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FDA-approvedVendors pendingFacts verified · 2026-05-25

Bacteriostatic Water

Also known as bac, bac water, bacteriostatic water, water, solution

Bacteriostatic Water for Injection (BWFI) is a sterile, non-pyrogenic preparation of water for injection containing 0.9% (9 mg/mL) benzyl alcohol as an antimicrobial preservative, manufactured to United States Pharmacopeia (USP) specifications. It is not a drug or a peptide; it is a pharmacopeial diluent approved by the FDA for reconstituting and diluting parenteral medications including lyophilized peptides, hormones, antibiotics, and biologics that are supplied as powders or concentrates. Unlike preservative-free sterile water for injection (single-use), the benzyl alcohol in BWFI inhibits microbial proliferation in the vial after the closure has been punctured, supporting multi-dose use for up to 28 days under USP standards. BWFI is supplied in multi-dose vials (commonly 10–30 mL) and is the diluent most peptide users select for lyophilized vials because it preserves potency between draws.

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Mechanism of action

Bacteriostatic Water has no pharmacological mechanism of action — it is a solvent (water for injection) with an added antimicrobial preservative. The active excipient, benzyl alcohol, is bacteriostatic rather than bactericidal: at the 0.

Bacteriostatic Water has no pharmacological mechanism of action — it is a solvent (water for injection) with an added antimicrobial preservative. The active excipient, benzyl alcohol, is bacteriostatic rather than bactericidal: at the 0.9% w/v (9 mg/mL) concentration specified by the USP monograph, it disrupts the integrity of the bacterial cytoplasmic membrane, increases membrane permeability, and interferes with microbial protein synthesis, slowing replication of typical contaminants introduced during repeated vial punctures (see FDA-approved labeling for parenteral products that incorporate the same vehicle, e.g., Solu-Medrol: https://www.accessdata.fda.gov/drugsatfda_docs/label/2011/011856s103s104lbl.pdf). In humans, benzyl alcohol is oxidized to benzoic acid, conjugated with glycine in the liver to hippuric acid, and renally excreted; this pathway is functionally absent in premature neonates, which underlies the historical "gasping syndrome" toxicity that drove FDA neonatal-use warnings (Gershanik et al., https://pubmed.ncbi.nlm.nih.gov/7133084/). At reconstitution volumes of 1–3 mL per peptide vial, the systemic benzyl alcohol exposure in adults is several orders of magnitude below any documented toxicity threshold (~99–234 mg/kg/day in affected neonates).

Pharmacokinetic properties

Half-life

N/A — solvent, not a drug. The benzyl alcohol excipient is oxidized to benzoic acid, conjugated to hippuric acid in the liver, and renally excreted (functional half-life of hours in adults; markedly prolonged in premature neonates).

Routes

subcutaneous · intramuscular · intravenous

Bioavailability

Used as a diluent/reconstitution solvent for lyophilized peptides and other powdered parenteral drugs. Benzyl alcohol systemic exposure is negligible at typical reconstitution volumes — well below the historically observed neonatal toxicity threshold of ~99 mg/kg/day.

Amino-acid sequence

Benzyl alcohol (the preservative): C7H8O (SMILES: C1=CC=CC=C1CO) at 0.9% w/v (~9 mg/mL)

Use & research dosing

Reconstitution of lyophilized peptide vialsMulti-dose dilution of injectable drugsInjection-supplies vehicle

Not a therapeutic agent and therefore has no dose. In peptide reconstitution, 1–3 mL of bacteriostatic water is commonly added to a lyophilized vial to dissolve the powder; the practitioner then withdraws measured insulin-syringe units of the resulting solution for administration. Per USP standards and FDA-approved labeling, a punctured multi-dose vial of bacteriostatic water should be discarded 28 days after first entry to limit microbial accumulation. Bacteriostatic water is NOT intended for large-volume IV dilution, intrathecal/epidural use, or as the diluent for any product whose label specifies preservative-free sterile water (e.g., certain monoclonal antibodies, some pediatric formulations, vaccines that prohibit benzyl alcohol). Aseptic technique — swabbing the closure with isopropyl alcohol before each entry and using a fresh sterile needle — is recommended. Store at controlled room temperature between draws.

Research-use framing only. SavePeptides sells nothing for human consumption. Doses above reflect reported research / self-experimentation ranges, not clinical recommendations.

Editorial perspective

Bacteriostatic Water is the standard 0.9% benzyl-alcohol-preserved sterile water used to reconstitute lyophilized peptide vials. It is NOT a peptide and has no pharmacological action of its own; its presence on a peptide marketplace reflects that it is sold as injection supplies alongside lyophilized peptide products. Some informal sources cite a 3% benzyl alcohol concentration, but the USP monograph and every FDA-approved BWFI label specify 0.9% w/v (~9 mg/mL). A few legacy compounded products specify slightly higher (e.g., 1.1%), but 0.9% is the canonical pharmacopeial standard.

— SavePeptides editorial desk · last updated 2026-05-25

Cautions & contraindications

Before researching this compound, note:

  • Contraindicated in neonates and very low birth-weight infants — benzyl alcohol toxicity ('gasping syndrome'; CNS depression, metabolic acidosis, cardiovascular collapse)
  • Avoid in pregnancy where preservative-free sterile water is preferred
  • Known benzyl alcohol hypersensitivity
  • Do not use for large-volume IV dilution — use preservative-free sterile water or normal saline
  • Do not inject undiluted as a hypotonic solution in large volumes (risk of hemolysis)
  • Do not use for intrathecal, epidural, or ocular routes
  • Discard 28 days after first puncture (USP standard)
  • Use aseptic technique at each entry; do not transfer contents between vials
  • Do not use if solution is cloudy or contains particulate matter
  • Confirm compatibility with the drug being reconstituted — some products require preservative-free diluent per label
  • Store at controlled room temperature; avoid freezing

Research foundation

The papers behind the page.

  1. [01]https://www.accessdata.fda.gov/drugsatfda_docs/label/2011/011856s103s104lbl.pdf
  2. [02]https://pubmed.ncbi.nlm.nih.gov/7133084/
  3. [03]https://pubmed.ncbi.nlm.nih.gov/6695984/
  4. [04]https://www.fda.gov/safety/recalls-market-withdrawals-safety-alerts/hospira-inc-issues-voluntary-nationwide-recall-one-lot-bacteriostatic-water-injection-usp-due
  5. [05]https://www.fda.gov/media/76873/download

Facts verified

2026-05-25

Confidence

high

What this means

  • not a peptide — solvent for reconstitution

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Bacteriostatic Water · SavePeptides