How Long Does a Reconstituted Vial Last?

The internet has settled on “28 days” as the answer. It is the wrong answer to this question — it is the right answer to a different one.

The evidence that no single number can be right is not an argument. It is a list. Seven US products that are reconstituted before use publish seven different in-use windows, and they run from use immediately to 60 days.

Where 28 days actually comes from

The manufacturer’s label for bacteriostatic water contains no discard period at all. No 28-day statement, no in-use period, nothing. The 28 days is a USP rule about multiple-dose containers in general: once punctured, such a container must not be used for more than 28 days unless the manufacturer specifies otherwise.

That is a rule about the water bottle. It tells you when to throw away your bacteriostatic water, and approved patient labelling repeats it in exactly that context — the tesamorelin patient instructions say to throw away any bacteriostatic water left in the bottle 28 days after first use.

It does not tell you how long your reconstituted drug is good for.

What approved labels say after reconstitution

These are the products that actually ship as a powder and tell you what to do with the solution once you have made it. Every figure below is from the product’s own FDA label.

• Tesamorelin (EGRIFTA SV) — reconstituted with sterile water and used immediately. No in-use period at all.
• Tesamorelin (EGRIFTA WR) — stored at room temperature, 20°C to 25°C (68°F to 77°F), and discarded 7 days after mixing. Do not freeze. Same molecule as EGRIFTA SV, different kit, and the label states the two are not substitutable.
• Somatropin (Genotropin, 5.8 mg and 13.8 mg cartridges) — refrigerated, up to 21 days after reconstitution.
• Somatropin (Genotropin, 5 mg and 12 mg cartridges) — refrigerated, up to 28 days after reconstitution.
• Somatropin (Humatrope cartridges) — up to 28 days refrigerated at 2°C to 8°C (36°F to 46°F), not left at room temperature for more than 30 minutes a day, and not frozen.
• HCG (Novarel) — refrigerate and use within 30 days.
• HCG (Pregnyl, and the Fresenius Kabi generic) — stable 60 days refrigerated.

Read that list twice, because two pairs in it settle the question on their own. Pregnyl and Novarel are the same molecule with 30 days between them. Genotropin disagrees with itself within one brand, giving 28 days to two cartridge sizes and 21 to the others.

Why the answers differ

The in-use window is a property of the finished formulation, not of the peptide. Four things move it, and none of them is visible from the molecule’s name:

• The diluent, and whether it is preserved. Genotropin’s split is the cleanest illustration — the cartridges whose supplied diluent contains a preservative are the ones given the longer window. The preservative-free MINIQUICK is not a multi-day container at all.
• The molecule’s own stability in solution. Lyophilisation exists because many peptides are far more stable dry than wet; how much more varies by peptide.
• Temperature, in whichever direction that product’s data supports. Reconstituted EGRIFTA WR is a room-temperature product with no refrigerated option on the label. Humatrope is the reverse, refrigerated with a 30-minute daily allowance out of the fridge. Cold is not universally the answer.
• The container and how often it is entered. A vial punctured once a day for a month is a different microbiological problem from one entered twice.

The bacteriostatic water label draws the same conclusion from the other direction: do not store reconstituted solutions of drugs for injection unless otherwise directed by the manufacturer of the solute.

The numbers people import from the wrong products

There is a second set of figures in circulation, and they are real label numbers — they just answer a different question. Ozempic, Wegovy, Saxenda and Zepbound are ready-to-use solutions. Nothing is reconstituted. Their in-use windows describe how long a manufactured solution lasts once you start using it:

• Ozempic — after first use, 56 days at controlled room temperature (15°C to 30°C) or refrigerated.
• Saxenda — after initial use, 30 days at controlled room temperature (15°C to 30°C) or refrigerated.
• Wegovy — from 2°C to 8°C, and if needed, prior to cap removal, from 8°C to 30°C for up to 28 days.
• Zepbound — refrigerated at 2°C to 8°C; each single-dose pen or vial may be kept at up to 30°C for a total of 21 days.

Four more numbers, four more disagreements, and none of them about a reconstituted solution. This is the most common version of the mistake: the figure sounds authoritative, and it is authoritative — for a product that is not the one in your hand.

USP <797> does not apply to you at home

People cite USP <797> beyond-use dating tables as though they set home storage limits. They do not. <797> states that compounding does not include mixing or reconstituting performed in accordance with directions in approved labelling, and that when preparing a product per approved labelling, the labelling must be followed.

So for an approved product, the label is the authority. For a product with no approved label at all — which is most of what gets reconstituted at home — there is no authority, and no honest source can give you a number.

What this leaves for a compounded vial

Nothing, and that is the finding rather than an evasion. An in-use window is an output of a stability programme: samples held at defined temperatures, assayed at intervals, against a specification. Compounded and grey-market peptide vials have no such programme behind them, so there is no window to publish — not 28 days, not 30, not any number.

The practical position that follows is unglamorous but honest. You cannot look up a shelf life for that vial, because one has never been measured. What you can do is stop treating a number borrowed from a different product as though it were one.

The question the calculator can answer

What it can tell you is whether your discard date arrives before you finish the vial. That depends only on your dose, your vial size and how often you inject, and it is arithmetic.

A 10 mg vial at 2 mg per dose gives five doses. Once weekly, that is five weeks of supply — but a 28-day window closes at four. You would be discarding a dose you paid for. Injecting twice weekly, the vial finishes in under three weeks and nothing is wasted.

Every competing calculator we looked at stops at the dose count. Ours puts it on a calendar, shows both dates, and tells you how many doses the discard date costs you — and folds that into cost per dose, since doses you throw away still cost money.

The per-drug figures above are also on the individual calculator pages, where each one sits next to the label it came from: tesamorelin, somatropin, HCG, tirzepatide and semaglutide.