What I have: cagrilintide · 4 mg/mL · two weeks.
I am asking for verification rather than opinion, ideally with something I can read myself.
It is possible the evidence exists and I am searching for the wrong term.
What would count as evidence here, and does it exist?
two weeks is 14 days and, on a weekly schedule, 2 stopper punctures out of one vial at 4 mg/mL. Set the chemical question aside for a moment, because the puncture count is the one with a convention attached: 14 days is 0.5 times the twenty-eight days conventionally allowed for a preserved multi-dose preparation once it has been entered. Chemically, 4 mg/mL is high enough that adsorption to the glass is a rounding error and low enough that it is not protecting you from anything. What 2 withdrawals do add is 2 opportunities to introduce air, 2 coring events on the same stopper, and a headspace that grows with every draw — none of which show up on a certificate and all of which are avoided by splitting into aliquots at reconstitution.
The honest answer is that most reported "degradation" is adsorption and dilution error rather than chemistry.
Hydrolysis cleaves the backbone, most readily at aspartate-proline and aspartate-glycine sequences, and is acid-catalysed. In a dry solid it barely proceeds at all.
| Pathway | Dominant when | Detected by |
|---|---|---|
| Deamidation | Solution, neutral to alkaline pH | RP-HPLC, +1 Da on MS |
| Oxidation | Light, trace metals, peroxides | RP-HPLC, +16 Da on MS |
| Hydrolysis | Solution, extremes of pH | RP-HPLC, fragment masses |
| Aggregation | Agitation, interfaces, high concentration | SEC, visual haze; often invisible on RP-HPLC |
| Freeze-concentration damage | Freeze-thaw of buffered solution | SEC, loss of recovered content |
A mass spectrum resolves most of this: minus eighteen is dehydration or succinimide, plus one is deamidation, plus sixteen is oxidation, and an unchanged mass with a shifted retention time is an isomer.
Deamidation via the succinimide intermediate is well characterised, with sequence-dependent rates highest for asparagine-glycine motifs.
The caveat is that none of these pathways can be seen by looking at a vial, and a clear solution can be substantially degraded.
Cold, dry, dark, still. Those four words cover most of the mitigation.
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsThe relevant point is that a mass shift of plus one dalton is deamidation and plus sixteen is oxidation, so degradation is often visible in a mass spectrum if anyone looks.
Light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.
Oxidation targets methionine, cysteine and tryptophan, adding sixteen daltons per oxygen. It is catalysed by trace metals and promoted by dissolved oxygen and by light.
Swirl, never shake. Aggregation is a handling problem more than a time problem.
Start with the sequence, because which pathways are available depends on which residues are present.
Deamidation converts asparagine or glutamine to the corresponding acid via a succinimide intermediate, adding one dalton. It is base-catalysed, accelerates above neutral pH and is the dominant aqueous pathway for many peptides.
Aggregation is physical: peptides unfold at air-liquid interfaces and associate. Shaking maximises that interface, which is why swirling and shaking produce visibly different outcomes on the same vial.
Apparent loss in a dilute preparation is usually adsorption rather than degradation and is worth ruling out first.
Sequence decides which pathways are even available. Check the residues.
Aggregation is a physical process and is the one most often caused by handling rather than by time.
Adsorption onto glass and plastic is significant at low concentrations — micrograms per millilitre — and negligible at milligrams per millilitre. It is the usual explanation for an apparent loss in a dilute preparation.
Sequence determines which pathways apply, so general statements are general.
A mass spectrum names the pathway. Plus one, plus sixteen, minus eighteen.
The short version: water enables most of it, oxygen enables oxidation, surfaces enable adsorption, and agitation enables aggregation.
Freeze-thaw cycling drives aggregation through concentration at the ice interface and pH shifts as buffer components crystallise out at different rates. Each cycle costs something.
At dilute concentrations, suspect adsorption before you suspect chemistry.
edited 8 Oct 2025 by deamidation_watch — removed a claim I could not source
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