Drug Concentration (mg/mL) Explained With Examples
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[Glossary · Mixing and measuring]

Concentration (mg/mL)

Also called mg/mL, strength, mg per mL, vial concentration · Reviewed

Definition: Concentration is how much drug is in each unit of volume, usually written as mg/mL, mcg/mL or units/mL. It is the number that links a dose (an amount of drug) to a volume (what you draw into the syringe). For a mixed vial, concentration is the drug amount divided by the liquid added.

The two formulas

  • Concentration = amount of drug ÷ volume of liquid.
  • Volume to draw = dose ÷ concentration.

Labels state it for ready-made products. Humulin R is 100 units/mL. The Omnitrope vial is 5 mg/mL after mixing. Egrifta SV is mixed as 2 mg in 0.5 mL, which is 4 mg/mL.

Worked example

10 mg vial mixed with 2 mL

  1. Concentration: 10 mg ÷ 2 mL = 5 mg/mL (5,000 mcg/mL).
  2. Volume for 500 mcg (0.5 mg): 0.5 ÷ 5 = 0.1 mL.
  3. On a U-100 syringe: 0.1 mL ÷ 0.01 mL per mark = 10 units.
  4. Check: 0.1 mL × 5 mg/mL = 0.5 mg.

If the same vial had been mixed with 1 mL, the concentration would be 10 mg/mL and the same 0.5 mg would be only 5 units. That is why a log entry needs the concentration it was measured against. Dose Track saves each vial with its concentration so the math stays tied to the right vial.

What goes wrong

In 2024 FDA reported dosing errors with compounded semaglutide vials. Causes included confusion between milliliters, milligrams and "units," providers converting mg to units or mL wrongly, and syringes far larger than the dose. Some patients took 5 to 20 times the intended dose.

  • Writing a dose in mL without the concentration.
  • Opening a new vial at a different strength and keeping the old volume.
  • Mixing up "mg/mL" with "mg per vial."

Read more on Dose Track: Peptide reconstitution calculator · GLP-1 units to mg charts

General education drawn from labels and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your product are the final word.
ReconstitutionReconstitution is adding a liquid, called a diluent, to a powdered drug so it dissolves into a solution… mcg vs mg (micrograms and milligrams)mg (milligram) and mcg (microgram) are units of weight. One milligram is a thousandth of a gram; one… Insulin syringe unitsThe units on an insulin syringe are marks of volume. On a U-100 syringe, 1 unit = 0.01 mL; on a U-40… U-100 syringeA U-100 syringe is an insulin syringe marked for insulin that holds 100 units per mL. Each unit mark… Bacteriostatic water (BAC water)Bacteriostatic water (BAC water) is sterile water for injection with a small amount of benzyl alcohol…

Frequently asked questions

How do I find the concentration of a mixed vial?+
Divide the amount of drug in the vial by the volume of liquid you added. A 10 mg vial with 2 mL is 5 mg/mL.
How do I turn a dose into a volume?+
Divide the dose by the concentration. 0.5 mg from a 5 mg/mL vial is 0.1 mL.
Why does concentration matter for logging?+
The same syringe volume holds a different dose at a different concentration. Without it, a logged volume cannot be turned back into a dose.

Sources

  1. Humulin R U-100 (insulin human) US prescribing information, DailyMed
  2. Omnitrope (somatropin) US prescribing information, DailyMed
  3. Egrifta SV (tesamorelin) US prescribing information, DailyMed
  4. FDA: Dosing errors associated with compounded injectable semaglutide products (2024)

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