Bacteriostatic-Water

Bacteriostatic Water for Injection, USP is a sterile, nonpyrogenic aqueous preparation containing 0.9 percent (9 mg/mL) benzyl alcohol as a bacteriostatic preservative, manufactured to the United States Pharmacopeia monograph specification and distributed under FDA oversight as a pharmaceutical-grade parenteral vehicle. Unlike Sterile Water for Injection, which contains no antimicrobial agent and is designated for single-use applications, Bacteriostatic Water for Injection is formulated specifically for multi-dose access, permitting repeated aseptic puncture of a single vial over a period of up to 28 days while maintaining microbiological integrity. The preparation is classified as a pharmaceutical vehicle rather than an active pharmaceutical ingredient; it carries no intrinsic therapeutic activity and is indicated exclusively as a diluent or solvent for drugs intended for intravenous, intramuscular, or subcutaneous injection, according to the labeling of the drug to be administered.

The bacteriostatic property of the formulation derives entirely from the benzyl alcohol excipient, a simple aromatic primary alcohol (C6H5CH2OH; CAS 100-51-6; molecular weight 108.14 g/mol) that exerts its antimicrobial effect principally through disruption of bacterial cell membrane phospholipid bilayer integrity and interference with cellular metabolic processes. The mechanism is bacteriostatic rather than bactericidal: at 0.9 percent concentration, benzyl alcohol inhibits the reproduction of common environmental contaminants (including Staphylococcus aureus and Pseudomonas aeruginosa) without achieving immediate sterilization of the solution. This distinction is operationally important, as the formulation depends on initial sterility at the point of manufacture and on aseptic technique during use to maintain the sterile state; the preservative serves as a secondary barrier against microbial proliferation following vial puncture.

Benzyl alcohol is metabolized in adult humans through a well-characterized hepatic oxidation pathway: alcohol dehydrogenase converts benzyl alcohol to benzaldehyde, aldehyde dehydrogenase converts benzaldehyde to benzoic acid, and benzoic acid is conjugated with glycine in the liver to form hippuric acid, which is excreted renally. Within six hours of oral administration of 1.5 g of benzyl alcohol, adult subjects excreted 75 to 85 percent of the dose as urinary hippuric acid, reflecting the efficiency of this metabolic pathway in mature individuals. However, in neonates (particularly premature infants), the enzymatic capacity for benzoic acid metabolism is developmentally immature, and repeated parenteral exposure to benzyl alcohol at cumulative doses of 100 to 240 mg/kg/day has been associated with a severe toxicity syndrome characterized by metabolic acidosis, gasping respirations, central nervous system depression, intraventricular hemorrhage, and cardiovascular collapse, termed the "gasping syndrome." This association, first reported in 1982 in the New England Journal of Medicine and subsequently confirmed by the FDA, resulted in a regulatory contraindication against the use of benzyl alcohol-containing preparations in neonatal patients.

The preparation is supplied in multi-dose glass or plastic flip-top vials, most commonly in a 30 mL presentation. The principal FDA-listed manufacturer is Hospira, Inc. (a Pfizer subsidiary), with the product distributed under NDC codes including 0409-3977. The USP monograph specifies a pH range of 4.5 to 7.0, a bacterial endotoxin limit of less than 0.5 USP Endotoxin Units per mL, and compliance with USP particulate matter, sterility, and container-closure integrity requirements. The preparation is isotonically and osmotically insufficient on its own and is not suitable for direct intravenous administration without prior dilution or reconstitution with the intended drug product; the tonicity of the final solution depends on the solute.

This monograph reviews the compound identification, history, molecular pharmacology (of the benzyl alcohol preservative), pharmacokinetics of benzyl alcohol, the preclinical and clinical evidence base for safety and toxicology, sourcing and quality verification considerations, reconstitution and handling protocols, interactions with peptide and protein solutes, the adverse event and safety signal profile (including neonatal contraindication), and a comparative assessment of five alternative parenteral vehicles against Bacteriostatic Water for Injection on five competency standards.