August 29, 2026
RESEARCH USE ONLY. Bacteriostatic Water for Injection, USP is a prescription pharmaceutical diluent. Products discussed on this site are sold strictly for laboratory and research purposes. Nothing on this page is medical advice, and nothing here is an administration or dosing recommendation for any person or animal.
Search “bacteriostatic water 28 day rule” and you will find a dozen pages telling you to discard the vial 28 days after first puncture. Almost none of them tell you which document says so. We went and read the labels — four separate FDA-approved product labels from four different labelers — and the number 28 does not appear on any of them.
That is not a gotcha. The 28-day convention is real, it is well founded, and there is a good reason to follow it. But it comes from somewhere other than where most people assume, it applies to a broader category than most people realize, and the difference matters if you are trying to reason carefully about a vial in front of you. So let’s do the unusual thing and open the actual documents.
The 28-day beyond-use date is not printed on the Bacteriostatic Water for Injection label. It comes from three other places: an FDA guidance document on labeling multiple-dose containers (October 2018), USP General Chapter <797>, and CDC injection-safety guidance that explicitly attributes the figure to USP.
The FDA guidance states it plainly: “The beyond-use date for an opened or entered (e.g. needle-punctured) multiple-dose container is 28 days, unless otherwise specified by the manufacturer on the label.” [1]
Sourced fact: That sentence governs multiple-dose containers as a class — any sterile parenteral container that has met antimicrobial effectiveness testing. [1] It is not a statement about bacteriostatic water specifically.
Inference: This is why the rule feels simultaneously universal and unsourceable. It is universal — it applies to every preserved multiple-dose vial, which is why practitioners encounter it constantly. And it is unsourceable in the place people look for it, because it was never a manufacturer statement about this one product.
We pulled the Structured Product Labels for Bacteriostatic Water for Injection, USP from DailyMed and searched them directly.
| Labeler | DailyMed Set ID | “28” present? | “discard” present? | “beyond-use” present? |
|---|---|---|---|---|
| Hospira, Inc. (NDA holder) | 87d6e9dc-fe3b-4593-ac9a-d7493d1959c7 [2] |
No | No | No |
| US MedSource, LLC | ccadcf46-6a6f-436b-9bbc-17e2983a335f [3] |
No | No | No |
| Henry Schein, Inc. | a833502e-a622-4e81-8c58-cef6ccb6c4c9 [4] |
No | No | No |
| HF Acquisition Co. (HealthFirst) | 99b0ef9b-600a-40dc-e053-2a95a90aa07e [5] |
No | No | No |
Sourced fact: The only multiple-dose statement on the Hospira label is descriptive, not temporal: “It is supplied in a multiple-dose container from which repeated withdrawals may be made to dilute or dissolve drugs for injection.” [2]
Sourced fact: The label’s PRECAUTIONS section does address handling, in three sentences: “Use aseptic technique for single or multiple entry and withdrawal from all containers.” · “When diluting or dissolving drugs, mix thoroughly and use promptly.” · “Do not store reconstituted solutions of drugs for injection unless otherwise directed by the manufacturer of the solute.” [2]
Inference: That third sentence is the one most often skipped, and it is arguably more consequential than the 28-day figure. It says the beyond-use date of whatever you dissolved is set by the solute’s manufacturer — not by the diluent, and not by the 28-day container rule. The 28 days describes how long the vial of water remains suitable for withdrawal. It says nothing about the stability of what you put into solution with it.
Three documents, in the order they matter.
1. FDA Guidance for Industry, October 2018. Titled Selection of the Appropriate Package Type Terms and Recommendations for Labeling Injectable Medical Products Packaged in Multiple-Dose, Single-Dose, and Single-Patient-Use Containers for Human Use. It defines a multiple-dose container as “a container of a sterile medication for parenteral administration (injection or infusion) that has met antimicrobial effectiveness testing requirements, or is excluded from such testing requirements by FDA regulation,” and then supplies the 28-day BUD quoted above. [1]
Sourced fact: FDA guidance documents are non-binding recommendations, not regulations. [1]
2. USP General Chapter <797>. The compounding standard. Its text is paywalled, so we are citing it through ASHP’s published crosswalk rather than presenting a direct quotation we could not retrieve. ASHP renders the USP position as: a multiple-dose container “may be assigned a BUD of 28 days unless otherwise specified by manufacturer labeling,” and adds the qualifier most secondary write-ups drop — “Use from initial entry cannot exceed 28 days or the assigned BUD, whichever is shorter.” [6]
3. CDC injection-safety guidance. CDC does not originate the number; it attributes it. Verbatim: “The United States Pharmacopeia (USP) General Chapter 797 recommends the following: An unopened multi-dose vial should be discarded according to the manufacturer’s expiration date. Once a multi-dose vial is opened (e.g., needle-punctured) the vial should be dated and discarded within 28 days unless the manufacturer states another date for that opened vial. The beyond-use-date should never exceed the manufacturer’s original expiration date.” [7]
Sourced fact: The clock starts at first puncture, and the 28-day BUD can only shorten the printed expiration date, never extend it. [7]
Inference: Read together, these three establish 28 days as a ceiling derived from container class and preservative performance, not from any measured property of this specific product. It is a conservative default that applies in the absence of manufacturer-specified alternative dating — which is precisely why the label’s silence is consistent with the rule rather than evidence against it.
Sourced fact: The Hospira label describes the product as “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.” [2]
Two concentrations, resolved by presentation in the HOW SUPPLIED section: the 30 mL plastic vial (NDC 0409-3977-03) carries 9 mg/mL; the 20 mL glass vial (NDC 0409-1093-04) carries 11 mg/mL. [2] The Henry Schein label, revised 10/2025, carries the same dual statement. [4]
Sourced fact: Not all bacteriostatic water is preserved with benzyl alcohol. The Fresenius Kabi (formerly APP Pharmaceuticals) package insert describes a product “packaged in multiple dose vials. It contains 0.12% methylparaben, 0.012% propylparaben. pH 4.5 to 7.0.” [8] That insert is dated July 2008; we could not locate a current DailyMed SPL for it, and note the age explicitly.
Inference: The blanket statement “bacteriostatic water contains 0.9% benzyl alcohol,” which appears on essentially every page currently ranking for this topic, is wrong in two independent ways. It ignores the 11 mg/mL presentation and it ignores paraben-preserved formulations entirely. Anyone with a documented benzyl alcohol sensitivity, or anyone reconciling a vial against a protocol, is being given a fact that may not describe the vial in their hand.
Other label constants worth having: pH 5.7, range 4.5 to 7.0. [2] Storage: “Store at 20 to 25°C (68 to 77°F). [See USP Controlled Room Temperature.]” [2]
Sourced fact: Benzyl alcohol belongs to the alcohol class of antimicrobial preservatives, which “exhibits rapid antimicrobial efficacy against a broad range of vegetative bacteria, viruses, and fungi but is not active against spores.” [9]
Sourced fact: Its mechanism is membrane-directed. The same review reports that benzyl alcohol “was attributed with membrane-active properties leading to increased membrane fluidity and reduced structural stability,” and that it “interferes with bacterial membrane properties, e.g., efflux pumps.” [9]
Sourced fact: Its activity is not uniform across organisms. Citing Karabit et al., the review reports benzyl alcohol at 1% showing greater antimicrobial activity against Gram-negative bacteria than against Gram-positive bacteria or fungi, with D-values at pH 5.0 of 5.48 for Staphylococcus aureus, 39.0 for Candida albicans, and 28.8 for Aspergillus niger — higher D-value meaning more resistant. [9]
Inference: “Bacteriostatic” means growth-inhibiting, not sterilizing, and the spectrum is uneven — fungi are markedly less susceptible than S. aureus, and spores are not covered at all. This is the pharmacological reason the 28-day ceiling exists and the reason aseptic technique is not made optional by the presence of a preservative. A preservative that suppresses vegetative bacteria buys time; it does not reset the clock at each entry.
Sourced fact: The label carries a boxed warning: “NOT FOR USE IN NEONATES.” [2]
Sourced fact: CONTRAINDICATIONS states: “Due to the potential toxicity of benzyl alcohol in neonates, solutions containing benzyl alcohol must not be used in this patient population. Parenteral preparations with benzyl alcohol should not be used for fluid replacement. Parenteral preparations containing benzyl alcohol should not be used in epidural or spinal anesthesia procedures. Bacteriostatic Water for Injection, USP must be made approximately isotonic prior to use.” [2]
Sourced fact: WARNINGS adds: “Intravenous administration of Bacteriostatic Water for Injection without a solute may result in hemolysis.” [2]
Sourced fact: The label’s single quantified benzyl alcohol figure: “experimental studies of small volume parenteral preparations containing 0.9% benzyl alcohol in several species of animals have indicated that an estimated intravenous dose up to 30 mL may be safely given to an adult without toxic effects.” It adds that “administration of an estimated 9 mL to a 6 kg infant or neonate is potentially capable of producing blood pressure changes.” [2]
Inference: That 30 mL figure is animal-study-derived and is not a daily dosing cap, though it is frequently repeated as one. Quote it whole or not at all.
Sourced fact: An FDA CDER Pediatric and Maternal Health Staff review describes the gasping syndrome as “characterized by central nervous system depression, metabolic acidosis, gasping respirations, and high levels of benzyl alcohol and its metabolites found in the blood and urine,” and states it “has been associated with benzyl alcohol dosages >99 mg/kg/day in neonates and low-birth weight infants.” [10]
Sourced fact: The same review records that “In May 1982, FDA in conjunction with the American Academy of Pediatrics (AAP) and CDC issued a bulletin containing strong recommendations to warn pediatricians and hospital personnel against using fluids and diluents preserved with benzyl alcohol in newborn infants.” [10] The originating clinical report is Gershanik et al., New England Journal of Medicine, 1982. [11]
Inference: The phrase “gasping syndrome” does not appear on the product label itself — it comes from the FDA review and the NEJM paper. Pages that put it in quotation marks and attribute it to the label are misattributing it.
Sourced fact: Sterile Water for Injection, USP “is a clear, colorless, odorless liquid. It is sterile, hypotonic, nonpyrogenic, and contains no bacteriostatic or antimicrobial agents.” [12]
Sourced fact: Its WARNINGS section reads: “Hypotonic and hemolytic. Do not inject until made approximately isotonic by addition of an appropriate solute, due to the possibility of hemolysis.” [12]
Sourced fact: For neonatal preparations, the bacteriostatic label directs the opposite way: “Where water is required for preparing or diluting medications for use in neonates, only preservative-free Sterile Water for Injection should be used.” [2]
Inference: The functional difference is single-entry versus repeated-entry. Sterile water has no preservative, so it carries no 28-day multiple-dose allowance and no benzyl alcohol contraindication. Bacteriostatic water trades the preservative-free profile for the ability to make repeated withdrawals from one container. Neither is categorically “better”; they answer different questions, and the neonatal case inverts the usual preference entirely.
Sourced fact: Bacteriostatic Water for Injection, USP is a prescription product. The Hospira label carries the statement “BACTERIOSTATIC WATER Rx only for Injection, USP,” and its marketing category is listed as New Drug Application (NDA). [2] The US MedSource label carries the same “Rx only” statement. [3]
Sourced fact: INDICATIONS AND USAGE is narrowly drawn: “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.” [2]
Sourced fact: CDC further advises: “Assign medications packaged as multi-dose vials to a single patient whenever possible,” and “If a multi-dose vial enters an immediate patient treatment area, dedicate it for single patient use only.” [7]
Note on label dating: The Hospira SPL footer reads “Revised: 08/2019” while the DailyMed record shows an update date of May 22, 2026. Cite both when precision matters.
This is not a protocol, a reconstitution guide, or a starting point for preparing anything for administration to a person or an animal. It reports what four FDA-approved product labels, one FDA guidance document, one FDA review, CDC guidance, an ASHP standards crosswalk, and one peer-reviewed pharmaceutics review actually say — and, where they say nothing, it says so.
Questions about clinical use, preparation, or whether any product is appropriate in a given situation belong with a licensed physician or pharmacist. Questions about a specific vial’s beyond-use dating in a compounding setting belong with a pharmacist working from the current USP <797>, which is the controlling document and which we were unable to quote directly because it is paywalled.
Important notice. The figures below are transcribed from the cited labels and guidance documents. They describe what those documents state. They are not instructions, and nothing in this section should be read as guidance for preparing or administering anything.
1. What do %, w/v, mg/mL, and USP mean on this label?
Percent w/v (weight per volume) expresses grams of solute per 100 mL of solution. So 0.9% w/v benzyl alcohol equals 0.9 g per 100 mL, which equals 9 mg per mL — the two figures on the Hospira label are the same number in two units. [2] The unit ladder runs g → mg → μg (also written mcg) → ng, each step a factor of 1,000. “USP” indicates the article conforms to the United States Pharmacopeia monograph for identity, strength, quality, and purity.
2. What preservative concentrations actually appear in the labels?
Three distinct formulations across the documents we retrieved: 0.9% (9 mg/mL) benzyl alcohol and 1.1% (11 mg/mL) benzyl alcohol, both on the Hospira label and tied to the 30 mL plastic and 20 mL glass presentations respectively [2]; and a paraben-preserved formulation at 0.12% methylparaben with 0.012% propylparaben. [8]
3. Does the 28-day period appear on the product label?
No. We searched four SPLs from four labelers and the strings “28,” “days,” “discard,” and “beyond-use” were absent from all of them. [2][3][4][5] The one Fresenius Kabi insert we found does carry a discard instruction, but it is untimed: “Discard unused portion.” [8]
4. So where does it come from, in one sentence?
FDA guidance on multiple-dose container labeling (October 2018) [1], USP General Chapter <797> [6], and CDC injection-safety guidance that attributes the figure to USP [7] — all describing multiple-dose containers as a class, not this product specifically.
5. When does the 28-day period start, and can it extend the printed expiry?
It starts at first puncture, and no: “The beyond-use-date should never exceed the manufacturer’s original expiration date.” [7] ASHP’s rendering of USP <797> adds that use from initial entry “cannot exceed 28 days or the assigned BUD, whichever is shorter.” [6]
6. Does the 28-day figure apply to whatever was dissolved in the water?
No, and this is the most consequential misreading in circulation. The 28 days describes the multiple-dose container of diluent. The label routes the other question elsewhere (see also our reconstitution handling guide): “Do not store reconstituted solutions of drugs for injection unless otherwise directed by the manufacturer of the solute.” [2]
7. Does the preservative make the vial sterile indefinitely?
No. Benzyl alcohol is bacteriostatic — growth-inhibiting — and is “not active against spores,” with substantially lower activity against fungi than against S. aureus. [9] The label directs aseptic technique “for single or multiple entry and withdrawal from all containers.” [2]
8. Where do all these numbers come from?
Every figure on this page is traceable to the numbered reference list below. If a claim here has no citation attached, treat it as our reasoning rather than as a sourced fact — we have labeled the two throughout.
Closing disclaimer. Bacteriostatic Water for Injection, USP is a prescription pharmaceutical product. Nothing in this FAQ is a preparation, storage, or administration instruction, and none of it is a substitute for the judgment of a licensed pharmacist or physician working from current USP standards.
PureLab Performance supplies bacteriostatic water and research compounds for laboratory research use. Every compound page on this site publishes its own specification block — lot, chromatographic purity, label claim, identity method and testing laboratory — or states plainly that the certificate is pending. We do not round that up.
In a topic where the most-repeated fact on the internet turns out not to be printed on the label at all, knowing exactly which document your information came from is the whole game. That is the same standard we apply to what goes in the vial.
RESEARCH USE ONLY — FULL DISCLAIMER. The products discussed on this page are supplied strictly for laboratory and scientific research purposes. They are not for human or veterinary use, and not for consumption. These statements have not been evaluated by the Food and Drug Administration. Nothing on this page is intended to diagnose, treat, cure, or prevent any disease in humans or animals. Bacteriostatic Water for Injection, USP is a prescription pharmaceutical product; consult a licensed physician or pharmacist regarding any clinical question. Nothing here constitutes medical or veterinary advice or a dosing, preparation, or administration recommendation for any person or animal.
USP General Chapter <797> is cited via reference 6 (ASHP) rather than quoted directly; the USP text is paywalled and we did not retrieve it.
