What are the categories of adrenergic drugs?

Adrenergic Drugs: Classification and Clinical Applications

Adrenergic drugs are categorized based on their receptor selectivity and clinical effects, with primary classifications including alpha-adrenergic agonists/antagonists and beta-adrenergic agonists/antagonists, each with distinct therapeutic applications and side effect profiles. 1

Alpha-Adrenergic Agents

Alpha-Adrenergic Agonists

• Used primarily as vasopressors to treat hypotension and shock 1
• Examples include:
  • Phenylephrine: Selective alpha-1 agonist used for severe hypotension; typical starting dose 0.5-2.0 mcg/kg/min 1
  • Norepinephrine: Predominantly alpha effects with some beta activity; used for severe hypotension with low peripheral resistance; typical starting dose 0.1-0.5 mcg/kg/min 1

Alpha-Adrenergic Antagonists

• Used for hypertension, pheochromocytoma, and prostatic obstruction 2
• Examples include:
  • Phentolamine: Non-selective alpha antagonist used in hypertensive emergencies induced by catecholamine excess; typical IV bolus dose 5 mg 1
  • Prazosin, doxazosin, terazosin: Selective alpha-1 antagonists causing dilation of resistance and capacitance vessels 3, 4
  • Phenoxybenzamine: Used in single ventricle physiology to reduce systemic vascular resistance 1

Clinical Pearl: Alpha-adrenergic blockers should NOT be given in cocaine-induced coronary vasospasm (Class III, LOE C) 1

Beta-Adrenergic Agents

Beta-Adrenergic Agonists

• Used for bronchodilation, cardiac stimulation, and vasodilation 1
• Examples include:
  • Dobutamine: Primarily beta-1 effects, used as inotrope for myocardial dysfunction 1
  • Epinephrine: Non-selective with dose-dependent effects; typical starting dose 0.1-0.5 mcg/kg/min; used for symptomatic bradycardia and severe hypotension 1

Beta-Adrenergic Antagonists (Beta-Blockers)

• Used for hypertension, arrhythmias, post-MI, and heart failure 5
• Categories include:
  • Selective beta-1 blockers: Metoprolol, bisoprolol, atenolol 1, 5
  • Non-selective beta blockers: Propranolol, timolol 6, 5
  • Beta blockers with alpha-blocking properties: Carvedilol, labetalol 5, 3
  • Beta blockers with intrinsic sympathomimetic activity (ISA): Pindolol 6

Clinical Pearl: In beta-blocker overdose, consider high-dose epinephrine infusion, glucagon, or glucose-insulin infusion for treatment (Class IIb, LOE C) 1

Mixed Adrenergic Agents

• Agents with multiple receptor activities:
  • Labetalol: Combined alpha-1 and non-selective beta antagonist; initial 0.3-1.0 mg/kg dose (maximum 20 mg) slow IV injection every 10 min 1
  • Epinephrine: Alpha and beta effects that vary with dosage 1
  • Dopamine: Dose-dependent effects on dopaminergic, beta, and alpha receptors; used at 5-10 mcg/kg/min for hypotension 1

Specialized Adrenergic Applications

Inodilators

• Agents that combine inotropic and vasodilator properties
• Reasonable to use in highly monitored settings for myocardial dysfunction with increased systemic or pulmonary vascular resistance (Class IIa, LOE B) 1

Adrenergic Drugs in Specific Clinical Scenarios

• For post-cardiac arrest care: Vasoactive drugs must be titrated at the bedside to secure intended effect while limiting side effects 1
• For beta-blocker toxicity: Consider glucagon, high-dose epinephrine, or glucose-insulin infusion 1
• For cocaine-induced vasospasm: Consider nitroglycerin and benzodiazepines; avoid alpha-blockers 1

Adverse Effects and Precautions

• Beta-blockers can cause bronchospasm, heart failure, bradycardia, heart block, and Raynaud's phenomenon 6
• Alpha-blockers may cause orthostatic hypotension and reflex tachycardia 2, 3
• Adrenergic drugs should not be mixed with sodium bicarbonate or alkaline solutions 1
• Catecholamines that activate adrenergic receptors may produce tissue necrosis if extravasation occurs; administration through a central line is preferred 1

Important: If extravasation develops with norepinephrine or other catecholamines, infiltrate 5-10 mg of phentolamine diluted in 10-15 mL of saline into the site of extravasation as soon as possible to prevent tissue death 1