Development of intravitreal drugs presents several challenges due to the delicate ocular environment and volume constraints of what can be safely administered in the eye. Formulation development of intravitreally administered drugs may necessitate the use of nonphysiological pH in order to accommodate manufacturing processes or achieve favorable drug properties. Clinical and nonclinical data show that intravitreal drugs formulated in the pH 5.5 to 7.4 range are well tolerated. The aim of this study was to provide ocular toxicity data for formulations in the pH 4.0 to 5.5 range following intravitreal administration in New Zealand White rabbits. This range was evaluated as part of formulation development for an intravitreal drug that necessitated the use of pH outside the available tolerability data for formulations. Toxicity was assessed by ophthalmic examinations, intraocular pressure (IOP) measurement, clinical observations, body weights, and microscopic analysis of ocular tissue. Histidine chloride pH 5.0 to 5.5 and acetate chloride pH 4.0 to 5.0 solutions were well tolerated, and no test article-related ocular inflammation, IOP changes, or gross or microscopic findings were observed in any eye. The data presented here add to the knowledge of pH ranges that can be explored for intravitreal drug formulation development.
Keywords: histopathology; intravitreal; pH; retina; toxicity.