Shelf life after reconstitution

Why it changes so sharply

Water is a reagent in hydrolysis and deamidation, and solution allows molecules to encounter one another and aggregate. Both routes were suppressed in the dry state and both resume immediately on dissolution.

What governs the window

• Temperature: refrigerated solution lasts considerably longer than one at room temperature
• Solvent: preserved versus unpreserved changes the microbiological limit, not the chemical one
• pH: sets which degradation routes dominate
• Concentration: higher concentrations aggregate more readily
• Number of entries: each admits air and possible contamination

Two different limits

There is a chemical limit — how long the peptide remains intact — and a microbiological one — how long the solution remains uncontaminated. Bacteriostatic water addresses the second and does nothing for the first. Both apply, and the shorter one governs.

Practical consequence

This is why material is supplied dry and reconstituted when needed, rather than reconstituted on receipt for convenience.