Practical guide

How to Reconstitute Peptides

A step-by-step reference for dissolving lyophilised peptide powder in bacteriostatic water — covering equipment, technique, concentration calculation, and sterile handling.

What is Reconstitution?

Lyophilised peptide is freeze-dried powder produced for long-term stability. In this dry form, the peptide cannot be administered directly — it must first be dissolved in a suitable liquid before use. Bacteriostatic water (BAC water) is the standard diluent because it contains 0.9% benzyl alcohol, which acts as a preservative and prevents bacterial growth across multiple draws from the same vial. Plain sterile water lacks this preservative and is unsuitable for multi-dose vials, as it provides no protection against microbial contamination after the first puncture.

Equipment You Will Need

Item	Purpose
Lyophilised peptide vial	The peptide in powder form
Bacteriostatic water (BAC water)	Diluent — 0.9% benzyl alcohol acts as preservative
1ml or 2ml drawing syringe + 21g or 23g needle	For transferring BAC water to peptide vial
Insulin syringe (U-100, 1ml)	For drawing doses after reconstitution
Alcohol swabs (70% isopropyl)	To sterilise vial rubber tops before puncture
Clean surface or sterile mat	To work on

Calculating Your Concentration

This is the most important step — getting concentration wrong leads to incorrect volumes being drawn. The formula is straightforward:

Concentration (mcg/ml) = (Vial size in mg × 1000) ÷ BAC water added (ml)

The reference table below shows common combinations:

Peptide amount	BAC water added	Concentration
5 mg	1 ml	5,000 mcg/ml
5 mg	2 ml	2,500 mcg/ml
5 mg	5 ml	1,000 mcg/ml
10 mg	1 ml	10,000 mcg/ml
10 mg	2 ml	5,000 mcg/ml
10 mg	5 ml	2,000 mcg/ml
2 mg	1 ml	2,000 mcg/ml
2 mg	2 ml	1,000 mcg/ml

Once you know the concentration, divide the desired dose (mcg) by the concentration (mcg/ml) to get the volume to draw (ml). For example: a 250 mcg dose at 5,000 mcg/ml = 0.05 ml = 5 units on a U-100 insulin syringe. Use the interactive Peptide Calculator to compute this automatically.

Step-by-Step Reconstitution Process

Wash hands thoroughly

Wash hands for at least 20 seconds with soap and water, or don sterile gloves. This is the foundation of sterile technique — skip it and all subsequent steps are compromised.

Wipe both vial tops with alcohol swabs

Use a fresh alcohol swab on the rubber septum of both the peptide vial and the BAC water vial. Allow to dry for 10–15 seconds before puncturing — wet alcohol can be carried into the vial by the needle.

Draw the desired volume of BAC water

Using a 1ml or 2ml syringe with a 21g or 23g needle, draw the calculated volume of bacteriostatic water from the BAC water vial. Refer to the concentration table above to determine the correct volume.

Inject BAC water slowly against the glass wall

Insert the needle into the peptide vial and angle it so the stream of BAC water runs gently down the inside of the glass wall rather than shooting directly onto the powder cake. This minimises mechanical disruption and helps preserve peptide structure during dissolution.

Do not shake — gently swirl or roll

Once BAC water has been added, gently swirl the vial in a circular motion or roll it slowly between your palms until the powder has fully dissolved and the solution appears clear. Shaking introduces mechanical shear force that can degrade peptide bonds.

Inspect the solution

A correctly reconstituted peptide solution should be clear and colourless. Any persistent cloudiness, visible particles, or unusual colouration may indicate contamination or peptide aggregation. Do not use a solution that fails visual inspection.

Label the vial with the date of reconstitution

Write the reconstitution date and concentration on the vial label or a piece of tape. Reconstituted peptides have a limited shelf life — without a date, it is impossible to track how long the solution has been stored.

Refrigerate immediately

Place the reconstituted vial in the refrigerator (2–8°C) straight away. Do not leave it at room temperature. See the storage guide for full temperature guidance and expected shelf life.

Common Mistakes to Avoid

Injecting air into the vial — this creates positive pressure that can make drawing doses difficult and may cause leakage. If this happens, tilt the vial and slowly release pressure by gently pulling back the plunger before removing the needle.
Shaking the vial — always roll or swirl gently. Shaking can physically damage peptide structure through shear forces and foaming.
Using plain sterile water for multi-dose vials — sterile water provides no bacteriostatic protection after first use. Use BAC water for any vial that will be punctured more than once.
Not wiping vial tops before puncture — the rubber septum is not sterile by default. Always swab with 70% isopropyl alcohol and allow to dry before inserting a needle.
Using a dull or previously used needle to puncture the stopper — a dull needle requires more force, increasing the risk of coring the stopper and introducing rubber particles into the solution. Always use a fresh, sharp needle.

How to Draw a Dose After Reconstitution

Before drawing from a refrigerated vial, swab the rubber top with a fresh alcohol swab. Draw a small volume of air into your insulin syringe equal to the dose volume you intend to draw — injecting this air into the vial first equalises pressure, making it easier to withdraw the solution smoothly.

Invert the vial, insert the needle, and slowly draw back the plunger to the desired volume marking. For insulin syringes reading in units: on a U-100 syringe, 1 unit = 0.01 ml. A 10-unit mark = 0.10 ml. See the syringes guide for a complete explanation of unit reading and syringe selection.

Key Takeaways

Reconstitution is the process of dissolving freeze-dried (lyophilised) peptide powder in a liquid diluent before administration.
Bacteriostatic water (BAC water) is the correct diluent for multi-dose vials — its 0.9% benzyl alcohol content prevents bacterial growth between uses.
Concentration (mcg/ml) = (vial size in mg × 1000) ÷ ml of BAC water added. Getting this right is essential for accurate dosing.
Always swirl or roll the vial gently — never shake. Shaking can degrade peptide structure.
Inject BAC water slowly against the glass wall, not directly onto the powder cake.
Label every reconstituted vial with the date and concentration immediately after preparation.
Refrigerate at 2–8°C immediately after reconstitution. Use the Peptide Calculator to determine the correct draw volume for any dose.

Peptide Calculator