How do I calculate the dose on a U-100 insulin syringe?

Concentration (mg/ml) = vial mg ÷ ml of bacteriostatic water added. Units to draw = (desired dose in mg ÷ concentration) × 100, because a U-100 syringe has 100 units per ml.

What water should I use to reconstitute peptides?

Always use bacteriostatic water for injection (0.9% benzyl alcohol), supplied by your TGA-licensed Australian compounding pharmacy. Never use tap, distilled, or sterile water alone for multi-dose vials.

How long does a reconstituted peptide last in the fridge?

Most reconstituted peptides are stable for 28 days at 2-8 °C in bacteriostatic water. Some (e.g. tirzepatide, semaglutide) follow the manufacturer label. Always confirm with your prescribing doctor and pharmacy label.

Can I shake the vial?

No. Swirl gently or invert slowly. Shaking introduces shear stress that can denature the peptide. Let the powder dissolve fully (usually 1-2 minutes) before withdrawing the first dose.

What if my dose calculation gives a non-whole number of units?

Round to the nearest 0.5 or 1 unit on a U-100 syringe (or use a U-50 syringe for finer dosing). If unsure, message your prescribing doctor before injecting — never guess.

AHPRA-reviewed · Australian doctors

Peptide reconstitution calculator

Work out concentration, draw volume, and units on a U-100 insulin syringe for any peptide vial. Built for Australian patients prescribed lyophilised peptides via the TGA SAS-B pathway.

Reconstitution calculator

Enter the vial strength your pharmacy dispensed, the bacteriostatic water you'll add, and your prescribed dose.

Vial peptide (mg)Bacteriostatic water (ml)Prescribed dose (mg)

Concentration: 2.50 mg/ml
Draw volume: 0.100 ml
U-100 syringe: 10.0 units
Doses per vial: 20.0

Educational tool only. Always cross-check with your prescribing doctor and the pharmacy label before injecting.

Sterile reconstitution — step-by-step

1
Wash hands and clean surface
Wash hands for 20 seconds, dry, and lay out a clean alcohol-wiped tray.
2
Wipe both vial stoppers
Alcohol swab the rubber stopper of the bacteriostatic water vial and the peptide vial. Let air-dry for 10 seconds.
3
Draw the bacteriostatic water
With a 3 ml syringe + 23G needle, withdraw the exact ml of bacteriostatic water you entered in the calculator.
4
Inject slowly down the side of the peptide vial
Aim the needle at the inside wall and inject the water slowly — do not blast directly onto the powder.
5
Swirl, do not shake
Roll the vial gently between your palms for 30-60 seconds until the powder fully dissolves to a clear solution.
6
Label with date + concentration
Write reconstitution date and mg/ml on the vial. Store at 2-8 °C (fridge), away from light. Use within 28 days unless your pharmacy says otherwise.

Cold-chain storage

Store reconstituted vials at 2-8 °C, upright, away from light. Most are good for 28 days; some up to 60 days per pharmacy label.

Right syringe

U-100 insulin syringes (0.3 ml or 0.5 ml) suit most doses. For very small doses, ask your pharmacy for a U-50.

When to stop

Discard if the solution is cloudy, discoloured, or contains particles. Contact your prescriber for a replacement vial.

Reconstitution FAQs

How do I calculate the dose on a U-100 insulin syringe?: Concentration (mg/ml) = vial mg ÷ ml of bacteriostatic water added. Units to draw = (desired dose in mg ÷ concentration) × 100, because a U-100 syringe has 100 units per ml.
What water should I use to reconstitute peptides?: Always use bacteriostatic water for injection (0.9% benzyl alcohol), supplied by your TGA-licensed Australian compounding pharmacy. Never use tap, distilled, or sterile water alone for multi-dose vials.
How long does a reconstituted peptide last in the fridge?: Most reconstituted peptides are stable for 28 days at 2-8 °C in bacteriostatic water. Some (e.g. tirzepatide, semaglutide) follow the manufacturer label. Always confirm with your prescribing doctor and pharmacy label.
Can I shake the vial?: No. Swirl gently or invert slowly. Shaking introduces shear stress that can denature the peptide. Let the powder dissolve fully (usually 1-2 minutes) before withdrawing the first dose.
What if my dose calculation gives a non-whole number of units?: Round to the nearest 0.5 or 1 unit on a U-100 syringe (or use a U-50 syringe for finer dosing). If unsure, message your prescribing doctor before injecting — never guess.

Medically reviewed by the PeptideDoctorAU Medical Review Panel — last reviewed 29 May 2026.

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