Proteins and peptide drugs have a great therapeutic potential and their usage in the treatment of various severe diseases has revolutionised the fields of pharmaceuticals and biotechnology. For successful therapeutic effects, various efforts have been made for effective delivery of proteins/peptide drugs through various routes of administrations. Parenteral and non-parenteral drug deliveries are regarded as significant routes of drug absorption. In addition to intravenous, subcutaneous and intramuscular routes, the oral route is more effective for protein and peptides therapeutics. However, there is a need to improve non-parenteral drug delivery systems (DDS) to increase drug absorption in a more effective way. The present narrative review was planned to describe routes and barriers for protein/peptide drugs and how to improve drug delivery systems in an effective way. For this purpose, numerous research articles were searched from year 2000-2021 using search engines like PubMed, Google Scholar, Medline and ISI Web of Knowledge, and Bioline International while applying different keywords such as 'protein and peptide drugs', 'drug delivery systems', 'parenteral and non-parenteral routes of drug delivery' and 'physicochemical barriers'. It was concluded that the success of the therapeutics is strongly influenced by the differential delivery of targeted antigen, the choice of targeting protein or peptide, and drug-release characteristics of the linker used. Furthermore, there should be an improvement in non-parenteral DDSs so that the drugs might be administered in an appropriate manner.
Keywords: Protein, Peptide, Drug delivery system, Parenteral drug delivery, Non-parenteral drug delivery, physico-chemical barriers..