Penetration of topical cyclosporine into the rabbit cornea, aqueous humor, and serum.

Systemic and ocular absorption of topically applied 10% cyclosporine ointment was determined in rabbit cornea, aqueous humor, and serum by radioimmunoassay. The concentration of the drug in the cornea reached a peak of 900 ng/mL three hours after application. Substantial levels were still present at 24 hours. Relatively low concentrations were measured in the aqueous humor and serum, suggesting corneal stromal pooling of this hydrophobic cyclic peptide. Topical ocular application of cyclosporine may reduce or eliminate the drug's systemic toxic effects while maintaining a therapeutic level of local immunosuppressive activity.