© 1989 Oxford University Press
research-article |
Corneal Toxicity Studies in Rabbits and Dogs with Hydroxyethyl Cellulose and Benzalkonium Chloride
Laboratories Merck Sharp & Dohme-Chibret, Research center, Department of Safety Assessment B P 134-Route de Marsat, 63203 Riom, France *Department of Safety Assessment Merck Sharp & Dohme, West Point, Pennsylvania 19486, U.S.A.
Received August 4, 1988; accepted March 28, 1989
Hydroxyethyl cellulose (HEC) is used as a viscosity-enhancing agent in ophthalmic formulations to prolong corneal contact time and increase intraocular drug levels. Benzalkonium chloride (BAK) is the preservative most frequently used in ophthalmic formulations. Corneal epithelia] changes were seen by slit lamp and light microscopic examination in rabbits but not dogs after multiple instillations of an ophthalmic vehicle containing 0.01% BAK and 0.5% HEC. Microscopically, there was sloughing of superficial epithelial cells and a slight loss of polarity of the basal cells. Formulations with 0.01% BAK and HEC, at concentrations between 0.3 and 0.8%, caused these changes but not with BAK or HEC alone. It was concluded that hydroxyethyl cellulose increased the viscosity and prolonged the contact time of BAK with cornea resulting in corneal epithelial damage in the rabbit. Physiological and anatomical features of the rabbit combined with the increased contact time were concluded to favor these changes in this species. The results confirm that the rabbit is a sensitive and unique species in studies of ocular toxicity of drugs.