The ocular route for systemic insulin delivery in the albino rabbit

The objective of this study was to determine the extent, pathways and effects of absorption promoters on the systemic absorption of insulin after topical solution instillation to the albino rabbit eye. The absorption promoters were polyoxyethylene-9-lauryl ether, Na glycocholate (GC), Na taurocholate and Na deoxycholate, all at a concentration of 1%. Plasma glucose concentration was measured in a glucose analyzer whereas plasma insulin concentration was measured using radioimmunoassay. The systemic bioavailability of insulin calculated from its area under concentration-time curve was in good agreement with that derived from the glucose concentration-time curve. The bioavailability was 5.7 to 12.6% with polyoxyethylene-9-lauryl ether, 4.9 to 7.9% with GC, 3.6 to 7.8% with Na taurocholate and 8.2 to 8.3% with Na deoxycholate, as compared to 0.7 to 1.3% in the absence of absorption promoters. The absorption promoting effect of GC was dependent on its concentration over the range of 0.1 to 2%. At 1%, the absorption promoting effect of GC persisted for about 5 min but disappeared by 15 to 30 min. The nasal mucosa contributed about 4 times more than the conjunctival mucosa to the systemic absorption of ocularly applied insulin. The conjunctival mucosa was, however, more discriminant in its sensitivity to the nature of the bile salts than the nasal mucosa. The former was most sensitive to Na deoxycholate and least to Na taurocholate. Collectively, our findings indicate that it is feasible to obtain hypoglycemia from ocularly administered insulin.