Bacteriostatic Water

Bacteriostatic water is not a therapeutic agent — it is a pharmaceutical preparation of sterile water preserved with 0.9% benzyl alcohol (9 mg/mL). The benzyl alcohol serves as a bacteriostatic preservative, meaning it inhibits bacterial growth and reproduction without necessarily killing all organisms (unlike bactericidal agents).

Benzyl alcohol's antimicrobial mechanism involves disruption of bacterial cell membrane integrity. The lipophilic benzyl group partitions into the phospholipid bilayer of bacterial membranes, disordering the lipid packing and increasing membrane permeability. This compromises the membrane's ability to maintain ion gradients and membrane potential, inhibiting active transport, ATP synthesis, and other membrane-dependent processes essential for bacterial reproduction. At 0.9% concentration, this effect is sufficient to prevent bacterial multiplication in reconstituted peptide solutions, maintaining sterility for the 28-day use period after first puncture.

For peptide reconstitution, bacteriostatic water is preferred over sterile water for injection (SWFI) when multi-dose vials will be used. SWFI lacks preservative and must be used immediately after opening, as a single needle puncture can introduce bacteria that will multiply freely in the absence of preservative. The 0.9% benzyl alcohol in bacteriostatic water prevents this microbial contamination during repeated vial access. The reconstitution technique matters: water should be directed against the vial wall and allowed to run down gently to dissolve the lyophilized peptide cake, rather than sprayed directly onto the powder, which can cause foaming and protein denaturation from the mechanical stress of bubble formation.