What is bioavailability? | Peptide glossary

When a substance is given by any route other than intravenous, part of it is lost before it reaches the blood: it is not absorbed, it is broken down on site or, if it goes through the gut, enzymes and the liver destroy it before it circulates (the so-called first-pass effect).

For peptides the oral route is especially hostile: stomach acid and intestinal proteases fragment them and, because of their size and charge, they cross the intestinal wall poorly. That is why the oral bioavailability of most peptides is very low and the subcutaneous route is the usual one in research and in peptide drugs.

There are exceptions achieved with formulation technology: oral semaglutide uses an absorption enhancer (SNAC) and even so its bioavailability is around 1%, which calls for much larger amounts than the subcutaneous route.

Why it matters in peptide research

When reading a study, the route of administration completely changes the interpretation: a result obtained intraperitoneally in rodents says nothing direct about what would happen by another route.

Related terms

Learn it in depth at the Peptide University

Routes of administration and bioavailability · Module 8
Pharmacokinetics: ADME and parameters · Module 2
Amylin, the oral route and the next generation · Module 3
Non-injectable routes: intranasal, oral and topical · Module 8
Technical fundamentals of subcutaneous administration · Module 8

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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).