Is ecnoglutide at 2 mg/mL stable enough for ten weeks of multi-withdrawal use?

Conditions: ecnoglutide · 2 mg/mL · ten weeks.

The claim is plausible, which is exactly why I want to check it.

I am able to read a paper if someone points me at one.

Has anyone verified this independently?

ten weeks is 70 days and, on a weekly schedule, 10 stopper punctures out of one vial at 2 mg/mL. Set the chemical question aside for a moment, because the puncture count is the one with a convention attached: 70 days is 2.5 times the twenty-eight days conventionally allowed for a preserved multi-dose preparation once it has been entered. Chemically, 2 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 10 withdrawals do add is 10 opportunities to introduce air, 10 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.

Answering this needs the physical state, since a dry powder is protected from most of these and a solution is protected from none.

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.

Reported and extrapolated stability by condition

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.

Swirl, never shake. Aggregation is a handling problem more than a time problem.

The 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.

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.

Stated carefully, light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.

Metal-catalysed oxidation of methionine is documented across peptide and protein formulations and is why chelators appear in some formulations.

Sequence decides which pathways are even available. Check the residues.

Stated carefully, asparagine and glutamine are the deamidation risk, and methionine is the oxidation risk.

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.

Specifically, 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.

Nothing here is medical advice, and research-use compounds are not approved for human use.

A mass spectrum names the pathway. Plus one, plus sixteen, minus eighteen.

edited 17 Jul 2024 by coldbox9 — added the citation requested in comments

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.

Deamidation via the succinimide intermediate is well characterised, with sequence-dependent rates highest for asparagine-glycine motifs.

Sequence determines which pathways apply, so general statements are general.

At dilute concentrations, suspect adsorption before you suspect chemistry.

Answer first: the degradation pathways worth knowing are hydrolysis, deamidation, oxidation, aggregation and adsorption, and each has a different trigger and a different mitigation.

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.

Apparent loss in a dilute preparation is usually adsorption rather than degradation and is worth ruling out first.

Cold, dry, dark, still. Those four words cover most of the mitigation.