What this guide covers, and what it does not
Reconstitution has two halves. The physical half is adding liquid to a freeze-dried powder. The numerical half is knowing what concentration results, and what that means on a syringe.
The first half belongs to the product. Every approved freeze-dried medicine comes with its own instructions, and they differ more than most people expect. So this guide gives no handling instructions of its own. Where it describes the physical stage, it quotes FDA-approved labelling and names the product. The second half is arithmetic, and that is worked through in full.
It does not cover sterile technique or how to inject, and it does not suggest a dose or a volume of liquid. For the concepts behind each step, see the longer peptide reconstitution guide.
Step 1. Read the labelling before anything is opened
The labelling decides almost every detail: which liquid, how much, how to mix, and how long the result may be kept. Four approved products show how much those answers vary.
| Product | Diluent named in the label | Mixing wording | After mixing |
|---|---|---|---|
| Egrifta SV (tesamorelin) | Sterile Water for Injection | “Mix by rolling the vial gently in your hands for 30 seconds. Do not shake.” | Use immediately, discard the rest |
| Egrifta WR (tesamorelin) | Bacteriostatic Water for Injection | “Move the vial in a circle (swirl)… Do not shake.” | Room temperature, discard after 7 days |
| Glucagon emergency kit | The diluent supplied in the kit | “Swirl the vial gently until the powder is completely dissolved” | Use immediately, discard the rest |
| Pregnyl (chorionic gonadotropin) | The preserved solvent supplied with it | “agitate gently until powder is completely dissolved… Do not shake.” | Refrigerate, discard after 60 days |
Two versions of the same drug, from the same manufacturer, use different diluents and have different rules afterwards. That is the single most useful fact in this article: there is no generic procedure to memorise. The instructions that matter are the ones that came with the product.
A vial sold “for research use” comes with no such instructions, because nobody has tested it for human use. No guide, this one included, can fill that gap.
Step 2. Identify the diluent
The diluent is the liquid that goes into the vial. The two most common are Bacteriostatic Water for Injection, which contains a preservative and comes in a multiple-dose container, and Sterile Water for Injection, which has no preservative and is labelled single-dose.
Many products supply their own diluent, as all four above do. Which one belongs with a product is stated in its labelling and is not a matter of preference. The reconstitution guide compares the two waters in detail.
Step 3. Settle the numbers first
Before any liquid moves, two numbers should be known and written down:
- The amount in the vial, from the label, usually in mg.
- The volume of diluent, in mL. For an approved product the labelling states it.
Doing the math now, not afterwards, is the best protection against mistakes. If the numbers produce a draw that does not fit the syringe, it is far better to find out on paper. How much BAC water to add explains what the volume does and does not change.
Step 4. What approved instructions say about mixing
This is where labels come close to speaking with one voice. Three of the four in the table say “Do not shake” outright, and the fourth says to swirl “gently”. The liquid is combined with the powder by rolling the vial between the hands, swirling it, or agitating it gently.
There is chemistry behind that. Peptides in solution can clump together, a process called aggregation, and a 2023 review of peptide stability lists agitation among the stresses that can cause it. Its advice is to “handle the peptides gently and avoid agitation or shear stress”.
The Instructions for Use for one of these products run to more than twenty numbered steps. They are not reproduced here. They belong to the product, and they are the part to follow to the letter.
Step 5. What the result should look like
Labels also describe the finished solution, and again they agree. Egrifta SV is to be used “only if the solution is clear, colorless and without particulate matter”. The glucagon kit says the solution should be “clear and of a water-like consistency”, and not used if it is cloudy or contains particles.
These describe those products. For anything else, a clear solution is not evidence of what the vial contains or whether it is sterile. Appearance can rule a vial out. It cannot rule one in.
Step 6. Work out the concentration
Now the arithmetic. The moment liquid is in the vial, the vial has a concentration.
A worked example, using arbitrary numbers that are not tied to any compound and are not a suggestion: a vial labelled 5 mg, with 2 mL added.
- 5 ÷ 2 = 2.5 mg/mL
- 2.5 × 1,000 = 2,500 mcg/mL
- One unit on a U-100 syringe is 0.01 mL, so one unit holds 2,500 ÷ 100 = 25 mcg
The reconstitution calculator does these three lines from your own numbers.
Step 7. Convert the amount into a syringe mark
The amount comes from a prescription or from your own records. It never comes from a calculator.
Continuing the example, an amount of 250 mcg is 250 ÷ 2,500 = 0.1 mL, which is 10 units. The peptide calculator runs steps 6 and 7 together and shows the mark on a syringe.
Then check the result against reality:
- Does it fit? A draw larger than the barrel cannot be measured in one go.
- Is it a whole unit? A 1 mL barrel is usually marked every 2 units. See how to read syringe units.
- Is the scale right? U-100 and U-40 are different rulers. See U-100 vs U-50 vs U-40.
- Are the units consistent? Mixing mg and mcg is an error of 1,000. See mcg vs mg.
Step 8. Label the vial and record it
Once liquid is in a vial, nothing on the label says how much went in or when. Those two facts now exist only if someone wrote them down.
For each vial, record the name and labelled amount, the date, the diluent and its exact volume, and the concentration. This is the record Peptrack keeps: the vial size and water are entered once, and the concentration stays attached to that vial for as long as you log against it.
Step 9. Follow the product’s rules for keeping it
The last column of the table in step 1 is the part people most often generalise. “Use immediately” and “discard after 60 days” are both correct, for different products, and two of those labels say the mixed solution must not be refrigerated at all. How to store reconstituted peptides explains why no single rule covers every product.
What is deliberately left out
This article does not teach sterile technique, needle handling or injection. Those are taught by a product’s Instructions for Use and by a pharmacist or prescriber, for a specific product. A web page that tried to replace that would be doing harm.
It also gives no dose and no volume of liquid for any compound. Many peptides are prescription-only or not approved for human use, and no calculator or article can make one safe or appropriate.
Sources
Factual statements in this article come from these primary sources, last checked in September 2026.
- DailyMed: Egrifta SV (tesamorelin) prescribing information and Instructions for Use
- DailyMed: Egrifta WR (tesamorelin) prescribing information and Instructions for Use
- DailyMed: Glucagon for Injection emergency kit (Amphastar) label
- DailyMed: Pregnyl (chorionic gonadotropin, Organon) label
- Nugrahadi PP et al. Designing formulation strategies for enhanced stability of therapeutic peptides in aqueous solutions: a review. Pharmaceutics 2023;15(3):935
