For simple diarrhea in dogs, metronidazole is usually the first thing your vet recommends. Although metronidazole is an antibiotic by class, it works as an anti-inflammatory in the intestinal mucosa. As such, regardless of the cause of the inflammation leading to diarrhea, metronidazole cools the flame. So, whether the diarrhea is due to stress, a change in diet, a dietary indiscretion (aka eating “dumb stuff”), or even a parasite or virus, metronidazole often helps, and research shows that it can help quickly.
metronidazole dosage for diarrhea
The typical dose of metronidazole for dogs for the treatment of simple, non-specific diarrhea in dogs is 5 to 10 mg/kg (milligrams of metronidazole per kilogram of dog weight) twice daily for five days. Metronidazole is a prescription medication that is dispensed as 250 mg or 500 mg tablets. You need to know which one you have.
For some dogs, a single dose is enough, especially when the cause is stress.
For chronic diarrhea, if metronidazole works and all other known causes of diarrhea have been ruled out, the condition is called “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:
- Inflammatory bowel disease (IBD) confirmed by biopsy, although steroids may also be necessary
- Giardia, a protozoan intestinal parasite, although fenbendazole is the treatment of choice
- Anaerobic bacteria, found mainly in the gastrointestinal tract and under the gums (periodontal disease)
- Intestinal clostridial infections
- Certain infections of the liver and gallbladder
- Liver disease resulting in neurological impairment (hepatic encephalopathy)
When metronidazole is used as an antibiotic, the dose range is usually 10 to 15 mg/kg twice daily.
Side effects
Metronidazole toxicity is rare but can occur, usually with high doses given over a long period of time. It appears as the sudden onset of severe neurological disorders, including:
- seizures
- tremors
- Rigidity
- Nod
- Lack of coordination (ataxia)
- Dilated pupils
- Confusion
- Nystagmus (rapid jerking of the eyeball from side to side)
With drug discontinuation, most dogs make a full recovery 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
- urine with blood
- Lethargy
- Weakness
- Neurological disorders
One final note: With the growing importance of antibiotic stewardship to combat increasingly alarming rates of antibiotic resistance, your vet may be reluctant to immediately prescribe metronidazole if requested for diarrhea. Trying a bland, probiotic diet may be suggested first for good reason.
