What I am working with: dulaglutide · 8 mg/mL · sixteen weeks.
This is asserted often enough that I assumed it was established, and then I went looking for the source.
I have searched the primary literature and found one paper that is adjacent but not on point.
Has anyone verified this independently?
sixteen weeks is 112 days and, on a weekly schedule, 16 stopper punctures out of one vial at 8 mg/mL. Set the chemical question aside for a moment, because the puncture count is the one with a convention attached: 112 days is 4 times the twenty-eight days conventionally allowed for a preserved multi-dose preparation once it has been entered. Chemically, 8 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 16 withdrawals do add is 16 opportunities to introduce air, 16 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.
To be exact about it, asparagine and glutamine are the deamidation risk, and methionine is the oxidation risk.
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.
| State | Condition | Usable window | Basis |
|---|---|---|---|
| Lyophilised solid | −20 °C, sealed, dry | 24–36 months | Supplier guidance |
| Lyophilised solid | 2–8 °C, sealed | 12–24 months | Supplier guidance |
| Lyophilised solid | 25 °C, sealed | 4–8 weeks | Extrapolated (Arrhenius) |
| Lyophilised solid | 40 °C, sealed | 1–2 weeks | Extrapolated |
| Solution, preserved | 2–8 °C | 28 days | USP microbiological convention |
| Solution, preserved | 25 °C | 3–7 days | Extrapolated |
| Solution, unpreserved | 2–8 °C | 24 hours | USP microbiological convention |
Windows for the solid state are chemical; windows for solution are microbiological and usually shorter than the chemical limit.
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.
Metal-catalysed oxidation of methionine is documented across peptide and protein formulations and is why chelators appear in some formulations.
Nothing here is medical advice, and research-use compounds are not approved for human use.
At dilute concentrations, suspect adsorption before you suspect chemistry.
Analytical standards and reagents with traceable certificates. Every quantitative result you read inherits the accuracy of the standard behind it.
Shop standardsAnswering this needs the physical state, since a dry powder is protected from most of these and a solution is protected from none.
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.
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.
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.
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.
Specifically, 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.
Aggregation at air-liquid interfaces is established from surface-tension and particle-count studies and is the basis for anti-agitation handling guidance.
The caveat is that none of these pathways can be seen by looking at a vial, and a clear solution can be substantially degraded.
Sequence decides which pathways are even available. Check the residues.
This is answerable from the chemistry rather than from anecdote, which is unusual and welcome.
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.
Cold, dry, dark, still. Those four words cover most of the mitigation.
Aggregation is a physical process and is the one most often caused by handling rather than by time.
Light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.
Swirl, never shake. Aggregation is a handling problem more than a time problem.
edited 9 Sept 2025 by deamidation_watch — removed a claim I could not source
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