Enrofloxacin is a quinolone antibiotic. General safety studies conducted at 5, 15, and 25 mg/kg have noted no adverse effects. In 1997, a flexible dosing range (5 to 20 mg/kg) once or divided twice daily was recommended. Shortly thereafter, reports of a possible link between enrofloxacin and vision problems (blindness, partial blindness, and mydriasis) occurred. Further safety studies were conducted, and in 2001 the label recommendation was changed to 5 mg/kg Q 24 H. In this study, 12 control cats and 12 cats treated with enrofloxacin, 50 mg/kg PO Q 24 H, were monitored for systemic and ocular changes. Cats were treated for 3, 5, or 7 days. Treated cats lost weight and decreased their food consumption; vomiting was noted in 10 of 12 cats receiving treatment. Blood pressure did not significantly change. Eight of 12 treated cats showed changes in behavior, including lethargy, marked caution, fractiousness, unkempt coat, incoordination, stiff gait, tremors, convulsions, blindness, ataxia, circling, seizures, ptyalism, and nystagmus. Ocular examinations were performed daily; on or before day 3 of treatment, there was a granular appearance or graying of the fundus. Other changes included vascular attenuation and generalized tapetal hyperreflectivity.  Electroretinography changes were noted. Morphologic changes in the photoreceptor layers were noted and correlated with the duration of therapy. In this study, enrofloxacin at 10 times the recommended dose resulted in retinal dysfunction as early as 1 day after administration. The mechanism of action is still unknown. Supported in part by Bayer Healthcare LLC, Animal Healthy Division

COMMENTARY: The association between retinal damage and enrofloxacin dose highlights an important point regarding the need for veterinarians to report adverse or even suspect adverse effects. Early safety studies with this drug did not reveal this risk, and it was not until the drug was in wide use that a dose-dependent effect on the retina was noted. The current recommendation for enrofloxacin is 5 mg/kg Q 24 H. In this study, the investigators noted that many of the treated cats had decreased food consumption and vomiting with associated weight loss at that dose. If cats are being treated for a significant length of time, body weight should be monitored. Alternatives to enrofloxacin include marbofloxacin, 2.75 to 5.5 mg/kg. No retinal changes have been reported with this drug when used up to 55 mg/kg orally Q 24 H. Retinal changes have been reported with orbifloxacin when used at doses of 45 and 75 mg/kg orally Q 24 H. Ideally, fluoroquinolones should be limited to infections for which a specific drug is the known drug of choice or in situations in which culture and sensitivity support their use. Owners should be informed of the possible risks and under what conditions drug therapy should be discontinued.

Ocular and systemic manifestations after oral administration of a high dose of enrofloxacin in cats. Ford MM, Dubielzig RR, Giuliano EA, et al. AM J VET RES 68:190-201, 2007.