Reconstitution, dosing & half-life math — done right, in seconds.
Bacteriostatic vs Sterile Water vs Saline
Three liquids come up constantly in reconstitution — bacteriostatic water, sterile water, and saline. They're easy to mix up, but the practical difference comes down to one thing: a preservative.
What each one is
Diluents
Bacteriostatic waterwater + ~0.9% benzyl alcohol
Sterile waterpure water, no preservative
Saline0.9% sodium chloride, no preservative
The preservative is the point
The benzyl alcohol in bacteriostatic water inhibits bacterial growth. That's what lets a reconstituted multi-dose vial be entered repeatedly over a period of days, rather than being discarded after one use. Sterile water and plain saline have no preservative, so they're generally treated as single-use.
Which is used to reconstitute?
For most multi-use peptide vials, bacteriostatic water is the common choice precisely because of that preservative. Saline shows up in contexts like intranasal sprays, where an isotonic, more comfortable solution is wanted — often blended with bacteriostatic water. The right choice depends on your specific product and how it's used.
It doesn't change the math
Whatever diluent you use, concentration is just peptide ÷ total volume. The diluent affects preservation and comfort, not the numbers — so the reconstitution calculator works the same either way.
What is the difference between bacteriostatic and sterile water?
Both are purified water for injection. The difference is a preservative: bacteriostatic water contains about 0.9% benzyl alcohol, which inhibits bacterial growth and lets a vial be entered multiple times over a period of days. Sterile water has no preservative and is generally intended for single use.
Can I use saline to reconstitute a peptide?
Saline (0.9% sodium chloride) is sometimes used, often alongside bacteriostatic water — for example in intranasal preparations where an isotonic, nose-friendly solution is desirable. Like sterile water, plain saline has no preservative. Follow the guidance appropriate to your specific product.
Why is bacteriostatic water used for multi-dose vials?
Its benzyl alcohol preservative slows microbial growth between uses, which is what allows a reconstituted vial to be drawn from more than once rather than discarded after a single use.
Does the type of water change the concentration math?
No. Concentration is simply the peptide amount divided by the total liquid volume, whatever the liquid is. The choice of diluent affects preservation and comfort, not the arithmetic.