Effect of permeation enhancers on beta-endorphin systemic uptake after topical application to the eye

Solutions of human beta-endorphin were applied topically to the eyes of rabbits. Atrial blood was collected and plasma beta-endorphin was assayed using a Nichols Diagnostics radioimmunoassay kit. Levels peaked rapidly (within 10-20 min) at greater than 5 ng/ml with 1% beta-endorphin and no enhancer, and then returned to background within 2 h. When the permeation enhancers Brij-78 or BL-9 were added to the formulation applied topically, plasma levels were elevated above 30 ng/ml and remained elevated above 1 ng/ml over 1 h. Plasma levels were actually higher after topical application using either enhancer than after intravenous injection at the collection points of 45 min and later. The data suggest that topical application to the eyes can be an efficacious method of systemic delivery of peptide drugs.