Drug Dose Unit Conversions
Medication dosing errors are among the most common — and preventable — causes of patient harm in healthcare settings. Understanding drug dose units and the relationships between them is a foundational skill for nurses, pharmacists, and prescribers.
Mass Unit Relationships
| Unit | Abbreviation | Equivalent |
|---|---|---|
| Gram | g | 1,000 mg = 1,000,000 mcg |
| Milligram | mg | 0.001 g = 1,000 mcg |
| Microgram | mcg or µg | 0.001 mg = 1,000 ng |
| Nanogram | ng | 0.001 mcg = 0.000001 mg |
Weight-Based Dosing
Many drugs are prescribed as mg/kg (milligrams per kilogram of body weight) to account for differences in pharmacokinetics across body sizes. The total dose = prescribed dose per kg × patient weight. For obese patients, confirm whether actual, ideal, or adjusted body weight should be used — this varies by drug class.
Infusion Rate Conversions
IV infusion rates can be expressed in multiple ways: mL/hr (for pump programming), mg/hr (total drug per hour), mcg/min (common for vasopressors), or mcg/kg/min (weight-based infusions). All are mathematically interconvertible given the drug concentration in the bag. The formula is: Dose rate (mcg/min) = [Infusion rate (mL/hr) × Concentration (mg/mL) × 1000] ÷ 60.
High-Alert Medications
The Institute for Safe Medication Practices (ISMP) identifies several high-alert drugs where dose calculation errors can cause serious harm: concentrated electrolytes (KCl, NaCl), insulin, heparin/LMWH, opioids, chemotherapy agents, and concentrated vasoactives. Independent double-check of calculations is required for these drugs in most hospital protocols.