How long does a reconstituted peptide stay usable?
It depends on the peptide and the diluent. Without data for the compound, a commonly used conservative rule for an opened multi-dose vial is 28 days refrigerated at 2–8 °C (USP General Chapter <797> (as summarised by the Minnesota Department of Health)). Treat that as an upper limit, not a target.
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Keeping it stable
Store the solution at 2–8 °C, shielded from light, and do not freeze and thaw it again and again. A solution made with bacteriostatic water, which contains a preservative, stays usable for longer than one made with plain sterile water.
Signs it should be thrown away
Throw the solution out if it turns cloudy, changes colour or contains visible particles. Dry lyophilized powder in a sealed vial keeps far longer, frequently 2+ years in the freezer.
Common questions
Can a reconstituted peptide be frozen?
Short-term freezing is sometimes mentioned as a way to extend storage, but each freeze-thaw cycle damages peptides. The safer course is to keep the solution refrigerated and stay within the conservative 28-day rule for an opened multi-dose vial.