Flagyl (Metronidazole) For Cats

At a glance

  • Drug Name: Metronidazole
  • Common names: Flagyl, Metizol, Protostat and Metrogel
  • Drug Type: Antibiotic, antiprotozoal
  • Used For: Treatment of anaerobic bacterial infections, protozoal infections, and inflammatory bowel disease
  • Species: Cats, dogs, humans, ferrets, horses, rabbits, rodents, birds and reptiles
  • Administered: Tablet, oral liquid, injection


Flagyl (Metronidazole) is a prescription-only antibiotic and antiprotozoal medication which is used to treat a wide variety of bacterial and protozoal infections in several animals including cats, dogs and humans.

Flagyl is a member of the drug classes amebicides and nitroimidazoles. The drug has not been approved for use in cats by the Food and Drug Administration (FDA) but is commonly prescribed extra-label by veterinarians.

Flagyl is on the WHO Model List of Essential Medicines.

What does Flagyl treat?

  • Protozoal infections which include Giardia, Trichomonas and Balantidium coli
  • Enteric and systemic anaerobic bacterial infections (anaerobic bacteria are bacteria that do not require oxygen for growth) such as dental infections, bone infections, gum disease, feline acne, internal abscess and as Flagyl can penetrate the blood-brain barrier to treat CNS infections
  • Perioperative surgical prophylaxis (colorectal surgery)
  • Adjunctive therapy of inflammatory bowel disease

Mechanism of action

Infected and inflamed tissue often has poor oxygen supply, and only anaerobic bacteria can survive. The exact mechanism of action is not entirely understood, but it is thought to disrupt DNA and nucleic acid synthesis in anaerobic bacteria. Susceptible bacteria include Bacteroides spp, Clostridium spp, Eubacterium spp, Fusobacterium spp, Veillonella spp,  Peptococcus spp, Peptostreptococcus spp and Prevotella spp.

Flagyl is also trichomonacidal and amebicidal in action, and its mechanism of action for its antiprotozoal activity is not understood.

Flagyl can modify cell-mediated immunity to control excessive immune reactions, particularly in the large intestine. Once again, the mechanism of action is not known.


  • Giardiasis: The Companion Animal Parasite Council (CAPC) recommends a dose of 25 mg per kilo to twice a day for 5 days.
  • Feline trichomoniasis: 30 – 50 mg per kg twice a day for 3-14 days.
  • Perioperative surgical prophylaxis: 15 mg per kg IV over 30-60 minutes to be completed 1 hour before surgery. Flagyl is usually used in conjunction with cefazolin.
  • Anaerobic infections: 15 mg per kg intravenously every 12 hours or 10 – 15 mg per kg.
  • Clostridial enteritis: 62 mg per cat by mouth every 12 hours for 5 days.
  • Adjunctive therapy of inflammatory bowel diseases: 10 – 15 mg per kg by mouth twice a day.

Administer tablets or capsules by mouth with food.

Missed dose

If you miss a dose, administer as soon as possible unless the next dose is due soon. If you miss more than one dose, consult your cat’s veterinarian. Do not give your cat two doses at once.

Overdose/acute toxicity

Seek immediate veterinary attention if your cat has ingested a higher than the prescribed dose of Flagyl.

Signs of intoxication include loss of appetite, vomiting, depression, dilated pupils, nystagmus, ataxia, head tilt, ataxia, tremors, seizures, bradycardia, rigidity and stiffness. These symptoms may develop due to acute overdoses or in some cats on long-term therapy.

Drug interactions

The following drug interactions have been reported or are theoretical in humans or animals and therefore may be of importance for cats receiving treatment. The use of Flagyl with the following drugs may not be contraindicated but potential risks and close monitoring may be necessary.

  • Busulfan
  • Cimetidine
  • Cyclosporine
  • Fluorouracil
  • Phenobarbital
  • Warfarin


Flagyl is contraindicated in cats who are hypersensitive to the drug or nitroimidazole derivatives.

It is not recommended for use in pregnant cats as it has been known to cause birth defects in laboratory animals

Do not administer to lactating cats or young kittens.

Use with caution in cats with kidney or liver disease.

Side effects

Most common:

  • Vomiting and loss of appetite due to nausea
  • Drooling due to the unpleasant taste (this is self-limiting)

Less common:

Because Flagyl can cross the blood-brain barrier, neurologic side effects can develop, these are more common in cats who are on long-term therapy or if the cat takes a high dose.

  • Central nervous toxicity (rarely) which can include nystagmus (repetitive, uncontrolled eye movements), ataxia (wobbly gait), head tilt, tremors and seizures
  • Genotoxicity (damage to the genetic information of a cell
  • Liver toxicity
  • Allergic reaction (hives, difficulty breathing)

If your cat experiences any of the above symptoms, speak to your cat’s veterinarian who may need to adjust the dose or change medication.

How is Flagyl supplied?

Flagyl is available in tablet, capsule or liquid suspension as well as injection. Due to the bitter taste, Flagyl may be compounded.


Keep the oral and liquid form in a refrigerator and shake well before use.

Tablets and capsules should be stored at temperatures below 30°C and protected from light.


Plumb, D.C. (2018). Veterinary drug handbook. Ames, Iowa: Iowa State Press.


  • Julia Wilson, 'Cat World' Founder

    Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio

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