Definition: Peptide degradation is the breakdown of a peptide drug into forms that may work less well or not at all. It can be chemical, where bonds in the molecule change, or physical, where molecules unfold or clump together. Heat, light, shaking, freezing and the wrong pH can all speed it up, and you usually cannot see it happen.
Chemical and physical breakdown
Reviews of protein and peptide drugs sort instability into two groups, chemical and physical (Manning 2010).
- Chemical: the molecule itself changes. FDA lists oxidation, deamidation and truncation (the chain being cut) as examples. In a lab study of a model peptide, very acidic liquid cut one bond in the chain, while above pH 6 the same peptide rearranged into a different form instead (Oliyai 1993).
- Physical: the molecule keeps its parts but loses its shape (unfolding, also called denaturation) or sticks to other molecules. See aggregation.
What speeds it up
FDA guidance on protein drugs says most of them "degrade on exposure to heat and light or with mechanical agitation." Labels turn that into handling rules:
- The Omnitrope label says to swirl the vial gently after adding the liquid and not to shake it, because "shaking may cause denaturation."
- Wegovy, Forteo and Humulin R labels all say do not freeze, and do not use if frozen. See freeze-thaw.
- Wegovy, Omnitrope and Humulin R labels say to protect the product from light. See light sensitivity.
Why it matters for your log
Breakdown is slow and mostly invisible. The Omnitrope label says not to use the mixed drug if it is cloudy or has particles, but a clear liquid is not proof that it is still at full strength. Time limits after mixing or first use are set per product: the Omnitrope vial must be used within 3 weeks of mixing, and a Forteo pen is thrown away 28 days after first use. Those limits belong to those products only. Dose Track saves each vial with the date you mixed it, so you can see how old a vial is when you log from it.
Read more on Dose Track: How long mixed peptides last · Peptide left out of the fridge · Peptide storage guides
General education drawn from labels and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your product are the final word.
Can you tell if a peptide has degraded by looking at it?+
Not reliably. Labels such as Omnitrope say not to use a mixed drug that is cloudy or has particles, but a clear liquid can still have lost strength.
What makes peptides break down faster?+
FDA guidance names heat, light and mechanical agitation such as shaking. Product labels also warn against freezing.
Does a preservative stop peptide degradation?+
No. A preservative such as benzyl alcohol limits bacterial growth. It does not stop chemical or physical breakdown, and one 2022 study found that the preservative m-cresol made a test peptide clump.