Label explainer

What is bacteriostatic water? Benzyl alcohol, shelf life, limits

By the Decadewise team Education only Last reviewed 27 July 2026 No calculator on this page

Short answer

The definition, from the label: bacteriostatic water for injection is a sterile, nonpyrogenic preparation of water for injection containing benzyl alcohol added as a bacteriostatic preservative.

How much preservative: 0.9%, which is 9mg per mL, in the plastic vial presentation, and 1.1%, which is 11mg per mL, in the glass one. The pH is 5.7, with a stated range of 4.5 to 7.0.

What it is for: the label states one indication only, diluting or dissolving drugs for intravenous, intramuscular or subcutaneous injection, following the instructions of the manufacturer of the drug being dissolved.

What the preservative buys and costs: it buys a multiple-dose container from which repeated withdrawals may be made, and it costs the neonate population, for whom the label is an outright contraindication.

The 28-day figure is not a shelf life and not a label statement: it is an in-use limit counted from first puncture, and it comes from the sterile compounding chapter that governs multiple-dose containers, not from this product's own prescribing information.

On this page

Short answer What the label says How much benzyl alcohol The newborn rule How long after opening What it is made of Does it sterilize? Same as sterile water? How to store the vial Around this page How this is sourced The disclaimer

What the label says it is, and what it leaves out

The description section is short: sterile, nonpyrogenic, water for injection, plus benzyl alcohol at one of two stated strengths, supplied in a multiple-dose container from which repeated withdrawals may be made to dilute or dissolve drugs for injection.

Bacteriostatic is a claim about growth, not about killing: the label names benzyl alcohol as a bacteriostatic preservative, and nothing in the document describes it as a sterilant or as a rescue for a container that has been contaminated.

The label makes no claim about the solute: there is no statement anywhere in it that the preservative stabilizes, protects or extends whatever gets dissolved into the water. The precautions point the other way, telling the reader not to store reconstituted drug solutions unless the manufacturer of the solute directs otherwise.

What is absent: no in-use interval, no statement about refrigeration of the diluted product, and no maximum volume for the preparation itself. None of the three labels read for this page states any of them.

How much benzyl alcohol a vial holds

The arithmetic is one multiplication: the stated concentration multiplied by the volume in the container. At 9mg per mL a 30mL vial holds 270mg of benzyl alcohol in total, and at 11mg per mL the 20mL fill in the glass vial holds 220mg.

Per withdrawal it is much smaller: at 9mg per mL, drawing 1mL carries 9mg of benzyl alcohol along with the water, drawing 2mL carries 18mg, and drawing 3mL carries 27mg.

Benzyl alcohol carried by the water, at the two label concentrations

Volume of water	At 0.9% (9mg per mL)	At 1.1% (11mg per mL)
0.5mL	4.5mg	5.5mg
1mL	9mg	11mg
2mL	18mg	22mg
3mL	27mg	33mg
whole vial, as supplied	270mg in the 30mL plastic vial	220mg in the 20mL fill

Multiplication on the two concentrations the label states. The rows above the last one are volumes drawn; the last row is the container total for each presentation the label lists, and the label describes the product as a diluent rather than something given at that volume. How supplied lists 0.9% as a 30mL plastic Fliptop vial and 1.1% as a 20mL fill in a 30mL glass Fliptop vial, so the two presentations differ in fill volume as well as in strength.

What the arithmetic does not settle: the benzyl alcohol warning carried on the glycopyrrolate injection label cited below says that although normal therapeutic doses of that product deliver amounts of benzyl alcohol substantially lower than those reported in association with the gasping syndrome, the minimum amount of benzyl alcohol at which toxicity may occur is not known. The multiplication above is exact. The threshold it would be compared against is one that label states is not known.

The newborn contraindication, and where it comes from

What the label says now: due to the potential toxicity of benzyl alcohol in neonates, solutions containing benzyl alcohol must not be used in this patient population, and where water is required for preparing or diluting medications for neonates, only preservative-free sterile water for injection should be used.

What that warning text describes: the gasping syndrome, characterized by central nervous system depression, metabolic acidosis, gasping respirations, and high levels of benzyl alcohol and its metabolites in blood and urine, associated with benzyl alcohol dosages above 99mg per kg per day in neonates and low-birth-weight neonates.

The additional signs it lists: gradual neurological deterioration, seizures, intracranial hemorrhage, blood abnormalities, skin breakdown, liver and kidney failure, hypotension, bradycardia and cardiovascular collapse.

Where the term appears in the indexed literature: a 1982 New England Journal of Medicine report titled The gasping syndrome and benzyl alcohol poisoning, a CDC report that June titled Neonatal deaths associated with use of benzyl alcohol, and an American Academy of Pediatrics statement the following year titled Benzyl alcohol: toxic agent in neonatal units. They are named here for what they are; none of the three is cited as the first record of the syndrome.

The contraindication is absolute rather than dosed: the label bars the population outright, and the warning text states that the minimum toxic amount is not known, so no threshold is printed to calculate against.

How long is an opened vial good for?

The label does not answer: three bacteriostatic water labels were read for this page, and none of them prints a discard interval after first entry. The 28-day figure is not a label statement.

The rule that does exist: USP General Chapter 797, the sterile compounding chapter, sets in-use time for the conventionally manufactured containers a compounder draws from, and its official questions and answers describe the requirement that multiple-dose containers not be used for more than 28 days unless otherwise specified on the labeling. The same document notes that compounding does not cover mixing or reconstituting done in accordance with directions in approved labeling.

It is a separate clock from the beyond-use date: the same document gives the example of a multiple-dose vial with a 60-day beyond-use date that still has to be discarded no later than 28 days after first puncture. Neither figure is the container's expiration date.

And it belongs to the container, not the contents: the 28 days describes how long the preserved diluent container may keep being entered. What happens to a drug dissolved in that water is the solute manufacturer's question, which is exactly where the label's precautions send it.

What is bacteriostatic water made of?

Two ingredients, and the label names both. Water for injection, which is the sterile nonpyrogenic base, and benzyl alcohol at 9mg per mL or 11mg per mL depending on the presentation, added as a bacteriostatic preservative. There is no buffer, no salt, and no stabilizer for anything dissolved into it. That composition is why the label still requires the finished preparation to be made approximately isotonic before use, and why it warns that intravenous administration without a solute may result in hemolysis. The preservative changes the container's working life and nothing about the water's tonicity.

Does bacteriostatic water sterilize anything?

No, and the word says so: bacteriostatic describes inhibition of bacterial growth, and the label calls benzyl alcohol a preservative rather than a sterilant.

The container starts sterile: the first sentence of the description calls the preparation sterile and nonpyrogenic, so the preservative is protecting a state that already exists.

Technique is still on the label: the precautions direct aseptic technique for single or multiple entry and withdrawal from all containers, and the label sets no exception for the preserved product.

Is it the same as sterile water?

No. The Hospira sterile water label cited below states that the product contains no bacteriostat, no antimicrobial agent and no added buffer, and that it is supplied only in single-dose containers, with the instruction not to reuse the container and to discard the unused portion. Bacteriostatic water carries the preservative and is supplied multiple-dose. The clauses that read the same on both are the indication sentence, the isotonicity requirement and the hemolysis warning. The two documents also differ in smaller ways, including which one states a pH and what the front panel carries, so the ingredient and the container are the difference that matters here rather than the only difference there is. The choice between them is a choice about how many times the container will be entered, and about whether benzyl alcohol is acceptable in the mixture.

How should the vial itself be stored?

At controlled room temperature. The label states storage at 20 to 25 degrees C, which is 68 to 77 degrees F, and refers to the USP controlled room temperature definition. There is no instruction to refrigerate the diluent, and none of the three bacteriostatic water labels read for this page mentions refrigeration at all. The label's other handling lines are about the seal and the solution rather than the temperature: do not use unless the solution is clear and the seal is intact, and inspect the reconstituted drug for clarity and for freedom from unexpected precipitation or discoloration before administration.

Around this page

The neighboring reads: five pages in the library we maintain, each carrying a piece this one only introduces.

Bacteriostatic water vs sterile water: the two water labels compared row by row, including the in-use clocks.
Bacteriostatic water vs saline: the salt question, the tonicity numbers, and the restrictions that attach to preserved saline.
Bacteriostatic water calculator: the water volume needed to reach a chosen concentration in a given vial.
How water volume changes your units: why the milliliters added rewrite every unit count that follows.
Storage after reconstitution: the vial once it holds liquid, and what the labels do and do not cover.
The Decadewise briefing: one label read or one tool like this, in your inbox once a week.

How this page is sourced

Three labels for one product: the Hospira label, a Henry Schein repackaged version and a US MedSource version were each read in full, which is how the absence of an in-use interval was established rather than assumed. The US MedSource record is a 2014 SPL whose only NDC is now inactivated, and it is cited as a historical label rather than a current one. The Hospira sterile water label is cited separately, for the comparison section only.

The gasping syndrome text is quoted from a label that carries it: the version quoted here is the benzyl alcohol warning printed on a current glycopyrrolate injection label, and it is quoted with its own scope intact rather than restated as a general finding.

The 1982 and 1983 records are cited by title: the three publications below are named for what they are, and no case counts or exposure figures from them are reported on this page, because their full texts were not retrievable for this review.

Last reviewed: 27 July 2026.

1
Hospira, Inc. Bacteriostatic Water for Injection, USP, prescribing information: description, indications, contraindications, warnings, precautions, how supplied. SPL version 20, effective 22 May 2026. DailyMed, U.S. National Library of Medicine. Current label.
2
Henry Schein, Inc. (repackager); the repackaged label names Hospira, Inc. as distributor of the source product. Bacteriostatic Water for Injection, USP, 30 mL multiple-dose vial, full prescribing information. DailyMed, U.S. National Library of Medicine. Current label.
3
BE Pharmaceuticals Inc. Glycopyrrolate Injection, USP, 0.2 mg/mL, prescribing information, benzyl alcohol warning. DailyMed, U.S. National Library of Medicine. Current label.
4
United States Pharmacopeia. General Chapter <797> Pharmaceutical Compounding, Sterile Preparations: frequently asked questions, updated 11 December 2023, questions 187, 188, 193 and 194. USP document.
5
Gershanik J, Boecler B, Ensley H, McCloskey S, George W. The gasping syndrome and benzyl alcohol poisoning. N Engl J Med. 1982;307(22):1384-1388. doi:10.1056/NEJM198211253072206. PMID 7133084.
6
Centers for Disease Control. Neonatal deaths associated with use of benzyl alcohol, United States. MMWR Morb Mortal Wkly Rep. 1982;31(22):290-291. PMID 6810084.
7
Committee on Fetus and Newborn, Committee on Drugs, American Academy of Pediatrics. Benzyl alcohol: toxic agent in neonatal units. Pediatrics. 1983;72(3):356-358. doi:10.1542/peds.72.3.356. PMID 6889041.
8
US MedSource, LLC. Bacteriostatic Water for Injection, USP, prescribing information. SPL version 1, updated 7 July 2014; the record's only NDC is now inactivated. DailyMed, U.S. National Library of Medicine. Archived label.
9
Hospira, Inc. Sterile Water for Injection, USP, prescribing information: description, contraindications, warnings, how supplied. SPL version 10, effective 18 March 2026. DailyMed, U.S. National Library of Medicine. Current label.

The disclaimer

Every page is reviewed by medical professionals before it ships, and written with longtime biohackers who were doing this before it was a trend. Reviewed still does not mean prescribed: nothing here is medical advice. It is research, trial data, and reported use, with the numbers intact so you can check them. For decisions about your body, see a doctor who can look at your labs.