“Bacteriostatic water” names a specific formula: sterile water for injection with 0.9% benzyl alcohol. “Reconstitution solution” names what a liquid is used for: turning a freeze-dried powder back into a solution. Many products called reconstitution solution are bacteriostatic water. Not all of them are.
| Bacteriostatic water | “Reconstitution solution” | |
|---|---|---|
| What the name means | A defined formula (USP) | Any liquid used to reconstitute a powder |
| Ingredients | Sterile water + 0.9% benzyl alcohol | Depends on the product: often bacteriostatic water, sometimes sterile water, saline or another diluent |
| How to tell | “Bacteriostatic Water for Injection” and benzyl alcohol on the label | Read the ingredient line |
When the two are the same product
Several sellers use “reconstitution solution” as the product name for bacteriostatic water. Reconstitution Solution (reconstitution-solution.co), for example, describes its vials as sterile water for injection preserved with 0.9% benzyl alcohol, made to the USP bacteriostatic formula, in 3 mL, 10 mL and 30 mL sizes. That is bacteriostatic water under another name, and everything on this site about bac water applies to it.
When they are different
Prescription medicines supplied as powders often come with their own diluent, which the manufacturer may call a reconstitution solution or diluent. That liquid is matched to that medicine: it may be sterile water, saline, or a solution with other ingredients, and it is not interchangeable with bacteriostatic water just because the job is the same. Some research diluents are also sold as “reconstitution solution” without a preservative.
Reconstitution solution for peptides
When people search for “reconstitution solution for peptides” they are usually looking for bacteriostatic water, because it is the diluent most associated with lyophilized peptides. The multiple-dose vial and the preservative suit a peptide that will be drawn from more than once. As with any diluent, the instructions for the specific peptide are what say which liquid to use.
Three questions that settle it
- Does the label list benzyl alcohol, and at 0.9% (9 mg/mL)?
- Is the container marked as a multiple-dose vial?
- Does the label carry a lot number and an expiry date?
Yes to all three is bacteriostatic water, whatever the front of the vial says.
Sources: DailyMed, Bacteriostatic Water for Injection, USP; supplier listing as published.