Bacteriostatic Water℞

A diluent is the liquid used to prepare a medication for administration. Some injectable medicines come as a powder that must be dissolved; this is called reconstitution. Others need dilution to reach the concentration specified in their prescribing instructions. Bacteriostatic water can perform either role when the medicine’s manufacturer identifies it as a compatible diluent.

The choice is specific to the medicine. Sterile water, bacteriostatic water and saline are not automatically interchangeable, and bacteriostatic water is intended for medication preparation—not injection on its own. [1]

“Bacteriostatic” refers to limiting bacterial growth. The featured 30 mL Hospira vial contains 0.9% benzyl alcohol for this purpose. The preservative does not protect against viruses or make a vial immune to contamination. Aseptic technique remains essential every time the vial is accessed.

That is a key distinction from Hospira’s preservative-free Sterile Water for Injection, which contains no antimicrobial agent and is supplied in single-dose containers. Leftover contents from a single-dose container should not be saved for another use, even for the same person. The medication’s requirements determine which formulation is appropriate. [1] [4] [5]

The multi-dose format permits repeated withdrawals from the same vial. The 30 mL on the label describes how much liquid the vial contains—not a medication dose or the amount to use for a particular preparation. That amount is determined by the medicine’s prescribing instructions.

Once punctured, a multi-dose vial has an opened-vial use period. CDC recommends dating it and discarding it within 28 days unless its manufacturer specifies a different period, never beyond the original expiration date. A prepared medication has separate storage and stability requirements: the diluent’s opened-vial period does not establish how long the mixed medicine can be kept. [1] [4]