Tapetal changes in beagle dogs. II. Ocular changes after intravenous administration of a macrolide antibiotic--rosaramicin.

Two studies were conducted to assess the toxicity of rosaramicin (a macrolide antibiotic) when given intravenously for 30 consecutive days to beagle dogs with and without a tapetum lucidum (a light reflecting structure within the choroid of the eye). In the initial study, groups of three tapetal dogs/sex were given 20, 40, or 80 mg of rosaramicin/kg, twice daily. Ophthalmoscopic examination during Week 4 revealed dose-related, bilateral ocular changes characterized by a brown-tan discoloration and general pallor or loss of reflectivity of the normally blue-purple or yellow-green, highly reflective tapetum lucidum. These findings were restricted to the tapetal fundus; recovery occurred between Weeks 4 and 10 of the postdose period. To further investigate these changes, a second study was conducted in which groups of three tapetal dogs were given rosaramicin or erythromycin lactobionate (comparative macrolide antibiotic) at 80 mg/kg, twice daily. A third group of atapetal dogs was given 80 mg of rosaramicin/kg, twice daily. A similar change was observed in tapetal dogs given 80 mg of rosaramicin/kg, twice daily, in the follow-up study, but not in the other two groups. No other compound-related changes were observed in either study. The ocular changes observed in dogs given rosaramicin were reversible and structure-specific, occurring only in animals possessing a tapetum lucidum.