Is metronidazole safe for dogs? Uses, dosage, side effects?
Key Points
- Metronidazole is an antibiotic used to treat bacterial infections and certain parasites. Some brand names it’s sold under include Flagyl, Metizol, Metrogel, and Protostat.
- Metronidazole is not FDA approved for use in dogs. It is typically prescribed off-label by veterinarians.
- Common side effects of metronidazole in dogs include diarrhea, drooling, and a change in urine color. More rare but serious side effects include tremors, muscle weakness, and liver damage.
Metronidazole is a safe antibiotic for dogs when given as prescribed by a veterinarian. Like most medications, it has its own set of warnings and side effects to be aware of. It might not be the best choice if your dog is pregnant, very young, has kidney problems, has liver problems, has a low white blood cell count, or has seizures.
What is Metronidazole Used for in Dogs?
Metronidazole can treat certain parasites and bacterial infections. Some examples of conditions veterinarians may prescribe metronidazole for include:
- Abscesses
- Amebiasis
- Anaerobic bacterial infections
- Inflammatory bowel disease
- Giardia infections
- Diarrhea caused by certain bacteria
- Trichomoniasis
It is commonly prescribed to treat diarrhea in dogs due to some of these infections, especially after failing dietary changes.
How Does Metronidazole Work in Dogs?
Metronidazole works the same way in dogs as it does in humans to treat infections. It prevents bacteria or parasites from growing by stopping DNA from being made. It also destroys DNA, which leads to death of the organism.
For inflammatory bowel disease, metronidazole is additionally thought to lower inflammation by having an immunosuppressive effect on the gastrointestinal mucosa.
How Much Metronidazole Should I Give My Dog?
The recommended dose of metronidazole is based on the reason your dog is taking it and their weight. Follow your veterinarian’s dosing instructions carefully. They might recommend a different dose if your dog has liver problems.
Some examples of common metronidazole doses in dogs include:
- Inflammatory bowel disease: 10 mg/kg to 15 mg/kg by mouth every 12 hours
- Giardiasis: 25 mg/kg by mouth every 12 hours
Your veterinarian will tell you how long you should give metronidazole to your dog. Make sure to finish the entire treatment course, even if your dog is feeling better. Stopping the antibiotic too early can cause your dog’s infection to come back or be harder to treat.
Never give metronidazole prescribed for humans to your dog. If your dog needs to take metronidazole, your vet can determine the safest and most effective dose for them.
How Do I Give Metronidazole to My Dog?
Metronidazole comes as capsules, tablets, and a liquid for home use. These are all given by mouth. It can be helpful to give the capsules or tablets hidden in a “pill pocket” treat. You can usually get these at your vet’s office and pet stores. You can also try to hide the medication in food that dogs enjoy (e.g., cheese, peanut butter).
Always provide your dog with plenty of fresh water when giving them their medication. This will help them wash it down so it reaches their stomach.
What if I Forget to Give My Dog a Dose of Metronidazole?
If you forgot to give your dog a dose of metronidazole, give the dose as soon as you remember. However, if it is already close to the next time the dose is due, just skip the missed dose and continue with your normal dosing schedule. Do not give your dog two doses to make up for a missed dose because this can lead to side effects.
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What are Metronidazole Side Effects in Dogs?
Common side effects of metronidazole in dogs include:
- Diarrhea
- Nausea and/or vomiting
- Excessive drooling
- Poor appetite
- Fatigue
- Reddish-brown urine color
More rarely, metronidazole may cause toxic nervous system side effects. This can lead to your dog not being able to move their legs (paralysis). It can also cause seizures or tremors. Recent veterinary studies have identified lower neurotoxicity thresholds than previously recognized, making safety monitoring even more critical. Your dog is at increased risk with higher doses and prolonged treatment.
Occasionally, metronidazole can cause damage to your dog's liver. Watch out for signs of liver damage, such as yellowing of the skin, gums, or eyes. Call your vet if this happens to your dog.
Another rare side effect of metronidazole is a skin problem called cutaneous vasculitis. This is when blood vessels in your dog’s skin become inflamed, and they can experience hair loss, swelling, or bruising on the skin.
Metronidazole can also cause a serious allergic reaction in some dogs. Signs and symptoms of an allergic reaction include:
- Hives
- Rash
- Fast heartbeat
- Trouble breathing
If your dog is showing any of the signs above, contact your veterinarian right away.
Does Metronidazole Interact with Other Medications My Dog Might Be Taking?
Yes. Metronidazole can interact with several other medications. Some examples of medications that can potentially interact with metronidazole include:
- Cimetidine
- Cyclosporine
- Phenobarbital
- Phenytoin
- Warfarin
This is not an all-inclusive list of interactions with metronidazole. Tell your veterinarian about any medications and supplements your dog is taking. They can help you screen for any interactions and help you manage them.
Do I Need a Prescription to Get Metronidazole for My Dog?
Yes, you will need to get a prescription from your dog’s veterinarian in order to give them metronidazole. Oftentimes you can pick it up directly from your vet’s office. However, you may need to pick the medication up at your local pharmacy.
Long-term Effects and Gut Microbiome Recovery
Metronidazole's action means it eliminates both harmful bacteria and beneficial gut flora, leading to microbiome imbalance that can persist long after treatment ends.
Timeline of Gut Flora Recovery
Immediate Effects (Days 1-7)
- Rapid reduction in both pathogenic and beneficial bacteria
- Temporary digestive sensitivity
- Possible soft stools or mild diarrhea
Short-term Recovery (Weeks 2-4)
- Gradual recolonization of beneficial bacteria
- Digestive function slowly normalizes
Long-term Recovery (Months 2-6)
- Complete microbiome restoration can take months
- Some dogs may experience prolonged digestive sensitivity
- Individual recovery varies based on dog's age, overall health, and diet
References
- American Kennel Club. 2024. Metronidazole for dogs.
- Dowling, P. M. 2023. Drugs Used to Treat Inflammatory Bowel Disease in Monogastric Animals. Professional version. Merck Veterinary Manual. Accessed August 4, 2024 at https://www.merckvetmanual.com/pharmacology/systemic-pharmacotherapeutics-of-the-digestive-system/drugs-used-to-treat-inflammatory-bowel-disease-in-monogastric-animals
- Flagyl [package insert]. Updated July 2024. Pfizer Laboratories Div Pfizer Inc. Accessed August 3, 2024 at https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a2883ca1-5a9a-4259-9d80-46ab67274384
- Gollakner R. Metronidazole. VCA Animal Hospitals. Accessed August 3, 2024 at https://vcahospitals.com/know-your-pet/metronidazole
- Mercer, M. A. 2022. Nitroimidazoles use in animals: Professional version. Merck Veterinary Manual. Accessed August 3, 2024 at https://www.merckvetmanual.com/pharmacology/antibacterial-agents/nitroimidazoles-use-in-animals?autoredirectid=19866
- Pilla, R., Gaschen, F. P., Barr, J. W., Olson, E., Honneffer, J., Guard, B. C., Blake, A. B., Villanueva, D., Khattab, M. R., AlShawaqfeh, M. K., Lidbury, J. A., Steiner, J. M., & Suchodolski, J. S. (2020). Effects of metronidazole on the fecal microbiome and metabolome in healthy dogs. Journal of veterinary internal medicine, 34(5), 1853–1866. https://doi.org/10.1111/jvim.15871
- Tauro, A., Beltran, E., Cherubini, G. B., Coelho, A. T., Wessmann, A., Driver, C. J., & Rusbridge, C. J. (2018). Metronidazole-induced neurotoxicity in 26 dogs. Australian veterinary journal, 96(12), 495–501. https://doi.org/10.1111/avj.12772
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