Dopamine

 Dopamine – Vasopressor & (Former) Inotrope

Mechanism of Action

• Dose-dependent adrenergic & dopaminergic agonist

  • 0.5–2 mcg/kg/min (low dose):
    Acts on dopamine (D1, D2) receptors in the kidneys → renal vasodilation, ↑ urine output.
    No evidence for renal protection → not recommended.

  • 2–10 mcg/kg/min (moderate dose):
    Predominantly β1 receptor activation (heart) → ↑ HR, ↑ contractility, ↑ CO.
    Still minor dopaminergic effects.

  • >10 mcg/kg/min (high dose):
    Predominantly α1 receptor activation (vasculature) → vasoconstriction → ↑ SVR, ↑ MAP.
    Some β1 effect persists.

Dosing & Pharmacokinetics

• Typical dose: 2–20 mcg/kg/min IV infusion (continuous, not bolus).

• Onset: ~5 min.

• Half-life: ~2 min (short; “fast on, fast off”).

• Metabolism: Hepatic & renal (MAO & COMT).

• Excretion: Inactive metabolites in urine.

• Administration: Central line preferred (extravasation risk).

Hemodynamic Profile

• Low dose: (no longer recommended) – theoretical renal vasodilation.

• Moderate dose: ↑ HR, ↑ contractility, ↑ CO (β1).

• High dose: ↑ SVR, ↑ MAP (α1 > β1).

Indications

• Rarely used in modern ICU practice.

• Possible niche use:

  • Symptomatic bradycardia with hypotension (2–10 mcg/kg/min; β1 effects).

  • Historically: septic shock, cardiogenic shock, “renal-dose” → not recommended now.

• Preferred alternatives: norepinephrine (shock), epinephrine (bradycardia, inotropy).

Contraindications / Cautions

• Pheochromocytoma.

• Allergy to sulfite-containing formulations.

• Caution in severe hypovolemia (risk of ischemia).

Adverse Effects

• Arrhythmias (esp. tachyarrhythmias, ventricular).

• Myocardial ischemia (↑ O2 demand).

• Peripheral & mesenteric ischemia.

• Extravasation injury → tissue necrosis (treat with phentolamine).

• Nausea, headache.

• Reduced GI perfusion.

Key Evidence

• SOAP II trial (NEJM 2010):

  • Compared dopamine vs norepinephrine in shock.

  • Dopamine → more arrhythmias, no mortality benefit.

  • Norepinephrine preferred.

• Meta-analysis (2000s):

  • Low-dose dopamine not protective against AKI.

• Pediatric septic shock trial (2011):

  • Dopamine vs epinephrine → lower mortality with dopamine.

  • Not generalizable to adults.

Clinical Pearls

• Dopamine is not first-line for any shock state.

• Arrhythmogenic & ischemic risk → norepinephrine safer.

• Consider only in bradycardia with hypotension (bridge therapy).

• Central line preferred to avoid limb-threatening extravasation.

Practice Questions

1. At 2–10 mcg/kg/min, dopamine’s primary receptor effect is:
   → β1 stimulation (↑ HR, ↑ contractility).

2. Major reason dopamine is not first-line in septic shock:
   → High risk of arrhythmias (per SOAP II trial).

3. Patient with cardiogenic shock, MAP 68 mmHg, HR 48 bpm — factor favoring dopamine over norepinephrine?
   → Coexisting bradycardia (dopamine increases HR).

Summary: Dopamine is an endogenous catecholamine with dose-dependent effects (D1/D2 → β1 → α1). Once widely used, it is now largely obsolete due to high arrhythmia risk and lack of proven benefit. Norepinephrine and epinephrine are safer and more effective alternatives.