Label every vial the same way, write the reconstitution date, and track remaining volume as starting volume minus the sum of every draw. When the running total hits the starting volume, the vial is empty.
A reconstituted vial holds two things: a liquid, and a record. The liquid is easy to see. The record is what most logs get wrong. Once a vial is mixed, three facts decide whether it is still usable and how much is in it: what it is, when it was reconstituted, and how much liquid remains after the draws taken so far. Track those three consistently and a vial can never surprise you. Skip any one of them and you are guessing.
This is a documentation problem, not a dosing one. Nothing here is about what to draw or how much. It is about keeping a running record precise enough that anyone reviewing it later, including you, can reconstruct the state of every vial on the shelf.
The three fields every vial record needs
A vial that is well tracked answers three questions without anyone having to open it or remember anything:
- Identity: what the vial contains and the peptide amount printed on the original label (for example, 10 mg).
- Reconstitution date: the day diluent was added. This is the clock that everything about vial age runs from, not the manufacture date and not the day you bought it.
- Remaining volume: the starting volume of diluent minus the total of every draw taken since.
Everything else in a good record supports one of these three. Get them written down in the same place, the same way, every time, and the rest is arithmetic.
Consistent labels: same fields, same order, every vial
The point of a label is not decoration, it is matching. When two vials sit side by side, you should be able to tell them apart at a glance and read the same fields in the same order on both. A label that changes format from vial to vial forces you to re-read and re-interpret each one, which is exactly where mix-ups start.
A consistent vial label captures:
- Contents and peptide amount from the original label (mg)
- Diluent type and the starting volume added (mL)
- The resulting concentration (mg/mL)
- Reconstitution date
- A short identifier if you have more than one vial of the same thing
The diluent type belongs on the label because it is part of the vial's identity, not a footnote. Different diluents behave differently over time, which is why the difference between BAC water and sterile water is worth understanding before you write the label rather than after. Whatever fields you choose, freeze the format. A record is only auditable if every entry follows the same shape.
The reconstitution date is the anchor
Once diluent is added, the vial has a starting point in time, and that date is the single most useful thing on the label. Every later question about the vial, how old it is, whether it is still within the window you have decided to use, how to order multiple open vials, is answered by comparing today against the reconstitution date. Without it, a half-full vial is an unlabeled risk: you know how much is left but not how long it has been sitting.
Write the date the moment you mix, not later from memory. If you keep more than one vial of the same contents, the reconstitution date plus a short identifier is what lets you use them in a deliberate order instead of grabbing whichever is closest. A record that pairs a remaining volume with a reconstitution date is complete. One with only volume is half a record.
Remaining-volume math: starting volume minus the sum of draws
This is the part people track in their heads and get wrong. The rule is one line:
Remaining volume (mL) = starting volume (mL) − sum of all draws (mL)
The starting volume is simply the diluent you added at reconstitution. Every time you remove liquid, that draw joins a running total. Remaining volume is the starting volume minus that total, and it only ever decreases. The vial is empty when the sum of draws equals the starting volume.
The one conversion to keep straight is units to milliliters, because draws are often read off the syringe in units, not mL. On a U-100 syringe, 100 units equals 1 mL, so each unit is 0.01 mL and mL = units ÷ 100. If you record draws in units, convert them the same way every time before subtracting. The mechanics of that scale are covered in reading units on an insulin syringe.
Consider a vial reconstituted with 2 mL of diluent. Suppose four draws are taken over time: 0.10 mL, 0.10 mL, 0.20 mL, and 0.15 mL. The sum of draws is 0.55 mL, so the remaining volume is 2 − 0.55 = 1.45 mL.
The value of doing it this way is that the record is self-checking. At any moment, remaining plus the sum of draws should equal the starting volume. If it does not, an entry is missing or mistyped, and you know to go looking before the number matters.
Knowing when a vial is due to be discarded
A vial reaches the end of its tracked life for one of two reasons, and a good record catches both. The first is volume: when the sum of draws equals the starting volume, there is nothing left to draw and the entry closes itself. The second is time: measured from the reconstitution date, a vial eventually passes whatever usable window you have decided to apply to it.
Whichever comes first ends the vial. That is precisely why the reconstitution date and the remaining volume have to live together in the same record. Volume alone cannot tell you a vial is old, and a date alone cannot tell you it is empty. Track both and the discard decision is just reading two numbers you already wrote down.
Keeping it together
None of this is difficult arithmetic. The difficulty is consistency: the same label format, the date written at mix time, and every draw subtracted from the same running total without exception. That is exactly the kind of bookkeeping that is easy to intend and easy to skip. PepSync's vial tracking keeps the starting volume, the reconstitution date, and every logged draw in one place, so the remaining volume is always current and each vial's state traces back to inputs you can review. Offline, private, and yours.
Frequently asked questions
How do you calculate the remaining volume in a reconstituted vial?
Subtract the sum of every draw taken from the starting volume of diluent. For example, a vial reconstituted with 2 mL that has had draws totaling 0.55 mL has 1.45 mL remaining.
What date should you write on a reconstituted vial?
Write the reconstitution date, meaning the day you added diluent, not the manufacture date or purchase date. It is the anchor for tracking how old the vial is and when it is due to be discarded.
How do you convert syringe units to milliliters when tracking draws?
On a U-100 syringe, 100 units equals 1 mL, so divide units by 100 to get milliliters. Convert every draw the same way before subtracting it from the remaining volume.