Delivery of systemic regular insulin via the ocular route in cats

Regular porcine insulin was administered as eye drops to eighty healthy, euglycemic cats. Insulin was applied alone and in combination with four different permeation enhancers. Serum glucose and insulin were monitored for four hours following the eye drops. Significant changes in both serum glucose and insulin occurred when the insulin was administered with 0.5% saponin, 0.5% Brij-78, 1% BL-9 and 2% BL-9. Insulin delivered alone and in the presence of Brij-99 did not significantly alter glucose and insulin concentrations. While effective as an absorption enhancer, 0.5% saponin caused transient ocular irritation in all the test subjects. Brij-99 was also irritating to some of the cats. Solutions containing Brij-78 and BL-9 were well tolerated. This study demonstrated that short-acting insulin is systemically absorbed in cats via the ocular route when applied with certain emulsants.