What you need
- The lyophilised peptide vial, with its lot number legible.
- Bacteriostatic water, or the solvent your protocol or the product data specify.
- Alcohol swabs and a sterile syringe that can measure your solvent volume accurately.
- A pen or label for the vial.
Storing the vial before reconstitution
Do peptides need to be refrigerated before reconstitution? For short periods, no. Sigma-Aldrich's handling guide states that lyophilised peptides stay stable at room temperature for days to weeks, which covers ambient shipping. For longer storage, Sigma recommends -20 °C or colder and Bachem recommends below -15 °C, both with protection from light and moisture.
Before you puncture or open a cold vial, let it reach room temperature. Both suppliers give the same reason: lyophilised peptides take up moisture from the air, and absorbed water lowers peptide content and stability.
Choosing the solvent
Bacteriostatic Water for Injection, USP, is sterile water with 0.9% benzyl alcohol (9 mg/mL) as a preservative; one Hospira presentation uses 1.1%. The label describes it as a multiple-dose container from which repeated withdrawals may be made, and the preservative is what lets you enter a reconstituted research vial more than once.
Plain sterile water has no preservative. Use it when an assay is sensitive to benzyl alcohol, and treat the vial as single-use.
Some sequences resist dissolving in water. Bachem suggests a small volume of DMSO followed by dilution for hydrophobic peptides, a little dilute acetic acid for basic peptides and dilute aqueous ammonia for acidic ones. If the product data sheet or your protocol names a solvent, use that.
Working out how much bacteriostatic water to add
Concentration is the peptide mass divided by the solvent volume. A U-100 insulin syringe holds 100 units per mL, so one unit is 0.01 mL. For a 10 mg vial:
- 1 mL gives 10 mg/mL, or 100 mcg per unit.
- 2 mL gives 5 mg/mL, or 50 mcg per unit.
- 2.5 mL gives 4 mg/mL, or 40 mcg per unit.
- 3 mL gives about 3.33 mg/mL, or about 33 mcg per unit.
A 5 mg vial in 2 mL gives 2.5 mg/mL, or 25 mcg per unit. More water means less peptide per unit and finer resolution when you measure; less water means smaller withdrawal volumes. Pick the volume that suits your protocol, then write it down before you start.
The peptide calculator at /calculator runs these numbers for you. You enter the peptide in the vial (mg), the bacteriostatic water added (mL) and the amount you want per withdrawal (mcg or mg). It returns the units to draw on a 0.5 mL or 1 mL U-100 insulin syringe, the concentration in mg/mL and mcg per unit, and the number of withdrawals per vial. It does not work backwards from a target concentration to a solvent volume. For that, divide the vial content by the concentration you want (10 mg at 4 mg/mL needs 2.5 mL), then enter the result to check it.
Encodex gives no dosing guidance. The amount per withdrawal is a figure from your own protocol.
Adding the water
- Swab both stoppers with alcohol and let them dry.
- Draw the measured volume of bacteriostatic water.
- Insert the needle at an angle and let the water run down the inside wall of the vial, rather than jetting it onto the cake.
- Swirl or roll the vial until the powder dissolves. Do not shake it.
- Inspect the solution. It should be clear and free of particles.
The FDA label for tesamorelin (Egrifta WR), a peptide drug supplied as a powder for reconstitution, gives the same instruction: swirl the vial, do not shake it, and use the solution only if it is clear, colourless and free of particulate matter. If a cloudy haze or flakes persist after gentle swirling and some time at room temperature, the peptide has either not dissolved or has aggregated, and you need to find out which before you use the vial.
Label it
Write three things on the vial: the reconstitution date, the concentration and the lot number from the original label. The date matters more than the day the parcel arrived, and the lot number keeps every result traceable to an assayed batch.
How long reconstituted peptides last
No single figure covers every peptide, because stability in solution depends on the sequence. Bachem lists asparagine, glutamine, methionine, cysteine and tryptophan as residues that shorten shelf life, and flags methionine, cysteine and tryptophan for oxidation.
Three reference points help:
- Sigma-Aldrich states that peptide solutions are generally stable for up to about a week at 4 °C, and recommends sterile buffer near pH 5 to 6 for anything kept longer.
- USP chapter 797, as summarised by the CDC, has an opened multiple-dose vial dated and discarded within 28 days unless the manufacturer specifies otherwise. That limit concerns sterility of the container. It is not stability data for your peptide.
- Product labels show how specific the answer is. Egrifta WR, a formulated tesamorelin product with its own excipients, is stored at 20 to 25 °C after mixing and discarded after 7 days. That figure belongs to that formulation and does not transfer to a research vial.
In practice, keep the solution at 2 to 8 °C and away from light, and plan your work around the shortest window your protocol allows. We know of no general figure for how long reconstituted research peptides last at room temperature.
Freezing and aliquots
For storage beyond a week or two, Sigma and Bachem both recommend dividing the solution into single-use aliquots and freezing them, at -20 °C or colder (Sigma) or below -15 °C (Bachem). Both advise against repeated freeze-thaw cycles. Freeze aliquots once and thaw each one once.
For research use only. Everything above describes laboratory practice and published research. It is not medical advice, not dosing guidance, and carries no implication of human or veterinary use.