Definition: Bacteriostatic describes something that stops bacteria from multiplying, without necessarily killing them. On a vial label it means a preservative has been added so the liquid can be entered with a needle more than once. It does not mean the vial stays sterile no matter what, and it says nothing about how long a mixed drug lasts.
Two bacteriostatic diluents
Hospira bacteriostatic diluents, from their DailyMed labels
| Bacteriostatic water | Bacteriostatic 0.9% sodium chloride |
|---|
| Base | Water for injection | Sodium chloride 9 mg per mL in water for injection |
| Preservative | Benzyl alcohol 0.9% (9 mg/mL) or 1.1% (11 mg/mL) | Benzyl alcohol 0.9% (9 mg/mL) |
| pH | 5.7 (4.5 to 7.0) | 5.0 (4.5 to 7.0) |
| Container | Multiple-dose | Multiple-dose |
| Newborns | Not for use in neonates | Not for use in neonates |
Both labels say the container allows "repeated withdrawals." The saline is described as isotonic (about the same salt level as body fluids). The water label says it must be made roughly isotonic before use.
What it does not promise
- It does not replace clean technique. Both labels say to use aseptic technique for every entry and withdrawal.
- It does not extend the life of the mixed drug. Both labels say: "Do not store reconstituted solutions of drugs for injection unless otherwise directed by the manufacturer of the solute."
- It does not suit every drug. The labels warn that some drugs may be incompatible with a liquid containing benzyl alcohol.
Ready-made multi-dose products use other antimicrobial ingredients. Humulin R and Forteo both list metacresol, and a 2022 study names benzyl alcohol and m-cresol as commonly used antimicrobial agents (Li 2022). See benzyl alcohol.
Read more on Dose Track: Bacteriostatic vs sterile water · How long mixed peptides last · Peptide reconstitution calculator
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.
Is bacteriostatic the same as sterile?+
No. Bacteriostatic water is sterile when sealed and also contains a preservative. "Bacteriostatic" refers to that preservative, which keeps bacteria from multiplying after the vial is opened.
What is the difference between bacteriostatic water and bacteriostatic saline?+
Both have 0.9% benzyl alcohol. The saline also has 9 mg of sodium chloride per mL, which makes it isotonic, and its labeled pH is 5.0 rather than 5.7.
Does bacteriostatic water make a mixed peptide last longer?+
No. The label says not to store mixed drugs unless the drug maker says to. How long a mixed drug lasts depends on the drug.