Determination of the retinal toxicity of intravitreal colistin in rabbit eyes

Purpose To determine the possible adverse effects and safe dose range of intravitreal colistin, an antibiotic, after its intravitreal application. Methods Twenty eyes of 20 adult male and female New Zealand white rabbits were selected. Various concentrations of colistin were prepared. In each rabbit, 0.1 mL of colistin solution or saline solution was injected intravitreally into the right eye. Electroretinographic recordings were taken before and 2 weeks after injection. Histopathological examination was made using a light microscope following enucleation and fixation procedures. In histopathologic cross-sections, the differences between drug-injected eyes and control eyes were evaluated. Results Electroretinographic examination showed a decrease of 30% as a significant value in the a and b wave amplitudes of the rabbits that injected 400 mu g/0.1 ml and higher concentrations. Histological examination revealed histiocytic infiltration, histiocytic vacuoles, inflammation, and retinal degeneration in rabbit eyes given 400 mu g/0.1 ml, 800 mu g/0.1 ml, and 1.6 mg/0.1 ml concentrations of colistin. Conclusion Based on our findings, the safe concentration of colistin is 0.2 mg/0.1 ml. Administration of 0.4 mg/0.1 ml was associated with cataract development, electrophysiological depression, and pathological changes in retinal layers.