Peptide Reconstitution

Reconstitution is the process of dissolving a lyophilized (freeze-dried) peptide into a sterile liquid to create an injectable solution. Most research and compounded peptides ship as a dry powder or puck in a sealed vial and must be reconstituted before use.

Why peptides are lyophilized

Peptides degrade in solution. Hydrolysis, oxidation, deamidation, and aggregation all accelerate in aqueous environments. Lyophilization removes water through sublimation (freezing then vacuum drying), producing a stable powder that can be stored for months or years without significant degradation.

Once reconstituted, the clock starts. Most peptide solutions remain stable for 3-4 weeks refrigerated (2-8°C), though some degrade faster and some slower depending on their amino acid composition.

Reconstitution solvent

Bacteriostatic water (BAC water) is the standard reconstitution solvent. It is sterile water containing 0.9% benzyl alcohol as a preservative. The benzyl alcohol inhibits microbial growth, which matters because the vial will be punctured with a needle multiple times over days or weeks.

Sterile water (without preservative) can be used but only if the entire vial will be used in a single session. Without the bacteriostatic agent, contamination risk increases with each needle puncture.

Normal saline (0.9% NaCl) is sometimes used, particularly for peptides that are poorly soluble at low ionic strength.

The reconstitution process

1. Allow the peptide vial to reach room temperature. Cold vials develop condensation when opened, introducing moisture.
2. Clean the vial tops. Swab both the peptide vial and BAC water vial with alcohol prep pads.
3. Draw the solvent. Using an insulin syringe or a mixing syringe, withdraw the desired volume of BAC water. Common volumes are 1 mL or 2 mL, depending on the desired concentration.
4. Add solvent gently. Insert the needle into the peptide vial and inject the BAC water slowly against the glass wall. Do not spray it directly onto the powder — high-pressure streams can denature the peptide through shear stress.
5. Swirl, do not shake. Gently roll or swirl the vial to dissolve the powder. Vigorous shaking creates foam, introduces air-liquid interfaces, and can cause mechanical denaturation. Some peptides dissolve instantly; others take several minutes.
6. Inspect the solution. The result should be clear and colorless. Cloudiness may indicate aggregation or contamination. Discard cloudy solutions.

Concentration calculation

The resulting concentration depends on how much solvent you add:

> Concentration (mcg/unit) = Peptide amount (mcg) / Solvent volume (units)

For a 5 mg (5,000 mcg) vial reconstituted with 2 mL (200 units) of BAC water:

> 5,000 mcg / 200 units = 25 mcg per unit

Each tick mark on a standard U-100 insulin syringe represents 1 unit. To dose 250 mcg, you would draw 10 units.

The peptide calculator on this site automates this calculation for any vial size and solvent volume.

Storage after reconstitution

• Refrigerate at 2-8°C (36-46°F). Do not freeze reconstituted peptides — ice crystal formation during freezing can denature the protein structure.
• Protect from light. Some peptides (notably those containing tryptophan or methionine) are photosensitive.
• Use within 3-4 weeks. Potency degrades over time in solution. Some practitioners use reconstituted peptides for up to 6 weeks, but stability data varies by peptide.
• Keep the cap on. Minimize unnecessary vial punctures to reduce contamination risk.

Common mistakes

• Shaking the vial — creates foam and can denature the peptide
• Using tap water or non-sterile water — contamination risk
• Freezing reconstituted solution — destroys peptide structure
• Leaving reconstituted vials at room temperature — accelerates degradation
• Using one syringe for multiple vials — cross-contamination risk

Related entries

• Bacteriostatic Water — the standard reconstitution solvent
• Reconstitution Protocol — step-by-step guide
• Subcutaneous Injection — the standard injection method