Metronidazole (brand name Flagyl®) is an antibacterial and antiprotozoal agent used in the treatment of certain anaerobic bacterial and protozoal infections, such as those caused by Giardia and Trichomonas. It is often used to treat diarrhea and other intestinal problems. The use of metronidazole to treat Giardia infections and most other infections in dogs and cats is off label or extra-label. Many drugs are commonly prescribed for off label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully.


The antibiotic metronidazole is used to treat a variety of infections caused by bacteria or parasites in humans. Metronidazole prevents bacteria from growing and reproducing. The most common use for this medication is to treat intestinal infections, but it can be used for a variety of illnesses, including ear infections and meningitis (brain and spinal cord infection). 

Metronidazole, also prescribed under the brand name Flagyl, is an oral medication commonly given to cats to treat both bacterial and protozoal infections, most of which can cause diarrhea. While this medication typically has minor side effects, it sometimes can cause serious neurological symptoms and allergic reactions that can be deadly. The most serious side effects occur with prolonged use or if your cat is given very high doses of metronidazole

Features of Metronidazole For Cats

  • Metronidazole (Flagyl) is an antibiotic that veterinarians prescribe to treat diarrhea or inflammatory bowel disease (IBD) in cats.
  • Diarrhea is the most common side effect of metronidazole, even though it can be prescribed to treat diarrhea. 
  • Metronidazole can cause serious side effects when used for long periods of time, including behavior changes and seizures.

Uses/benefits of Metronidazole For Cats

Metronidazole may be prescribed if your cat is experiencing diarrhea or inflammatory bowel disease (IBD). Metronidazole is not FDA-approved for use in animals and is used off-label for cats. Since metronidazole can harm unborn cat babies, it should be avoided in pregnant cats. Metronidazole can also enter a cat’s milk and harm young kittens, so it’s not recommended for nursing cats either. This medication should also be used carefully in cats with seizures and kidney or liver issues. Cats with these conditions may be more likely to have serious side effects from metronidazole.

Metronidazole Side Effects

  • Most common: clinical signs related to the bad taste or GI upset.
  • Dogs and cats: excessive salivation, gagging, regurgitation, pawing at the mouth, nausea, vomiting, and decreased appetite are the most frequent complaints.
  • Less common or rare: diarrhea, depression, lethargy, weakness, low white blood cell count, liver failure and blood in the urine, or dark urine due to pigment changes. Neurologic signs may be seen after accidental overdose or, more commonly, with long-term moderate-to-high-dose therapy as to treat difficult bacterial infections. Signs often begin seven to 12 days following the start of treatment.
  • Horses: side effects are not associated commonly with metronidazole. The major problem with using this drug is its bad taste. Many horses stop eating when this drug is mixed with feed and a reliable method of administration must be found.


  • Metronidazole causes birth defects in laboratory animals. It should be avoided in pregnant animals, especially in the first trimester. Some metronidazole is excreted in breast milk and it should not be used in lactating animals.
  • Metronidazole should not be used in young puppies and kittens.
  • Metronidazole should be avoided or used with caution, at reduced doses, in animals with kidney or liver disease.


  • Drug Name: Metronidazole for Dogs and Cats
  • Common Name: Flagyl®, Metizol®, Protostat®, Metrogel®
  • Drug Type: Antibiotic, antiprotozoal
  • Used For: Prevention and treatment of bacterial and parasitic infections
  • Species: Dogs, Cats
  • Administered: Tablet, Oral liquid, Injectable
  • How Dispensed: Prescription only
  • FDA Approved: No

Prices of Metronidazole For Cats

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