Bacteriostatic Water
Sterile water for injection containing 0.9% benzyl alcohol as a bacteriostatic preservative
- Class
- Reconstitution solvent
- Half-life
- N/A
- Route
- —
- Cadence
- —
- Evidence
- Human clinical trials
Overview
Bacteriostatic water is sterile water with 0.9% benzyl alcohol added to prevent bacteria from multiplying after you open the vial. It's the standard solvent for reconstituting freeze-dried peptides — the step where you turn the powder into an injectable liquid. The benzyl alcohol doesn't kill bacteria outright, but it stops them from reproducing, which means you can draw from the same vial multiple times over weeks without it spoiling. USP-approved, widely available, and the reason your reconstituted peptide doesn't go bad after the first injection.
The alternative is sterile water (no preservative), which is single-use only — once you open it, you either use it all or throw it away. For most peptide users who dose daily or multiple times per week, that's wasteful and impractical. Bacteriostatic water lets you reconstitute a 5 mg vial, dose what you need, and come back days later for the next injection without contamination risk. Standard shelf life after first use is 28 days when refrigerated and handled with clean technique.
This is a supply item, not a therapeutic peptide — it has no direct biological effect. But it's the single most important thing you'll use in peptide handling, and choosing the wrong solvent (or skipping sterile technique) is the fastest way to ruin your peptides or introduce an infection.
Safety considerations
A few of the safety signals worth knowing — the full list, with dosing context and what to monitor, is inside AIx Core.
- Not approved for neonates — benzyl alcohol causes 'gasping syndrome' in newborns, a potentially fatal toxicity. Use preservative-free sterile water for any infant application.
- Never inject bacteriostatic water alone intravenously — it's hypotonic and will cause red blood cell lysis (hemolysis). Only use as a diluent for other drugs.
- Not for epidural or spinal injection — benzyl alcohol is contraindicated in neuraxial procedures.
+ 3 more safety notes inside AIx Core →
Commonly monitored
Markers and signals people track when researching Bacteriostatic Water.
- Injection-site reactions (redness, swelling — usually means contamination or poor technique)
- Vial expiry — discard 28 days after first puncture
- Cloudiness or particles in the vial — sign of contamination, discard immediately
- Reconstituted peptide stability — most peptides stay stable 10–14 days in BAC water when refrigerated; check the peptide's specific data
Frequently asked questions
What is Bacteriostatic Water?
Sterile water for injection containing 0.9% benzyl alcohol as a bacteriostatic preservative. Bacteriostatic water is sterile water with 0.9% benzyl alcohol added to prevent bacteria from multiplying after you open the vial. It's the standard solvent for reconstituting freeze-dried peptides — the step where you turn the powder into an injectable liquid. The benzyl alcohol doesn't kill bacteria outright, but it stops them from reproducing, which means you can draw from the same vial multiple times over weeks without it spoiling. USP-approved, widely available, and the reason your reconstituted peptide doesn't go bad after the first injection.
What is the half-life of Bacteriostatic Water?
N/A — Not a therapeutic agent — functions as a diluent for lyophilized peptides.
Is Bacteriostatic Water approved for human use?
Bacteriostatic Water is investigational — not approved by the FDA, EMA, or MHRA for human use at the time of writing.
What does the evidence show for Bacteriostatic Water?
Evidence tier: Human clinical trials. USP monograph (DailyMed) specifies 0.9% (9 mg/mL) benzyl alcohol; pH 4.5–7.0. This is the pharmaceutical standard used in all major brands (Hospira/Pfizer, etc.).
What is commonly monitored when researching Bacteriostatic Water?
Commonly tracked markers + signals: Injection-site reactions (redness, swelling — usually means contamination or poor technique), Vial expiry — discard 28 days after first puncture, Cloudiness or particles in the vial — sign of contamination, discard immediately, Reconstituted peptide stability — most peptides stay stable 10–14 days in BAC water when refrigerated; check the peptide's specific data.
Open this in AIx Core for the full picture
Mechanism breakdown, receptor pathway diagram, full safety list, monitored items, source citations, and one-tap add-to-protocol. Free with any account.