Collapsed lyophilized cake: RETA-3 20mg

In a normal lyophilized vial the dried peptide sits as a puck, a solid cake that covers the bottom of the vial. During one lyophilization run, the cake in a RETA-3 20mg vial pulled in on itself and ended up as a small, dense piece about the size of a pencil eraser.

A collapsed cake looks wrong, and we wanted to know if it was more than cosmetic. Collapse can sometimes come with leftover moisture or a loss of material, so before calling it a looks-only issue we sent vials from that run out for a full panel.

The chromatogram shows a single clean peak with nothing else beside it.

Cake collapse is a known event in freeze-drying. It changes the physical structure of the dried cake, not the molecule. Common reasons:

• Drying ran warmer than the formulation can hold. Every formulation has a collapse temperature. If the product goes above it during primary drying, while ice is still being removed, the structure softens and falls in on itself.
• Low solids in the vial. A peptide fill with little or no bulking agent makes a light, delicate cake. There's less to hold its shape, so it shrinks more easily as it dries.
• Position on the shelf. Vials near the edges of a shelf usually run warmer than the ones in the middle. That's why collapse tends to show up in some vials from a run and not others.
• Moisture after the cycle. A vial that picks up moisture after drying, from a stopper that didn't fully seat or from exposure before capping, can see the cake shrink down.

The shrinkage was physical. Net content came in at 20.44 mg, both vials tested above 99.8% purity, and the endotoxin, microbial, metals and fentanyl screens all passed. The collapsed cake didn't reduce the amount of peptide or its purity.

Residual moisture (Karl Fischer) wasn't part of this panel. A dense, collapsed cake can also take a little longer to dissolve than a normal one. Add the diluent slowly down the side of the vial and swirl gently rather than shaking.