Comparison · two FDA labels side by side
Sterile Water for Injection vs Bacteriostatic Water
Both are sterile water for injection. One contains no preservative and is single-dose; the other contains benzyl alcohol and is multiple-dose. Everything else on their labels follows from that difference.
Sterile Water for Injection, USP contains “no bacteriostat, antimicrobial agent or added buffer” and is supplied “only in single-dose containers”. Bacteriostatic Water for Injection, USP contains 0.9% benzyl alcohol and is supplied in multiple-dose vials. Both are labelled only for diluting or dissolving drugs for injection.
The two labels compared
| Sterile Water for Injection, USP | Bacteriostatic Water for Injection, USP | |
|---|---|---|
| Preservative | None (“no bacteriostat, antimicrobial agent or added buffer”) | Benzyl alcohol 0.9% (9 mg/mL); 1.1% in one glass vial |
| Container | Single-dose only | Multiple-dose |
| Indication | Diluting or dissolving drugs for IV, IM or subcutaneous injection | The same |
| Neonates | The label’s named choice for preparing a newborn’s medication | “NOT FOR USE IN NEONATES” |
| Given IV on its own | “may result in hemolysis” | “may result in hemolysis” |
| Storage | 20 to 25 °C | 20 to 25 °C |
| Hospira sizes | 1, 10, 20, 50 and 100 mL vials | 30 mL plastic (0.9%); 20 mL in a 30 mL glass vial (1.1%) |
| Status | Rx only | Rx only |
What sterile water for injection is
Hospira’s label calls Sterile Water for Injection, USP “a sterile, nonpyrogenic preparation of water for injection which contains no bacteriostat, antimicrobial agent or added buffer and is supplied only in single-dose containers to dilute or dissolve drugs for injection.”
It shares the bacteriostatic product’s indication word for word, and the same warning that intravenous use “without a solute may result in hemolysis.” The label also states that it “must be made approximately isotonic prior to use.”
Hospira lists it in a wider range of sizes than its bacteriostatic water, from a 1 mL glass vial to a 100 mL glass vial, because a single-dose container is sized to the dose it will make up.
Why the preservative matters
A needle through a rubber stopper is a route for bacteria into the vial. In sterile water nothing slows their growth, which is why the product is single-dose: the first entry is the only one it is labelled for. Benzyl alcohol is bacteriostatic. It stops bacteria multiplying between entries, which is what allows “repeated withdrawals” from a bacteriostatic vial.
The preservative is also the reason for every restriction on bacteriostatic water. Benzyl alcohol “has been associated with toxicity in neonates”, so for newborns the label names preservative-free sterile water instead.
When each is named
Neither product is chosen on its own merits: the label of the drug being prepared names its diluent. Prescription labels show both in use:
| Product | Diluent on its label |
|---|---|
| Novarel (hCG) | Bacteriostatic Water for Injection |
| Egrifta WR (tesamorelin) | Bacteriostatic Water for Injection, supplied in the pack |
| Serostim 4 mg (somatropin) | Bacteriostatic water |
| Serostim 5 mg and 6 mg | Sterile water, one dose per vial |
Serostim’s label also switches its 4 mg vial to sterile water where benzyl alcohol has to be avoided, with the same single-dose limit.
Telling the vials apart
- Bacteriostatic: “Bacteriostatic Water for Injection, USP”, “Multiple-dose”, “0.9% benzyl alcohol added”, “NOT FOR USE IN NEONATES”.
- Sterile: “Sterile Water for Injection, USP”, “Single-dose”, “FOR DRUG DILUENT USE”, no preservative listed.
Online listings sometimes call sterile water “bac water”. The ingredient line is the part that settles it: if benzyl alcohol is not listed, it is sterile water. For where each is sold, see where to buy bacteriostatic water for injection.
Questions
What is sterile water for injection?
A sterile, nonpyrogenic water for injection with no bacteriostat, antimicrobial agent or added buffer, supplied only in single-dose containers to dilute or dissolve drugs for injection.
Is sterile water for injection the same as bacteriostatic water?
No. Bacteriostatic water contains 0.9% benzyl alcohol and is multiple-dose; sterile water for injection contains no preservative and is single-dose.
Can sterile water for injection be used more than once?
Its label supplies it only in single-dose containers. Without a preservative, a vial is labelled for one entry.
Why is sterile water used for newborns instead of bacteriostatic water?
Benzyl alcohol has been associated with toxicity in neonates, so the bacteriostatic water label names preservative-free Sterile Water for Injection for preparing their medications.
Do both need a prescription?
Both Hospira products are labelled “Rx only”.
Sources
- DailyMed: Sterile Water for Injection, USP (Hospira): description, indications, warnings, how supplied.
- DailyMed: Bacteriostatic Water for Injection, USP (Hospira).
- DailyMed labels for Novarel, Egrifta WR and Serostim.
- USP General Chapter <797>; CDC, Preventing Unsafe Injection Practices.
Reviewed against the current DailyMed labels on 11 October 2026.