Units in Medication Dosing: Heparin, Insulin, and Penicillin
Shows the work. Every example is computed with the formula and numbered steps. For study and exam practice, not for patient care.
Units: A measure of a drug's biological activity, used instead of weight for drugs such as heparin, insulin, and penicillin G.
Some drugs are measured by what they do rather than what they weigh. Heparin, insulin, and penicillin G are labeled and ordered in units, and their strengths read like “heparin 5,000 units/mL” or “penicillin G 5 million units”. Units don’t convert to mg: calculate in units from start to finish.
Write the word “units”. The ISMP list of error-prone abbreviations says never to abbreviate it: a handwritten “U” can be read as a zero or a 4, a tenfold or larger overdose, and “IU” can be read as IV or 10. ISMP marks both as items on The Joint Commission’s “Do Not Use” list.
Continuous heparin and insulin infusions are ordered in units/hr, and the pump is set in mL/hr, so you divide by the bag’s concentration.
Heparin 1,300 units/hr IV is ordered. The bag is heparin 12,500 units in 250 mL.
- Solve for
- Pump rate (mL/hr)
- Ordered dose per hour
- 1,300 units/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.
- mL/hr = 1,300 units/hr ÷ 50 units/mL = 26 mL/hr.
- 26 mL/hr is exact, so no rounding is needed.
Answer 26 mL/hr
The units/hr calculator solves the same problem in either direction.
Sources
- List of Error-Prone Abbreviations, Symbols, and Dose Designations — Institute for Safe Medication Practices (ISMP)
- DailyMed: drug labeling — U.S. National Library of Medicine
- Clinical Calculations: With Applications to General and Specialty Areas — Elsevier (Kee, Marshall, et al.)