidazole (1200mg/day for a week as far as I remember) and another antibiotic at the same time and it completely cleared up my infection.

I think the problem is that in the West, doctors are not very familiar with giardiasis and tend to give lower doses than they're supposed to which encourages resistance. I was lucky that my doctor had experience with giardiasis (he was originally from India) and knew what dose to give me and in combination with what other antibiotic. So I was treated in one week and the infection never returned.

Post 1

Tinidazole is the best treatment for giardiasis. Not only does metronidazole not work, but it's also dangerous. My doctor said that metronidazole has been shown to be carcinogenic in animal studies. I don't think any doctor in America should be prescribing metronidazole for giardiasis at this point.

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