How many freeze-thaw cycles will tirzepatide at 10 mg/mL tolerate?

For reference: tirzepatide · 10 mg/mL.

I have read the obvious sources and they disagree with each other, so I would rather ask people who have actually done this.

I have a working setup and a notebook, and I am prepared to be told that my setup is inadequate if that is the answer.

So: what is the actual procedure, and which steps matter as opposed to being ritual?

In practice, thawing at room temperature rather than in warm water reduces the interfacial stress.

Buffer salts crystallise at different points during freezing. Sodium phosphate is the classic example: the dibasic form crystallises first and the pH of the residual liquid falls by several units. That pH excursion is the real damage in many cases.

Count cycles rather than worrying about degrees. Minus twenty and minus eighty differ far less than one cycle and five do.

The caveat is that aggregation is invisible in a clear solution below the threshold where it becomes visible.

Dry powder tolerates cycles far better than solution does.

Answering this needs to know whether the material is dry or in solution, since a dry powder is largely indifferent to a temperature cycle.

During freezing, solutes are excluded from the ice lattice and concentrate into the residual liquid. Local concentrations can rise many-fold, which promotes aggregation independently of temperature.

The part that matters: let a frozen vial reach room temperature before opening it. Opening a cold vial in humid air condenses water into the cake, which raises residual moisture and undoes what lyophilisation achieved.

Condensation onto cold lyophilised material on opening is a recognised handling error and is the basis for the equilibrate-before-opening rule.

Aliquot before the first freeze. That is the whole answer.

Buffer components crystallise at different rates during freezing, which shifts pH locally by a surprising amount.

A dry lyophilised powder is much less affected by a temperature cycle because there is no liquid phase for anything to concentrate into. Condensation on a cold vial opened warm is the real risk there.

Aliquoting to eliminate repeated cycles is standard laboratory practice for exactly this reason.

Count cycles, not degrees. The cycle is the damaging event.

edited 23 May 2024 by coldpack_88 — added the placebo-arm figures

The relevant physics is ice-front concentration: as water crystallises, everything dissolved is concentrated into the shrinking liquid phase, including buffer salts.

Thaw slowly at room temperature or in the refrigerator rather than in warm water. Rapid warming creates local thermal and concentration gradients that promote aggregation.

Aliquoting itself is a handling step and introduces its own contamination opportunity.

Let a frozen vial reach room temperature before opening, or you condense water into it.