Short answer: Bacteriostatic water is sterile water with 0.9% benzyl alcohol (some vials 1.1%) added as a preservative, so it comes in multi-dose vials. Sterile water for injection has no preservative and comes only in single-dose containers: discard what is left. Benzyl alcohol is not for use in newborns. Use whichever diluent your product's label specifies.
| Bacteriostatic Water for Injection, USP | Sterile Water for Injection, USP | |
|---|---|---|
| Preservative | 0.9% (9 mg/mL) or 1.1% (11 mg/mL) benzyl alcohol | None: no bacteriostat, antimicrobial agent or buffer |
| Container | Multiple-dose vial; repeated withdrawals allowed | Single-dose containers only |
| After first use | Opened multi-dose vials: discard within 28 days unless the manufacturer says otherwise (CDC, citing USP <797>) | Do not reuse; discard unused portion |
| pH | 5.7 (4.5 to 7.0) | Not stated on the Hospira label |
| Newborns | WARNING: not for use in neonates | No benzyl alcohol warning |
| Storage | 20-25°C (68-77°F) | 20-25°C (68-77°F) |
Neither water is meant to be injected on its own. Both labels describe them as diluents for drugs that need dissolving, and the sterile water label warns that giving it intravenously without a solute may cause hemolysis.
The manufacturer picks the diluent and tests the product with it. Some examples from current US labels:
The pattern is consistent: products meant to be drawn from many times come with a preservative; single-use products come with plain sterile water. The day count after mixing is set by the drug's own stability testing, not by the water.
Most research-peptide guides mix with bacteriostatic water because the vial is drawn from many times. No FDA label covers these, and we found no published study of how long the mixed vial stays stable in a fridge. The preservative limits bacterial growth; it does not tell you how long the peptide itself stays intact. See how long mixed peptides last and the reconstitution calculator for the water-to-units math.
The bacteriostatic water label says benzyl alcohol has been associated with toxicity in neonates and should not be used in them. CDC reported neonatal deaths linked to benzyl alcohol in flush solutions, with metabolic acidosis and gasping respirations, and FDA recommended against benzyl-alcohol flushes and diluents for newborns. FDA-approved labels for other benzyl-alcohol products describe this as the "gasping syndrome" in premature infants.