dopamine

Dose-dependent D1 → beta-1 → alpha-1 agonist and endogenous precursor of norepinephrine. Largely superseded — SOAP II showed twice the arrhythmia rate versus norepinephrine and higher mortality in cardiogenic shock. Retains a small role in symptomatic bradycardia. The “renal dose” myth is dead.

mechanism

dose	dominant receptor	effect
1–5 mcg/kg/min	D1 (renal, splanchnic)	vasodilation, ↑renal blood flow, natriuresis — no clinical benefit
5–10 mcg/kg/min	beta-1	↑contractility, ↑HR, ↑CO
>10 mcg/kg/min	alpha-1	vasoconstriction, ↑SVR, ↑MAP

dose–receptor ranges overlap substantially

Receptor selectivity by dose is a teaching construct, not a reliable bedside phenomenon — you cannot predict which effect you’ll get in a given patient.

Net haemodynamics: ↑↑HR, ↑CO, ↑MAP, ↑SVR (at higher doses)

dosing

Range: 2–20 mcg/kg/min
Symptomatic bradycardia (ACLS): 5–20 mcg/kg/min, second-line after atropine, alongside epinephrine 2–10 mcg/min and pacing
PK: onset ~5 min · half-life ~2 min · metabolised by MAO/COMT
Caution with MAOIs — markedly prolonged and exaggerated effect; reduce dose substantially

key points

Symptomatic bradycardia unresponsive to atropine is its main surviving niche (ACLS algorithm)
“Renal dose” dopamine is dead — Bellomo, Lancet. 2000 showed no renal protection, no reduction in RRT, no survival benefit
If a question offers dopamine vs norepinephrine for shock, norepinephrine wins — SOAP II and arrhythmias
Endocrine/immune effects: suppresses prolactin and TSH, blunts hypoxic ventilatory drive, may impair T-cell function

adverse effects

Tachyarrhythmia — the headline problem: AF, SVT, VT (~24% vs 12% with norepi in SOAP II)
↑Mortality in cardiogenic shock vs norepinephrine
Extravasation necrosis — phentolamine
Tachyphylaxis with prolonged use

evidence

SOAP II (2010) — vs norepinephrine in 1,679 shock patients: no overall mortality difference, but ~2x arrhythmic events (24% vs 12%) and higher 28-day mortality in the cardiogenic shock subgroup. Practice-changing
Bellomo, Lancet. 2000 — low-dose dopamine did not prevent renal dysfunction, reduce RRT, or improve survival
Meta-analyses consistently favour norepinephrine over dopamine in septic shock