Subcutaneous, Nasal, and Oral Peptide Formulations: Bioavailability Comparison and Barriers

Selecting the optimal delivery route for a therapeutic peptide requires balancing patient compliance with physiological bioavailability barriers.

• Estimated Bioavailability: 70% to 95%+
• Pharmacokinetics: Direct deposition into subcutaneous adipose microvasculature. High systemic absorption with zero exposure to destructive gastrointestinal acid and digestive proteases.
• Considerations: Gold-standard route for high molecular weight and hydrophilically charged peptides.

• Estimated Bioavailability: 10% to 50%
• Pharmacokinetics: Rapid trans-mucosal absorption across highly vascularized respiratory epithelia. Partially bypasses the blood-brain barrier via olfactory and trigeminal nerve pathways.
• Best suited for: Neuropeptides (such as Semax and Selank) intended for central nervous system target engagement.

• Estimated Bioavailability: Typically < 1% without specialized carriers; 1% to 5% with absorption enhancers (e.g. SNAC carrier with oral semaglutide).
• Barriers: Complete destruction by gastric pepsin and hydrochloric acid (pH 1.5 - 2.0), pancreatic proteases in the duodenum, and failure to cross tightly packed enterocyte epithelial membranes.