Drug Concentration (mg/mL, units/mL): How to Find and Use It
Shows the work. Every example is computed with the formula and numbered steps. For study and exam practice, not for patient care.
Concentration: The amount of drug in each unit of volume, such as mg/mL or units/mL; for an IV bag, the drug in the bag divided by its volume.
Concentration says how much drug is in a given volume. A vial label may state it directly (“50 mg/mL”), or as an amount per volume (“250 mg/5 mL”). For an IV bag, work it out: divide the drug in the bag by the mL in the bag.
Every volume calculation runs through the concentration:
- mL to give = ordered dose ÷ concentration
- mL/hr = ordered dose per hour ÷ concentration
- dose per hour = mL/hr × concentration
Match units before you divide: a bag labeled in mg with an order in mcg needs a mg-to-mcg conversion first.
A heparin infusion of 12,500 units in 250 mL is running at 20 mL/hr. How many units/hr is the client receiving?
- Solve for
- Dose per hour
- Pump rate
- 20 mL/hr
- Drug in the bag
- 12,500 units
- Bag volume
- 250 mL
Formula mL/hr = ordered units/hr ÷ units per mL.
- Concentration = 12,500 units ÷ 250 mL = 50 units/mL.
- units/hr = 20 mL/hr × 50 units/mL = 1,000 units/hr.
- 1,000 units/hr is exact, so no rounding is needed.
Answer 1,000 units/hr
Sources
- Clinical Calculations: With Applications to General and Specialty Areas — Elsevier (Kee, Marshall, et al.)
- Calculate with Confidence — Elsevier (Morris)