Reconstitution guide
Most peptides ship as a freeze-dried powder that has to be dissolved before use. This guide explains how laboratories do it and why each step matters.
This is general laboratory practice. Approved medicines come with their own mixing instructions, and those always come first. Nothing here is medical advice.
What reconstitution is
Reconstitution means adding a liquid (the diluent) to a lyophilized powder so it becomes a solution of known strength. Powder is shipped because it is far more stable than liquid. Once dissolved, a peptide starts to break down faster, so timing, temperature and cleanliness matter. See Storage and stability for why.
Choosing a diluent
- Sterile water has no preservative. It suits a vial that will be used once.
- Bacteriostatic water is sterile water with benzyl alcohol (0.9% in common products) to slow microbial growth, so a vial can be entered more than once 4. Its label says it is not for use in newborns, because benzyl alcohol is toxic to them 4.
- Some peptides need a specific diluent (for example, a weak acid or saline) to dissolve fully. The supplier's data sheet or the drug label says which.
The steps labs follow
- Check the vial. Match the label and lot number to the certificate of analysis. Note the amount of peptide in the vial.
- Let it reach room temperature. Opening a cold vial pulls in moisture from the air.
- Work clean. Wash hands and wipe the rubber stopper of both vials with an alcohol swab, and let it dry.
- Add the diluent slowly. Aim the stream at the glass wall, not straight onto the powder, so it does not foam.
- Swirl, do not shake. Gently roll or swirl until the powder is gone. Shaking can damage peptides and cause clumping.
- Inspect it. The solution should be clear. Cloudiness, particles or color changes suggest a problem.
- Label it. Write the concentration, the date it was mixed and the diluent used.
- Store it cold. Most reconstituted peptides are kept refrigerated (2 to 8 C) and away from light, then used within the time the supplier or label states.
Picking the volume of liquid
The amount of liquid does not change how much peptide is in the vial. It only changes the concentration. More liquid makes each unit hold less peptide, which makes small amounts easier to measure. Less liquid packs more into each unit. Labs often pick a volume that turns common amounts into round syringe numbers. Try it in the calculator.
| 10 mg vial + liquid | Concentration | Peptide per U-100 unit |
|---|---|---|
| 1 mL | 10 mg/mL | 100 mcg |
| 2 mL | 5 mg/mL | 50 mcg |
| 3 mL | 3.33 mg/mL | 33.3 mcg |
| 5 mL | 2 mg/mL | 20 mcg |
Common problems
- Powder will not dissolve: some sequences need a different diluent; check the data sheet before adding more water.
- Foam: let it settle; foam means the liquid was added too fast or shaken.
- Contamination: every needle entry is a chance for microbes. Gray-market vials have been found with endotoxin, which no filter or diluent removes. See Quality and lab testing.