Semaglutide reconstitution calculator

For compounded vials dispensed on prescription by a US 503A pharmacy. Enter the strength on the label, the diluent volume your pharmacy specified and the amount it stated, and this returns the volume and the units on a U-100 syringe.

Peptide

Vial size (mg)

Bacteriostatic water (ml)

Desired dose

Syringe or pen

Compounded vials only. Compounded medicines are not FDA-evaluated for safety, efficacy or quality, and a branded pen is a metered device this arithmetic does not describe.

Draw to

5units

on a U-100 insulin syringe (0.05 ml)

Concentration: 5 mg/ml; 5000 mcg/ml
Volume to draw: 0.05 ml
Doses per vial: 40
Syringe capacity: 100 units

How this is calculated

concentration (mg/ml)  = vial mg / water ml            = 10 / 2 = 5
concentration (mcg/ml) = concentration mg/ml x 1000    = 5000
volume to draw (ml)    = dose mcg / concentration mcg  = 250 / 5000 = 0.05
insulin units          = volume ml x 100               = 0.05 x 100 = 5
doses per vial         = floor(water ml / volume ml)   = floor(2 / 0.05) = 40

100 units = 1 ml on every U-100 insulin syringe. Barrel size changes how much it holds,
never what a unit means.

What a compounded vial is

In the United States, semaglutide is also supplied as a compounded preparation: a 503A pharmacy prepares it against an individual prescription, and it arrives as a vial of powder or solution with the pharmacy's own preparation instructions. That is a different product and a different regulatory category from a manufactured, FDA-approved pen, which is a metered device and is not reconstituted at all. This calculator describes vials only.

Compounded medicines are not evaluated by the FDA for safety, efficacy or quality. The strength on the label, the diluent, the volume to add and the amount to draw all come from the pharmacy that dispensed it, and they vary between pharmacies for the same molecule. Prepare exactly as your pharmacy instructs; these figures are arithmetic, not a prescribing instruction.

Strengths and diluent volumes

Compounded vials are commonly dispensed at 5mg and 10mg, with the diluent volume specified by the pharmacy. A 10mg vial in 2ml is 5 mg/ml, or 5000 mcg/ml, which puts small amounts into the first few graduations of the barrel.

Because the concentration is a pharmacy determination rather than a convention, two vials with identical labels from different pharmacies can produce different readings on the same syringe. Enter the figures from the label and the instructions you were given, not a figure from elsewhere.

Storage and stability, in general terms

Compounded vials are dispensed with a beyond-use date, which is the pharmacy's own determination for that preparation and is typically much shorter than the shelf life of a manufactured product. It appears on the label, and it is the figure that applies.

Refrigeration, protection from light and avoidance of freezing are the general expectations for this class of preparation, and a compounded vial is not returned to room temperature for storage once it has been chilled. None of this overrides what the dispensing pharmacy states. Prepare exactly as your pharmacy instructs; these figures are arithmetic, not a prescribing instruction.

Frequently asked questions

How do I work out units from a compounded vial?

Divide the strength on the label by the diluent volume to get the concentration, divide the amount by that concentration to get millilitres, then multiply by 100. A 10mg vial in 2ml is 5000 mcg/ml, so 250mcg is 0.05ml, which is 5 units on a U-100 syringe. Prepare exactly as your pharmacy instructs; these figures are arithmetic, not a prescribing instruction.

Why is the units figure so small?

Because the amounts are small relative to the concentration. Five units sits in the first graduations of the barrel, where a small misreading is proportionally large — which is why a 0.3ml syringe, with the finest graduations, is often what a pharmacy supplies for a vial like this.

Is a compounded vial the same as a branded pen?

No. A pen is a manufactured, FDA-approved, metered device: nothing is reconstituted and nothing is drawn into a syringe. A compounded vial is prepared by a pharmacy against a prescription and is not FDA-evaluated for safety, efficacy or quality. The arithmetic here describes vials only.

My pharmacy gave a volume in millilitres rather than units. Is that different?

No, it is the same measurement on a different scale. On a U-100 syringe 100 units is exactly 1 millilitre, so 0.05ml is 5 units. If the two figures disagree, the pharmacy's is the one to follow and worth querying with them.

Does this page tell me how much to use?

No. It converts a quantity your prescription already specifies into a volume and a unit reading on a syringe. It recommends no amount, no frequency and no duration, and it names no supplier.

Before you use this

This tool performs arithmetic only. It does not recommend a dose, a frequency, a duration or a supplier. Many peptides discussed online are not approved by the FDA for the uses people describe. Compounded medicines are supplied on prescription and should be prepared exactly as your pharmacy instructs. Talk to a prescriber or pharmacist before preparing or administering anything.

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