Metronidazole: Uses, Dosing & Side Effects

Updated in December 2023

Metronidazole is an antibiotic indicated for the treatment of conditions like giardiasis, amebiasis, trichomoniasis, and vaginitis caused by Gardnerella vaginalis. It is a medication that is effective for the treatment of infections caused by bacteria and protozoans that are sensitive to this substance. 

This medication should be used as prescribed by your doctor or nurse practitioner. It can be found in many forms, such as pills, ointment, oral suspension, vaginal tablets, vaginal gel and injectable solution. 

Metronidazole can be accessed at the pharmacy with a prescription signed by a licensed health care professional. 

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Common uses

Metronidazole is prescribed for the treatment of:

  • Infections in the small intestine caused by Giardia lamblia (otherwise known as giardiasis);
  • Infections caused by amebas (otherwise known as amebiasis) 
  • Infections caused by Trichomonas species (otherwise known as trichomoniasis)
  • Vaginitis caused by Gardnerella vaginalis;
  • Infections caused by anaerobic bacteria, like Bacteroides fragilis, and other bacteria, like Fusobacterium sp, Clostridium sp, and Eubacterium sp 
  • Bacterial septicemia 
  • Endocarditis caused by Bacterioides sp;
  • Abdominal cavity infections (e.g. liver abscess, abdominal abscess, peritonitis) caused by anaerobic bacteria 

Metronidazole can also be prescribed by the doctor to prevent infections following colorectal or intestinal surgeries. 

Recommended dosing

Metronidazole dosing depends on the infection to be treated and the medication route selected by the doctor: 

1. Trichomoniasis 

The recommended dose is a single-time dose of 2 g. The doctor an also prescribe 250 mg twice a day for 10 days, or 400 mg twice a day for 7 days. Treatment can be extended if needed for up to 4 to 6 weeks. 

Sexual partners should also be treated with a single dose of 2 g to prevent reciprocal re-infections.

2. Vaginitis and urethritis caused by Gardnerella vaginalis

The recommended dose is a single dose of 2 g, followed by another 2 g dose 48 hours later. The doctor may also opt to prescribe 400 to 500 mg twice a day for 7 days. 

Sexual partners should also be treated with a single dose of 2 g. 

3. Giardiasis

The recommended dose for adults is one 250 mg pill, three times per day for 5 days. 

Children between 1 and 5 years of age can take 5 mL of oral suspension twice a day for 5 days. Children between 5 and 10 years of age can take 5 mL of oral suspension, three times a day for 5 days. 

4. Amebiasis

For treatment for intestinal amebiasis, the recommended dose is 500 mg, four times a day for 5 to 7 days. Treatment of liver amebiasis will have a slightly longer treatment, and the recommended dose is 500 mg, four times a day for 7 to 10 days. 

5. Infections caused by anaerobic bacteria 

Infections caused by anaerobic bacteria in adults and children over 12 can be treated with one 400 mg pill, three times a day for 7 days or as indicated by the doctor. 

Children under 12 should ideally be prescribed oral suspension, and dosing is typically 7.5 mg for every kilogram of body weight, taken three times per day for 7 days. 

6. Prophylaxis for surgical infections

Metronidazole can be taken preventively to reduce the risk of a surgical infection. Generally, the recommended dose for adults and children over 12 is 500 mg every 8 hours, administered as an IV or IM starting 48 hours before the surgery. The last dose should be administered at least 12 hours before the surgery. 

Possible side effects

Some side effects that may occur during treatment with metronidazole include nausea, vomiting, diarrhea, stomach ache, a metallic taste in the mouth, loss of appetite, headache, excessive fatigue and dizziness.

More serious side effects may occur, such as seizures, peripheral neuropathy, tingling, and increased sensitivity or pain in the hands or feet. You should consult your doctor if you experience any of these symptoms. 


Metronidazole should not be used by anyone with an allergy to this medication or any of its components. 

It should not be used by women who are pregnant or breastfeeding without a doctor’s knowledge. 

Metronidazole pills should not be taken by children under 12 years old.