Glossary
Bacteriostatic water
Also called BAC water, Bac water, Bacteriostatic water for injection
Sterile water with a small amount of benzyl alcohol added as a preservative, so a vial can be punctured more than once. It is the default liquid for mixing multi-dose peptide vials.
In more detail
The approved product is Bacteriostatic Water for Injection, USP. Its label lists 0.9% benzyl alcohol (9 mg per mL), with some sizes at 1.1%, and describes it as a multiple-dose container meant only as a diluent. The label stores the unopened vial at room temperature (20 to 25 C) and carries a boxed note that it is not for use in newborns.
Plain sterile water has no preservative. Guides treat it as single-use: mix and use the same day, or expect a much shorter window. BAC water is what makes a vial you draw from for weeks practical.
How long an opened vial lasts: CDC guidance, based on USP Chapter 797, is to date a punctured multi-dose vial and discard it within 28 days unless the maker says otherwise. Most peptide guides borrow that same 28 days for mixed peptide vials. That figure is about the preservative and contamination, not about how long a given peptide stays potent. CDC also notes the preservative does not fully protect against contamination, so clean technique still matters.
Why it matters
The wrong liquid either shortens your vial's life (sterile water) or is not sterile at all (tap or distilled water). Keep opened BAC water in the fridge and dated, as many guides advise.
Related terms
- ReconstitutionAdding a sterile liquid, usually bacteriostatic water, to a vial of freeze-dried peptide powder so it becomes an injectable solution with a known strength.
- Sterile techniqueThe set of habits that keep germs out of a vial, syringe and injection site: clean hands, swabbed stoppers and skin, new needles, and never touching anything that should stay sterile.
- Peptide stabilityHow long a peptide keeps its structure and strength. It depends on the molecule, whether it is dry or in solution, temperature, light and handling.
- DrawPulling liquid from a vial into a syringe. To draw a dose is to measure the number of units you need on the syringe.
- Vial headspaceThe air space above the powder or liquid in a sealed vial. Its pressure, often a partial vacuum on sealed powder vials, affects how water goes in and how doses come out.
Peptides where this comes up
Sources
Each source is labeled by where the information comes from. How we label sources
- RegulatoryBacteriostatic Water for Injection, USP: prescribing information(opens in a new tab)
Pfizer (Hospira) labeling · checked
- RegulatoryPreventing unsafe injection practices(opens in a new tab)
CDC · checked
- Competitor guideBacteriostatic water refrigeration(opens in a new tab)
peptidesexplorer.com · checked
- Competitor guideBAC water vs sterile water for peptides(opens in a new tab)
peptiq.io · checked
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