Drug-induced changes in dogs after long term application of a beta-blocker

Ocular irritation studies are important in the safety evaluation of ocular formulations. There are many reports on acute ocular irritation studies, but almost nothing about prolonged ocular instillation of ophthalmic formulations. This report discusses the predominantly lymphocytic infiltrates seen in the limbus corneae and eyelids of dogs treated with 1 and 2% solutions of L-653,328, an ocular hypotensive beta-adrenoceptor antagonist, for up to 53 weeks. The number of animals affected and severity of the lesions increased with time and concentration. A minimal effect was seen microscopically with the 2% solution as early as 14 weeks. Rabbits treated similarly for 14 weeks had no such changes. The first and only clinical sign in dogs was diffuse pinkness of the bulbar conjunctiva seen from Drug Week 22 onwards. Although not seen with similar molecular structures, given the equivocal results in sensitization studies and the long time required for the development of change, delayed contact hypersensitivity was suspected as the cause of the ocular infiltrates. Simple chronic irritation was not ruled out, however. These findings suggest that delayed contact hypersensitivity in dogs may be a phenomenon not limited to skin, but may also involve the eye after repeated ocular instillation.