Reconstitution Guide
Bacteriostatic Water vs Sterile Water for Peptides
Bacteriostatic water and sterile water can both be used as diluent vehicles when a product specifically permits them, but they are not the same product. The main label-level difference is the preservative: bacteriostatic water contains benzyl alcohol and is supplied as a multiple-dose product, while sterile water contains no bacteriostat or antimicrobial agent and is supplied for single-dose use.
| Feature | Bacteriostatic Water | Sterile Water |
|---|---|---|
| Preservative | Benzyl alcohol | None |
| Container labeling | Multiple-dose | Single-dose |
| Reconstitution math | Vial amount ÷ liquid volume | Vial amount ÷ liquid volume |
What is bacteriostatic water?
DailyMed labeling describes Bacteriostatic Water for Injection as sterile, nonpyrogenic water containing benzyl alcohol added as a bacteriostatic preservative. It is supplied in a multiple-dose container from which repeated withdrawals may be made to dilute or dissolve compatible drugs.
What is sterile water for injection?
DailyMed labeling describes Sterile Water for Injection as sterile, nonpyrogenic water with no bacteriostat, antimicrobial agent, or added buffer. It is supplied for single-dose use, and unused portions are discarded according to the product labeling.
Does the diluent change concentration math?
No. If a vial contains 10mg and the calculation uses 2mL of liquid, the resulting arithmetic concentration is 5mg/mL regardless of whether the permitted diluent is bacteriostatic water or sterile water. Product-specific labeling determines which diluent is appropriate; BACToBasics only explains the math.
Related BACToBasics tools
Use the calculators for concentration and syringe-unit arithmetic, or read the beginner guide for a broader explanation of reconstitution terminology.
FAQ
What is the difference between bacteriostatic water and sterile water?
Bacteriostatic Water for Injection contains benzyl alcohol as a bacteriostatic preservative and is supplied in a multiple-dose container. Sterile Water for Injection contains no bacteriostat or antimicrobial agent and is supplied for single-dose use.
Does bacteriostatic water change the reconstitution math?
No. The concentration math still depends on the amount in the vial divided by the liquid volume. The type of diluent does not change the arithmetic relationship between vial amount and mL.
Does sterile water contain benzyl alcohol?
No. Sterile Water for Injection labeling states that it contains no bacteriostat, antimicrobial agent, or added buffer.
Is bacteriostatic water labeled as a multiple-dose product?
Yes. Current DailyMed labeling describes Bacteriostatic Water for Injection as a multiple-dose product from which repeated withdrawals may be made to dilute or dissolve compatible drugs.
Sources
This page summarizes product-label differences and reconstitution math for educational purposes. It does not tell you which diluent to use for a specific medication or peptide; follow the applicable product labeling and qualified clinical guidance.