Stated plainly: dulaglutide · eight weeks · 30 °C.
I keep seeing this stated as a fact with no explanation attached, and unexplained facts make me suspicious.
My background is quantitative but not chemical, so I can follow an equation more easily than a hand-wave.
Why does this happen, and what would falsify the usual explanation?
eight weeks is 56 days, which at 30 °C is on the order of 317 refrigerated days. 30 °C is 25 kelvin above the 5 °C middle of a 2–8 °C refrigerator. The ten-degree rule of thumb — degradation rate roughly doubling per 10 K — makes that about 5.7 times the refrigerated rate, which is an order-of-magnitude statement and not a shelf life. In solution the routes that matter are hydrolysis of the backbone, deamidation at Asn, and physical association — the first two cost content, the third costs neither until it precipitates. Over 56 days at 30 °C you should expect all three to have moved, and a purity figure to have noticed only some of them. Reconstituted material has no certificate; the one in the box describes the powder.
Start with the sequence, because which pathways are available depends on which residues are present.
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.
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.
Swirl, never shake. Aggregation is a handling problem more than a time problem.
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Browse resultsIt helps to be literal here: asparagine and glutamine are the deamidation risk, and methionine is the oxidation risk.
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.
Sequence decides which pathways are even available. Check the residues.
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.
Worth being precise here: 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.
At dilute concentrations, suspect adsorption before you suspect chemistry.
edited 22 Nov 2025 by aine_mulcahy — reworded for clarity after a comment
Mechanically, this is answerable from the chemistry rather than from anecdote, which is unusual and welcome.
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.
Nothing here is medical advice, and research-use compounds are not approved for human use.
Cold, dry, dark, still. Those four words cover most of the mitigation.
Answering this needs the physical state, since a dry powder is protected from most of these and a solution is protected from none.
Light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.
Adsorption losses at low concentrations are quantified in formulation studies and are the reason carrier proteins are used in dilute preparations.
A mass spectrum names the pathway. Plus one, plus sixteen, minus eighteen.
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