Dose, volume, and units are three views of one number
A dose is an amount of peptide, usually written in micrograms. A syringe cannot measure micrograms; it measures volume. So a dose only becomes drawable once the concentration of the vial is known, and the concentration depends entirely on how much bacteriostatic water was added.
This is why the same 250 mcg dose is a different mark on the syringe for two people holding identical vials. The dose has not changed. The dilution has.
The same 250 mcg dose from a 5 mg vial, at three different dilutions.
| Water added | Concentration | Volume to draw | U-100 units |
|---|---|---|---|
| 1 mL | 5 mg/mL | 0.05 mL | 5 units |
| 2 mL | 2.5 mg/mL | 0.10 mL | 10 units |
| 3 mL | 1.67 mg/mL | 0.15 mL | 15 units |
Converting between mcg and mg
One milligram is one thousand micrograms. Doses are commonly written in mcg while vials are labelled in mg, so the conversion sits in the middle of nearly every peptide calculation and is a common place for an error to enter.
| Micrograms (mcg) | Milligrams (mg) |
|---|---|
| 100 mcg | 0.1 mg |
| 250 mcg | 0.25 mg |
| 500 mcg | 0.5 mg |
| 1,000 mcg | 1 mg |
| 2,500 mcg | 2.5 mg |
How many doses a vial holds
Divide the vial strength by the dose, with both in the same unit. A 5 mg vial against a 250 mcg dose is 5 mg ÷ 0.25 mg, which is 20 doses. The diluent volume does not change this. It changes how much liquid each of those 20 doses occupies, not how many there are.
