Benzyl Alcohol in Bacteriostatic Water: Why 0.9%?
By the BacWaterPep editorial team · Updated
Short answer. Benzyl alcohol is the preservative that makes water 'bacteriostatic': at 0.9% (9 mg/mL) it inhibits bacterial growth in a vial that is entered repeatedly. It is measured on every lot, typically by gas chromatography, and must sit inside a range such as 0.8–1.0% (v/v).
| Chemical | Benzyl alcohol, C7H8O, CAS 100-51-6 (PubChem CID 244) |
|---|---|
| Usual concentration | 0.9% — 9 mg per mL (Hospira label); some co-packs use 1.1% |
| Our acceptance range | 0.9% ± 0.1% (v/v), GC-FID against a reference standard |
| Effect | Bacteriostatic (inhibits growth), not bactericidal; no effect on viruses |
| Known hazard | Toxic to neonates at high cumulative exposure (gasping syndrome) |
Why a range, not a single number
Too little preservative weakens the bacteriostatic effect; too much adds unnecessary benzyl alcohol. A lot's COA should show the measured content and the limit, not only 'conforms'.
How it is tested
- Identity: GC retention time and FTIR against a benzyl alcohol reference.
- Content: GC-FID with an external reference, reported in % v/v.
- Effectiveness: a preservative challenge test (USP <51> style) on the released formulation.
Safety boundary
Benzyl alcohol caused severe and fatal toxicity in premature infants exposed to large cumulative amounts (Gershanik 1982), and labels for bacteriostatic water exclude neonatal use. Treat it as a reagent: follow the SDS.
Not all 'bac water' is the same
A 1.1% co-pack exists for one medicine (FDA label), and some sellers do not state the concentration at all. Ask for the measured value on the lot COA.
Sources
- PubChem — Benzyl alcohol (CID 244)
- DailyMed — Bacteriostatic Water for Injection, USP (0.9% benzyl alcohol), Hospira label
- FDA label with a 1.1% benzyl alcohol bacteriostatic water co-pack (BLA 761074)
- Gershanik et al. 1982, The gasping syndrome and benzyl alcohol poisoning, N Engl J Med (PubMed 7133084)
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