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Metronidazole Description

Metronidazole for dogs and cats is an antiprotozoal medication and antimicrobial antibiotic used to treat various infections. It is primarily used to treat inflammatory bowel diseases (such as Giardia, Entamoeba, Balantidium, and Trichomonas). It is typically dispensed in tablet form.

This antibiotic is also effective against tetanus, liver disease, periodontal disease, oral infections, Inflammatory Bowel Disease (IBD), some skin conditions, and other bacterial infections associated with diarrhea or sepsis. It works by rapid absorption in the GI tract, metabolized by the liver, and is then excreted by urine or feces.

Metronidazole (which only targets anaerobic bacteria) is commonly used with other antibiotics when an animal has been diagnosed with a mixed bacterial infection.

Metronidazole Side Effects in Dogs and Cats

There may be some risks when taking metronidazole. Please monitor animals in your care for these possible issues.

Common Side Effects:

  • Loss of appetite
  • Drowsiness, lethargy, or fatigue
  • Dizziness or loss of balance
  • Gagging, nausea, or vomiting
  • Upset stomach
  • Diarrhea
  • Constipation
  • Blood in urine
  • Drooling
  • Swollen tongue
  • Dry mouth
  • Fever
  • Cough or sneezing
  • Runny nose
  • Toxicity
  • Seizures 
  • Allergic reaction

Less Common Side Effects:

Long-term use may result in rare side effects such as insomnia, low blood platelet count, liver damage, or neurological conditions.

Other less common, but serious side effects include liver failure, blood in the urine (or dark urine), or low white blood cell count.

Side Effects for Dogs & Cats:

  • Pawing at the mouth
  • Gagging, regurgitation, nausea, vomiting, or diarrhea.
  • Excessive salivation
  • Decreased appetite
  • Depression, lethargy, or weakness.
  • Low white blood cell count 
  • Liver failure
  • Blood in the urine, or dark urine.

Side Effects for Horses:

Horses may refrain from eating foods that are mixed with the medication because of the taste. If the horse refuses to take the medication with food because of the bitterness, the drug must be given in an alternative way.

When to Call the Veterinarian

Call the vet’s office right away if you notice any of these issues:

  • Allergic reactions or anaphylaxis: Swelling, difficulty breathing, throat closing, or hives. Animals experiencing a severe allergic reaction need immediate medical care. 
  • Neurological problems: Seizures, staggering, stiffness, strange movements, or behavior. 

If the animal accidentally takes too much of the medication or has been on the medication for a prolonged period of time, call the vet if you notice any of the following:

  • Seizures or tremors
  • Stiffness
  • Irregular or abnormally slow heartbeat.
  • Dilated pupils


Metronidazole Instructions

Metronidazole is dispensed in capsule, tablet, and liquid suspension forms. Compounding is another option (to reduce the bitter taste). Compounding also makes the medication easier to administer to cats. Injections of this medication can be given at the veterinary clinic or hospital.

In pill form, metronidazole is taken by mouth with food.  Metronidazole may taste very bitter to animals, so avoid crushing the tablets as this will make it more of a challenge to get your pet to ingest it. Medication in liquid form should be well-shaken before use.

Metronidazole dosing takes effect between 1 and 2 hours. This medication works gradually, so look for improvements after a few days.

Use as directed by your veterinarian. Dosage will vary depending on the condition of the animal. If you experience problems with administering the medication, call the vet for help.

Metronidazole for Dogs Dosage

Metronidazole usually comes in tablet strengths of 250 to 500 mg per pill to be taken orally. The typical dose is 5-20 mg/kg of the animal’s body weight in divided doses.

Always follow the dosing directions and advice given by your veterinarian.

Metronidazole for Cats Dosage

For cats, the standard dose is 3-20 mg/kg of your pet’s body weight in divided doses. Again, this is given orally according to the directions given by your veterinarian.

Metronidazole Precautions

This medication should be avoided or used with caution in certain situations.

Situations when animals should not take metronidazole: 

  • Pregnant or nursing dogs.
  • Dogs with a history of kidney or liver disease.
  • Animals with a history of allergies or sensitivity to similar drugs.
  • Animals in a weakened state.

Note: Women who are pregnant should avoid handling this medication. Inhaling dust from this medication may be harmful. Wash your hands thoroughly after handling the medication.

Use metronidazole with caution in animals who:

  • Are on blood thinners
  • Have liver disorders
  • Are puppies or kittens

List of drugs that may have interactions:

  • Some chemotherapy drugs.
  • Cimetidine (Tagamet)
  • Phenytoin (Dilantin)
  • Cyclosporine 
  • Phenobarbital  
  • Warfarin (Coumadin)
  • Some vitamins, supplements, or herbal remedies.

Be sure to mention any medications the animal is currently taking and supply a complete medical history to reduce risks with taking metronidazole.


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