Retinal toxicity of intravitreal sparfloxacin, ofloxacin, and imipenem in a rabbit model

To determine whether intravitreal sparfloxacin, ofloxacin, and imipenem at varying concentrations cause retinal damage, 50 eyes from 25 rabbits were u tilized in the experimental protocol. The rabbits were classified into thre e groups each containing 15 eyes. Five eyes in each group were given high-, moderate-, or low-dose antibiotic into the vitreous. Group 1 eyes were inj ected with sparfloxacin 100 mu g, 50 mu g or 2.5 mu g; group 2: ofloxacin 2 00 mu g, 100 mu g, or 10 mu g; group 3: imipenem 10 mu g, 5 mu g, Or 0.5 mu g. Five control eyes were given intravitreal balanced salt solution. All e yes were examined by indirect ophthalmoscopy before and after intravitreal injections and at 24 h, 1 week, and 2 weeks after injection. All eyes were enucleated at 2 weeks and fixed for histological evaluation. Except for sev en eyes injected with 10 mu g or 5 mu g imipenem, which demonstrated trace vitreal reaction, no other eyes revealed vitreal inflammation by indirect o phthalmoscopy, By light microscopy, of five eyes injected with sparfloxacin 100 mu g, three had retinal damage but no vitreal inflammation; one had bo th retinal damage and vitreal inflammation. Of five eyes injected with spar floxacin 50 mu g, only one was abnormal with both retinal damage and vitrea l inflammation. Of five eyes injected with ofloxacin 200 mu g, one had reti nal damage, one had vitreal inflammation, and one had both retinal damage a nd vitreal inflammation. Of the five eyes injected with ofloxacin 100 mu g, none showed retinal toxicity but three showed vitreal inflammation. All 10 eyes injected with 10 mu g Or 5 mu g imipenem had mild vitreal inflammatio n but no retinal damage. None of 15 eyes given sparfloxacin 2.5 mu g, oflox acin 10 mu g, Or imipenem 0.5 mu g had vitreal inflammation or retinal dama ge. Eyes given high or moderate doses of any study antibiotic that showed n o inflammation or retinal damage by light microscopy were randomly selected for transmission electron microscopy (TEM), which documented retinal toxic ity. In addition, TEM con firmed the absence of retinal damage in all 15 ey es given the low dose of intravitreal antibiotics. Intravitreal injection o f low-dose sparfloxacin, ofloxacin, and imipenem is nontoxic to the retina. TEM should be done in eyes that are normal by light microscopy to determin e whether retinal toxicity is present.