Bacteriostatic Water for Injection: what the label says

Description

The label describes the product in one sentence: “a sterile, nonpyrogenic preparation of water for injection containing 0.9% (9 mg/mL) or 1.1% (11 mg/mL) of benzyl alcohol added as a bacteriostatic preservative.”

“Sterile” means the contents are free of living organisms when sealed. “Nonpyrogenic” means free of the fever-causing substances bacteria leave behind. “Bacteriostatic” means the preservative stops bacteria multiplying; it does not kill them, and it does not make a contaminated vial safe.

The “USP” in the name means the product meets the United States Pharmacopeia monograph for bacteriostatic water for injection, the published quality standard for its identity, strength and purity.

What it is used for

The indication on the label is narrow:

“This parenteral preparation is indicated only for diluting or dissolving drugs for intravenous, intramuscular or subcutaneous injection, according to instructions of the manufacturer of the drug to be administered.”Bacteriostatic Water for Injection, USP, Indications and Usage

In other words, it is a diluent. A drug supplied as a powder, or one that must be diluted before it is given, is mixed with it. The choice of diluent belongs to the maker of that drug: several prescription products supplied as powder name bacteriostatic water as their diluent, including Novarel (hCG), Egrifta WR (tesamorelin) and the 4 mg vial of Serostim (somatropin).

Who it is not for

The label’s contraindications and warnings all concern the benzyl alcohol:

• Neonates. “Due to the potential toxicity of benzyl alcohol in neonates, solutions containing benzyl alcohol must not be used in this patient population.” Where water is needed to prepare a newborn’s medication, the label names “only preservative-free Sterile Water for Injection”.
• Fluid replacement. Preparations with benzyl alcohol “should not be used for fluid replacement.”
• Epidural and spinal procedures. They “should not be used in epidural or spinal anesthesia procedures.”

Labels of individual drugs can add to this list. Serostim’s, for example, also names known hypersensitivity to benzyl alcohol.

Precautions

On its own, water carries far fewer dissolved particles than blood, and the label’s main precaution follows from that: “Intravenous administration of Bacteriostatic Water for Injection without a solute may result in hemolysis,” the rupture of red blood cells. It also states that the product “must be made approximately isotonic prior to use.”

The remaining precautions point back to the drug being prepared. The label refers the reader to “the manufacturer’s instructions for choice of vehicle, appropriate dilution or volume for dissolving the drugs to be injected,” and says a solution is not used “unless the solution is clear and seal intact.”

How it is supplied

Hospira’s label lists two presentations, both sold to pharmacies in trays of 25:

Hospira is part of Pfizer, and the label lists Pfizer Healthcare India as a manufacturer. Other labelers and repackagers list their own bacteriostatic water for injection on DailyMed, with the same 0.9% benzyl alcohol and the same “NOT FOR USE IN NEONATES” warning. Research suppliers also sell 3 mL, 10 mL and 30 mL vials of bacteriostatic water outside the pharmacy channel.

Storage and opened vials

The label gives one storage instruction: 20 to 25 °C (68 to 77 °F), controlled room temperature. It gives no refrigerated range and no day count for an opened vial.

The commonly quoted 28-day figure comes from elsewhere. USP General Chapter <797>, the pharmacy compounding standard, gives an opened or punctured multiple-dose container a beyond-use date of 28 days “unless otherwise specified by the manufacturer”, and CDC injection-safety guidance follows the same rule. The printed expiry date still applies, whichever comes first.

Prescription status

Bacteriostatic Water for Injection, USP carries “Rx only” on its labeling and tray, the federal legend for a prescription drug. US pharmacies therefore fill it at the counter rather than stocking it on the shelf. Price-comparison sites listed the average retail cash price of a 30 mL vial at $23.76 (GoodRx) and $28.79 (Rx.com) on 8 October 2026.

How CVS, Walgreens, Walmart and Amazon handle it is covered in bacteriostatic water at pharmacies, and the online suppliers in where to buy bacteriostatic water for injection.

Questions