Bacteriostatic Water for Peptides

What bacteriostatic water is

Here is what the official label says (DailyMed label):

• It is sterile water made for injection.
• It has 0.9% benzyl alcohol (9 mg per mL) in plastic vials, or 1.1% (11 mg per mL) in glass vials.
• The benzyl alcohol is there as a preservative.
• It comes in a vial made for more than one use.
• Its pH is about 5.7, with a range of 4.5 to 7.0.
• The label says to store it at 20 to 25 C (68 to 77 F).
• It is only meant to dilute or dissolve drugs, not to be used on its own.

The label also says not to use it unless the liquid is clear and the seal is intact. For the whole label in plain words, see what is bacteriostatic water.

Why freeze-dried peptides need a liquid

Many peptides are sold as a dry powder. This powder is made by freeze-drying, also called lyophilizing. Lab guides say peptides keep best as a dry powder, not as a liquid (Bachem). A review of protein drugs gives the reason: in liquid form these molecules are not stable for long, so makers often freeze-dry them to get a usable shelf life (Wang, 2000).

The powder has to be dissolved before it can be measured out in mL. That step is called reconstitution. The liquid you add is called the diluent. See how to reconstitute peptides for the steps.

What the preservative does, and what it does not do

The label calls benzyl alcohol a "bacteriostatic preservative." It is the reason the vial can be labeled for more than one use. Sterile water has no preservative, so its vial is for one use only.

The preservative does not make the vial last forever, and it does not make up for poor clean technique. The label says to use clean (aseptic) technique every time you enter any vial. The 28 day limit still applies once it is opened.

Bacteriostatic water vs sterile water vs saline

This table uses facts from the official labels plus CDC guidance. The CDC cells are marked.

The 28 day rule comes from the CDC, not the labels (CDC). More detail is in bacteriostatic water vs sterile water.

How much water? The math, not a number

This page will not tell you how much water to add, because your product's own instructions set that amount. The water label says the same thing: check the drug maker's instructions for how much liquid to use.

What we can show is the math. The strength of the mix is:

mg in the vial divided by mL of water added = mg per mL

So 10 mg in 2 mL gives 5 mg per mL. Adding more water makes each mL weaker, but it does not change the total in the vial. The mixing chart shows the result for common numbers.

How long it lasts after opening

The CDC says an opened multi use vial should be dated and thrown out within 28 days, unless the maker gives a different date (CDC). USP chapter 797 sets the same 28 day limit (USP 797, VA copy).

This limit is for the water vial. A vial of mixed peptide has its own limit. Read how long bacteriostatic water lasts for more.

How to store it

The label says to keep unopened vials at 20 to 25 C (68 to 77 F), which is normal room temperature. A separate guide covers whether it needs to go in the fridge.

When bacteriostatic water is the wrong choice

It is not the right liquid for every product. The label says to check the drug maker's instructions for the choice of liquid. Some products call for something else, so always follow the product's own instructions.

The label also has warnings:

• It is not for use in newborns, because of the benzyl alcohol.
• Some drugs do not mix well with benzyl alcohol. The label says to ask a pharmacist.
• If the liquid is cloudy or the seal is broken, the label says not to use it.