Lab Reference• 6 min read
How to Reconstitute a Peptide (Step-by-Step Laboratory Reference)
Reconstitution is the process of dissolving a lyophilized (freeze-dried) peptide into sterile diluent — usually bacteriostatic water — to produce a known concentration. The math is straightforward once you separate vial size, diluent volume, and per-administration volume.
The core formula
Concentration (mg/mL) = vial size (mg) ÷ diluent volume (mL). Example: 10 mg vial + 2 mL bac-water = 5 mg/mL.
Per-administration volume (mL) = desired dose (mg) ÷ concentration (mg/mL). Example: 0.5 mg dose ÷ 5 mg/mL = 0.1 mL (10 units on a 100-unit insulin syringe).
Step-by-step
- Bring both vials to room temperature on a clean bench.
- Swab both rubber stoppers with a fresh isopropyl pad and let dry.
- Draw the chosen volume of bacteriostatic water into a sterile syringe.
- Insert the needle into the peptide vial at a shallow angle so the stream of water runs down the inner glass wall — never directly onto the lyophilized cake.
- Remove the needle and gently swirl the vial. Do not shake. Allow 1–3 minutes for full dissolution; lyophilized peptides typically dissolve clear within seconds.
- Date and label the vial with the concentration and reconstitution date.
- Store at 2–8 °C. Most peptides retain potency for 28 days reconstituted; smaller fragile peptides closer to 14.
Why bacteriostatic water (and not sterile water)
Bacteriostatic water contains 0.9 % benzyl alcohol, which inhibits bacterial growth in multi-use vials. Plain sterile WFI has no preservative and is appropriate for single-use formulations only.
Common mistakes
- Shaking the vial after reconstitution — can denature fragile peptides like GHK-Cu and oxytocin
- Spraying water directly onto the cake — can foam and trap air bubbles
- Re-using a needle between vials — defeats the entire sterile-technique reason for bac-water
- Forgetting to label — concentration is invisible once the vial is mixed