Bacteriostatic Water

Bacteriostatic water for injection (BWFI) is a purified water for injection typically containing 0.9% benzyl alcohol as bacteriostatic agent. It is specifically formulated for reconstitution of lyophilized drugs and peptides intended for repeated assays over several days, benzyl alcohol preventing bacterial proliferation after each vial draw.

Unlike sterile water for injection (SWFI, preservative-free) that must be used immediately after opening, bacteriostatic water allows multi-dose use over a typical 28-day period at 2-8°C after first rubber stopper puncture. This property makes it the preferred reconstitution solvent in peptide research for peptides gradually consumed (repeated tests, staggered in vitro experiments, multi-day animal protocols).

Typical technical specifications: pH 4.5-7.0, endotoxins < 0.25 EU/mL, USP <71> validated sterility, osmolality 15 mOsm/kg, packaging in 10, 20 or 30 mL vials with red or gray chlorobutyl stopper. Major manufacturers (Hospira Pfizer, Fresenius Kabi, B.Braun) meet the USP <1> standard for water for injection.

In RUO research, bacteriostatic water use is nearly systematic for reconstituting lyophilized peptides: it ensures sterility during use duration, avoids bacterial contamination of long in vitro protocols, and preserves peptide chemical purity (slightly acidic pH unfavorable to deamidation and hydrolysis). Classic ratio is 1 mL water per mg lyophilized peptide, adjusted to desired final concentration.

Watch the contraindications: benzyl alcohol is toxic to newborns (gasping syndrome) and may be incompatible with certain sensitive cell cultures (final concentration > 0.1% benzyl alcohol may be cytotoxic). For critical cellular uses, prefer simple sterile water (SWFI) with immediate use and sterile aliquoting.