Systemic delivery of insulin through eyes to lower the glucose concentration.

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An attempt has been made in this study to develop a simple, economical and painless method for the delivery of insulin systemically without using parenteral routes. Insulin was shown to be absorbed effectively into systemic circulation through the eyes. With 0.125% (0.031 mg/25 microliters), 1% (0.25 mg/25 mg/25 microliters) insulin instilled topically into the eyes, systemic blood concentrations of 1.3 ng/ml, 9 ng/ml, and 24 ng/ml, respectively, could be attained. When 25 microliters of 1%, 2% and 5% insulin plus 1% saponin solution were instilled into eyes they reached 63 ng/ml, 89 ng/ml and 195 ng/ml, respectively in the systemic circulation. These results indicate that the systemic absorption of 1% insulin through the eyes can be enhanced at least 7-fold when 1% of the surfactant, saponin, was added to the solution. However, the insulin absorption was not affected by aminopeptidase inhibition nor by the change of pH in the range of 5 to 8. Most importantly, the blood glucose was reduced concomitantly with the increase of blood insulin when 50 microliters of 1% insulin in 1% saponin solution was instilled in the eyes. The blood glucose of alloxan-treated diabetic animals reduced drastically from 370 mg % to 185 mg % in 90 min and further to 75 mg % in another 150 min. In normal animals, 25 microliters of 1% insulin in 1% saponin reduced blood glucose from 102 mg % to 50 mg % in an hour and blood glucose remained low for at least 3 hrs. These results indicate that insulin can be delivered systemically through the eyes, particularly with the surfactant enhancers, such as saponin. This new method is economical and simple as compared with parenteral administration and/or minipump implantation. It is hoped that this new method would improve patients' compliancy in using insulin for diabetes treatment.