Metronidazole reduced cyst shedding in cats experimentally infected with Giardia lamblia.4 The maximum daily dose should not exceed 50 mg/kg (Table 1) since this has been associated with neurotoxicosis in cats.5 Signs of toxicosis include lethargy, vomiting, ataxia, vocalization, and seizures. These signs usually resolve within five
to seven days of discontinuing the drug. Cats find metronidazole unpalatable and may salivate profusely after administration
of broken tablets. This unpalatability can be managed by compounding the drug into capsules of smaller doses or placing partial
tablets in gelatin capsules for administration.
Sulfadimethoxine is a bacteriostatic antimicrobial approved to treat sulfonamide-sensitive bacterial infections in dogs and
cats and bacterial enteritis associated with coccidiosis in dogs. Enteric coccidiosis (Cystoisospora species) remains an important cause of copious, watery diarrhea in cats less than 1 year of age. Sulfadimethoxine therapy
is not FDA-approved for treating coccidiosis in cats (Table 1) and has been associated with treatment failures in acute cases.
Toltrazuril and ponazuril
Recent limited studies have examined the efficacy of toltrazuril for treating coccidiosis in kittens and puppies.6
Toltrazuril is only available in the United States through compounding pharmacies, and quality control may be a concern. An
effective toltrazuril dose is 30 mg/kg administered orally one time, or 15 mg/kg every 24 hours for three days; patients can
be retreated after 10 days if necessary.6
Ponazuril (Marquis—Bayer Animal Health) is an equine antiprotozoal paste with efficacy against canine Cystoisospora species.7 It is not FDA-approved for use in companion animals but may be administered to cats as a single 30-mg/kg dose if standard
anticoccidial therapy fails to clear oocysts from feces and the diarrhea persists.8 Marquis contains 150 mg ponazuril per gram of paste. Dilution of one syringe (120 ml of paste) in 21 ml of water results
in a 135-mg/ml solution. This solution should be protected from light and shaken well before use.