Most of the confusion around reconstituted peptides is not pharmacology. It is one division, done once, and then read off a syringe barrel that was never labelled in milligrams.
A lyophilised vial states a mass, in milligrams. You add a volume of bacteriostatic water, in millilitres. That gives a concentration:
concentration (mg/mL) = vial strength (mg) / water added (mL)To draw a dose:
volume to draw (mL) = dose (mg) / concentration (mg/mL)Worked: a 5 mg vial plus 2 mL of water is 2.5 mg/mL. A 0.25 mg dose is 0.25 / 2.5 = 0.1 mL.
A U-100 insulin syringe is graduated in insulin units, not millilitres. The conversion is fixed:
100 units = 1 mL, so 1 unit = 0.01 mLSo the 0.1 mL above is 10 units on the barrel. Nothing about the syringe knows the peptide, the vial strength, or the diluent volume. It only measures volume. Every mistake I have seen comes from treating a unit mark as if it meant a dose.
The volume of water is a free choice, and it is the lever that decides how readable your doses are. Aim for a concentration where a normal dose lands between roughly 10 and 40 units on the barrel. Below about 5 units the graduation error becomes a large fraction of the dose. Above about 50 units you are injecting more volume than necessary and you will run the vial dry sooner than the schedule expects.
If you would rather not redo the division every time you change vial strength, a Peptide Tracker & Calculator does the arithmetic and the unit conversion in one place. The reconstitution calculator takes vial strength, diluent volume and target dose and returns the syringe reading directly.
A log that only records "took my dose" is useless three months later. The fields that actually answer questions are:
date and time
vial lot, or at least which vial, and the date it was reconstituted
concentration in mg/mL, written down rather than remembered
dose in mg and the units drawn
injection site
anything you noticed in the following 48 hours
The concentration field is the one people skip and the one that matters most. When you open a new vial and mix it differently, every prior "units drawn" entry becomes uninterpretable without it.
Reconstituted peptide is refrigerated, not frozen, and the clock starts at mixing, not at opening. Write the reconstitution date on the vial with a marker. Bacteriostatic water contains benzyl alcohol as a preservative, which is what makes multi-dose use reasonable at all; sterile water without a preservative does not.
Unfamiliar terms turn up constantly in this area, and most of them are ordinary once defined. A short glossary of peptide and GLP-1 terms is a faster way through it than searching each one separately.
Recompute the concentration from the vial label and the volume you actually added.
Divide the dose by that concentration, then multiply by 100 to get units.
Confirm the number is in a range you can read on the barrel.
Write the number in the log before drawing, not after.
None of this is medical advice, and dose selection is not an arithmetic question. The arithmetic just needs to stop being the part that goes wrong.