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Metronidazole For Dogs: What it is Used for and Guidelines for Safety

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Dog owners today are armed with more tools for keeping their dogs healthy and fit than ever before. Modern medicine has radically improved how well, and how long, our companion animals live. For both humans and dogs, antibiotics continue to be a potent ally in the fight against disease and infection.

What is Metronidazole?

Metronidazole, commonly known by the brand name Flagyl, is a strong antibiotic primarily used as an anti-diarrheal to treat inflammation of the large intestine. It is also used for other illnesses and conditions in dogs, cats, and horses, as well as to treat bacterial infections in humans. It is often used in combination with other antibiotics.

Metronidazole is a prescription-only medication that can be taken orally or externally, depending on the illness being treated. It is not yet approved by the FDA for veterinary use (it is approved for human use), but metronidazole is commonly prescribed by veterinarians for their canine patients.

What Is Metronidazole Used For?

Like most antibiotics, metronidazole is prescribed to treat a variety of conditions, and to relieve their symptoms, such as:

  • Giardia (and other parasites)
  • Inflammatory Bowel Disease (IBD)
  • Oral and dental infections
  • Other bacterial infections that cause diarrhea or sepsis


Giardia is a microscopic parasite that lives in a dog's intestine. It is transmitted by infected water, soil, or food

Courtesy CDC

How Does it Work?

Metronidazole works by destroying and preventing the creation of DNA in the infecting organisms.

Unlike most other drugs, metronidazole is able to treat central nervous system infections by penetrating the blood-brain barrier. In order to thrive, your dog’s body parts need good circulation and oxygen. Tissue that is damaged usually has poor oxygen circulation. In these areas, only certain pathogens that do not require oxygen can thrive. Metronidazole inhibits repair enzymes in the cells that exist in these unoxygenated (anaerobic) environments.

Guidelines For Safe Use

Metronidazole is considered very safe. However, it should not be prescribed to pregnant females or young puppies. It may also not be suitable for pets with:

  • Kidney disease
  • Liver disease
  • Neutropenia
  • Seizure disorders

As with any medication for your pet, always speak to your vet before use, and tell her about any other medicine your dog is taking and other medical conditions. Be cautious when using the drug for extended periods of time, since adverse effects are more common during long-term use.

Does Metronidazole Have Side Effects?

Though it's rare, contact a vet right away if your pet suffers any neurotoxic effects, such as paralysis in all four legs, or has an allergic reaction—hives, rash, rapid heartbeat, or difficulty breathing. An allergic reaction can become dangerous quickly, or even life-threatening.

Some common side effects your dog may experience:

  • Nausea/Vomiting
  • Diarrhea
  • Drooling
  • Gagging/regurgitation
  • Fatigue
  • Loss of appetite
  • Blood in urine
  • Fever

Dogs who receive too much of this medicine, or those treated with metronidazole for extended periods of time, will need emergency veterinary attention if they experience:

  • Irregular or abnormally slow heartbeat
  • Tremors
  • Seizures
  • Stiffness
  • Dilated pupils

Intestinal inflammation, parasites, bacterial infections, and their accompanying symptoms, such as diarrhea, are serious adversaries for our dogs. Thankfully, we are able to utilize powerful medical weapons such as metronidazole to help keep them from harm.

Do you have trouble giving your dog medication? Here are a few tips.


Note: This article is designed to help inform you about metronidazole (Flagyl) in dogs and is not meant to take the place of veterinary advice and consultation.

Sources: Centers for Disease Control and Prevention, Merck Veterinary Manual, PetMD, Veterinary Place, WebMD

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