How to reconstitute peptides

What reconstitution actually is

Peptides are usually supplied lyophilised, which is a freeze-dried powder sitting in a sealed vial. Reconstitution is adding a sterile liquid, called a diluent, so the powder dissolves and can be drawn into a syringe.

Adding liquid does not change how much peptide is in the vial. The vial holds what it holds, whether you add one millilitre of diluent or three. What changes is the concentration, and therefore how much liquid carries a given amount of peptide.

The only maths involved

Concentration is the amount in the vial divided by the volume of diluent you add, expressed in mg per mL. Working out what to draw is your intended amount divided by that concentration, then multiplied by 100, because a U-100 syringe is marked in 100 units per mL.

The reconstitution calculator does that arithmetic on the numbers you type in. It converts units and works out a concentration. It does not decide what those numbers should be.

Bacteriostatic water and sterile water are not the same

Bacteriostatic water for injection is sterile water containing a preservative, benzyl alcohol, which inhibits bacterial growth. Sterile water for injection has no preservative. The distinction matters because it changes how a vial behaves once the seal has been pierced.

Both are manufactured products with their own FDA-approved labelling, and that labelling is the authority on the diluent, not a peptide website. Worth knowing what it actually says: the approved labelling for Bacteriostatic Water for Injection describes a multiple-dose container from which repeated withdrawals may be made, tells you to use aseptic technique for single or multiple entry, says to mix thoroughly and use promptly when diluting or dissolving drugs, and says not to store reconstituted solutions unless the manufacturer of the drug being dissolved directs otherwise. It carries a boxed warning that it is not for use in neonates.

The labelling also sets out what the product is for: diluting or dissolving drugs for intravenous, intramuscular, or subcutaneous injection, according to the instructions of the manufacturer of the drug being given. Research peptides have no such manufacturer instructions, which puts that use outside what the label covers.

Where the 28 day figure comes from

You will see "28 days" repeated constantly in peptide circles, usually attributed to the bacteriostatic water label. It is not on that label. No FDA-approved bacteriostatic water labelling specifies a discard interval after first entry.

The figure does have an FDA source, just a different one: FDA has said it generally recommends that vials containing multiple doses of sterile medications be used within 28 days after first use, because the risk of contamination increases after that. That is general guidance about multiple-dose sterile vials, not a statement about any particular peptide in any particular solution.

Where the rest of the detail lives

The step-by-step walkthrough, including the reconstitution notes and storage information held for each compound, is in the guides and the peptide library on the homepage. The reconstitution calculator works out concentration and units from the numbers you enter.

All of it is general reference information. How much diluent to add for your vial, what to draw, and how long a mixed vial stays suitable are decisions with consequences, and PepCaddie does not make them for you: that is a conversation with a qualified clinician, alongside the labelling of the products actually in front of you.