Metronidazole for Dogs: What to Expect With This Common Antibiotic

Antibiotics can be valuable options to treat your sick dog. But antibiotic resistance — when antibiotics cannot kill germs — is a real problem. Because of this issue, veterinarians try treatments in a certain order, avoiding antibiotics when they can.

But this isn’t always possible because some infections and conditions require these types of medications to be properly treated.

Metronidazole (Flagyl) is a commonly prescribed antibiotic for dogs with diarrhea and other gastrointestinal problems. Since this is a human medication, you may be concerned about how it might affect your pet. Let’s take a closer look.

Metronidazole for dogs at a glance

What is metronidazole for dogs, and how does it work?

Metronidazole is a prescription antibiotic used to treat many types of infections. It works by stopping bacteria or parasites from growing and multiplying. Metronidazole can also reach the central nervous system and bones, making it helpful for brain, spinal cord, and bone infections. 

What is metronidazole used for in dogs?

Metronidazole is commonly prescribed to dogs to treat infections and inflammatory conditions that cause diarrhea. It is also sometimes used to treat inflammatory bowel disease (IBD). Veterinarians use metronidazole as an off-label medication since it is not FDA approved for dogs.

How is metronidazole dosed and given to dogs?

When given at home, metronidazole comes as an oral tablet or capsule. Because it can have a bitter flavor, you may want to disguise it with peanut butter or another favorite treat of choice. Many veterinary clinics also carry an oral liquid form of metronidazole. The liquid form can be helpful if your dog has issues swallowing pills.

Metronidazole should be fully absorbed within 1 to 2 hours, but it may take a few days for your dog’s symptoms to improve. Even if they’re feeling better, be sure your dog finishes all the pills prescribed unless your vet tells you otherwise. This will help make sure the infection is gone.

What is the dosage of metronidazole for dogs?

The dosage for metronidazole is based on how much your dog weighs, and it varies depending on what’s causing their infection. For conditions that require metronidazole, veterinarians prescribe about 5 mg per pound of body weight. Most times, your dog will take the medication twice a day for 5 to 7 days.

Keep in mind the dosage your veterinarian prescribes for your dog will depend on many factors. Your vet will determine the best dose and length of treatment depending on how well your dog responds to the medication and if they develop side effects.

What are the side effects of metronidazole in dogs?

Metronidazole can lower the amount of healthy gut bacteria in dogs, which in turn may cause more diarrhea. Its bitter flavor may also cause more drooling than usual.

Other common side effects of metronidazole are:

• Nausea and vomiting

• Gagging

• Feeling more tired than usual

• Lower appetite

• Discolored urine

• Fever

What are the most serious risks of metronidazole for dogs?

All medications carry serious risks, including metronidazole, but thankfully they are very rare. These problems are more likely to happen if your dog is taking this medication at high doses or for a long time.

Contact the emergency pet hospital right away if you notice any of the following:

• Hives, fast heart rate, or trouble breathing — signs of a possible allergic reaction

• Changes to emotional behavior, such as seeming more depressed or lethargic than usual

• Trouble walking, tremors, enlarged pupils, rapid eye movements, twitching, or seizures

Metronidazole is not safe in pregnant dogs because it can cause birth defects to the fetus. This medication is also not safe for nursing dogs because it passes into breast milk and can be harmful to young puppies. Lastly, it is not the best option to give metronidazole to dogs with seizures or kidney or liver problems.

Are there any interactions between metronidazole and other medications?

Various medications can interact with metronidazole. It’s important to let your vet know all medications, over-the-counter products, and supplements your dog is taking before starting this antibiotic.

Metronidazole can interact with the blood thinner warfarin (Coumadin) and raise the risk of bleeding. If your dog is taking both medications, the vet may temporarily lower the warfarin dose before starting metronidazole. Your pet may also need closer monitoring while taking this combination.

Cimetidine (Tagamet), a heartburn remedy, can also interact with metronidazole. Metronidazole will have a stronger effect when taken with cimetidine, so your dog is more likely to experience antibiotic-related side effects if they take this combination.

Lastly, seizure medications, such as phenobarbital and phenytoin (Dilantin), can stop metronidazole from working as well. If your dog is taking these medications regularly, your veterinarian will most likely choose a different antibiotic. It can be risky to stop seizure medications.

It’s important to note that these are not the only interactions for metronidazole — just some of the most notable. Please provide your vet a complete list of all medications your dog takes before starting metronidazole, so they can make sure your pet can safely combine everything.

Are there any alternatives to metronidazole for dogs with diarrhea?

Yes. Alternative treatments are available depending on what’s causing your dog’s diarrhea. Besides infections, other possible causes of diarrhea in dogs include IBD, tumors, and pancreas problems. Diarrhea can sometimes also be a lingering side effect caused by other antibiotics.

Other medications that might be used to treat diarrhea in dogs include:

• Fenbendazole (Panacur C) for Giardia infections

• Tylosin (Tylan) for IBD

• Sulfasalazine (Azulfidine) for IBD

Keep in mind that most acute diarrhea — meaning not caused by a chronic condition like IBD — resolves within a week whether your dog takes medication for it or not. If you see blood in your dog’s stools at any point, contact your vet right away. If your dog still has diarrhea after 7 days and hasn’t been taking anything for it, consult your veterinarian.

Are medications always necessary to treat diarrhea in dogs?

No. Supportive care — like diet changes, adequate hydration, introduction of fiber, and use of probiotics — is sometimes tried before medications. For example, during the first 12 to 24 hours of diarrhea, your vet may recommend withholding food or providing small meals every few hours.

Dietary changes may include adding fiber or trying hypoallergenic dog food if your vet feels a food allergy might be the culprit. Canned pumpkin is an excellent source of fiber you can add to your dog’s meal. Your vet may also recommend adding fiber with Metamucil or coarse wheat bran.

You may also be instructed to make these dietary suggestions along with antibiotics like metronidazole. Regardless of whether you are providing your dog medications, supportive care, or both, it’s important to follow your vet’s recommendations. This will help ensure your furry friend gets back to feeling like themself as quickly as possible.