Systemic delivery of enkephalin peptide through eyes

Leu-enkephalin is one of the important peptides which could become useful drugs in the clinics because of its analgesic action and its availability in mass quantity through biotechnology production. It is found in this study that enkephalin can be effectively absorbed systemically through eyes without using a surfactant as absorption enhancer. Enkephalin at 0.125% (31.25 micrograms/25 microliter) reached a plateau of blood concentration at 11.5 ng/ml in 3-4 hrs and stayed high for 8-9 hrs. In contrast, the blood concentration of enkephalin declined rapidly after i.v. administration with a T1/2 of less than 30 min and reached the lowest point at 22 ng/ml in 5 hrs. With higher concentrations at 1% (.25 mg/25 microliter) and 5% (1.25 mg/25 microliter) similar absorption kinetics was observed except that they reached higher plateau of blood concentration at 72 ng/ml and 233 ng/ml, respectively.