Norepinephrine Dosage Calculation Formula
Norepinephrine is dosed as a continuous IV infusion at 0.02-0.5 mcg/kg/min (typically starting at 0.1-0.5 mcg/kg/min), titrated to achieve a mean arterial pressure (MAP) of 65 mmHg. 1, 2
Standard Concentration Preparation
- Add 4 mg of norepinephrine to 250 mL of D5W to yield a concentration of 16 mcg/mL 2
- Alternative concentration: Add 1 mg norepinephrine to 100 mL saline for a 10 mcg/mL solution 2
Dosing Formula Components
Weight-Based Calculation
- Dose (mcg/min) = Desired dose (mcg/kg/min) × Patient weight (kg) 1, 2
- Infusion rate (mL/h) = [Dose (mcg/min) × 60] ÷ Concentration (mcg/mL) 2
Example Calculation
For a 70 kg patient starting at 0.1 mcg/kg/min using 16 mcg/mL concentration:
- Dose = 0.1 mcg/kg/min × 70 kg = 7 mcg/min
- Infusion rate = (7 mcg/min × 60) ÷ 16 mcg/mL = 26.25 mL/h 2
Alternative Non-Weight-Based Dosing
- Start at 0.5 mg/h (approximately 8-12 mcg/min), titrate by 0.5 mg/h every 4 hours to maximum 3 mg/h 2
- This approach is commonly used in hepatorenal syndrome and some septic shock protocols 2
Critical Dosing Considerations
Actual Body Weight vs Ideal Body Weight
- Use actual body weight for dosing calculations in all patients, including morbidly obese 3, 4
- Weight-based dosing using actual body weight does not increase tachycardia risk in obese patients despite greater total drug exposure 3
- Morbidly obese patients receive higher cumulative doses but have similar safety profiles 4, 5
Dosing Range and Titration
- Typical dosing range: 0.1-2 mcg/kg/min 2
- Start low (0.1-0.5 mcg/kg/min) and titrate every 5-15 minutes during initial resuscitation 2
- Target MAP of 65 mmHg for most patients 1, 2
When to Add Second-Line Vasopressors
- Add vasopressin 0.03 units/min when norepinephrine reaches 0.25 mcg/kg/min and hypotension persists 1, 6
- Consider adding epinephrine 0.1-0.5 mcg/kg/min as alternative to vasopressin 1
- Do NOT escalate norepinephrine beyond moderate doses (>0.25 mcg/kg/min) without adding adjunctive agents 1
Pediatric Dosing Formula
- Start at 0.1 mcg/kg/min, titrate to effect, typical range 0.1-1.0 mcg/kg/min 2
- Maximum doses up to 5 mcg/kg/min may be necessary in some children 2
- "Rule of 6" for simplified preparation: 0.6 × body weight (kg) = mg of norepinephrine diluted to 100 mL saline; then 1 mL/h delivers 0.1 mcg/kg/min 2
Administration Requirements
- Administer through central venous access whenever possible to minimize extravasation risk 1, 2
- If central access unavailable, peripheral IV or intraosseous can be used temporarily 2
- Place arterial catheter as soon as practical for continuous blood pressure monitoring 1
- Ensure minimum 30 mL/kg crystalloid bolus before or concurrent with norepinephrine initiation 1, 2
Common Pitfalls to Avoid
- Never mix norepinephrine with sodium bicarbonate or alkaline solutions—it becomes inactivated 2
- Do not delay norepinephrine for complete fluid resuscitation if systolic BP <70 mmHg—start immediately while continuing fluids 2
- Avoid escalating norepinephrine beyond 0.25 mcg/kg/min without adding vasopressin or epinephrine 1
- If extravasation occurs, infiltrate phentolamine 5-10 mg diluted in 10-15 mL saline immediately to prevent tissue necrosis 2