What are the mechanisms of action and typical dosing for each vasopressor used to treat hypotension?

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Last updated: September 11, 2026 • View editorial policy

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How Each Vasopressor Works

Norepinephrine is the first-line vasopressor for most hypotensive states, working primarily through α1-adrenergic vasoconstriction with some β1-inotropic support, while other vasopressors serve specific roles based on their distinct receptor profiles and hemodynamic effects. 1

Norepinephrine (First-Line Agent)

Mechanism: Potent α1-adrenergic agonist causing peripheral vasoconstriction, with moderate β1-adrenergic effects providing inotropic support 2

Dosing: Start 0.1–0.5 mcg/kg/min (7–35 mcg/min in 70-kg adult), titrate to MAP ≥65 mmHg 2

Clinical Use:

  • Severe hypotension with low systemic vascular resistance
  • Septic shock (strong recommendation, moderate evidence) 1
  • In sepsis specifically, improves renal blood flow and urine output despite theoretical concerns about renal vasoconstriction 2

Key Caveat: Relatively contraindicated in hypovolemia; may increase myocardial oxygen demand in ischemic heart disease 2. Requires central line when possible due to tissue necrosis risk with extravasation 2

Epinephrine (Second-Line/Adjunct)

Mechanism: Mixed α and β-adrenergic agonist. At low doses (<0.3 mcg/kg/min), predominantly β-effects (tachycardia, inotropy, decreased SVR). At higher doses (>0.3 mcg/kg/min), α-vasoconstriction dominates 3

Dosing: Start 0.1–0.5 mcg/kg/min (7–35 mcg/min in 70-kg adult) 2

Clinical Use:

  • Add to norepinephrine when additional agent needed for blood pressure 1
  • Symptomatic bradycardia when atropine/pacing fails 2
  • Anaphylaxis with hemodynamic instability 2
  • Preferred over dopamine in infants with marked circulatory instability 3

Key Caveat: High individual variability in response; titrate carefully 3

Vasopressin (Adjunctive Agent)

Mechanism: Non-adrenergic vasopressor acting on V1a receptors causing vasoconstriction without direct cardiac effects

Dosing: Fixed dose 0.03 units/min (do NOT exceed 0.03–0.04 units/min) 1

Clinical Use:

  • Add to norepinephrine to raise MAP or decrease norepinephrine dose (weak recommendation, moderate evidence) 1
  • NOT recommended as single initial vasopressor 1
  • May preferentially improve glomerular filtration through efferent arteriole effects 4

Key Caveat: Higher doses reserved only for salvage therapy. Associated with increased risk of digital ischemia 5

Dopamine (Limited Role)

Mechanism: Dose-dependent effects through dopaminergic and indirect adrenergic stimulation:

  • 2–5 mcg/kg/min: dopaminergic (renal/splanchnic vasodilation)
  • 5–10 mcg/kg/min: β-adrenergic (inotropy)

  • 10 mcg/kg/min: α-adrenergic (vasoconstriction) 3

Dosing: Start 5–10 mcg/kg/min 2

Clinical Use:

  • Alternative to norepinephrine ONLY in highly selected patients with low tachyarrhythmia risk and absolute/relative bradycardia (weak recommendation) 1
  • Hypotension with symptomatic bradycardia 2

Critical Pitfall: Do NOT use low-dose dopamine for "renal protection"—this practice is NOT supported by evidence and is explicitly recommended against (strong recommendation, high evidence) 1. Doses >20 mcg/kg/min cause excessive vasoconstriction 3

Phenylephrine (Rarely Used)

Mechanism: Pure α1-adrenergic agonist causing vasoconstriction without inotropic effects 2

Dosing: Start 0.5–2.0 mcg/kg/min (35–140 mcg/min in 70-kg adult) 2

Clinical Use:

  • Severe hypotension with low SVR 2
  • NOT recommended in septic shock except when: (a) norepinephrine causes serious arrhythmias, (b) cardiac output is high with persistently low BP, or (c) salvage therapy 1

Key Caveat: Detrimental effects on microcirculatory perfusion 4. Avoid as routine agent.

Dobutamine (Inotrope, Not Vasopressor)

Mechanism: Selective β1 and β2-adrenergic agonist. The (+) isomer provides β-effects while (–) isomer has α1-effects that counterbalance, resulting in increased contractility with little change or reduction in SVR 2

Dosing: Start 5–10 mcg/kg/min 2

Clinical Use:

  • Persistent hypoperfusion despite adequate fluids and vasopressors (weak recommendation) 1
  • Low cardiac output from poor myocardial function 3
  • NOT a vasopressor—may worsen hypotension through vasodilation 2

Milrinone (Inodilator)

Mechanism: Phosphodiesterase III inhibitor causing inotropy and vasodilation with minimal effect on myocardial oxygen demand 2

Dosing: Load 50 mcg/kg over 10 minutes, then infuse 0.375 mcg/kg/min 2

Clinical Use:

  • Low cardiac output with increased systemic or pulmonary vascular resistance 3
  • May cause less tachycardia than dobutamine 2

Key Caveat: Long half-life with delayed steady-state; fluid administration often required due to vasodilation 3

Critical Administration Principles

Central Line Preferred: Norepinephrine and other catecholamines cause tissue necrosis with extravasation. If extravasation occurs, infiltrate 5–10 mg phentolamine in 10–15 mL saline immediately 2

Avoid Alkaline Solutions: Do NOT mix adrenergic drugs with sodium bicarbonate—they are inactivated in alkaline solutions 2

Titration Required: All vasopressors (except vasopressin) must be titrated at bedside to achieve intended effect while limiting adverse effects 2

Target MAP: Initial target of 65 mmHg for most patients, though individualization may be needed for chronic hypertension 1

References

4
Guideline

a global perspective on vasoactive agents in shock.

Intensive Care Medicine, 2018

5
Research

Evidence Maps of Vasopressor Use in Adult Patients With Septic Shock: An Umbrella Review.

British journal of hospital medicine (London, England : 2005), 2026

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