Adrenergic Antagonists
Overview
Overview
Adrenergic antagonists prevent receptor activation by endogenous or administered catecholamines. They include alpha blockers, beta blockers and combined alpha/beta blockers.
Classification
Classification
Classification is based on receptor selectivity, reversibility and ancillary actions. Major groups are nonselective alpha blockers, selective alpha-1 blockers, nonselective beta blockers, beta-1-selective blockers and mixed alpha-1/beta blockers.
Mechanism of action
Mechanism of action
Alpha antagonists reduce vasoconstriction and smooth-muscle tone in the prostate. Beta antagonists reduce cardiac stimulation and renin release; combined agents add alpha-1-mediated vasodilation.
Important members
Important members
Phenoxybenzamine, phentolamine, prazosin, tamsulosin, propranolol, timolol, metoprolol, bisoprolol, esmolol, carvedilol and labetalol illustrate the major subgroups.
Clinical uses
Clinical uses
Uses include hypertension with specific indications, ischaemic heart disease, arrhythmia, heart failure, benign prostatic hyperplasia, pheochromocytoma preparation, glaucoma, migraine prevention and essential tremor.
Adverse effects
Adverse effects
Hypotension, dizziness, syncope, bradycardia and fatigue are common class-dependent problems. Alpha blockers cause orthostasis; beta blockers may cause heart block or bronchospasm.
Contraindications and precautions
Contraindications and precautions
Select the antagonist according to receptor target and comorbidity. Avoid abrupt beta-blocker withdrawal and avoid initiating beta blockade before alpha blockade in catecholamine-secreting tumours.
References
- Nachawati D, Patel JB. Alpha-Blockers. NCBI Bookshelf. Updated 2025. SOURCE:NCBI:ALPHA_BLOCKERS:2025
- Farzam K, Jan A. Beta Blockers. NCBI Bookshelf. Updated 2023. SOURCE:NCBI:BETA_BLOCKERS:2023