NCLEX Review Guide: Adrenergic Agonists in Cardiovascular Pharmacology

Alpha and Beta Receptor Stimulation

• Adrenergic agonists stimulate sympathetic nervous system receptors, mimicking the effects of epinephrine and norepinephrine to increase cardiac output and vascular tone.
• Alpha-1 receptors cause vasoconstriction when stimulated, increasing blood pressure and systemic vascular resistance.
• Beta-1 receptors increase heart rate, contractility, and conduction velocity when activated, primarily affecting cardiac muscle.
• Beta-2 receptors cause bronchodilation and vasodilation in skeletal muscle, though cardiovascular effects are secondary.

Epinephrine (Adrenaline)

• Non-selective adrenergic agonist used for cardiac arrest, anaphylaxis, and severe bronchospasm with immediate onset of action.
• Stimulates all adrenergic receptors causing increased heart rate, contractility, blood pressure, and bronchodilation simultaneously.

Norepinephrine (Levophed)

• Primarily alpha-1 agonist with some beta-1 activity, used as first-line vasopressor for septic shock and severe hypotension.
• Causes potent vasoconstriction with minimal effect on heart rate due to reflex bradycardia from increased blood pressure.

Dopamine

• Dose-dependent receptor activity - low doses affect dopamine receptors, moderate doses stimulate beta-1, high doses activate alpha-1 receptors.
• Used for cardiogenic shock and heart failure, with renal protective effects at low doses through dopaminergic stimulation.

Dobutamine

• Selective beta-1 agonist that increases cardiac contractility with minimal effect on heart rate or blood pressure.
• Preferred inotrope for heart failure exacerbations and cardiogenic shock when blood pressure is adequate.

Therapeutic Uses

• Cardiogenic shock requires careful drug selection - dobutamine for contractility, norepinephrine for blood pressure support.
• Septic shock treatment prioritizes norepinephrine as first-line vasopressor due to superior outcomes compared to dopamine.
• Cardiac arrest protocols specify high-dose epinephrine (1mg IV) every 3-5 minutes during CPR for maximum adrenergic stimulation.

Administration Protocol

1. Establish central venous access for vasopressors when possible
2. Start with lowest effective dose and titrate based on response
3. Monitor continuous cardiac rhythm and blood pressure
4. Assess peripheral perfusion and urine output hourly
5. Wean gradually to prevent rebound hypotension

Common Adverse Effects

• Dysrhythmias including ventricular tachycardia and fibrillation due to increased automaticity and conduction velocity.
• Tissue necrosis from extravasation of vasopressors, requiring immediate intervention with phentolamine infiltration.
• Hypertensive crisis can occur with excessive dosing or in patients with underlying cardiovascular disease.
• Myocardial ischemia may result from increased oxygen demand exceeding coronary perfusion capacity.

Contraindications & Precautions

• Avoid in patients with pheochromocytoma unless alpha-blockade established first to prevent hypertensive crisis.
• Use cautiously in coronary artery disease due to increased myocardial oxygen demand and potential for ischemia.