Feline visual changes associated with enrofloxacin

Dear Sir:

We wish to comment on feline visual changes associated with enrofloxacin, following publication of the article by Abrams-Ogg et al (Can Vet J 2002;43:53–54). These changes occur rarely — 1 report per 122 414 treated cats — even though enrofloxacin has an extensive history of use when compared with other veterinary fluoroquinolones. The dosage of enrofloxacin prescribed for the cat described by Abrams-Ogg et al was well in excess of the manufacturer's recommended dosage.

In our recent year-2000 feline safety study, early results indicated that adverse effects on the visual system are seen at high doses of enrofloxacin. Bayer Inc. immediately and proactively communicated new dosage information to veterinarians. The revised dosage for cats was not to exceed 5 mg/kg bodyweight (BW) once daily. Upon completion of the study, a second letter was sent to veterinarians with updates on the new label and dosage, as approved by the Veterinary Drugs Directorate (previously Bureau of Veterinary Drugs). The current label dosage for cats is 5 mg/kg once daily for up to 30 days. The flexible regimen of 5 to 20 mg/kg BW once daily for up to 30 d remains unchanged for dogs.

The historical case described by Abrams-Ogg et al had a variety of clinical challenges, including hepatopathy and pyelonephritis, and a history of visual changes prior to enrofloxacin use. The plasma levels of enrofloxacin may have been markedly elevated because of the combination of drug overdose and compromised clearance. In some other reported cases, concurrent clinical conditions may have contributed to the visual changes. Therefore, it is important to fully investigate all cases of visual changes suspected of being associated with enrofloxacin before reaching a conclusion.

All adverse cases suspected of being associated with the use of enrofloxacin that are reported to Bayer Inc.'s technical veterinary services are thoroughly investigated with a panel of tests, including ocular examination and electroretinographic recordings by a board certified veterinary ophthalmologist. As an ethical and responsible company committed to animal health, Bayer Inc. feels strongly that the collection of such data is paramount in helping to elucidate the true cause of the clinical signs. This workup is important support for practitioners faced with a suspect adverse event.

This investigative support, along with Bayer Inc.'s cooperative initiatives with the veterinary ophthalmology community, its close correspondence with the Veterinary Drugs Directorate, and its timely communication plan (1,2), should give practitioners the confidence to use Baytril, according to label directions, safely and effectively.