How to reconstitute peptides, step by step

To reconstitute a peptide, you add a measured amount of sterile liquid (usually bacteriostatic water) to the powder in the vial, let it dissolve with a gentle swirl rather than a shake, and label the vial with its new concentration. The amount of water never changes how much peptide is in the vial; it only sets how concentrated the liquid is, and so how many units you draw on a U-100 insulin syringe. The peptide calculator does that math for your vial, your water and your prescribed dose.

What “reconstitute” means

Many peptides are supplied as a freeze-dried (lyophilized) powder because freeze-drying significantly improves their storage stability; in water they’re only marginally stable (Izutsu, 2018). Reconstituting means dissolving that powder back into a liquid you can draw into a syringe.

People often ask about reconstitution vs dilution. Reconstitution turns a dry powder into a liquid. Dilution adds more liquid to something that’s already a liquid. The math is the same idea in both cases: the drug amount stays fixed while the volume changes.

What you need

• The peptide vial, with its label showing the amount in mg.
• The diluent named on your label or by your pharmacist. This is often bacteriostatic water, but not always.
• A new, sterile syringe and needle for mixing. Some prescription kits include a larger syringe just for this: the Egrifta WR kit uses a 3 mL syringe for mixing and separate syringes for injecting.
• Alcohol swabs, a pen or label, and a sharps container.

How to reconstitute a vial

These steps follow the patient instructions in MedlinePlus and the FDA-approved instructions for Egrifta WR, a peptide medicine that is mixed at home.

1. Prepare a clean space

   Clear and wipe a flat surface. Wash your hands well with soap and water and dry them.

2. Check both vials

   Read both labels and their expiry dates. Don’t use anything out of date. Look at the powder: if it’s discolored or has particles in it, don’t use it and call your pharmacy.

3. Clean the stoppers

   Remove the plastic caps. Wipe each rubber stopper with a fresh alcohol swab and let it air-dry. Don’t touch the stoppers afterward.

4. Draw the water

   Take a new syringe. Pull the plunger back to the amount of water your label or pharmacist specifies, which fills the syringe with air. Push the needle into the water vial, inject that air (this stops a vacuum forming), turn the vial upside down and draw the water. Tap out large bubbles and check the amount again.

5. Add it slowly, down the side

   Push the needle through the peptide vial’s stopper and let the water run slowly down the inside wall of the glass. Serostim’s label says to aim the stream at the vial wall “to prevent foaming”.

6. Swirl, don’t shake

   Gently swirl or roll the vial until the powder has dissolved. Both the Egrifta WR and Serostim labels say not to shake. If there’s foam, let the vial rest for a few seconds.

7. Inspect the liquid

   It should be clear, with no particles. If it stays cloudy, discolored or has bits in it, don’t use it; call the pharmacist who dispensed it.

8. Label and store it

   Write the date you mixed it and its concentration on the vial, for example “5 mg/mL, mixed Nov 3”. Then store it exactly as the label says (see how to store peptides).

9. Dispose of the mixing syringe

   Put the used syringe and needle straight into a sharps container. Never reuse or share needles or syringes. The CDC’s rule is “One Needle, One Syringe, Only One Time” (CDC).

The math, worked through

Here is a worked example. The numbers are for illustration only and are not a dose.

A vial contains 10 mg. You add 2 mL of water.

• Concentration: 10 mg ÷ 2 mL = 5 mg/mL
• Each unit is 0.01 mL, so each unit holds 5 × 0.01 = 0.05 mg (50 mcg)
• If your prescriber’s amount is 0.5 mg: 0.5 ÷ 5 = 0.1 mL = 10 units

Change only the water and the units change too:

More water gives bigger unit numbers, which are easier to measure, but more liquid per injection. Some numbers, like 12.5 units, fall between the lines on a syringe; see how to read an insulin syringe. The reconstitution calculator does this math for any vial, and the bac water calculator shows how a volume relates to the units each dose reads. Use the volume on your label or from your pharmacist.

Common mistakes

• Shaking the vial. Labels for reconstituted peptide medicines say to swirl, not shake.
• Mixing up units and milligrams. “Units” on an insulin syringe measure volume, not drug. The FDA has received reports of people drawing 5 to 20 times their intended amount after confusing mL, mg and units (FDA).
• Not writing the concentration down. Weeks later, nobody remembers whether it was 1 mL or 2 mL.
• Reusing a needle or syringe, even your own, even “just for mixing”.
• Adding more water than the vial holds. See how much water a vial can hold.
• Injecting too much air into the vial. MedlinePlus notes that too much air can force liquid back out of the syringe.

Questions people ask