Rapid toxicological model for use in assessing ocular drugs

Nonsteroidal antiinflammatory drugs (NSAIDs) were applied to corneas either by in vitro or in vivo methods. The in vitro method involved excising and mounting corneas in a perfusion system at 37 degrees and exposing drug for 2.5 h. The in vivo methods represent either topical administration to the rabbit eye or topical in vivo infusion using a fixed well which permitted a constant concentration (0.05 per cent) to be applied to the eye of anesthetized rabbits for up to 120 min. An overlay grid procedure using scanning electron microscopy (SEM) showed less per cent endothelial damage with in vivo methods than with the in vitro method of administration, but per cent damage depended on which section was viewed. Damage to the epithelium and endothelium were also assessed by quantitative carboxyfluorescein and Janus green staining and uptake procedures, respectively, following drug exposure by the in vivo infusion method. Results for the epithelium indicated that the more lipophilic NSAIDs damaged the epithelial layer to a greater degree than newly synthesized hydrophilic NSAIDs. Damage to the epithelium correlated to the surface activity of the NSAIDs. Qualitative assessment of epithelial and endothelial toxicity can be performed with SEM and transmission electron microscopy (TEM) while vital staining procedures and the SEM grid procedure can be used to quantitatively assess corneal toxicity. The staining methods, however, possess advantages over SEM and TEM procedures in that they are rapid and do not require laborious preparation. As a result of these characteristics, the vital staining procedures could be used as part of a biopharmaceutical screening technique in evaluating new ophthalmic drugs.