Why there is no standard number
Once a peptide is dissolved, the reactions that break it down can run faster than in dry powder. How fast depends on its sequence, the pH, the concentration, what else is in the liquid and the temperature. Two peptides in the same fridge can behave very differently.
For this reason ICH guidance says the stability of a freeze-dried product after reconstitution must be demonstrated for the conditions and the maximum storage period that are stated for it. A shelf life is a measured result, not a rule of thumb.
Chemical and physical changes
In solution, peptides can deamidate, oxidise or break at weak bonds. They can also aggregate, where molecules clump together. Concentration, pH, temperature, agitation and contact with surfaces all affect aggregation.
Opening the container matters too
Each time a container is opened, there is a chance of contamination. EMA guidance on in-use stability testing covers exactly this: it asks for tests of physical, chemical and microbial quality over the period a multidose container is in use, including any reconstitution step.
Even sterile, preserved liquids carry a caution: one manufacturer's bacteriostatic water labelling says that anything dissolved in it should be mixed thoroughly and used promptly.
Where to look
For a licensed product, the in-use storage period is on its labelling. Research peptides are for laboratory research only and are not approved medicines, so the only guide is stability data from the manufacturer or the lab for that specific compound. A day count without such data behind it should not be relied on.
Educational information only. Nothing here is medical advice, dosing guidance or a recommendation to use any substance. Research peptides are not approved medicines and are not for human or animal consumption. Speak to a qualified professional and follow the law where you are.
