Millions of cats and dogs have been treated successfully with enrofloxacin since 1990. The drug is broad-spectrum and has a favorable tissue distribution, making it the drug of choice for many infectious diseases. At its introduction, the dose was 2.5 mg/kg PO every 12 hours. In 1997, the recommended dose became a once-daily treatment of 5 to 20 mg/kg. However, the new dosing guidelines were often exceeded. Ophthalmologists began to observe that a small proportion of cats became blind due to retinal degeneration after receiving enrofloxacin. It is estimated that 1 of every 122,414 (0.0008%) cats treated develop this problem, and it now being seen with other fluoroquinolones. The retinal degeneration appears to be dose- and concentration-dependent (rather than idiosyncratic), related to large doses or plasma concentrations of drug, rapid IV infusion, prolonged courses of treatment, and age. Other factors may also cause this reaction, including drug interaction and drug accumulation due to altered metabolism or prolonged exposure to ultraviolet light during antibiotic administration.

Commentary: Fluoroquinolones can be given to cats with limited risk of developing retinal degeneration as long as the manufacturer's guidelines are followed. Dose restriction may be indicated in older cats and cats with retinal impairment.

Fluoroquinolone-induced retinal degeneration in cats. Wiebe V, Hamilton P. JAVMA 221:1568-1571, 2002.