What Is Bacteriostatic Saline Used For? The Label Answer

• Bacteriostatic saline is labelled as a diluent: a sterile, preserved 0.9% sodium chloride solution intended for use only after a medicine that requires dilution or dissolving has been added to it.
• It is never used on its own. The product information says so directly, and the same line appears on bacteriostatic water.
• Which diluent a medicine takes is fixed by that medicine's own product information, not by the diluent's label and not by a retailer.
• “Bacteriostatic” is what allows the multi-dose label: the benzyl alcohol preservative holds bacterial growth in check between entries.
• The label rules out use in neonates and warns about the preservative. Those warnings are on the vial for a reason and are reproduced here.

The short answer

Bacteriostatic 0.9% Sodium Chloride Injection, USP is labelled by its manufacturer as a diluent: a sterile, non-pyrogenic, isotonic solution of sodium chloride (9 mg/mL) with benzyl alcohol (9 mg/mL) added as a bacteriostatic preservative, supplied in a multiple-dose vial and “designed for parenteral use only after addition of drugs that require dilution or must be dissolved in an aqueous vehicle prior to injection.” That sentence is the whole of the labelled use. It is not a medicine and it is not used by itself.

What “diluent” means

A diluent is the liquid a medicine is dissolved or diluted in before it can be measured by volume. Some medicines are supplied as a dry powder that must be reconstituted; others are supplied concentrated and must be diluted. In both cases the medicine's own product information names the diluent it is compatible with, the volume, and the handling. The diluent's label does not carry that information, because the diluent does not know what it will be mixed with. That is why a retailer cannot tell you what to prepare with it, and this site does not.

Why a preserved saline exists at all

Plain 0.9% sodium chloride for injection is preservative-free and its container is labelled for a single withdrawal. Once the seal is broken there is nothing in it to hold bacterial growth in check, so the remainder is discarded. Bacteriostatic saline adds benzyl alcohol at 0.9%, which inhibits the growth of most common bacteria that might be introduced when the vial is entered, and that is what lets the manufacturer label the vial multiple-dose. What bacteriostatic means defines the word, and how the 0.9% benzyl alcohol preservative works covers the mechanism.

The choice between the preserved and preservative-free presentation is therefore not a preference: a preparation that will be drawn from repeatedly is generally specified with a preserved diluent, and a preparation whose product information calls for a preservative-free diluent takes the plain one. The specification decides it.

Saline or water?

Bacteriostatic saline and bacteriostatic water differ in one thing: the salt. Bacteriostatic water has no solute; bacteriostatic saline is isotonic 0.9% sodium chloride. Both carry the same preservative and both are labelled multi-dose diluents. Which one a medicine is prepared with is, again, a line in that medicine's product information. Bacteriostatic saline vs bacteriostatic water sets them side by side, with sterile water and plain saline.

What the label rules out

The manufacturer's product information carries a boxed warning: not for use in neonates, because benzyl alcohol has been associated with toxicity in that group. It also states that the solution is for drug diluent use only, and — on bacteriostatic water — that intravenous administration without a solute may cause haemolysis. These are the manufacturer's warnings, reproduced because they are the part of the label most often left off a listing. The product information itself is linked from the documentation page.

What this page is not

It is not advice about what to prepare, how, or in what volume. Bacteriostatic saline is a diluent or solvent, not a ready-to-administer medicine; compatibility, preparation and use follow the product information of whatever is being prepared, under qualified healthcare-professional direction. Aus BAC Supply supplies the sealed manufacturer vial and gives no dosing, preparation or administration advice. What to check in any supplier is on sourcing and integrity.