The formula, and why each term is there
Norepinephrine is prescribed as a dose per kilogram per minute, but an infusion pump is programmed in millilitres per hour. The conversion between the two is a single formula:
Rate (mL/hr) = dose (mcg/kg/min) x weight (kg) x 60 / concentration (mcg/mL)
Each term does one job. Dose x weight gives the total drug delivery in mcg/min. Multiplying by 60 converts that to mcg per hour. Dividing by the concentration, the mcg of drug in each mL of bag fluid, converts mcg per hour into mL per hour. The reverse conversion, used to check what a running infusion is actually delivering, is the same equation solved for dose: dose (mcg/kg/min) = rate (mL/hr) x concentration (mcg/mL) / (weight (kg) x 60). Every error with this calculation comes from one of three places: a factor of 1,000 between mg and mcg, the wrong weight, or a concentration that does not match the bag actually hanging. The calculator removes the arithmetic; it cannot remove the need to confirm the bag.
The standard concentrations
| Bag | Concentration | Rate for 0.1 mcg/kg/min at 70 kg |
|---|---|---|
| 4 mg in 500 mL | 8 mcg/mL | 52.5 mL/hr |
| 4 mg in 250 mL | 16 mcg/mL | 26.25 mL/hr |
| 8 mg in 250 mL | 32 mcg/mL | 13.13 mL/hr |
| 16 mg in 250 mL | 64 mcg/mL | 6.56 mL/hr |
| 4 mg in 1,000 mL (the dilution described in the FDA label) | 4 mcg/mL | 105 mL/hr |
Concentration is simply amount divided by volume, with the amount converted from mg to mcg: 4 mg in 250 mL is 4,000 mcg / 250 mL = 16 mcg/mL. The table shows the practical consequence: doubling the concentration halves the rate for the same dose. Concentrated bags exist for patients who need high doses without high fluid volumes, and dilute bags for finer control at low doses. A bag change without a rate recalculation doubles or halves the dose the patient receives, which is why this conversion is rechecked at every bag change and every handover.
Worked example
A 70 kg patient is to receive norepinephrine 0.1 mcg/kg/min from the standard 4 mg in 250 mL bag. Concentration: 4,000 mcg / 250 mL = 16 mcg/mL. Total dose rate: 0.1 x 70 = 7 mcg/min. Rate: 7 x 60 / 16 = 26.25 mL/hr. Checking backwards from the pump: 26.25 mL/hr x 16 mcg/mL = 420 mcg/hr = 7 mcg/min, and 7 / 70 = 0.1 mcg/kg/min. If the same patient is switched to the 8 mg in 250 mL bag (32 mcg/mL) at the same dose, the rate becomes 13.13 mL/hr; on the 16 mg in 250 mL bag (64 mcg/mL) it becomes 6.56 mL/hr. Same patient, same dose, three different numbers on the pump, all correct, which is exactly why the concentration field in this calculator cannot be skipped.
Reference titration table (70 kg)
Pump rates for a 70 kg patient at the two most common concentrations, computed with the formula above. Use the calculator, not this table, for any other weight.
| Dose (mcg/kg/min) | Total (mcg/min) | Rate at 16 mcg/mL (mL/hr) | Rate at 32 mcg/mL (mL/hr) |
|---|---|---|---|
| 0.05 | 3.5 | 13.13 | 6.56 |
| 0.1 | 7 | 26.25 | 13.13 |
| 0.2 | 14 | 52.5 | 26.25 |
| 0.3 | 21 | 78.75 | 39.38 |
| 0.5 | 35 | 131.25 | 65.63 |
What the FDA label doses, and how the two unit systems meet
The FDA-approved label for Levophed (norepinephrine bitartrate injection) indicates the drug to raise blood pressure in adult patients with severe, acute hypotension, and doses it in mcg/min, not per kilogram. Section 2.2: after an initial dosage of 8 to 12 mcg per minute via intravenous infusion, assess patient response and adjust dosage to maintain the desired hemodynamic effect, monitoring blood pressure every two minutes until the desired effect is achieved and then every five minutes for the duration of the infusion; typical maintenance intravenous dosage is 2 to 4 mcg per minute. Translated into weight-based units at 70 kg, the label's initial range is about 0.11 to 0.17 mcg/kg/min and its typical maintenance range about 0.03 to 0.06 mcg/kg/min; at 100 kg the same mcg/min figures are 0.08 to 0.12 and 0.02 to 0.04 mcg/kg/min. Modern critical care practice prescribes weight-based doses and titrates to a mean arterial pressure target: the Surviving Sepsis Campaign 2021 guideline recommends norepinephrine as the first-line vasopressor in septic shock and an initial mean arterial pressure target of 65 mm Hg. This calculator converts between the units and deliberately does not recommend a dose; the dose is whatever the patient's blood pressure requires, set by the treating team.
Administration rules from the label that travel with the number
Section 2.1 of the label sets three conditions around the infusion. Correct hypovolemia first: address hypovolemia before initiation, and if the patient does not respond, suspect occult hypovolemia. Infuse into a large vein, avoiding infusions into leg veins in the elderly or in patients with occlusive vascular disease of the legs, and avoid the catheter tie-in technique. Taper, never stop abruptly: when discontinuing, reduce the flow rate gradually, because sudden cessation may result in marked hypotension (section 5.2). The warnings add the extravasation rule (section 5.1): norepinephrine that leaks into tissue can cause local necrosis from its vasoconstrictive action, and an area of extravasation should be infiltrated as soon as possible with 10 to 15 mL of saline solution containing 5 to 10 mg of an adrenergic blocking agent (phentolamine). The label also warns of cardiac arrhythmias, particularly in patients with underlying heart disease (5.3), and that the product contains sodium metabisulfite, which may cause allergic type reactions in susceptible patients (5.4). On preparation (section 2.3), the label describes adding one 4 mg vial to 1,000 mL of 5% dextrose containing fluid to produce a 4 mcg/mL dilution, notes that dextrose reduces loss of potency from oxidation, that administration in saline alone is not recommended, and that higher concentration solutions are used in patients requiring fluid restriction, which is the origin of the 16, 32 and 64 mcg/mL bags in routine use.
Sources
LEVOPHED (norepinephrine bitartrate) injection, for intravenous use. FDA-approved prescribing information (DailyMed, setid c4de72a8-2a75-4984-ce90-e4870226dc12): section 1 (indicated to raise blood pressure in adult patients with severe, acute hypotension); section 2.1 (correct hypovolemia before initiation; infuse into a large vein; avoid leg veins in the elderly and in occlusive vascular disease; reduce the rate gradually on discontinuation); section 2.2 (initial dosage 8 to 12 mcg per minute, titrated to the desired hemodynamic effect, blood pressure monitored every two minutes then every five minutes; typical maintenance intravenous dosage 2 to 4 mcg per minute); section 2.3 (preparation: one 4 mg vial in 1,000 mL of 5% dextrose containing fluid gives 4 mcg/mL; dextrose protects against oxidation; higher concentrations for fluid restriction); section 3 (injection 4 mg/4 mL, 1 mg/mL norepinephrine base); sections 5.1 to 5.4 (tissue ischemia and extravasation management with 10 to 15 mL of saline containing 5 to 10 mg of an adrenergic blocking agent; hypotension after abrupt discontinuation; cardiac arrhythmias; sulfite allergic reactions). Conversion formula: standard infusion mathematics, rate (mL/hr) = dose (mcg/kg/min) x weight (kg) x 60 / concentration (mcg/mL). Guideline context: Evans L, Rhodes A, Alhazzani W, et al. Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021. Critical Care Medicine. 2021;49(11):e1063-e1143 (norepinephrine as the first-line vasopressor in septic shock; initial mean arterial pressure target of 65 mm Hg).