Definition: Benzyl alcohol is the preservative in bacteriostatic water and bacteriostatic saline, usually at 0.9%, which is 9 mg per mL. It keeps bacteria from multiplying so a vial can be entered more than once. It is not safe for newborns, which is why these labels carry a neonate warning. It may also make some injections sting less.
Hospira bacteriostatic water comes with 0.9% (9 mg/mL) or 1.1% (11 mg/mL) benzyl alcohol. A percent here means grams per 100 mL, so 0.9% is 0.9 g in 100 mL, or 9 mg in each mL.
Benzyl alcohol in a mixed vial (2 mL is an example volume)
A 1982 report in the New England Journal of Medicine tied a "gasping syndrome" in newborns to benzyl alcohol poisoning (Gershanik 1982). The Omnitrope label says benzyl alcohol has been linked to serious harm and death, mostly in children, and describes the syndrome as nervous system depression, acid buildup in the blood, gasping breaths and high blood levels of benzyl alcohol, linked to more than 99 mg/kg per day in newborns and low-birth-weight babies. It also asks prescribers to count benzyl alcohol from all sources.
The bacteriostatic water label says it must not be used in neonates and that only preservative-free sterile water should be used for them. It also says animal studies suggest an adult could get up to about 30 mL into a vein without toxic effects.
A 2022 review found five studies where botulinum toxin mixed with benzyl alcohol saline hurt less around the eyes and face than when mixed with plain saline (Hunt 2022). The effect is not universal: in a randomized study of 124 shoulder joint injections, saline with benzyl alcohol gave slightly higher pain scores afterward (Storey 2014).
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