Metronidazole is an antibiotic that is used to treat a range of infections in both dogs and humans. Metronidazole for dogs is most frequently prescribed for diarrhea but sometimes may be used to treat conditions like some liver and gall bladder infections, inflammatory bowel disease (IBD), and parasitic protozoal infections such as giardia. For simple diarrhea in dogs—loose watery stool without clear indicators of a more severe health issue—your veterinarian will likely first recommend a bland diet and probiotics.
Although metronidazole is an antibiotic by class, anecdotally, it seems to work as an anti-inflammatory on the intestinal mucosa. As such, regardless of what is causing the inflammation that is resulting in diarrhea, metronidazole seems to 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 Dogs With 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.
What Metronidazole Is Used for in Dogs
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)
- Clostridia 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 of Metronidazole for Dogs
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.
I’ve been trying to add comments and send you and WDJ messages
for 6 days now. Doing something wrong I guess because they are
not showing up or being responded to.
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!
We nearly lost one of our dogs because of Metronidazole a few years ago. It is true that she had been taking it long term for an unremitting case of diarrhea that turned out to be resistant giardia. Her neurological symptoms got so bad that we thought she had a brain tumor and thought she might need to be euthanized. Luckily, the specialist at the emergency room at a nearby veterinary school had just read an article on unusual reactions to the drug and recognized the symptoms right away! It did make our local vet far more cautious about using the drug, however, and she new warns all her clients of what to look out for in their dogs!