How long does a reconstituted peptide vial last in the fridge?

Where does the 28-day number come from?

From infection control, not from chemistry. The CDC's injection safety guidance states that once a multi-dose vial is opened, meaning needle-punctured, it should be dated and discarded within 28 days unless the manufacturer states another date for that opened vial, and that the beyond-use date should never exceed the manufacturer's original expiration date. The CDC cites USP General Chapter 797 as the source of the 28-day figure.¹

That rule is about the container. It limits how long a vial that has been entered with a needle may keep being entered, on the grounds that each puncture is a chance for contamination. It says nothing about whether the molecule dissolved inside is still intact on day 27.

The bacteriostatic water label points the same way. Bacteriostatic Water for Injection contains 0.9% benzyl alcohol, added as a bacteriostatic preservative, and is supplied in a multiple-dose container from which repeated withdrawals may be made. The same label says: do not store reconstituted solutions of drugs for injection unless otherwise directed by the manufacturer of the solute.² In other words, the water's own label hands the storage question back to the peptide.

What do real peptide labels say?

Three FDA-approved products, all freeze-dried peptides that are reconstituted before use, give three different answers.

• Genotropin (somatropin), reconstituted with a diluent that contains the preservative m-cresol: store under refrigeration at 2 to 8 degrees C between uses for up to 28 days, and discard the cartridge and any unused medication after 28 days. The same product's preservative-free MiniQuick presentation may be refrigerated for up to 24 hours before use and is used once and discarded.³
• Humatrope (somatropin), reconstituted with its supplied preservative-containing diluent: reconstituted cartridges are stable for up to 28 days when refrigerated at 2 to 8 degrees C.⁴
• Egrifta SV (tesamorelin), reconstituted with Sterile Water for Injection: administer immediately following reconstitution and throw away any unused solution, and do not freeze or refrigerate the reconstituted solution.⁵

Same category of product, answers from "now" to "four weeks". The difference tracks two things: what the manufacturer tested, and whether the diluent carries a preservative. The products that allow 28 days are the ones whose diluent contains one, and the preservative-free presentations collapse to 24 hours or to immediate use.³⁵

Bacteriostatic versus sterile water: what changes?

Only one thing, but it matters. Bacteriostatic water carries benzyl alcohol to inhibit microbial growth in a container that will be entered more than once.² Sterile water for injection carries no preservative, which is why the labels that pair a peptide with sterile water also say to use the solution at once.⁵

The preservative is also the reason the bacteriostatic water label warns that benzyl alcohol has been associated with toxicity in neonates and states, in capitals, that the product is not for use in neonates.² It is a preservative with a safety profile of its own, not a neutral ingredient.

Neither water changes how much peptide is in the vial. The volume you add sets only the concentration, which is the arithmetic the bacteriostatic water page and the reconstitution page work through.

What about compounded and research-labelled vials?

A compounded product carries a beyond-use date assigned by the pharmacy that made it, and the CDC's rule that a beyond-use date never exceeds the manufacturer's expiration date applies to it as much as to anything else.¹ That printed date is the answer for that vial, and no figure from a forum overrides it.

A vial sold as research-labelled has no human-use label at all, so it has no tested beyond-use date either. The CDC's multi-dose vial guidance is written for labelled medications,¹ not for products that carry no label, so it supplies no validated storage or reuse period for them, and nothing published tells you how stable that particular peptide is in solution. Anyone who gives you a confident number for it is guessing.

How does Protocol Her handle the date?

The app records the date you reconstituted a vial and seeds a discard reminder 28 days later. That default is the container convention described above, not a stability claim, and the sheet says so in its own words: many people set this around 28 days after reconstituting, refrigerated, and you should set the date that fits your vial, which you can change at any time. The date picker sits right there, so a 24-hour product or a pharmacy's beyond-use date is a one-tap edit.

Three days before the date you set, the app sends a reminder whose text reads "Your vial discard reminder is in 3 days" and names no compound. Once the date passes, the vial shows as past your discard date, never as expired or unsafe, because the app has no basis to assert either. Pens are tracked separately, with no reconstitution date, since there is nothing to reconstitute.