How reconstitution works

Lyophilized peptide arrives as a dry cake at the bottom of the vial. Adding bacteriostatic water dissolves it into a solution at a known concentration, and that concentration is what turns a target dose into a number of units on the syringe.

The only formula you need

Concentration (mg/mL) = peptide in the vial (mg) ÷ bacteriostatic water added (mL). From there, volume to draw (mL) = dose (mg) ÷ concentration, and because insulin syringes are marked in U-100 units, units = mL × 100.

Choosing how much water to add

More water means a lower concentration and a larger, easier-to-read draw. Less water means a smaller draw and fewer wasted drops, but doses become hard to measure precisely. As a rule of thumb, aim for a dose that lands between 10 and 40 units on the syringe — the calculator flags it when your numbers fall outside that comfortable band.

Adding the water without wrecking the peptide

Run the bacteriostatic water slowly down the inside wall of the vial rather than blasting it directly onto the cake. Let it dissolve on its own, and swirl gently if needed. Never shake a peptide vial — the shear forces and foaming can denature the peptide.

Storage after reconstitution

Once in solution, peptides are far less stable than the dry powder. Keep reconstituted vials refrigerated, protect them from light, and treat bacteriostatic water’s benzyl alcohol as what makes multi-dose use possible in the first place. Compound-specific guidance is on each product page alongside the certificate for that batch.

A note on IU

“IU” on an insulin syringe is a volume marking, not a measure of peptide mass: 1 IU equals 0.01 mL. The calculator treats it that way, so switching the dose unit to IU tells you how much peptide sits at that mark for your specific concentration.