Mechanism · Pharmacokinetics
An in-depth technical analysis of pharmacokinetic properties governing peptide efficacy. This guide explores the structural modifications, primarily acylation and pegylation, that dictate absorption rates and metabolic resistance in systemic circulation.
Native peptides typically exhibit extremely poor oral bioavailability (< 1%) due to rapid hydrolysis by digestive proteases (pepsin, trypsin) and the physical barrier of the intestinal epithelium. Absorption kinetics following subcutaneous (SC) administration depend heavily on molecular weight and local tissue vascularity.
Schematic, GLP-1 receptor agonist
Illustrative only
The native GLP-1 hormone has a half-life of approximately 1.5 to 2 minutes. Therapeutic analogs employ several strategies to evade rapid renal and enzymatic clearance:
Attachment of a C16 or C18 fatty diacid chain promotes non-covalent binding to serum albumin, shielding the peptide from renal filtration.
Amino acid substitution (e.g., Aib8) creates steric hindrance, preventing cleavage by dipeptidyl peptidase-4.
Covalent attachment of polyethylene glycol increases hydrodynamic radius above the renal filtration threshold (~65 kDa).
| Compound | Class | Bioavailability (SC) | Half-life (t½) | Extension Mechanism |
|---|---|---|---|---|
| Native GLP-1 | Endogenous Hormone | N/A (rapid degradation) | ~1.5 – 2 min | None, native sequence |
| Semaglutide | GLP-1 RA | ~89% | 165 h (~1 week) | Aib8 substitution + C18 fatty diacid (albumin binding) |
| Tirzepatide | GLP-1 / GIP Dual Agonist | ~80% | 116.5 h (~5 days) | Aib2 substitution + C20 fatty diacid |
| Liraglutide | GLP-1 RA | ~55% | 13 h | C16 fatty acid conjugation (γ-glutamate linker) |
Simulated plasma concentration following single subcutaneous administration.