Pharmacology
Bioavailability
Bioavailability is the fraction of an administered dose of a substance that reaches the systemic circulation unchanged.
Detailed Explanation
For peptides, bioavailability is a critical challenge because digestive enzymes rapidly degrade peptide bonds. Most peptides have very low oral bioavailability (<1%) and require parenteral administration (subcutaneous or intramuscular injection). Exceptions include MK-677 (>60% oral bioavailability) and Noopept. Modifications like pegylation (PEG-MGF) and fatty acid conjugation (Semaglutide) can extend half-life and improve bioavailability.