How to reconstitute peptides

“Peptide” alone is not enough information to complete a reconstitution record. Record the full product name, form (dry powder, pre-mixed liquid, pen), vial strength or concentration, source, and every visible direction. A lyophilized vial from a 503B pharmacy, a compounded liquid, and a research-labeled material are different products with different instruction sets.

If the product requires reconstitution, the label or accompanying instructions should name the diluent, final volume, and storage conditions. Missing instructions belong with the dispensing pharmacy or clinician, not a generic online recipe.

Bacteriostatic Water for Injection, USP is a sterile water preparation with benzyl alcohol as a preservative. Its label says that the volume used to dilute or dissolve an injectable drug depends on that drug's manufacturer-recommended concentration, dose, and route. Read the DailyMed label.

Not every peptide uses bacteriostatic water. Some require sterile water, normal saline, or a manufacturer-supplied diluent. Using the wrong diluent can affect stability, sterility, or compatibility. Use the diluent type and volume from your product instructions, not a forum post.

For more on bacteriostatic water, what it is, and how long it lasts, see the BAC water guide.

Vial amount

Copy the printed amount and unit exactly. Milligrams, micrograms, and liquid concentration are not interchangeable.

Diluent type

Record the named diluent: bacteriostatic water, sterile water, saline, or other. Do not assume BAC water unless instructions say so.

Liquid volume

Copy the instructed final volume in milliliters. This number sets your concentration.

Storage and dates

Keep the storage conditions, beyond-use date, and in-use instructions. The water label does not set the mixed peptide's discard date.

Open questions

Save the pharmacy or clinician contact for any unclear diluent, volume, container type, storage, or discard timing.

Divide the vial amount by the final liquid volume to get concentration. Then divide the instructed amount by that concentration to get the draw volume. A U-100 syringe conversion applies only when the physical syringe is actually U-100: one milliliter equals 100 units on that scale.

Example (arithmetic only, not a recommendation): A 10 mg vial brought to 2 mL gives 5 mg/mL. If an instructed amount is 0.5 mg, then 0.5 ÷ 5 = 0.1 mL, which equals 10 units on a U-100 syringe. Change any input and the result changes.

The reconstitution calculator lets you enter confirmed values and review concentration, milliliters, and the U-100 conversion together. It does not choose the values.

Clean the vial stopper with an alcohol swab. Draw the confirmed volume of diluent into a syringe, insert the needle through the stopper, and inject slowly against the inside wall of the vial. Direct impact on the lyophilized cake can damage the peptide or cause excessive foaming.

Once the liquid is added, gently swirl or roll the vial until the powder fully dissolves. Do not shake vigorously. A clear solution without visible particles is the typical target, but check your product instructions for specific appearance criteria.

After reconstitution, label the vial with the concentration (e.g., 5 mg/mL), the date mixed, and the discard date or beyond-use window from your instructions. If no discard date is provided, ask the dispensing pharmacy before the first use.

CDC injection-safety guidance calls for clean preparation areas, aseptic technique, and a new sterile needle and syringe for every access and administration. Discard a vial if sterility is compromised or in doubt. Read the CDC guidance.

The bacteriostatic water label applies to the water product, not to the mixed peptide. After reconstitution, storage conditions, temperature limits, and beyond-use dates come from the peptide product instructions, not from the diluent.

Most reconstituted peptides require refrigeration at 2–8°C (36–46°F). Some products have specific room-temperature limits or freezing instructions. If your instructions do not address a scenario, ask the dispensing pharmacy or prescriber.

For more on storage timing, see the reconstituted peptide fridge life guide and the peptide storage and travel guide.