Intravitreal toxicity of the Kenalog vehicle (benzyl alcohol) in rabbits

Purpose: To test the toxicity of intravitreal injections of benzyl alcohol. Methods: Nine New Zealand rabbits were injected with either a control or a test article at elevating concentrations. The test article was benzyl alcohol calculated to give final injected concentrations of 0.0073%, 0.022%, 0.073%, 0.222%, and 0.733% benzyl alcohol. The 0.022% concentration corresponds to the concentration of benzyl alcohol in human eyes when 0.1 mL of commercial Kenalog (Bristol-Myers Squibb, Princeton, NJ) is used. Baseline examination of the rabbits was performed along with postinjection examinations on days 1, 3, 7, and 14. The eyes were enucleated and examined by light and electron microscopic examinations. Results: Eyes injected with benzyl alcohol concentrations of 0.073%, 0.222%, and 0.733% displayed changes in the outer retina including loss of, and shortening of, outer segments and photoreceptors. Conclusions: Benzyl alcohol at concentrations modestly higher than what is present in commercial Kenalog is toxic to the rabbit eye. This has been shown in other organ systems. If commercial preserved Kenalog is to be used clinically, decanting the supernatant or using other means to remove the benzyl alcohol may be considered, especially if a volume of > 0.1 mL of solution is used. We hypothesize that the noninfectious inflammation seen clinically after Kenalog injection is due to the presence of a toxic preservative at unsafe concentrations.