Systemic delivery of polypeptide drugs through ocular route

Because of rapid developments in biotechnology, numerous peptides are now available for clinical treatment of various diseases. In order to avoid parenteral injections, alternative routes of drug administration have been investigated. Among them, the ocular route seemed to be the most feasible one because a) it could deliver precise doses of drugs just like injections; b) it was much easier and less expensive to administer eyedrops than an injection; c) the rate of systemic absorption through the ocular route was as fast as an injection; d) eye tissues were much less sensitive to the development of immunological reactions than other tissues; e) the drug absorbed via the ocular route would avoid the first passage through hepatic circulation to reach the sites of action before liver metabolism; and f) no tolerance and ocular side effects could be detected after long-term (three months) daily administration of insulin eyedrops.