Bacteriostatic Water

Bacteriostatic water consists of sterile water for injection to which 0.9% benzyl alcohol has been added as a preservative. The alcohol is not a sterilant: it holds back bacterial multiplication without killing organisms already present — the literal sense of "bacteriostatic". Because growth is suppressed, a reconstituted vial can be accessed several times during a working period rather than thrown away after a single withdrawal.

Its role in the peptide lab

For lyophilized research peptides that will be sampled more than once, it is the standard reconstitution solvent. Common lab practice is to store the preserved vial in the fridge and to regard about 28 days as the customary in-use period, following the labelling norm for preserved multi-entry pharmaceutical diluents. Wipe the stopper with an alcohol pad and use a new needle for every entry.

Where it is not suitable

Benzyl alcohol does not suit every application. It is contraindicated in neonatal preparations, it may encourage aggregation in some protein formulations, and it is usually left out wherever a preservative would disturb cell-based assays. In those cases, plain sterile water or a defined buffer is preferable.

Why the choice counts

The solvent you pick determines how long a solution remains usable and whether entering it repeatedly can be justified. The concentration calculation for the peptide stays exactly the same.

Related terms

bacteriostatic · preservative (benzyl alcohol). Compare in bacteriostatic vs sterile water, or see Bacteriostatic Water.