Peptides are handled in two quite different physical states, and the storage picture is different for each. Treating them as one thing is where most of the confusion starts.
| Lyophilised powder | Reconstituted solution | |
|---|---|---|
| Physical state | Freeze-dried solid | Liquid |
| General stability | Typically the more stable state | Typically less stable |
| Usual storage | Per labelling, often refrigerated | Per labelling, usually refrigerated |
| In-use window | Governed by the expiry date | Counted from first entry |
| Main sensitivities | Moisture, heat, light | Heat, light, temperature cycling, agitation |
Before reconstitution
Lyophilised powder is freeze-dried specifically because removing water improves stability. Its main enemies are moisture, heat, and light. The stopper and the sealed vial handle the first; the other two are down to where it is kept.
- Storage temperature is per the labelling. Refrigeration is common, but some products are specified differently.
- Light exposure is generally minimised, and the carton is usually doing a job, not just carrying branding.
- The expiry date on the vial governs the unopened product.
After reconstitution
Once diluent is added, the vial becomes a liquid with a finite in-use window. Two things typically govern it: the preservative in the diluent, and the stability of the peptide itself in solution. Bacteriostatic water is commonly labelled for up to 28 days from first entry, but that describes the water, not the compound dissolved in it. The peptide has its own characteristics.
The date that matters is first entry, meaning the first time the stopper was punctured. Not the purchase date, not the reconstitution date if those differ, and not the date the box was opened. This is a small distinction that becomes impossible to reconstruct three weeks later, which is exactly why it is worth recording at the time.
Temperature cycling
A vial that goes fridge → bench → fridge → bench, twice a day, experiences considerably more thermal stress than one taken out once and returned once. Repeated cycling is typically treated as more of a concern than a single brief excursion, which is a useful thing to know because the fix is a matter of routine rather than equipment: take the vial out once, do what is needed, put it back.
Freezing
Lyophilised powder is sometimes stored frozen for long-term purposes, per labelling. Reconstituted solution is a different matter. Freezing a solution introduces ice crystal formation and freeze-thaw stress, and it is generally not something done on an ad-hoc basis. Whether either applies to a given product is a labelling question.
Travel
Travel introduces three problems at once: keeping temperature stable, keeping the vial physically intact, and carrying documentation. The general shape of the answer:
- 1Carry-on rather than checked
Hold luggage is neither temperature-controlled nor gently handled, and it is occasionally elsewhere.
- 2Insulated case, not direct ice contact
A medication travel case with a gel pack held away from direct vial contact avoids both heat and an unintended freeze.
- 3Keep the labelling with the product
Original packaging and pharmacy labelling identify what the vial is, which matters at a security checkpoint.
- 4Carry the prescription documentation
Requirements differ by country and are worth checking against the destination before travelling rather than at the airport.
- 5Check the destination rules in advance
Import rules for prescription medicines vary considerably. This is a question for your healthcare professional and the relevant border authority.
What is worth recording
Storage discipline mostly comes down to knowing the dates. Four are typically useful: the date the vial was reconstituted, the date of first entry, the diluent volume added, and the manufacturer expiry. The first three are things only you know, and none of them are reconstructable later.
