Is liraglutide at 2.5 mg/mL stable enough for twelve weeks of multi-withdrawal use?

For reference: liraglutide · 2.5 mg/mL · twelve weeks.

I would like to know whether this claim survives contact with evidence.

If the answer is "nobody has tested that", I would like that stated so I can stop looking.

Is this actually true, and what is the evidence?

twelve weeks is 84 days and, on a weekly schedule, 12 stopper punctures out of one vial at 2.5 mg/mL. Set the chemical question aside for a moment, because the puncture count is the one with a convention attached: 84 days is 3 times the twenty-eight days conventionally allowed for a preserved multi-dose preparation once it has been entered. Chemically, 2.5 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 12 withdrawals do add is 12 opportunities to introduce air, 12 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.

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

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

Stated carefully, 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.

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

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.

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.

Mechanically, 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.

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

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.

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.

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.

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

edited 12 Apr 2025 by tare_and_weigh — removed a claim I could not source

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.

Adsorption losses at low concentrations are quantified in formulation studies and are the reason carrier proteins are used in dilute preparations.

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

The short version: water enables most of it, oxygen enables oxidation, surfaces enable adsorption, and agitation enables aggregation.

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.

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

At dilute concentrations, suspect adsorption before you suspect chemistry.