Bacteriostatic water shelf life

Bacteriostatic water for injection is sterile water with one addition: 0.9% (9 mg/mL) benzyl alcohol, a preservative that holds bacterial growth in check. That preservative is the whole reason it is sold in a multiple-dose vial - you can enter it again and again to mix or dilute injectable compounds, rather than throwing it out after one use. It is the standard diluent for reconstituting peptides.

The widely repeated 28-day figure is not vendor folklore. It comes from USP General Chapter <797>, which assigns a 28-day beyond-use date to a punctured multiple-dose container unless the manufacturer says otherwise. That number is tied to USP <51> antimicrobial-effectiveness testing - the window over which a preservative like benzyl alcohol is expected to keep doing its job. After 28 days, that assurance lapses, so the convention is to discard the vial even if water obviously does not "expire" the way a drug does.

One honest caveat: that 28-day standard was written for pharmacy-handled, professionally punctured vials. It is a sensible ceiling to borrow, not a guarantee about a vial kept and re-entered at home - clean technique still matters.

Store bacteriostatic water at controlled room temperature. It does not need to be refrigerated, and it should not be frozen. Keep the vial capped, wipe the stopper before each draw, and keep it out of direct heat and sunlight. A neonate-toxicity warning and a high-volume caution apply to the benzyl alcohol itself - relevant context, though far outside a typical small reconstitution volume.

The diluent you choose is what decides how long the mixed peptide lasts. Bacteriostatic water's preservative is why a reconstituted peptide keeps for weeks refrigerated; plain sterile water, with no preservative, drops that to roughly a day. If you are deciding how much water to add, the reconstitution calculator does the math.