Tritrichomonas foetus in cats: ronidazole and its risks
1-year-old Siamese cat from a cattery with chronic large-bowel diarrhoea, flatulence and fresh blood in the faeces. Faecal PCR confirms Tritrichomonas foetus. Previous treatment with fenbendazole and metronidazole was ineffective.
Ronidazole treatment is chosen. What should you warn the owner about?
chevron_right Show answer and explanation
A. That it can cause acute kidney injury, so creatinine will need to be measured daily
Nephrotoxicity is not the characteristic adverse effect of ronidazole; neurotoxicity is.
B. That its main adverse effect is neurotoxicity, so it must be stopped if signs appear, and that it is unlicensed in cats and must be handled with gloves
Correct. As a nitroimidazole, it can cause lethargy, ataxia, tremors or seizures, which usually resolve on withdrawal. Being unlicensed, informed consent is needed, and because of its carcinogenic potential the owner should handle it with gloves.
C. That it should be given together with metronidazole to boost efficacy
Both are nitroimidazoles: combining them adds neurotoxicity, and metronidazole is not effective against T. foetus.
D. That a single dose is enough to cure the infection
It is given for about two weeks, and even then relapse or a persistent carrier state may occur.
lightbulb Key takeaway
Ronidazole is the only drug with proven efficacy against feline T. foetus, but it has a narrow safety margin. Confirm the diagnosis by PCR before treating, give it once daily and ask the owner to watch for neurological signs. The cat may remain a carrier even when the diarrhoea improves.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.