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Vasopressor, catecholamine

Norepinephrine

Norepinephrine is an endogenous catecholamine and potent vasopressor used as first-line therapy for septic shock and distributive hypotension. It acts primarily on alpha-1 adrenergic receptors to increase systemic vascular resistance. The most testable fact: norepinephrine is the preferred initial vasopressor in septic shock.

Practice questionsHigh-yield facts
Drug classCatecholamine vasopressor and inotrope
MechanismAlpha-1 and beta-1 adrenergic agonist; increases SVR and cardiac output
Main usesSeptic shock, distributive shock, acute hypotension
Key adverse effectTissue necrosis and ischemia from extravasation
5 min readFor medical studentsUpdated 2026-10-14

Mechanism of action

Norepinephrine is a direct-acting sympathomimetic that binds to alpha-1, alpha-2, and beta-1 adrenergic receptors. Its predominant action is alpha-1 receptor stimulation, leading to arterial and venous vasoconstriction and increased systemic vascular resistance (SVR). This alpha-adrenergic effect is responsible for its potent vasopressor activity.

Norepinephrine also stimulates beta-1 receptors in the myocardium, producing positive inotropic and chronotropic effects that increase cardiac output. However, the reflex bradycardia from elevated blood pressure often offsets the direct chronotropic effect. Beta-2 receptor activity is minimal at clinical doses.

The increase in mean arterial pressure (MAP) improves perfusion to vital organs, particularly in distributive shock states where peripheral vasodilation predominates. Norepinephrine restores vascular tone without significantly increasing myocardial oxygen demand compared to pure beta-agonists.

High-yield for exams
  • Norepinephrine is the first-line vasopressor for septic shock (alpha-1 > beta-1 activity)
  • Primary mechanism: alpha-1 receptor agonist causing vasoconstriction and increased SVR
  • Extravasation causes tissue necrosis; treat with phentolamine (alpha-blocker) infiltration
  • Administer via central line as continuous IV infusion; very short half-life (1-2 minutes)
  • MAO inhibitors potentiate norepinephrine, causing hypertensive crisis
  • Preferred over dopamine in septic shock (lower mortality, fewer arrhythmias)
  • Improves renal perfusion in shock by increasing renal perfusion pressure
  • Beta-blockers with norepinephrine cause unopposed alpha stimulation and severe hypertension

Indications

Norepinephrine is the first-line vasopressor for septic shock according to Surviving Sepsis Campaign guidelines. It is indicated for acute hypotensive states that are refractory to fluid resuscitation, particularly distributive shock syndromes.

Primary indications

  • Septic shock: Preferred initial agent to restore MAP ≥65 mmHg
  • Distributive shock: Neurogenic shock, anaphylaxis (after epinephrine), drug-induced vasodilation
  • Cardiogenic shock: Adjunct when hypotension persists despite inotropic support
  • Acute hypotension: During anesthesia, in critical care settings

Norepinephrine is administered as a continuous intravenous infusion via central venous access due to the risk of extravasation. Dosing follows institutional protocols and is titrated to hemodynamic targets. It is not used for chronic management or in outpatient settings.

Pharmacokinetics

Norepinephrine must be administered intravenously as a continuous infusion; it is not active orally due to extensive first-pass metabolism. The drug is rapidly distributed throughout the body and does not cross the blood-brain barrier in significant amounts.

Metabolism occurs primarily via two enzymatic pathways: catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO). These enzymes rapidly inactivate norepinephrine in the liver, kidneys, and sympathetic nerve endings. Metabolites include normetanephrine, vanillylmandelic acid (VMA), and 3-methoxy-4-hydroxyphenylglycol (MHPG), which are renally excreted.

The onset of action is immediate upon infusion, with peak effects within 1-2 minutes. The duration of action is very short, approximately 1-2 minutes after discontinuation, due to rapid uptake into sympathetic nerve terminals and enzymatic degradation. This short half-life necessitates continuous infusion and allows for rapid titration.

Norepinephrine infusions are typically prepared in dextrose or saline solutions and must be protected from light to prevent oxidation.

Adverse effects

The adverse effect profile of norepinephrine is largely related to excessive adrenergic stimulation and vasoconstriction. Most effects are dose-dependent and reversible upon discontinuation or dose reduction.

Major adverse effects

  • Tissue necrosis and ischemia: Extravasation causes severe local vasoconstriction and tissue injury; phentolamine is the antidote
  • Peripheral ischemia: Excessive vasoconstriction may compromise perfusion to digits, limbs, or splanchnic organs
  • Cardiac arrhythmias: Ventricular tachycardia, ventricular fibrillation, especially with hypoxia or acidosis
  • Hypertension: Excessive increase in blood pressure, risk of hemorrhagic stroke
  • Myocardial ischemia: Increased myocardial oxygen demand in susceptible patients

Other adverse effects

  • Reflex bradycardia from elevated MAP
  • Anxiety, headache, tremor
  • Decreased renal perfusion at very high doses
  • Hyperglycemia from beta-2 effects
  • Metabolic acidosis if tissue hypoperfusion persists

Extravasation management: Immediately stop the infusion, infiltrate the affected area with phentolamine (5-10 mg diluted in saline) to reverse alpha-mediated vasoconstriction, and elevate the extremity.

Contraindications and warnings

Norepinephrine has few absolute contraindications given its use in life-threatening shock states, but several relative contraindications and warnings exist.

Contraindications

  • Hypersensitivity to norepinephrine or sulfites (some formulations contain sulfite preservatives)
  • Hypovolemic shock without adequate fluid resuscitation (vasopressors worsen tissue perfusion when intravascular volume is depleted)
  • Peripheral vascular disease (relative): Risk of severe ischemia
  • Mesenteric or peripheral vascular thrombosis (relative): May worsen ischemia

Warnings and precautions

  • Pregnancy: Category C. Use only if benefit outweighs risk; may reduce uterine blood flow
  • Extravasation risk: Administer via central line when possible; monitor IV site continuously
  • Cardiac disease: Use cautiously in coronary artery disease, recent myocardial infarction
  • Hyperthyroidism: Enhanced sensitivity to catecholamines
  • Acidosis and hypoxia: Increase risk of arrhythmias; correct underlying abnormalities
  • Sulfite sensitivity: Some formulations may trigger allergic reactions in susceptible individuals

Continuous hemodynamic monitoring (arterial line, central venous pressure) is standard during norepinephrine infusion.

Drug interactions

Norepinephrine interacts with medications that affect adrenergic transmission, catecholamine metabolism, or cardiovascular function.

Major interactions

  • MAO inhibitors (phenelzine, tranylcypromine): Severely prolong and intensify norepinephrine effects; increased risk of hypertensive crisis
  • Tricyclic antidepressants (amitriptyline, imipramine): Block neuronal reuptake of norepinephrine, potentiating pressor effects
  • Beta-blockers (propranolol, labetalol): Unopposed alpha stimulation may cause severe hypertension and reflex bradycardia
  • Alpha-blockers (phentolamine, prazosin): Antagonize vasopressor effects
  • General anesthetics (cyclopropane, halothane): Sensitize myocardium to catecholamines; increased arrhythmia risk

Other interactions

  • Ergot alkaloids (ergotamine): Additive vasoconstriction, risk of severe ischemia
  • Cocaine, amphetamines: Enhanced sympathomimetic effects, severe hypertension
  • Thyroid hormones: Increased cardiovascular effects
  • Antihistamines, atropine: May potentiate pressor response

Concurrent use of multiple vasopressors (vasopressin, epinephrine, phenylephrine) is common in refractory shock and requires careful titration and monitoring.

Clinical pearls

  • Norepinephrine is the first-line vasopressor in septic shock per international guidelines; superior to dopamine in reducing mortality
  • Administer via central venous catheter to minimize extravasation risk; peripheral access is acceptable temporarily if central access is delayed
  • Phentolamine infiltration is the treatment for extravasation: 5-10 mg in 10 mL saline injected subcutaneously around the site
  • Norepinephrine has minimal direct effect on pulmonary vascular resistance compared to other vasopressors, making it safer in right ventricular dysfunction
  • Target MAP ≥65 mmHg in most patients; higher targets (MAP 75-85) may benefit those with chronic hypertension
  • Despite concerns about renal vasoconstriction, norepinephrine improves renal perfusion in septic shock by restoring renal perfusion pressure
  • Add vasopressin (not as first-line) if norepinephrine requirements are escalating; this is the typical second vasopressor
  • Monitor for lactic acidosis as a sign of inadequate tissue perfusion despite improved blood pressure
  • Compatibility: Stable in dextrose and saline; incompatible with alkaline solutions (degradation occurs)
  • Norepinephrine causes less tachycardia than epinephrine or dopamine, making it preferable when heart rate control is important
  • Weaning: Taper slowly once hemodynamic stability is achieved to avoid rebound hypotension
  • In cardiogenic shock, combine with inodilators (dobutamine, milrinone) rather than using norepinephrine alone
Mnemonic

NorEpi = North (rises BP): Norepinephrine raises blood pressure primarily through alpha-1 vasoconstriction, making it the go-to vasopressor when pressure goes 'north' in septic shock.

Practice questions

1. A 58-year-old man with gram-negative sepsis develops hypotension (BP 78/42 mmHg) despite receiving 4 liters of crystalloid. Heart rate is 118/min, and lactate is 4.2 mmol/L. Central venous access is established. Which of the following is the most appropriate initial vasopressor?

Answer: B. Norepinephrine is the first-line vasopressor for septic shock according to Surviving Sepsis Campaign guidelines and has demonstrated mortality benefit over dopamine. It provides strong alpha-1 mediated vasoconstriction to restore blood pressure while maintaining cardiac output. Dopamine causes more arrhythmias and is no longer recommended as first-line. Vasopressin is typically added as a second agent if norepinephrine requirements escalate, not used as monotherapy initially.

2. A 65-year-old woman on norepinephrine infusion for septic shock develops blanching and coolness of her right hand around the peripheral IV site. The infusion is immediately stopped. Which of the following is the most appropriate immediate management?

Answer: B. This is norepinephrine extravasation causing local tissue ischemia from alpha-adrenergic vasoconstriction. The treatment is immediate infiltration of the affected area with phentolamine (an alpha-blocker), typically 5-10 mg diluted in saline, to reverse the vasoconstriction and prevent tissue necrosis. Warm compresses alone are insufficient. This is a medical emergency requiring prompt pharmacologic reversal with an alpha-antagonist to restore perfusion.

3. A 52-year-old man on tranylcypromine for depression presents to the emergency department with fever, altered mental status, and hypotension (BP 72/40 mmHg) concerning for septic shock. After fluid resuscitation, he remains hypotensive. Which of the following is most important before initiating norepinephrine?

Answer: B. Tranylcypromine is a monoamine oxidase inhibitor (MAOI). MAOIs prevent the breakdown of norepinephrine, causing severely prolonged and intensified effects that can lead to hypertensive crisis. While norepinephrine may still be necessary in life-threatening shock, much lower doses must be used with extremely close monitoring, and alternative vasopressors should be strongly considered. This is a critical drug interaction that can be fatal if not recognized and managed appropriately.

Frequently asked questions

How does norepinephrine work?

Norepinephrine works by stimulating alpha-1 and beta-1 adrenergic receptors. The predominant alpha-1 effect causes vasoconstriction of arteries and veins, increasing systemic vascular resistance and blood pressure. Beta-1 stimulation provides some positive inotropic effect on the heart. This combination makes it highly effective at restoring blood pressure in distributive shock states like sepsis, where pathologic vasodilation is the primary problem.

What are the side effects of norepinephrine?

The most serious side effect is tissue necrosis from extravasation, which requires immediate phentolamine infiltration. Other significant adverse effects include peripheral ischemia from excessive vasoconstriction, cardiac arrhythmias (especially ventricular), severe hypertension, and myocardial ischemia. Patients may also experience reflex bradycardia, anxiety, headache, and decreased organ perfusion at very high doses. Continuous hemodynamic monitoring is essential during norepinephrine infusion.

Is norepinephrine a controlled substance?

No, norepinephrine is not a controlled substance under the DEA schedules. It is a prescription medication used exclusively in hospital settings for acute management of shock and severe hypotension. Because it must be administered as a continuous intravenous infusion with intensive monitoring, it has no potential for abuse or diversion and is not subject to controlled substance regulations.

Norepinephrine vs epinephrine — what is the difference?

The key difference is receptor selectivity and clinical use. Norepinephrine is primarily an alpha-1 agonist (with some beta-1 activity), making it a pure vasopressor used for septic shock. Epinephrine has equal alpha and beta activity, providing both vasoconstriction and potent cardiac stimulation, making it the drug of choice for anaphylaxis and cardiac arrest. Epinephrine causes more tachycardia and has greater metabolic effects (hyperglycemia, hypokalemia). Norepinephrine is preferred in septic shock, while epinephrine is used when both cardiac stimulation and vasoconstriction are needed.

Why is norepinephrine first-line for septic shock?

Norepinephrine is first-line because clinical trials show it reduces mortality compared to dopamine in septic shock. Its strong alpha-1 activity directly addresses the pathologic vasodilation that defines distributive shock, restoring vascular tone and improving organ perfusion pressure. It causes fewer arrhythmias than dopamine, has minimal effect on pulmonary vascular resistance, and actually improves renal perfusion by increasing mean arterial pressure. International guidelines from the Surviving Sepsis Campaign consistently recommend norepinephrine as the initial vasopressor of choice.

Conditions it is used for

Septic shockDistributive shockNeurogenic shockAcute hypotensionCardiogenic shockAnaphylactic shockVasodilatory shock
epinephrinedopaminevasopressinphenylephrinedobutaminemilrinoneephedrinemidodrine

Sources and further reading

DailyMed (FDA labels)StatPearls (NCBI Bookshelf)MedlinePlusWHO ATC/DDD index: C01CA03

Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.