Does aggregation dominate for cagrilintide held at 30 °C?

Stated plainly: aggregation · cagrilintide · 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.

Is the standard explanation correct, and if so, what is the evidence for it?

The honest answer is that published stability data for these specific molecules in a research-grade presentation essentially does not exist, so what you get is extrapolation from the licensed formulations and from general peptide chemistry. That extrapolation is reasonable. It is still extrapolation.

The temperature dependence is roughly Arrhenius over the range that matters, which in practice means every ten degrees of increase roughly doubles to triples the rate. Ten days at thirty degrees is therefore comparable to something on the order of a month or two at four degrees — bad, but not the catastrophe it feels like when you open a warm parcel.

In practice, on re-freezing something that thawed in transit: if it arrived as a lyophilised solid that warmed but never got wet, re-freezing costs you nothing except the thermal cycle. If it arrived as a solution that thawed, re-freezing adds a second transition and therefore a second dose of ice-front shear. The asymmetry is worth internalising.

Minimise transitions rather than minimising temperature. One freeze and one thaw is fine; five is a different question.

The relevant detail is that freeze-thaw damage happens at the moving ice front, not at the storage temperature. Once the sample is frozen solid and cold, very little is happening. The damage is done during freezing and thawing, which is why the number of cycles matters and the duration of the hold mostly does not.

For the solid state, residual moisture is the dominant variable. A cake at two per cent water is considerably more stable than the same cake at six per cent, because water is both a reactant in hydrolysis and a plasticiser that lowers the glass transition temperature. This is why a desiccant in the outer packaging is not theatre, and why opening a cold vial in a humid room is a genuine error — you condense water onto the cake.

The 28-day figure for a reconstituted preserved vial is microbiological, not chemical. Chemically, a well-behaved peptide at 5 mg/mL at 4 °C will typically lose well under a per cent of content per month. The reason to respect the date is bioburden, and bioburden is a function of how many times you have opened it, not of the calendar.

Where community-submitted samples with known thermal excursions have been tested at Janoshik or Medutest, the recurring finding is that lyophilised material tolerates warm transit far better than intuition suggests, while reconstituted material shipped warm does not. The asymmetry is consistent enough to plan around.

If the material arrived warm and it was lyophilised, test it and proceed on the result. If it arrived warm and it was in solution, the result is more likely to be interesting than reassuring.

edited 15 Sept 2025 by w_okoye — added a caveat about sampling

Put another way, degradation is not one process, and which one dominates depends on the condition you are asking about. In solution at refrigerated temperature the rate-limiting pathway is usually deamidation and hydrolysis; at room temperature aggregation overtakes them; frozen, the damage happens during the transitions rather than during the hold.

Aggregation is the failure mode that reverse-phase HPLC is worst at detecting, because a large soluble aggregate may not elute at all and an insoluble one is filtered out during sample preparation. If your purity result comes back normal but the vial looks hazy, believe the vial. Size-exclusion chromatography is the method that sees this.

Worth stating: research-use-only material has no stability programme behind it at all, so any beyond-use date you apply is your own construct.

Store solid, store cold, store dry, and reconstitute what you will use rather than what fits in the vial.

edited 15 Sept 2025 by lyoph_cake — corrected a unit error in the worked example

The relevant detail is that the lyophilised solid is far more robust than anything anyone says about it, and the solution is far less robust. Most of the confusion in this area comes from advice about one being applied to the other.

Adsorption to the container is a real loss at low concentration. For a peptide at 0.1 mg/mL in an untreated glass vial, single-digit percentage losses to the wall are plausible; at 5 mg/mL it is negligible. This is one of several reasons not to reconstitute to a very dilute working solution and store it.

The licensed semaglutide and tirzepatide presentations carry in-use periods of several weeks at room temperature in their labelling, which is the closest thing to real stability data in this space — and it applies to a buffered, surfactant-containing, preservative-containing formulation, not to a reconstituted research vial.

The practical rule is that time and temperature multiply, so shorten whichever one you control.

edited 1 Oct 2025 by Dr_Nadia_Farsi — expanded the table to cover the lower concentration