Reconstitution and storage

A vial arriving cold or at room temperature should be brought to room temperature before it is opened. Opening a cold vial draws moist air onto cold glass, and a lyophilisate is hygroscopic: the water it picks up is water the freeze-drying removed.

Note the batch number on the label before anything else, because after reconstitution the label is the only remaining link between the material and any analysis of the lot it came from.

The solvent goes down the inside wall of the vial rather than directly onto the powder. A peptide film disturbed by a jet of liquid can foam, and foaming is mechanical stress on the molecule.

Swirl, do not shake. Dissolution of a few milligrams is usually a matter of a minute or two at room temperature. If material remains after several minutes, more time or a slightly larger volume is the answer; agitation is not.

Bacteriostatic water - sterile water with 0.9% benzyl alcohol - is used where a sealed vial will be entered more than once, because the benzyl alcohol is what makes repeated entry possible rather than requiring the vial to be discarded after a single withdrawal.

The volume of solvent sets the concentration, and nothing else. The vial holds the mass it holds, regardless of how much liquid is added.

• 5 mg in 1 ml gives 5.00 mg/ml
• 5 mg in 2 ml gives 2.50 mg/ml
• 5 mg in 5 ml gives 1.00 mg/ml

The consequence is at the syringe. A U-100 syringe carries one hundred graduations to the millilitre, so one graduation is 0.01 ml whatever the vial contained. At a high concentration a small mass occupies less than a graduation, and a volume below two graduations cannot be measured out with any confidence - which is an argument for a larger solvent volume, not for a more careful hand.

The peptide calculator does this arithmetic and warns when a volume falls below what a syringe can resolve.

Unopened lyophilisate. −20 °C, protected from light. Lyophilised peptides are stable in transit at room temperature for up to about 30 days, which is why shipments within the union need no cold chain.

After reconstitution. 2-8 °C, protected from light. A solution is far less stable than a powder: hydrolysis and oxidation both need water, and reconstitution supplies it.

In-use period. A vial reconstituted with bacteriostatic water is conventionally treated as usable for 28 days from the first entry. The benzyl alcohol limits bacterial growth; it does not stop chemical degradation of the peptide, and the two are different clocks.

Freeze-thaw. Each cycle costs material. Where a solution will be used over a period, dividing it into single-use volumes at the point of reconstitution avoids repeatedly thawing the whole stock.

• Shaking instead of swirling, and the foam that follows.
• Opening a cold vial and condensing water into the powder.
• Leaving a reconstituted vial at room temperature between uses.
• Sunlight on the bench, for anything light-sensitive.
• Reconstituting the whole vial when a fraction was needed, then freezing and thawing it repeatedly.