The time-honored approach to delivering drugs to the ocular surface is through the use of liquid drops and semisolid ointments. Such delivery systems, however, are not efficient at delivering therapeutic concentrations of drugs to the cornea and intraocularly. Over the past several years, we tested the biopolymer, collagen, as a means of delivering both hydrophilic and hydrophobic drugs to the ocular surface. This study summarizes results obtained using the hydrophobic drug, cyclosporine, incorporated into collagen shields and collagen particles. Corn oil drops containing cyclosporine were used as the control. Groups of anesthetized rabbits were fitted with collagen shields containing cyclosporine, treated topically with collagen particles containing cyclosporine suspended in an ocular surface lubricant, or given topical drops of corn oil containing cyclosporine. At intervals after a single treatment with one of the drug formulations, corneas, aqueous humor, and blood were collected for analysis of cyclosporine concentration. With either of the two collagen vehicles, peak concentrations of the drug were found in the cornea 4 hours after application. The corn oil vehicle yielded a significantly lower and earlier peak concentration (1 hour after application). By 8 hours, significant amounts of the drug were still present in the corneas of the collagen-treated animals, whereas drug levels in the corn oil treatment group had returned to baseline. Drug delivery profiles in the aqueous humor were similar, except that the amounts of drug were five times lower. No cyclosporine was detected in the blood from any of the treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)