Peptide Reconstitution and Storage: What FDA Labels Say

Search for how to reconstitute a lyophilized peptide and you will find a consistent set of rules: use bacteriostatic water, aim for the vial wall, swirl rather than shake, refrigerate, use within 28 days. Some of that is right some of the time. None of it is universally right, and the reason is easy to demonstrate: the same drug substance, tesamorelin, ships in two FDA-approved products whose labels give completely opposite instructions on the diluent, the storage temperature and the beyond-use date.

This article reads seven current FDA labels and reports exactly what each one specifies. It is not a how-to and not a protocol. It contains arithmetic — division, performed on numbers that labels printed, and checked against volumes those same labels independently state — and it contains no suggestion of what any dose should be. That distinction is the whole design of this page and of our reconstitution calculator: the calculator divides a dose by a concentration, and both numbers have to come from somewhere else.

The same molecule, two opposite sets of instructions

Tesamorelin is the cleanest possible demonstration, because both products are the same peptide from the same sponsor.

EGRIFTA SV. Section 2.2 of its label instructs: "Use only the diluent provided, Sterile Water for Injection, to reconstitute EGRIFTA SV. Reconstitute 1 vial of EGRIFTA SV lyophilized powder with 0.5 mL of diluent (2 mg per 0.5 mL). Mix by rolling the vial gently in your hands for 30 seconds. Do not shake." Then the part that matters most: "Administer 0.35 mL of EGRIFTA SV immediately following reconstitution and throw away any unused solution and diluent. If not used immediately, discard the reconstituted solution. Do not freeze or refrigerate the reconstituted solution¹."

EGRIFTA WR. Section 2.2 of its label instructs: "Use only the diluent provided, Bacteriostatic Water for Injection, to reconstitute EGRIFTA WR. Reconstitute 1 vial of EGRIFTA WR lyophilized powder with 1.3 mL of diluent (8 mg per mL). Move the vial in a circle (swirl) to mix all the powder and liquid. Do not shake." And: "One reconstituted EGRIFTA WR vial provides daily doses for 7 consecutive days... Store reconstituted EGRIFTA WR at room temperature at 20°C to 25°C (68°F to 77°F). Discard unused solution of EGRIFTA WR 7 days after mixing. Do not freeze²."

Line those up. One product forbids refrigerating the reconstituted solution and requires immediate use; the other specifies room-temperature storage for a week. One uses sterile water, the other bacteriostatic water. One reconstitutes to 4 mg/mL, the other to 8 mg/mL. Both are tesamorelin. Any rule general enough to cover both is too general to be useful, and any rule specific enough to be useful is wrong about one of them.

The diluent carries the beyond-use date, not the drug

The tesamorelin pair suggests it. A single somatropin label proves it, because it makes both choices for the same product line.

Serostim's section 2.2 gives two separate instructions depending on vial size, and the difference is entirely the diluent: "Reconstitute SEROSTIM 5 mg vial or 6 mg vial with 0.5 mL to 1 mL of diluent, Sterile Water for Injection. Use the reconstituted solution immediately and use only one dose per vial for one patient. Discard any unused portion." Versus: "Reconstitute SEROSTIM 4 mg vial with 0.5 mL to 1 mL of diluent, Bacteriostatic Water for Injection with 0.9% benzyl alcohol as a preservative... SEROSTIM 4 mg vial reconstituted with Bacteriostatic Water for Injection with 0.9% benzyl alcohol as preservative may be refrigerated at 2°C to 8°C (36°F to 46°F) for up to 14 days³."

Same molecule, same label, same page — and one gets zero hours while the other gets fourteen days, because one has an antimicrobial preservative in it and the other does not. The label then makes the causal relationship explicit by reversing it: if the patient has a known hypersensitivity to benzyl alcohol, or is pregnant or lactating, the instruction is to "instead reconstitute with Sterile Water for Injection and use only one dose per vial³." Change the diluent and the beyond-use date changes with it, on the same drug, for the same patient.

That is the actual rule underneath all the folk guidance about 28 days: a beyond-use date is a property of the preserved container system, not of the peptide dissolved in it.

What bacteriostatic water actually is, per its own label

Since the diluent is doing this much work, its own label is worth reading rather than assuming.

Bacteriostatic Water for Injection, USP is "a sterile, nonpyrogenic preparation of water for injection containing 0.9% (9 mg/mL) or 1.1% (11 mg/mL) of benzyl alcohol added as a bacteriostatic preservative... supplied in a multiple-dose container from which repeated withdrawals may be made to dilute or dissolve drugs for injection⁴." Two things there catch people out. It is not one product — the benzyl alcohol concentration differs by package, 9 mg/mL in the 30 mL plastic vial and 11 mg/mL in the 20 mL glass vial on the label reviewed here. And the multiple-dose designation is the whole reason it exists.

The label carries a warning in its display panel and its warnings section: "WARNING: NOT FOR USE IN NEONATES." Its contraindications section states: "Due to the potential toxicity of benzyl alcohol in neonates, solutions containing benzyl alcohol must not be used in this patient population. Parenteral preparations with benzyl alcohol should not be used for fluid replacement. Parenteral preparations containing benzyl alcohol should not be used in epidural or spinal anesthesia procedures⁴."

And then the sentence that settles the entire "which diluent should I use" question at the level of principle: "Consult the manufacturer's instructions for choice of vehicle, appropriate dilution or volume for dissolving⁴." The diluent's own label defers to the drug's label. So does this article. Our full page on bacteriostatic water covers the diluent itself in depth, and our generic reconstitution walkthrough covers the mechanics.

Other diluents, and instructions that contradict each other

Sterile water and bacteriostatic water are not the only options on real labels, and the handling instructions are not consistent even in direction.

Sodium chloride, and shake vigorously. ChiRhoStim (human secretin) is a lyophilized peptide reconstituted with saline, and its instruction is the opposite of tesamorelin's: "Dissolve the contents of the ChiRhoStim 16 mcg vial in 8 mL of 0.9% Sodium Chloride Injection, USP, to yield a concentration of 2 mcg/mL. Shake vigorously to ensure dissolution⁵." Anyone who has absorbed "never shake a peptide" as a universal law is contradicted by an FDA label.

Cosyntropin. Cortrosyn's section 2.4: "Aseptically reconstitute the lyophilized powder in the vial using 1 mL of 0.9% Sodium Chloride Injection, USP and gently swirl. After reconstitution, the final concentration of CORTROSYN reconstituted solution is 0.25 mg/mL... If the CORTROSYN reconstituted solution is not used immediately, discard the unused CORTROSYN reconstituted solution⁶." Its storage section adds the reason in one clause: the product "is intended as a single-dose injection and contains no antimicrobial preservative. Any unused portion should be discarded⁶."

Thyrotropin alfa. Thyrogen's section 2.2 is the one label here that specifies a graded beyond-use date rather than a binary one: "Reconstitute each 0.9 mg vial of THYROGEN with 1.2 mL of Sterile Water for Injection, USP to yield a single-dose solution containing 0.9 mg/mL of thyrotropin alfa that delivers 1 mL (0.9 mg). Gently swirl the contents of the vial until all the material is dissolved. Do not shake... The reconstituted THYROGEN solution must be injected within 3 hours unless refrigerated. If necessary, the reconstituted solution can be stored refrigerated at a temperature between 2°C and 8°C (36°F to 46°F) for up to 24 hours, while avoiding microbial contamination⁷." Three hours at room temperature, 24 hours refrigerated, from a sterile-water reconstitution with no preservative at all.

Storage before reconstitution splits just as widely. Both tesamorelin products are stored at 20°C to 25°C in the original box to protect from light¹²; Serostim's cartons are stored at 15°C to 30°C³; Thyrogen is stored refrigerated at 2°C to 8°C in the original carton⁷; Cortrosyn is stored at 20°C to 25°C⁶. There is no default.

The arithmetic, and where the numbers come from

FDA labels do this arithmetic themselves, and one of them writes out the formula. ChiRhoStim's section 2.2 instructs, verbatim: "Total dose (mcg) = patient's weight (kg) x prescribed dose (mcg/kg). Total injection volume (mL) = total dose (mcg) divided by the concentration of the reconstituted solution (2 mcg/mL). Round the total injection volume to the nearest tenth of a mL⁵."

That is the entire operation. Volume equals dose divided by concentration. Note what the label supplies and what it does not: it supplies the concentration, because that is a property of the product and the reconstitution step. The dose is prescribed — the label's own word — and comes from outside the calculation.

Worked on labeled numbers only, each one checked against a figure the same label states independently:

• •EGRIFTA SV. 2 mg in 0.5 mL is 4 mg/mL. The label instructs administering 0.35 mL, and 0.35 mL × 4 mg/mL = 1.4 mg — which is the labeled dose for this product¹. The arithmetic closes.
• •EGRIFTA WR. The label states the reconstituted concentration as 8 mg per mL and one dose as 1.28 mg in 0.16 mL. Check it: 1.28 mg ÷ 8 mg/mL = 0.16 mL, matching exactly. Seven of those doses is 7 × 0.16 mL = 1.12 mL out of the 1.3 mL reconstituted, which is why the label can state that one vial provides daily doses for seven consecutive days².
• •Thyrogen. 0.9 mg in 1.2 mL of diluent is specified by the label as yielding 0.9 mg/mL that delivers 1 mL. And 0.9 mg ÷ 0.9 mg/mL = 1 mL, matching the label's stated delivered volume⁷. The gap between 1.2 mL added and 1 mL delivered is the overfill, and it is exactly why the concentration should be read off the label rather than computed from the volume you injected.

⚠ Every milligram figure above is a number an FDA label printed for an FDA-approved product used in the population that label describes. None of them is transferable to anything else, and none is a suggestion. Our reconstitution calculator performs precisely the division ChiRhoStim's label writes out, on a concentration and a dose the reader supplies — it does not propose either number, and it never will.

Two traps worth naming directly

The population header on a dose-volume table. Cortrosyn's label contains a table pairing doses with reconstituted volumes: 0.125 mg / 0.5 mL, and 0.25 mg / 1 mL. It looks exactly like a general reference table. It is headed "Recommended CORTROSYN Dose for Pediatric Patients," and its two rows are age bands — birth to less than 2 years, and 2 to 17 years. The adult recommended dose sits in a different section entirely⁶. Lifting a volume out of a labeled table without reading which population the table describes is one of the easiest and most consequential errors available on this topic, and it is easy to make precisely because the table is real and the numbers in it are correct.

A compounded vial has no label in this sense. Everything above describes FDA-approved products whose reconstitution volume, resulting concentration, storage temperature and beyond-use date were reviewed and are printed. A compounded lyophilized peptide carries whatever the compounding pharmacy assigned, and a compounded product is not FDA-reviewed for identity, strength or purity before sale. The beyond-use date on such a vial is that pharmacy's number for that preparation — it is not a class rule and it cannot be inferred from a different product's label, including any of the seven above. If you cannot find it, the pharmacy that dispensed it is the only source for it.

For the specific case of tesamorelin, our page on what its label actually specifies for dosing and our page on what its trials reported for safety cover the rest of that label. Our sermorelin provider rankings are the board most readers of this page are comparing, and our sermorelin dosing reference covers a compound with no current FDA label at all — which is the harder version of every question on this page.

The bottom line

There is no universal reconstitution rule, and the clearest proof is that the same peptide, tesamorelin, ships in two FDA-approved products whose labels disagree on the diluent, the storage temperature and the beyond-use date — immediate use with refrigeration forbidden on one, seven days at room temperature on the other. Beyond-use dating tracks the diluent's preservative system rather than the peptide: a single somatropin label gives the sterile-water presentation zero hours and the bacteriostatic-water presentation fourteen refrigerated days. Even "don't shake" is not universal, because one FDA label says shake vigorously. The arithmetic that converts a dose into a volume is simple enough that a label writes it out — volume equals dose divided by concentration — and the number it cannot supply is the dose, which belongs to a prescriber and to the specific vial in front of you.

That same arithmetic is where most GLP-1 dosing errors start, because an insulin syringe reports volume in units rather than in millilitres. Our units-versus-milligrams explainer covers why the branded labels alone carry five different tirzepatide concentrations and three for semaglutide, which is what makes a single unit-to-milligram conversion table impossible rather than merely imprecise.