ABSTRACT
Presently, peptide and protein drugs are almost exclusively marketed for parenteral administration. This is because these drugs face formidable enzymatic and penetration barriers, when administered orally. A limitation of the parenteral route for delivery of peptides and proteins is the extremely short half-lives of these drugs, being in the order of a few minutes. This demands repeated administration that is inconvenient to the patient. Also, parenteral administration is mostly done under the supervision of a health-care professional, thereby adding to the cost of the health-care system. For these reasons, nonparenteral routes of administration are being actively investigated. Another alternative is to develop controlled release parenteral formulations, where a single injection may release the drug over a month or even longer. Twice-a-year depot injections for leuprolide encapsulated in polymer are available as an alternative to once-a-day injections of the solution formulation (Schwendeman, Shah, Bailey, & Schwendeman, 2014).
