By mouth, most peptides are broken down before they are absorbed. The intravenous route avoids that problem but produces very high, brief peaks and is impractical outside a clinical setting. The subcutaneous route is the middle ground: the peptide is absorbed gradually into the capillaries and the lymphatic system, generally with high bioavailability.
The rate of absorption depends on the size of the molecule, its tendency to form aggregates at the depot site and the formulation. Large or lipidated molecules tend to be absorbed more slowly and to pass in greater proportion through the lymphatic route.
Other routes are of research interest: intranasal (studied for neuropeptides such as Semax or Selank because of their access to brain regions), topical (cosmetic peptides such as GHK-Cu) and oral with absorption enhancers.
Data from a study are only comparable if the route is the same. Changing the route changes the kinetics, the total exposure and often the result.
Related terms
Learn it in depth at the Peptide University
- Non-injectable routes: intranasal, oral and topical · Module 8
- Complementary monographs (16–20) · Module 14
- Routes of administration and bioavailability · Module 8
- Technical fundamentals of subcutaneous administration · Module 8
- Pharmacokinetics: ADME and parameters · Module 2
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Definition for educational and scientific purposes. It is not medical advice or a recommendation for use. NeoPeptidos products are sold labelled for research use only (RUO).