Sterile water for injection

Sterile water for injection is purified water that has been sterilised and sealed, with nothing else added. Because it contains no preservative, any bacteria introduced when a needle passes through the stopper can grow freely in the solution. That makes it appropriate for a vial that is reconstituted and used at once, and inappropriate as a diluent for a multi-dose vial, where bacteriostatic water is the standard.

There are two situations in which sterile water is the better choice. A few peptides are sensitive to benzyl alcohol, the preservative in bacteriostatic water, and their stability data is only available in preservative-free diluent. And some research protocols specify that a whole vial is reconstituted and consumed in a single session, in which case a preservative adds nothing.

Either way, the arithmetic of reconstitution is identical: the volume of diluent sets the concentration, and the dosage calculator works the same for both.