Metronidazole Works Like Magic in Dogs

For simple, non-specific diarrhea, metronidazole helps many dogs with a single dose.

By
Dr. Eileen Fatcheric, DVM
-
Published:
2
Female veterinarian giving medication to dog owner in veterinary surgery
Magic, mysterious, malevolent metronidazole: This drug works like magic for most cases of diarrhea in dogs, but it’s mysterious because how it works is not well understood. And, sadly, it has a malevolent side in the form of a rare but serious side effect called metronidazole toxicity. The point is that, as wonderful as metronidazole is, it’s still a prescription drug for good reason. Credit: Wetemd61 | Getty Images

For simple diarrhea in dogs, metronidazole is usually the first thing your veterinarian recommends. Although metronidazole is an antibiotic by class, it works as an anti-inflammatory on the intestinal mucosa. As such, regardless of what is causing the inflammation that is resulting in diarrhea, metronidazole cools the flame. So, whether the diarrhea is due to stress, a diet change, dietary indiscretion (aka eating “dumb stuff”), or even a parasite or virus, metronidazole often helps, and research shows it can help quickly.

Metronidazole Dosage for Diarrhea

Typical metronidazole dosage for dogs for treatment of non-specific, simple diarrhea in dogs is 5 to 10 mg/kg (milligrams of metronidazole per kilogram of the dog’s weight) twice a day for five days.  Metronidazole is a prescription drug dispensed as a 250 mg or 500 mg tablet. You need to know which you have.

For some dogs, a single dose is sufficient, especially when stress is the cause.

For chronic diarrhea, if metronidazole works and all other known causes of diarrhea have been ruled out, the condition is given the name “antibiotic-responsive diarrhea.” How it works is a mystery. That it works is a fact.

Metronidazole Treatments

In dogs, metronidazole is also used to treat:

  • Biopsy-confirmed inflammatory bowel disease (IBD), although steroids also may be necessary
  • Giardia, a protozoan intestinal parasite, although fenbendazole is the treatment of choice
  • Anaerobic bacteria, which are mostly found in the gastrointestinal tract and underneath the gums (periodontal disease)
  • Clostridial intestinal infections
  • Certain liver and gall bladder infections
  • Liver disease resulting in neurologic impairment (hepatic encephalopathy)

When metronidazole is used as an antibiotic, the dose range is typically 10 to 15 mg/kg twice a day.

Side Effects

Metronidazole toxicity is rare, but it can occur, usually with high doses given for an extended period. It shows up as sudden onset of severe, neurologic derangements, including:

  • Seizures
  • Tremors
  • Stiffness
  • Head tilt
  • Incoordination (ataxia)
  • Dilated pupils
  • Confusion
  • Nystagmus (rapid eyeball jerking back and forth)

With discontinuation of the drug, most dogs fully recover within a few days. Treatment for metronidazole toxicity is supportive care.

Additional, less scary but possible side effects of metronidazole include:

  • Nausea
  • Vomiting
  • Diarrhea
  • Loss of appetite
  • Weakness
  • Bloody urine
  • Lethargy
  • Weakness
  • Neurologic derangements

One final note: With the increased importance of antibiotic stewardship to combat increasingly alarming rates of antibiotic resistance, your veterinarian may be reluctant to immediately prescribe metronidazole upon request for diarrhea. Trying a probiotic and bland diet may be suggested first for good reason.

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2 COMMENTS

  2. Well, that worked. I’ll try again.

    My original messages concerns cerenia. I also found a similar blog
    about metronidazole. PLEASE! These and other drugs may work
    magically for some dogs but not all. Please go to Washington State
    University site for MDR1 study. Cerenia is one of the drugs that will
    kill collies. It has killed at least 2 of mine before WSU even found
    the connection. Please research these drugs that you are highly
    recommending and at least qualify your remarks for any dogs
    that could have a fatal reaction.
    Alice Roth

    One of my previous emails to WDJ:
    On 4/21, I received a blog article via email that I responded to
    customer service. I couldn’t find/figure out how to respond
    directly. I have not heard back anything. Cerenia is a
    wonderful drug for many dogs. Unfortunately, some it will
    kill. I’ve lost at least 2 collies to it. Washington State University conducted a study of dogs (collies) with a genetic
    disease called MDR1. They maintain a list of drugs that
    are fatal, cerenia is one. This is important for collie owners
    to know, especially when so highly recommended. Please
    update your articles and please respond. I don’t know how
    to add something to the blog or I would have.
    Please respond!