How to read a vial label
Every calculation starts from the label. The two numbers that matter for the arithmetic are the amount in the vial and, on vials that come already mixed, the concentration. The rest of the label tells you what the product is, who made it and how long it may be used.
What is on the label
| Label item | What it tells you | Used in the calculation? |
|---|---|---|
| Drug name | What the vial contains | No, but confirm it matches the prescription |
| Amount or strength | Total mg (or mcg, or IU) in a dry vial; mg/mL in a liquid vial | Yes |
| Total volume | mL of liquid in a pre-mixed vial | Sometimes, to find the total amount |
| Lot or batch number | Which production batch the vial came from | No |
| Expiration date | Manufacturer's date for the unopened product | No |
| Beyond-use date (BUD) | Date set by a compounding pharmacy after which the preparation should not be used | No |
| Single-dose or multiple-dose | Whether the vial is meant to be entered once or more than once | No |
| Pharmacy label (Rx number, patient, prescriber, directions) | The dispensing record and your instructions | The directions give the prescribed amount |
Dry (lyophilized) vials: find the total amount
A freeze-dried vial states one amount, for example "10 mg". That is the total in the vial, and it is the number for the "amount in the vial" field of the calculator. The concentration does not exist yet; it is created when water is added.
Check the unit as well as the number. Most vials are in mg. Some are in mcg, where 5,000 mcg is 5 mg (see mcg vs mg). Some are in IU, which cannot be turned into mg without the product's own factor (see IU vs mg).
Pre-mixed vials: find the concentration
A vial that arrives as a liquid has already been through the first step. Its label gives a concentration, and usually a total volume.
| Label reads | Concentration | Total in vial | 10 units on a U-100 syringe holds |
|---|---|---|---|
| 5 mg/mL, 2 mL | 5 mg/mL | 10 mg | 0.5 mg |
| 2.5 mg/mL, 4 mL | 2.5 mg/mL | 10 mg | 0.25 mg |
| 10 mg/mL, 1 mL | 10 mg/mL | 10 mg | 1 mg |
Two formats cause misreads:
- "10 mg/2 mL" means 10 mg in the whole 2 mL, which is 5 mg/mL. It does not mean 10 mg in each mL. Divide the first number by the second to get the per-mL figure.
- "5 mg/mL" on a 2 mL vial means the vial holds 10 mg in total, not 5 mg.
To use the calculator with a pre-mixed vial, enter the total amount and the total volume, so "5 mg/mL, 2 mL" goes in as 10 mg and 2 mL. No water is added to a pre-mixed vial unless the label or pharmacist says so.
Lot number
The lot (or batch) number identifies the production run. It is how a manufacturer or pharmacy traces a vial if there is a recall or a quality question.
Expiration date and beyond-use date
These are two different dates set by two different parties.
- An expiration date is set by the manufacturer for the product in its original, unopened container, stored as labelled.
- A beyond-use date is set by the pharmacy for a compounded or repackaged preparation. It is the date, and sometimes time, after which that preparation should not be used.
A vial that you mix yourself may also have an in-use period that starts when water is added. That period depends on the product and is given in its instructions or by your pharmacist. This site does not give storage times. Use the dates and storage directions on your own label, and ask the pharmacy if any of them is missing or unclear.
Before you calculate
- The name on the vial matches the prescription.
- You have the amount and its unit: mg, mcg or IU.
- You know whether that figure is a total or a per-mL concentration.
- The date on the label has not passed.
- The amount to draw comes from the directions on the pharmacy label, not from a chart.
Then run the numbers on the calculator or the page for your compound under calculators by peptide, and check the result by hand. If the label has two substances, the blend calculator takes both amounts.
Questions
Does the mg on a vial mean per mL or the whole vial?
On a dry, freeze-dried vial the figure is the total amount in the vial. On a liquid vial, "mg/mL" is the amount in each mL, and a format such as "10 mg/2 mL" is the total amount in the total volume, which works out to 5 mg/mL.
What is a beyond-use date?
A beyond-use date (BUD) is the date a compounding pharmacy assigns to a preparation, after which it should not be used. It is different from a manufacturer's expiration date, which applies to the unopened original product.
What is the lot number on a vial for?
It identifies the production batch so the manufacturer or pharmacy can trace the vial in a recall or quality investigation. It is not used in any dose calculation.
How do I use a calculator with a pre-mixed vial?
Multiply the concentration by the total volume to get the total amount, then enter that amount and that volume. A vial labelled 5 mg/mL, 2 mL goes in as 10 mg and 2 mL.