Which Mixing Agent to Use for Your Peptides?

When mixing peptides for injection, the choice between Bacteriostatic Water (BW or BAC) and Sterile Saline (NSS – Normal Saline Solution) has important implications for peptide stability, safety, and usability.

Bacteriostatic water contains a small amount of benzyl alcohol (usually 0.9%), which acts as a preservative to inhibit bacterial growth. This allows a reconstituted solutions to be stored for multiple uses over a longer period, typically longer than 28 days when kept refrigerated and stored in clean conditions. In theory this makes bacteriostatic water a preferred option for people using a small number of multi-dose vials or protocols that span over a number of weeks, however when used for solubilising peptides there are limitation with the use of bacteriostatic water, more detail on this mentioned below.

Sterile saline in contrast contains no preservatives but is harder to produce as it has been filtered and sterilized. This means it’s ideal for shorter term use applications, because once opened the water is theoretically no longer sterile.

Using NSS to mix peptides is suitable if you plan to use the entire dose in a short period, ideally inside 14 days, but can carry a slightly higher risk of bacterial contamination if the peptide vials are not stored and prepared properly. For this reason, using sterile water requires good storage practice, precise timing and dosage planning to avoid wastage.

It must be noted that in some cases Bacteriostatic Water can be a major disadvantage for solubilising lyophilised peptides due to the benzyl alcohol, which may alter the solubility or stability of some delicate peptides, although this is uncommon with peptides like BPC-157 or TB-500. Longer peptides maybe prone to destabilisation from the benzyl alcohol contained within the bacteriostatic water and is not recommended for use with these. The addition of BAC water can make the appearance of the peptide cloudy or change the viscosity. We always recommend Normal Saline Solution (NSS) for maintaining peptide lifespan and stability.

Why is the injection site itchy or leaving a red rash - Another consideration of Bacteriostatic Water is the potential for sensitivity or allergic reaction to benzyl alcohol in some people. Although rare, reactions can include irritation at the injection site or systemic effects. Additionally, BW is not typically recommended for use in infants or during pregnancy due to possible toxicity with prolonged exposure

Isotonicity matters - If your peptide vial is stored properly then we recommend using sterile saline as it is an isotonic and matches the same salt concentrations as your body, causing less irritation when injected. Sterile water is not an isotonic and can lead to haemolysis of cells due to water entering the cell causing them to swell and burst, leaving a sensation of constant itchiness, soreness and redness at the injection site.

While NSS avoids the preservative-related issues, its lack of antimicrobial properties means good aseptic technique must be followed when using it. Once a peptide is reconstituted with NSS, it should ideally be used with in the dosing guidelines or discarded if not in use for more than a month.

Regardless if Bacteriostatic Water or NSS is used for mixing your peptide, correct storage condition and usage protocols always apply. Once mixed your peptide must be stored in a fridge below 4 degrees Celsius but not frozen, it should be also stored away from food in a separate sealable clean container, ideally wiped or sprayed with methanol to create a pathogen free environment. Before each injection the top of the vial should be wiped with a clean alcohol wipe pad to remove any possible contaminant before the injecting needle pierces the vial bung.

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