Reconstitution

Also known as: recon · mixing

Reconstitution is dissolving a freeze-dried (lyophilized) powder in a measured volume of liquid to make a solution of known concentration for injection.

Many peptides are shipped as a dry, freeze-dried powder because they are more stable that way. Before use, you add a measured volume of a sterile diluent, most often bacteriostatic water, to the vial and let the powder dissolve. The volume you add sets the concentration of the solution, and the concentration sets how much liquid holds each dose.

Approved peptide labels show the expected technique. The EGRIFTA WR (tesamorelin) instructions, for example, say to clean the vial tops with alcohol swabs, inject the diluent into the vial, move the vial in a circle to mix, not shake it, let any foam settle, and use the solution only if it is clear and free of particles.

Why it matters

Reconstitution sets up every dose that follows. If you add a different volume of water than the one your dose math assumes, every dose from that vial is off by the same ratio. Writing down the vial mass and water volume, and calculating the concentration once, prevents that.

It is also the point where a stable powder becomes a less stable solution. The BAC water label says reconstituted solutions should not be stored unless the drug's manufacturer says they can be, and approved products set their own in-use limits after mixing. For most research peptides no such limit has been tested, so mix only what you will use in a reasonable time. It helps to pick a water volume that makes your usual dose a whole number of units on your syringe, and to use the same volume for every vial.

How to calculate it

Note the vial's labeled mass (mg) and decide how much diluent (mL) you will add.
Wash your hands and wipe the vial stoppers with alcohol swabs.
With a new sterile syringe, draw the planned volume of bacteriostatic water and add it to the peptide vial.
Swirl gently until dissolved; do not shake. Let any foam settle.
Inspect the solution: use it only if clear and free of particles.
Label the vial with the concentration and the date you mixed it.

Concentration (mcg/mL) = vial mg × 1000 ÷ mL of water added

Worked example

A 5 mg vial plus 2 mL of bacteriostatic water: 5 × 1000 ÷ 2 = 2500 mcg/mL. A 250 mcg dose is 250 ÷ 2500 × 100 = 10 units on a U-100 syringe (0.10 mL). Check: 0.10 mL × 2500 mcg/mL = 250 mcg.

Common mistakes

Adding a different water volume from the one your dose math uses.
Shaking the vial hard instead of swirling gently.
Using the solution when it is cloudy, discolored or has particles.
Not labeling the vial with concentration and mix date.
Mixing several vials at once that will sit for long periods with no stability data.

Sources

Prescribing informationEGRIFTA WR (tesamorelin) for injection - prescribing information and instructions for use. DailyMed, U.S. National Library of Medicine, 2025.
Prescribing informationBacteriostatic Water for Injection, USP (Hospira) - prescribing information. DailyMed, U.S. National Library of Medicine, 2019.
ReviewLyophilization and development of solid protein pharmaceuticals. Int J Pharm, 2000. PMID 10967427.

Page updated October 3, 2026. How we grade evidence: methodology.

Related Terms

BAC Water

Bacteriostatic water (BAC water) is sterile water for injection with 0.9% benzyl alcohol added as a preservative, used to dissolve drugs for injection.

Concentration (mcg/mL)

Concentration (mcg/mL) is how many micrograms of peptide are in each milliliter of solution; it converts a dose by weight into a volume to draw.

Units (Insulin Syringe)

Units on an insulin syringe are volume markings; on a U-100 syringe, 1 unit = 0.01 mL and 100 units = 1 mL. They are not a dose by themselves.

Drawing Dose

Drawing a dose means pulling a measured volume of solution from a vial into a syringe, removing air bubbles, and setting it to the exact mark.

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