Improvement of systemic absorption of insulin through eyes with absorption enhancers.

A painless, simple, and practical method has been developed for systemic delivery of peptide drugs through eyes. In order to increase the amount of peptides absorbed into systemic circulation, effects of enhancers on insulin absorption into systemic circulation and reduction of blood glucose concentration have been studied. Saponin showed the highest potency to enhance insulin absorption, while Tween 20 was the least effective. The efficacy order of seven compounds studied can be arranged as follows: saponin greater than fusidic acid greater than BL-9 = EDTA greater than glycocholate = decamethonium greater than Tween 20. Since 1% of saponin reached the maximum effect to enhance insulin absorption and decrease blood glucose concentration, not more than 1% of saponin should be used for enhancing peptide absorption through eyes.