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me-troe-NI-duh-zol - Pronunciation guide

Brand Names

  • Flagyl
  • Protostat


Prescription medicationMetronidazole is used as an antibiotic to treat anaerobic bacterial infections. Anaerobic bacteria cannot live in the presence of oxygen. It is also used as an antiprotozoal to treat Giardia infections. Metronidazole is readily absorbed from the intestinal tract into the bloodstream.


Metronidazole is used as an antibiotic and as an antiprotozoal drug to treat Giardia infections that result in an infectious form of severe diarrhea. It is commonly used with other antibiotics to treat pleuropneumonia, peritonitis, abdominal abscesses, and other severe infections caused by aerobic and anaerobic bacteria. Veterinarians often prescribe it to prevent infection after colic or after abdominal surgery, when mixed bacterial infections are a risk.

Metronidazole is absorbed rectally and may be used with very sick animals when weight loss and appetite loss are problems.

Dosage and Administration

Prescription medicationMetronidazole
Method Dosage
(click row for calculator)
Concentration Period Duration
Oral or Rectal 15 mg/kg 250 mg/tablet 4 times a day NA
Oral or Rectal 15 mg/lb 375 mg/tablet 4 times a day NA
Oral or Rectal 15 mg/lb 500 mg/tablet 4 times a day NA
Oral or Rectal 20 mg/kg 250 mg/tablet 2 times a day NA
Oral or Rectal 20 mg/lb 375 mg/tablet 2 times a day NA
Oral or Rectal 20 mg/lb 500 mg/tablet 2 times a day NA


  • Federal law restricts this drug to use by or on the order of a licensed veterinarian.
  • Extra-label use of drugs in treating animals is allowable only by licensed veterinarians within the context of a valid veterinarian-client-patient relationship, and does not include drug use in treating animals by the layman (except under the supervision of a licensed veterinarian).
  • Calculator is for educational purposes only. Follow your veterinarian's instructions regarding use of this, or any medication.

Side Effects

Drug side effects are not commonly associated with metronidazole.  In other species of animals, neurological symptoms are sometimes observed when the animal is on long-term, moderate-to-high doses.


Metronidazole causes birth defects in laboratory animals and should be avoided in pregnant or lactating animals.

Metronidazole is not FDA approved for use in horses, however it is commonly used and considered accepted practice.  It is a prescription drug and should be used only by or on the lawful written or oral order of a licensed veterinarian.

Metronidazole would be forbidden in any drug-free competition. It is important to check with the individual regulatory organization.


Metronidazole increases the effect of anticoagulants, such as warfarin.

Cimetidine can interfere with the liver's ability to break down metronidazole and the dose may have to be reduced.


No information is found on overdose in the horse.


Flagyl Medtronidazole SolutionFlagyl Medtronidazole Solution

Metronidazole TabletsMetronidazole Tablets



About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.