The pharmaceutical-grade peptide diluent. Hospira/Pfizer Bacteriostatic Water (NDA 018802) is the FDA-approved standard — sterile water + 0.9% benzyl alcohol that lets you re-puncture a multi-dose vial for ~28 days. Here’s when to use it, when not to, and why neonates have a black-box history with this preservative.
Bacteriostatic Water for Injection (BAC water) is sterile water with 0.9% (9 mg/mL) benzyl alcohol added as an antimicrobial preservative. The USP-NF monograph specifies pH 5.7 (range 4.5–7.0) and the benzyl alcohol concentration. The preservative makes the vial “bacteriostatic” (prevents bacterial growth) but not sterile-after-puncture — you still want clean technique — which is what allows multi-dose use over a window of days to weeks.
For peptide reconstitution this is the dominant default: most peptides are stable in BAC water at the typical reconstitution pH, and the preservative lets you draw multiple doses out of one vial without needing a fresh sterile diluent each time. Compare that to Sterile Water for Injection (SWFI), which has no preservative and is single-use only.
FDA-approved as Hospira/Pfizer Bacteriostatic Water for Injection USP, NDA 018802. USP-NF monograph. Available by prescription, OTC at some pharmacies depending on state, and through 503A compounding pharmacies.
Not all “BAC water” is equal. The Hospira/Pfizer 30 mL multi-dose vial (NDC 0409-3977-03) is the FDA-approved pharmaceutical product manufactured under FDA-inspected GMP — sterilized under validated processes, tested for endotoxins, and labeled with an FDA-cleared in-use shelf life. Hospira was acquired by Pfizer on September 3, 2015; current packaging is “Hospira, Inc., Lake Forest, IL — A Pfizer Company.”
Compounded BAC water from peptide-supply pharmacies (Empower, Hallandale, etc.) is also widely sold and many are reputable, but a 503A compounder isn’t held to the same FDA-approved-product standards. Sterility assurance and endotoxin specs vary by pharmacy.
“Research grade” BAC water sold by peptide research-chemical sites is a separate category. Sterility, endotoxin, and preservative-concentration assurance is whatever the seller claims. For injection, this category should be avoided in favor of pharmaceutical or 503A-compounded sources.
Benzyl alcohol at 0.9% prevents bacterial replication but doesn’t actively kill organisms already inside the vial. Translation: clean injection technique still matters. The preservative buys you a safe re-entry window of about 28 days.
Per USP <797> and the FDA-approved label, the in-use beyond-use date for a punctured Hospira vial is 28 days at controlled room temperature (20–25 °C). Most peptide reconstitution practice refrigerates after first puncture for additional peptide-stability margin even though the preservative itself doesn’t require it.
Slightly acidic. This is fine for most peptides but is exactly why IGF-1 LR3 aggregates within days in BAC water — LR3 needs a more acidic environment (0.6% acetic acid) to stay soluble.
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Start Tracking FreeBAC water’s prominent “not for use in neonates” warning traces to a real and well-documented incident. In 1982, NICUs at multiple hospitals saw a cluster of newborn deaths from metabolic acidosis, seizures, and gasping respirations. The cause: high cumulative exposure to benzyl alcohol from frequent BAC-water flushes of indwelling catheters and IV lines. Premature infants lack the mature glycine-N-acyltransferase enzyme adults have, so they accumulate benzyl alcohol’s toxic metabolite (benzoic acid) instead of clearing it.
A 1–3 mL BAC-water injection delivers about 0.13–0.39 mg/kg of benzyl alcohol per dose — two to three orders of magnitude below the documented adult tolerated load. The neonate warning is real and important; it is not a meaningful concern for an adult using BAC water for peptide injection. People with documented benzyl alcohol allergy are the relevant adult exclusion.
BAC water’s pH 5.7 is too neutral for LR3. The peptide aggregates within days. Acetic-acid reconstitution gives ~28-day stability. See the IGF-1 LR3 guide.
Per the 1982 incident and AAP statement, BAC water is contraindicated in newborns. Sterile Water for Injection (no preservative) is the substitute, single-use only.
Rare but real. Skin reactions to multi-dose vaccines or local anesthetics that contain benzyl alcohol are the typical history. If documented, use Sterile Water for Injection plus single-use vial discipline.
Vendor literature splits. Most peptide-supply pharmacies recommend BAC water for PEG-MGF reconstitution; some communities use 0.6% acetic acid by analogy with IGF-1 LR3. There is no published peer-reviewed PK comparison to settle this. The dominant practice is BAC water; if your supplier specifies otherwise, follow their instruction.
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Controlled room temperature (20–25 °C / 68–77 °F). Excursions allowed to 15–30 °C. Don’t freeze. Keep out of direct sunlight.
28-day BUD at controlled room temperature per USP <797> and the Hospira label. Many peptide users refrigerate the punctured vial as a defensive habit — the preservative itself doesn’t require it, but cold storage gives margin against any borderline-contaminated draw.
Most BAC water vials outlive the peptide they’re reconstituting. A typical compounded peptide vial is reconstituted to last ~28 days; the BAC water 30 mL vial typically lasts months across many peptides. Date each vial when you first puncture it.
| Diluent | When to Use | In-use BUD |
|---|---|---|
| Bacteriostatic Water (this guide) | Default for most peptides. Multi-dose use OK. | 28 days |
| Sterile Water for Injection (SWFI) | Single-dose use, neonate-safe, benzyl alcohol allergy | Single use |
| 0.6% Acetic Acid | IGF-1 LR3, IGF-1 DES, peptides that aggregate at neutral pH | ~28 days |
| 0.9% Sterile Sodium Chloride (saline) | When isotonic vehicle is preferred or for nasal spray formulations | Single use unless preserved |
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