Penetration of 2% cyclosporin eyedrops into human aqueous humour.

The penetration into the eye and the systemic absorption of 2% cyclosporin eye drops were determined by polarisation immunofluorescent assay of cyclosporin in the aqueous humour and plasma of 30 patients at the time of cataract surgery. The results were then compared with the corresponding results after oral administration at a dosage of 5 mg/kg/day to three further patients. The maximum intraocular concentration (24 (SD 9) mg/l) was achieved four hours after topical administration. This level was slightly less than that found in aqueous humour (28 (SD 10) mg/l) 12 hours after systemic administration of the drug at a dosage of 5 mg/kg/day. Both these levels are below the minimum therapeutic level (50-100 mg/l). Topical application of cyclosporin A did not produce detectable levels in plasma at any time. These results indicate that the efficacy of cyclosporin A in the control of intraocular inflammation is attributable to its systemic immunoregulatory effect rather than to the local ocular effect.