Drug-induced retinal toxicity in albino rabbits: The effects of imipenem and aztreonam

Purpose. To test the toxic action of two antibiotics, imipenem and aztreonam, on the functional and morphologic integrity of the albino rabbit retina. Methods. Two commercial drugs were used-Tienam, which contains imipenem, and Azactam, which contains aztreonam. Different doses of these drugs were injected intravitreally. Retinal function was assessed from the electroretinogram (ERG) and the visual evoked potential (VEP). Retinal structure was examined at the light microscopic level. Results. Imipenem did not affect the ERG and the VEP responses or the morphology of the retina up to a total injected dose of 0.98 mg (2 mg Tienam). Aztreonam was not toxic to the albino rabbit retina up to a total injected dose of 2.8 mg (5 mg of Azactam). Severe functional and morphologic retinal damage was seen when 10 mg of Azactam was injected. A similar degree of damage was seen when a dose of 5 mg L-arginine, an ingredient of Azactam, was injected into the vitreous. Conclusions. Imipenem and aztreonam are nontoxic to the albino rabbit retina oncentrations that are 500-fold higher than their effective dose against bacterial infection. Azactam is highly toxic at high levels (more than 10 mg injected into the vitreous). Most of the toxicity could be explained by the L-arginine content of the drug.