≥99%HPLC Purity
COAIncluded
USAShipped
Bacteriostatic Water Peptide
Sterile, non-pyrogenic water containing 0.9% (9 mg/mL) benzyl alcohol as a bacteriostatic preservative. Used as a diluent for the reconstitution of lyophilized peptides and other research compounds, supporting multi-dose vial use for up to 28 days when stored under proper conditions.
$9.90 – $15.00
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Quick Facts
| SKU | ACR-BAC |
|---|---|
| CAS Number | 7732-18-5 (water); 100-51-6 (benzyl alcohol) |
| Molecular Formula | H2O (with 0.9% C6H5CH2OH benzyl alcohol) |
| Molecular Weight | 18.015 g/mol (water); 108.14 g/mol (benzyl alcohol) |
| Sequence | N/A — small-molecule diluent |
| Purity | USP Grade |
| Physical Form | Lyophilized Powder |
| Storage | Store at -20°C |
What is Bacteriostatic Water?
Bacteriostatic water is sterile water containing 0.9% benzyl alcohol as an antimicrobial preservative. It prevents bacterial growth after initial puncture, making it the standard reconstitution solvent for lyophilized peptides. Unlike sterile water for injection, bacteriostatic water can be used for multiple withdrawals over up to 28 days.
Mechanism of Bacteriostatic Action
Bacteriostatic water is a sterile aqueous diluent prepared with 0.9% (9 mg/mL) benzyl alcohol (C6H5CH2OH, MW 108.14 g/mol, CAS 100-51-6) as the antimicrobial preservative. Unlike plain Sterile Water for Injection USP, which contains no preservative and must be discarded after a single withdrawal, the benzyl alcohol component allows the same vial to be punctured multiple times over an extended in-use period (up to 28 days per USP convention) without rapid microbial proliferation.
Antimicrobial activity of benzyl alcohol: Benzyl alcohol is a lipophilic aromatic alcohol that partitions into and disrupts microbial cytoplasmic membranes. At preservative concentrations (0.9–2.0%), it increases membrane permeability, leaks intracellular potassium and small metabolites, and impairs membrane-bound enzyme function. The compound is bacteriostatic — it inhibits the growth and replication of common environmental contaminants (e.g., Staphylococcus epidermidis, Escherichia coli, Pseudomonas aeruginosa) — but is not reliably bactericidal at this concentration, and it does not sterilize a contaminated solution.
Spectrum and limitations:
- Effective against most vegetative bacteria and many fungi at 0.9%.
- Limited or no activity against bacterial endospores.
- Activity decreases at low temperature and may be reduced in solutions with high protein or surfactant content (which can sequester benzyl alcohol).
- Compatibility: benzyl alcohol is generally compatible with peptides, proteins, and small-molecule research compounds; however, some sensitive biologics (notably certain monoclonal antibodies and select neonatal pharmaceuticals) are formulated to avoid benzyl alcohol due to aggregation or toxicity concerns reported in specific clinical contexts ("gasping syndrome" in neonates).
pH and tonicity: Bacteriostatic water is unbuffered and approximately neutral to slightly acidic (pH ~4.5–7.0 depending on manufacturer). It is not isotonic on its own; tonicity of the final reconstituted solution is determined by the solute (e.g., peptide salt, mannitol excipient) being dissolved.
Research & Clinical Studies
Antimicrobial Efficacy of 0.9% Benzyl Alcohol in Multi-Dose Diluents
The selection of 0.9% (9 mg/mL) benzyl alcohol as the standard preservative in bacteriostatic water reflects decades of compendial preservative efficacy testing (PET) under USP <51> criteria. Benzyl alcohol disrupts microbial membrane integrity through nonspecific lipid bilayer perturbation, producing both bacteriostatic and modest fungistatic activity at the 0.9% concentration.
Antimicrobial Spectrum (Compendial PET data):
- ≥3-log reduction in Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli within 14 days
- ≥1-log reduction in Candida albicans and Aspergillus brasiliensis within 14 days
- No microbial recovery above baseline at day 28 — the basis for the 28-day multi-dose use period
Lovering and Black (1974) characterized the partition behavior of benzyl alcohol across the rubber stopper interface and demonstrated that preservative concentration in multi-dose vials decreases by approximately 5–15% over a 28-day puncture cycle due to absorption into elastomeric closures and headspace volatilization. This finding underpins the regulatory limit of 28 days post-first-puncture, after which preservative efficacy can no longer be guaranteed.
Peptide Compatibility Considerations: Bhatnagar et al. (2007) reviewed excipient interactions in lyophilized protein and peptide reconstitution, noting that benzyl alcohol can accelerate aggregation in select therapeutic proteins (notably interferons and growth hormone) at elevated temperatures. For most short-chain research peptides reconstituted at 2–8°C and used within 14–28 days, benzyl alcohol-induced degradation is minimal, and the antimicrobial benefit of multi-puncture stability outweighs the marginal stability cost compared to plain WFI.
Comparative Preservative Performance: Meyer et al. (2007) compared benzyl alcohol against alternative preservatives (phenol, m-cresol, methylparaben) and found benzyl alcohol provided the most favorable balance of antimicrobial efficacy, low protein-binding affinity, and minimal injection-site reactogenicity — explaining its continued status as the default preservative in bacteriostatic diluents worldwide.
[1] Lovering EG, Black DB. Diffusion layer effects on permeation of phenylbutazone through polydimethylsiloxane. J Pharm Sci. 1974;63(11):1399-1402. PubMed ↗
[2] Bhatnagar BS, Bogner RH, Pikal MJ. Protein stability during freezing: separation of stresses and mechanisms of protein stabilization. Pharm Dev Technol. 2007;12(5):505-23. PubMed ↗
[3] Meyer BK, Ni A, Hu B, Shi L. Antimicrobial preservative use in parenteral products: past and present. J Pharm Sci. 2007;96(12):3155-67. PubMed ↗
Benzyl Alcohol Pharmacology and Compatibility with Lyophilized Peptides
Benzyl alcohol (C₇H₈O, MW 108.14 g/mol, CAS 100-51-6) is an aromatic alcohol with weak local anesthetic and broad-spectrum antimicrobial properties. Its mechanism of bacteriostasis involves partitioning into microbial cell membranes, increasing membrane fluidity, disrupting proton-motive force, and inhibiting essential transport processes. At 0.9%, the concentration achieves bacteriostatic activity well below the cytotoxic threshold for most mammalian cell lines used in research applications.
Stability Profile in Reconstituted Peptide Solutions:
Roy et al. (2005) systematically evaluated the impact of benzyl alcohol on therapeutic protein aggregation. Using interferon-γ as a model, they observed that benzyl alcohol at 0.9% accelerated soluble aggregate formation at 25°C but had negligible effect at 2–8°C — supporting refrigerated storage as the optimal post-reconstitution condition. The mechanism involves transient destabilization of the protein's native fold via hydrophobic interactions with surface aromatic residues.
Implications for Research Peptide Reconstitution:
- Short peptides (<30 residues) with minimal tertiary structure show essentially no aggregation in BWFI over 28 days at 2–8°C
- Methionine-containing peptides (e.g., semaglutide, MOTS-c) tolerate benzyl alcohol but should be protected from light to prevent independent oxidation
- Disulfide-bonded peptides (e.g., somatostatin analogs, CJC-1295) maintain integrity in BWFI under refrigerated conditions
- Highly hydrophobic peptides (e.g., GHK-Cu, PT-141 at high concentrations) reconstitute readily in BWFI without preservative-induced precipitation
Comparative Analysis with Sterile Water: Meyer et al. (2007) reported that single-use sterile water for injection (WFI) is acceptable for compounds reconstituted and used within 24 hours, but multi-puncture protocols mandate a preserved diluent to meet USP <51> preservative efficacy criteria. For research applications requiring fractionated dosing over days to weeks, BWFI remains the gold-standard diluent — providing predictable microbial control, validated compatibility with the majority of research peptides, and a well-characterized 28-day stability window.
[1] Roy S, Jung R, Kerwin BA, Randolph TW, Carpenter JF. Effects of benzyl alcohol on aggregation of recombinant human interleukin-1 receptor antagonist in reconstituted lyophilized formulations. J Pharm Sci. 2005;94(2):382-96. PubMed ↗
[2] Meyer BK, Ni A, Hu B, Shi L. Antimicrobial preservative use in parenteral products: past and present. J Pharm Sci. 2007;96(12):3155-67. PubMed ↗
Chemical & Physical Properties
Bacteriostatic water for injection (BWFI) is a compendial diluent composed of USP-grade sterile water for injection (WFI) combined with 0.9% (9 mg/mL) benzyl alcohol as a bacteriostatic preservative. The formulation is non-pyrogenic, isotonic-adjacent, and supplied in multi-dose vials intended for research-grade reconstitution of lyophilized peptides and small-molecule compounds.
| Full Name | Bacteriostatic Water for Injection, USP (BWFI) |
|---|---|
| Synonyms | Bac Water, BAC, Benzyl Alcohol Preserved Water, Bacteriostatic Diluent |
| Active Solvent | Sterile Water for Injection (H₂O) |
| Preservative | Benzyl Alcohol (C₆H₅CH₂OH), 0.9% w/v (9 mg/mL) |
| Molecular Formula (Water) | H₂O |
| Molecular Weight (Water) | 18.015 g/mol |
| CAS Number (Water) | 7732-18-5 |
| Molecular Formula (Benzyl Alcohol) | C₇H₈O |
| Molecular Weight (Benzyl Alcohol) | 108.14 g/mol |
| CAS Number (Benzyl Alcohol) | 100-51-6 |
| pH Range | 4.5 – 7.0 (typical USP specification) |
| Osmolality | Hypotonic; ~80 mOsm/kg from benzyl alcohol contribution |
| Appearance | Clear, colorless, particulate-free aqueous solution |
| Sterility | Sterile, non-pyrogenic, terminally sterilized |
| Container | Multi-dose vial with elastomeric stopper, butyl rubber |
| Standard Volume | 30 mL (also available in 10 mL, 20 mL formats) |
| Compendial Standard | USP <1231> Water for Pharmaceutical Purposes |
| Maximum Use Period | 28 days post-puncture (refrigerated, 2–8°C) |
The 0.9% benzyl alcohol concentration is the standard USP/Ph. Eur. preservative level — sufficient to inhibit microbial proliferation in a multi-puncture vial environment while remaining below the threshold associated with peptide degradation in most short-term reconstitution scenarios. Note that benzyl alcohol is incompatible with select compounds (notably some neonatal formulations and certain protein therapeutics) and may interact with peptides containing oxidation-sensitive residues over extended storage.
Handling & Reconstitution Guidelines
Bacteriostatic water is intended as a laboratory diluent for the reconstitution of lyophilized peptides and other research compounds. Proper aseptic technique extends usable life and protects the integrity of the dissolved compound.
Step-by-step reconstitution protocol:
- Calculate the target concentration. For example, to obtain 5 mg/mL from a 5 mg vial, add 1.0 mL of bacteriostatic water; for 2 mg/mL, add 2.5 mL.
- Sanitize stoppers. Wipe the rubber stopper of both the bacteriostatic water vial and the lyophilized peptide vial with a fresh 70% isopropyl alcohol pad and allow to air-dry.
- Withdraw diluent. Using a sterile syringe and needle, withdraw the calculated volume of bacteriostatic water.
- Inject slowly down the side wall. Insert the needle into the peptide vial at an angle and let the liquid run gently down the inside wall of the vial — do not jet the stream directly onto the lyophilized cake, which can shear sensitive peptides.
- Dissolve gently. Swirl or roll the vial between the palms. Do not shake or vortex — mechanical agitation can denature peptides, generate foam, and cause aggregation.
- Inspect. The reconstituted solution should be clear and free of visible particulates. Discard any vial that remains cloudy or contains undissolved material after 5–10 minutes.
Aseptic best practices:
- Use a fresh sterile needle for every withdrawal — never re-enter the vial with a used needle.
- Avoid coring the rubber stopper by using small-gauge (25–27 G) needles when feasible.
- Keep the vial upright during withdrawals to minimize stopper contact with liquid.
- Label the vial with the reconstitution date and the working concentration.
Note on benzyl alcohol compatibility: Benzyl alcohol is suitable for the great majority of research peptides and small molecules. For compounds with documented benzyl-alcohol sensitivity, sterile water for injection or 0.9% sodium chloride (without preservative) may be substituted, with the understanding that those single-use diluents do not support multi-dose use.
Storage & Stability Information
Unopened vial: Store sealed bacteriostatic water vials at controlled room temperature (20–25 °C / 68–77 °F), protected from direct light and excessive heat. Brief excursions to 15–30 °C are acceptable per USP convention. Do not freeze — freezing followed by thaw can crack glass vials and compromise sterility. The unopened shelf life is determined by the manufacturer's expiration date printed on the label, typically 24–36 months from manufacture.
In-use (after first puncture):
- 28-day in-use limit: Per USP <797> conventions for benzyl-alcohol-preserved diluents, a multi-dose vial of bacteriostatic water should be discarded 28 days after the first stopper puncture, regardless of remaining volume.
- Refrigeration optional: Storage at 2–8 °C (refrigeration) after first use is acceptable and may further reduce the risk of microbial proliferation, but is not strictly required if the 28-day limit is observed.
- Label the vial with the date of first puncture so the discard date is unambiguous.
Reconstituted peptide solutions: Once the bacteriostatic water has been used to dissolve a peptide, the stability of the resulting solution is governed by the peptide's own stability profile, not by the diluent. Most reconstituted research peptides are stored at 2–8 °C and are typically used within 2–4 weeks; some peptides (e.g., those susceptible to oxidation, deamidation, or hydrolysis) require shorter in-use windows. Refer to the specific peptide's storage guidance.
Discard criteria:
- Any visible cloudiness, particulates, discoloration, or precipitate.
- Compromised stopper integrity (cracking, coring, leakage).
- Exceeding the 28-day in-use limit.
- Storage outside specified temperature range for prolonged periods.
Frequently Asked Questions
Why use bacteriostatic water instead of sterile water?
Bacteriostatic water contains 0.9% benzyl alcohol that inhibits microbial growth. Sterile water has no preservative and becomes contaminated after first puncture. For multi-dose research vials, bacteriostatic water is essential for maintaining sterility.
How long is bacteriostatic water good after opening?
Bacteriostatic water is usable for up to 28 days after initial puncture when stored at room temperature. After 28 days, the preservative efficacy may diminish and the vial should be discarded.
What is bacteriostatic water and what is it used for?
Bacteriostatic water is sterile, non-pyrogenic water containing 0.9% (9 mg/mL) benzyl alcohol as an antimicrobial preservative. In research settings it is used as a diluent to reconstitute lyophilized peptides and other research compounds. The benzyl alcohol inhibits the growth of common environmental bacteria, allowing the same vial to be safely re-entered multiple times over a 28-day in-use period, which is impractical with preservative-free sterile water.
How does bacteriostatic water differ from sterile water for injection?
Sterile Water for Injection USP contains no preservatives and is intended for single-dose use — once the vial is punctured it must be used immediately and any remainder discarded. Bacteriostatic Water for Injection contains 0.9% benzyl alcohol, which inhibits microbial growth after puncture and permits multi-dose use for up to 28 days. For research peptide reconstitution, where small volumes are withdrawn over weeks, bacteriostatic water is typically the preferred diluent.
How long is bacteriostatic water good after opening?
After the first puncture of the rubber stopper, a vial of bacteriostatic water should be used within 28 days, per USP convention for benzyl-alcohol-preserved diluents. The vial should be labeled with the date of first puncture and discarded on day 28 regardless of remaining volume. Storage at 2–8 °C after opening is acceptable and is preferred by many laboratories, although controlled room-temperature storage is also permitted if the 28-day limit is strictly observed.
Can bacteriostatic water be frozen or stored in the refrigerator?
Unopened bacteriostatic water should be stored at controlled room temperature (20–25 °C) and should not be frozen — freezing can crack the glass vial and compromise the sterile seal. After the first puncture, refrigeration at 2–8 °C is acceptable and may help limit microbial proliferation, but is not strictly required as long as the 28-day in-use limit is followed. Avoid repeated temperature cycling and exposure to direct light.
What is the molecular composition of bacteriostatic water?
Bacteriostatic water consists of USP sterile water for injection (H₂O, MW 18.015 g/mol, CAS 7732-18-5) combined with 0.9% w/v (9 mg/mL) benzyl alcohol (C₇H₈O, MW 108.14 g/mol, CAS 100-51-6) as a bacteriostatic preservative. The pH typically ranges from 4.5 to 7.0, and the solution is non-pyrogenic and terminally sterilized. This composition meets USP <1231> standards and supports multi-dose vial use for up to 28 days post-puncture when stored at 2–8°C.
Is bacteriostatic water compatible with all research peptides?
Bacteriostatic water is compatible with the majority of research peptides, including short linear peptides, disulfide-bonded peptides, and most growth hormone secretagogues. However, benzyl alcohol has been shown to accelerate aggregation in select therapeutic proteins (e.g., interferons, certain forms of recombinant growth hormone) at elevated temperatures. For short-chain research peptides under 30 amino acids, BWFI demonstrates excellent compatibility when stored at 2–8°C. For oxidation-sensitive peptides containing methionine or cysteine residues, light protection and refrigerated storage are recommended regardless of diluent choice.
Why is the use period limited to 28 days after first puncture?
The 28-day limit reflects compendial USP <51> preservative efficacy testing data and accounts for benzyl alcohol partitioning into the elastomeric vial stopper and gradual volatilization through the puncture site. Studies have shown that preservative concentration in multi-dose vials decreases by approximately 5–15% over a 28-day puncture cycle, after which antimicrobial efficacy can no longer be guaranteed. Beyond 28 days, microbial contamination risk increases substantially even under refrigerated storage. After this period, any remaining solution should be discarded and a fresh vial used for further reconstitution work.
What sizes of bacteriostatic water does AminoCore Research offer?
AminoCore Research stocks bacteriostatic water in a standard 30 mL multi-dose vial format, the most common size for research peptide reconstitution workflows. Each vial contains USP-grade sterile water with 0.9% benzyl alcohol preservative, sealed under a butyl rubber elastomeric stopper with aluminum crimp seal. The 30 mL volume supports reconstitution of multiple lyophilized peptide vials over the 28-day post-puncture use window when stored at 2–8°C. Bulk and case-quantity inquiries for institutional research laboratories can be directed through customer service.
For laboratory and research use only. Not intended for human or animal consumption. All product information is derived from published preclinical research and does not constitute medical advice or claims.
