Definition: Bacteriostatic water (BAC water) is sterile water for injection with a small amount of benzyl alcohol added as a preservative. The benzyl alcohol slows the growth of bacteria, so the vial can be punctured more than once. It is made only for mixing (diluting or dissolving) other drugs, not for injecting on its own.
What the label says
The Hospira label for Bacteriostatic Water for Injection, USP, gives these facts:
- It contains 0.9% (9 mg/mL) or 1.1% benzyl alcohol "as a bacteriostatic preservative."
- It comes in a multiple-dose vial "from which repeated withdrawals may be made."
- It is "for drug diluent use only," for drugs given into a vein, a muscle or under the skin.
- It is not for use in newborns; benzyl alcohol has been linked to toxicity in neonates.
- Unopened, it is stored at room temperature, 20 to 25°C (68 to 77°F).
Some approved drugs ship with their own bacteriostatic water. Novarel (hCG) comes with 10 mL containing 0.9% benzyl alcohol. The Omnitrope 5.8 mg vial comes with diluent containing 1.5% benzyl alcohol. Use the diluent the label names.
Why it matters when you track doses
The amount of BAC water you add sets the strength of the vial. Change the water and every dose volume changes with it. That is why the mix volume belongs in your log next to the vial, along with the date you mixed it. Dose Track saves each vial with its mix date and concentration, so later doses are measured against the right number.
5 mg vial mixed with 2 mL of BAC water
- Concentration: 5 mg ÷ 2 mL = 2.5 mg/mL, which is 2,500 mcg/mL.
- One mark on a U-100 insulin syringe is 0.01 mL.
- Per mark: 2,500 mcg/mL × 0.01 mL = 25 mcg.
- So 250 mcg is 250 ÷ 25 = 10 units (0.1 mL). Check: 0.1 mL × 2.5 mg/mL = 0.25 mg = 250 mcg.
Common mix-ups
- BAC water is not sterile water. Sterile water for injection has no preservative and is single-dose. See bacteriostatic vs sterile water.
- The preservative does not make the drug last longer. It limits bacterial growth. How long the mixed drug stays potent depends on the drug, and only approved products have tested answers.
- It is not an injection by itself. The label warns that giving it into a vein without a dissolved drug may cause hemolysis (bursting of red blood cells).
Read more on Dose Track: Bacteriostatic vs sterile water · Peptide reconstitution calculator · How long mixed peptides last
General education drawn from labels and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your product are the final word.
What is in bacteriostatic water?+
Sterile water for injection plus benzyl alcohol as a preservative. The Hospira label lists 0.9% (9 mg/mL) or 1.1% benzyl alcohol, and the pH is about 5.7.
Can bacteriostatic water be used more than once?+
Yes. The label calls it a multiple-dose container from which repeated withdrawals may be made. The preservative is what allows this.
Does the amount of BAC water change the dose?+
It changes the concentration, so it changes the volume you draw for the same dose. The total amount of drug in the vial stays the same.