Metronidazole for Dogs: A Vet’s Guide to Dosage and Side Effects


Metronidazole is an antibiotic and antiprotozoal medication commonly used in dogs for multiple reasons, most commonly to treat diarrhea.

Let’s take a closer look at what this drug is, when it should and should not be used, possible side effects, and more.

What is metronidazole for dogs?

Metronidazole, also known by its trade name Flagyl, is an antimicrobial drug effective against certain anaerobic bacteria and protozoa. Metronidazole kills susceptible microorganisms by interfering with their DNA structure and causing subsequent cell death.

Metronidazole has the ability to penetrate many tissues in the body, including the central nervous system and abscesses. It is also believed to have anti-inflammatory effects in the gut. The drug is metabolized by the liver and excreted in urine and faeces.

Because metronidazole has not been approved by the Food and Drug Administration (FDA) for use in veterinary medicine in the United States, it is prescribed “off label” for dogs and cats.

When is metronidazole used in dogs?

Metronidazole can be used to treat several types of bacterial and protozoan infections, including:

  • Infections of the gastrointestinal tract, such as those with Clostridium difficile (“C.diff”) and Giardia
  • Abscess or other collections of pus
  • Hepatic encephalopathy
  • Peritonitis
  • Tooth infections
  • Meningitis
  • Genital tract infections

Metronidazole is often used in combination with other antibiotics to enhance its spectrum of activity, which is particularly useful in cases where multiple bacterial species are identified.

Additionally, it may be given after certain gastrointestinal surgeries to prevent infection. It can also be used as a radiosensitizer for dogs undergoing radiation therapy for solid tumors, which means it makes it easier to kill cancer cells with radiation therapy and makes small doses of radiation more effective.

Metronidazole Dosage for Dogs

According to NOAH Compendium of Technical Data Sheets for Veterinary Drugs (opens in a new tab)the recommended dose of metronidazole for dogs is 50 mg/kg/day (or about 22 mg/lb/day) for 5-7 days. It can be divided into 25 mg/kg (or about 11 mg/lb) twice a day. day if needed.

However, the appropriate dose may vary depending on the type and severity of the infection. You should never give your dog metronidazole (or any other medication!) without consulting your veterinarian first.

Metronidazole comes in different oral formulations, including tablets, capsules, and liquids. It can also be given by injection at your local veterinary clinic. Many oral formulations have a bitter taste, so they are better tolerated when taken with food. The medicine should be stored in a cool, dry and safe place in its original packaging.

Oral metronidazole usually starts working a few hours after ingestion, but it may take a few days to start seeing improvements. If you feel your dog is not improving, contact your veterinarian to see if your dog needs to be re-evaluated or if any changes should be made to his treatment plan.

Sick dog lying on the couch

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Side Effects of Metronidazole in Dogs

Metronidazole is generally safe for dogs, but few may experience side effects. The most common side effects include:

  • Nausea
  • Vomiting
  • Diarrhea
  • lack of appetite
  • Regurgitation
  • Excessive drooling (due to the bitter taste of the medicine)
  • Lethargy
  • Reddish-brown urine

The most concerning side effect is neurotoxicity, which can present as tremors, incoordination, and seizures. This is usually seen when high doses are given for a prolonged period and can be life threatening. According to the NOAH Compendium, neurological signs occur very rarely after administration of metronidazole (ie less than 1 in 10,000 animals).

Other rare side effects of metronidazole include liver toxicity, which may manifest as reduced appetite and jaundice, and reversible bone marrow depression with a subsequent reduction in some white blood cells.

If your dog experiences any side effects, you should contact your veterinarian for advice as soon as possible. If you are concerned that your dog has overdosed on metronidazole, consult a veterinarian immediately.

Factors to Consider Before Giving Metronidazole to Dogs

Several factors should be considered before giving metronidazole to a dog:

Allergies / Pregnancy

Metronidazole should not be given to dogs with known allergies to the drug. Additionally, metronidazole is not safe in pregnant or nursing animals. For these reasons, people allergic to metronidazole and pregnant/nursing women should avoid handling the medicine or, if unavoidable, should wear gloves. The tablets should not be crushed as this can create airborne powders which can be inhaled.

Kidney/liver disease and seizure disorders

Since metronidazole is metabolized in the liver and excreted by the kidneys, it should be avoided or used with caution in dogs with liver or kidney disease.

It should also be avoided in dogs with neutropenia (ie, low neutrophils, a type of white blood cells) or seizure disorders when possible. Your veterinarian will weigh the pros and cons of metronidazole treatment based on your pet’s medical history.

Other drugs

Metronidazole is known to react with drugs such as cimetidine, cyclosporine, phenobarbital, phenytoin, warfarin, and some chemotherapy drugs, so concurrent use may reduce the effectiveness of one or both drugs .

It’s extremely important to tell your veterinarian about all medications you give your dog, whether over-the-counter (eg, Pepto Bismol) or a prescription drug such as Gabapentin, Tramadol, or Apoquel. , to ensure that the treatment will be effective and to minimize the risk of side effects.

veterinary examination dog

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Metronidazole for Diarrhea in Dogs

Metronidazole is most commonly used in veterinary medicine to treat cases of diarrhea. In recent years, however, there has been increasing evidence that metronidazole is not as helpful for gastrointestinal conditions as once thought.

Most cases of diarrhea resolve with only supportive treatment and do not need antibiotics at all. Some studies have even shown that metronidazole can cause long-term changes in the gut microbiome in dogs. It should therefore only be used when absolutely necessary, such as when culture and susceptibility have identified metronidazole as an effective antimicrobial. in the presence of sepsis.

Where can I buy metronidazole for dogs?

Metronidazole is a prescription drug, so it must be dispensed by your veterinarian or a pharmacy. Most veterinary clinics charge a small fee for written prescriptions to take elsewhere, which should be considered before deciding where to fill your prescription.


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