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Ronidazole for Cats

By Barbara Forney, VMD

Last reviewed: 7/14/2022

Commonly prescribed for: Infections Due to Tritrichomonas Foetus and Infections Due to Giardia

Species: Cats

Therapeutic Class: Antiprotozoal

Basic Information

Ronidazole is a nitroimidazole antibiotic/antiprotozoal from the same family as metronidazole. It is toxic to protozoa by virtue of the disruption of protozoal DNA. Ronidazole is considerably more effective than metronidazole in treating trichomonal infections. There is also some research that indicates that it may be effective to treat Giardia in dogs.

Although drugs from this family are used to treat trichomonal infections in birds, it is important not to use ronidazole in food animals due to concerns regarding carcinogenicity. Ronidazole is well-absorbed following oral administration. It is not FDA-approved for either human or animal use in the United States therefore it is only available through compounding pharmacies.


Ronidazole is an anti-protozoal drug that is effective against Tritrichomonas foetus in the cat. Although the efficacy has been demonstrated in multiple studies, there is relatively little published information on this drug. Ronidazole is given orally for 14 days. It is compounded into capsules because, like metronidazole, it is very bitter tasting.

Side Effects

  • The most-common side effects are anorexia, nausea, and vomiting.
  • Rare, but more-serious side effects are neurologic and may include weakness, ataxia, twitching, and seizures. Usually neurologic signs will resolve by simply discontinuing the drug, but in some instances they may worsen initially before improving. In these cases it may take as long as four weeks before there is a complete resolution of clinical signs.


  • Ronidazole is considered to be possibly carcinogenic. The FDA prohibits its use in food animals. Human contact should be minimized (always wear gloves).
  • In order to avoid neurotoxicity it is important to work with an accurate body weight. The dosage may be further reduced in kittens.
  • Ronidazole is teratogenic and should not be used in pregnant animals.

Drug Interactions

  • Most of the drug interactions listed for Ronidazole are extrapolated from experience with Metronidazole.
  • Ronidazole may increase the levels of the following drugs: Cyclosporine, systemic Tacrolimus, Fluorouacil, Lithium.
  • Cimetidine, and Ketoconazole decrease the metabolism of Ronidazole, and could increase the incidence of neurotoxicity.
  • Ronidazole should not be used with Oxytetracyclines, Phenobarbital, Rifampin, or Phenytoin. These drugs either antagonize or increase the metabolism of Ronidazole.
  • Alcohol should be avoided due to the possibility of a disulfiram reaction.
  • Ronidazole should be avoided in animals receiving coumarin anticoagulants due to increased clotting times.


If oral overdose is recognized promptly, gut-emptying protocols may be helpful. If neurologic signs occur, supportive nursing care may be required for some time.
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Popular Ronidazole Dosage Forms

Dosage options starting at $0.49 per dose

Metronidazole: Tiny Tabs

Metronidazole: Tiny Tabs

Compressed oral tablets that are smaller than a Tic-Tac®

Metronidazole: Quad Tab

Metronidazole: Quad Tab

Quarter-scored tablets for maximum flexibility in oral dosing.

Metronidazole: Gourmeds Chewable Tablets

Metronidazole: Gourmeds Chewable Tablets

Flavored chewable oral tablets.