Molecule to Medicine: Advances in Protein and Peptide Drug Delivery Systems

Protein-and peptide-based drug delivery systems represent an important class of novel drug delivery technologies due to their high specificity, potent biological activity, and essential roles in physiological regulation.Proteins and peptides are fundamental biomolecules composed of amino acids linked by peptide bonds and function as enzymes, hormones, structural components, and immunological mediators.Peptides typically consist of short amino acid sequences with relatively low molecular weight, whereas proteins are larger macromolecules with complex three-dimensional structures.Despite their therapeutic potential, protein and peptide drugs face significant formulation and delivery challenges, including poor oral bioavailability, enzymatic degradation, rapid systemic clearance, and limited membrane permeability.Consequently, parenteral routes such as intramuscular, intravenous, and subcutaneous administration are most commonly employed.To overcome these limitations and enhance pharmacokinetic and pharmacodynamic performance, several advanced strategies have been developed, including chemical modification, carrier-based delivery systems, mucoadhesive polymers, enzyme inhibitors, absorption enhancers, and permeation-enhancing techniques.This review provides a comprehensive overview of the structure, classification, properties, biological functions, and delivery challenges of protein and peptide therapeutics.Additionally, it highlights contemporary strategies and advanced drug-delivery approaches to improve stability, bioavailability, and therapeutic efficacy.