What to Record When You Reconstitute a Vial
Mixing a vial is the one moment its concentration is decided, and every draw afterwards depends on it. Record six things then and there: the date and time, which vial, which diluent and how much of it, the resulting concentration, the discard-by date you were given, and where the vial is kept. Pepti saves the amount in the vial, the water you added, the date you mixed it and where it is kept against the vial on your iPhone; it does not work out the concentration. It never tells you what dose to take or how much water to add.
By Tessaro Pty Ltd, the maker of Pepti · Reviewed
This page is about the record you make when you reconstitute a vial, not about the technique of doing it. It sets out what to write down, why the diluent belongs in the record, and where the discard date comes from. The arithmetic itself is covered in our walk-through of what to draw. It is written by the maker of Pepti, so read the Pepti-specific parts as a description of our own app.
Get Pepti on the App StoreWhy the moment of mixing matters
A vial of freeze-dried powder has an amount but no concentration. The concentration comes into existence when liquid goes in, and it is fixed by a single choice: how much liquid. From then on, every volume you draw and every unit you count on a syringe is a consequence of that one number.
That is why the record has to be made at the time. A week later, the amount on the label is still printed on the vial, but the volume of water you added is printed nowhere. If it was not written down, the only source is memory.
The six things to record
- Date and time mixed — the actual clock time. It is the start of whatever discard period applies to the vial.
- The vial — the compound, the amount in the vial as printed, and its lot or batch number. Our guide to reading a vial label explains each field.
- The diluent — what it was, how much you added, and the diluent’s own lot number and expiry date.
- The resulting concentration — the amount in the vial divided by the volume added, written with its unit.
- The discard-by date — taken from the label or from the source of your material. If none was given, write that down.
- Where it is stored — so the vial and its record can be matched up again.
The diluent is part of the record
Two diluents come up more than any others, and their own labels describe how they differ.
| Diluent | What its US label says | Container |
|---|---|---|
| Bacteriostatic Water for Injection | Has “benzyl alcohol added as a bacteriostatic preservative” | “supplied in a multiple-dose container from which repeated withdrawals may be made” |
| Sterile Water for Injection | “contains no bacteriostat, antimicrobial agent or added buffer” | “supplied only in single-dose containers” |
Which one to use is not a choice this page makes for you. Approved products name their diluent: the US label for tesamorelin for injection, for example, supplies Sterile Water for Injection in the same pack as the vial (FDA label, DailyMed). Both diluent labels also carry the caution that “Some drugs for injection may be incompatible in a given vehicle”, which is the reason to follow the instruction that came with your own product instead of a general habit.
For the record, the point is simpler. Write down which diluent went into the vial, along with its lot and expiry, because two vials of the same compound mixed with different diluents are not the same preparation. How much of it to add is a separate question; our page on bacteriostatic water volume covers what that choice changes.
After mixing: the discard date comes from the product
Both diluent labels carry the same instruction about what happens next: “Do not store reconstituted solutions of drugs for injection unless otherwise directed by the manufacturer of the solute”. In plain terms, the water does not decide how long a mixed vial may be kept. The product being mixed does.
And products differ. The tesamorelin label, to take one approved example, says “If not used immediately, discard the reconstituted solution” and adds “Do not freeze or refrigerate the reconstituted solution”. Other labels allow a stated period of storage. That is why the discard-by date is its own field in the record.
For a compounded vial, the date comes from the pharmacy that prepared it; a compounded drug does not carry an approved product label (FDA, Compounding and the FDA). For a research peptide it comes from whoever supplied the material. This page supplies no figure for either. The storage and expiry guide goes into the dates in more detail.
The arithmetic, as variables
The calculation behind a reconstitution record is short.
concentration = peptide in vial ÷ water added volume to draw = your figure ÷ concentration syringe units = volume × 100 (U-100 syringe)
Nothing in it is a judgement once the inputs are fixed. The free reconstitution calculator on this site does both divisions and the unit conversion. The tool converts a figure you supply; it does not choose it.
Change the water, change everything
The trap in reconstitution records is carrying a number from one vial to the next. Add a different volume of water to the next vial and every unit count you had memorised is wrong, because the vial is the same but the concentration is not. The same applies if the next vial holds a different amount, or comes from a different pharmacy.
The fix is procedural: every vial gets its own reconstitution entry, made from that vial’s label and that day’s volume, and no draw is logged against a vial until its entry exists.
A reconstitution entry, field by field
| Field | What to write | What it lets you answer later |
|---|---|---|
| Mixed on | Date and clock time | How old is this vial today? |
| Vial | Compound, amount as printed, lot number | Which batch did these injections come from? |
| Diluent | Type, volume added, its lot and expiry | Was this vial prepared the same way as the last? |
| Concentration | Amount divided by volume, with the unit | Was each draw volume right for the figure I was working to? |
| Discard by | The date you were given, or a note that none was given | Should this vial still be in use? |
| Stored | Which fridge or shelf | Which vial does this record belong to? |
How Pepti records a reconstitution
In Pepti the reconstitution entry belongs to the vial. You enter the amount in the vial and the volume of water you added, the vial is marked as reconstituted with the date, and each injection you log afterwards is linked to it. The app does not calculate the concentration, the volume to draw or syringe units; the free calculator on this site does that arithmetic.
Alongside that, the vial record holds the vendor, the lot or batch number, the expiry date and where it is stored, and Pepti alerts you when its expiry or use-by date is approaching. For material that arrives already in solution there is no mixing step: you enter the strength printed on the label instead.
What Pepti will not do is make the decisions that sit upstream of the record. It does not choose the diluent, the water volume or the figure you are working to. See also how to track peptide cycles and the guide to choosing a peptide tracking app.
Sources (4)
- Bacteriostatic Water for Injection, USP — US product label. FDA label (DailyMed)
- Sterile Water for Injection, USP — US product label. FDA label (DailyMed)
- Tesamorelin for injection — US FDA label, dosage forms, storage and handling. FDA label (DailyMed)
- US Food and Drug Administration — Compounding and the FDA: Questions and Answers. fda.gov
Common questions
What should I write down when I reconstitute a peptide?
Record the date and time you mixed it, the compound and the amount in the vial as printed, the vial's lot number, the diluent you used with its volume, lot and expiry, the resulting concentration, the discard-by date you were given, and where the vial is stored. Make the entry before the vial goes back into storage, because the water volume is printed nowhere and memory is the only other source.
What is the difference between bacteriostatic water and sterile water?
According to their US labels, Bacteriostatic Water for Injection has benzyl alcohol added as a bacteriostatic preservative and is supplied in a multiple-dose container from which repeated withdrawals may be made. Sterile Water for Injection contains no bacteriostat, antimicrobial agent or added buffer and is supplied only in single-dose containers. Which one to use is set by the instructions for your own product, not by this page.
Can I store a vial after I have reconstituted it?
Only as the product's own instructions allow. The labels for both common diluents say not to store reconstituted solutions of drugs for injection unless otherwise directed by the manufacturer of the product being mixed. Product labels then differ: the US label for tesamorelin for injection, for example, says to discard the solution if it is not used immediately. Record the discard-by date you were given for your own vial.
Does Pepti tell me how much water to add?
No. You record the amount in the vial, the volume of water you added and the date you mixed it, and Pepti keeps them with the vial; it does not calculate the concentration, the volume to draw or syringe units. The diluent and the water volume are decided by the instructions for your own product, not by the app.
Does Pepti tell me what dose to take?
No, nowhere, by design. You enter a figure you already have and Pepti records it with the date, time, injection site and vial. It never suggests, recommends, or calculates what that figure should be. That is a decision for you and whoever directs your care, and Pepti stays on the record-keeping side of that line.
Is my data private?
Pepti has no account and no sign-up, and your protocol and health data stay on the device. There is no cloud sync. That data leaves your phone only if you turn on the AI coach or lab-report import, both behind one consent switch, and then only your coach messages with the app context they need, or the report you import, are sent to Pepti's server and processed by Anthropic. With both off, none of it is held on a server for anyone to lose, sell, or hand over.
If you mix your own vials and want each reconstitution saved against the vial it belongs to, with the dates kept, Pepti is built for that. If you keep a notebook, the six fields above are the entry to write.
Get Pepti on the App StoreThis page describes record-keeping. It does not tell you how to reconstitute any product, which diluent to use or how much, and it provides no dose figure and no schedule.
Not medical advice. Pepti is a record-keeping tool, not a medical device.
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