Alpha Blockers
Overview
Overview
Alpha blockers inhibit alpha-adrenergic receptor effects. Their clinical actions depend on whether blockade is nonselective, alpha-1 selective or alpha-2 selective, and these subgroups should not be treated as interchangeable.
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Classification
Classification
Alpha antagonists include irreversible nonselective blockade with phenoxybenzamine, reversible nonselective blockade with phentolamine, selective alpha-1 blockers such as prazosin, doxazosin and terazosin, uroselective alpha-1A blockers such as tamsulosin, and uncommon alpha-2 antagonists.
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Mechanism of action
Mechanism of action
Alpha-1 blockade relaxes arteriolar and venous smooth muscle and can relax prostate and bladder-neck smooth muscle. Alpha-2 blockade increases norepinephrine release by removing presynaptic feedback inhibition, explaining the greater tachycardia with nonselective alpha blockade.
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Important members
Important members
Important members are phenoxybenzamine, phentolamine, prazosin, doxazosin, terazosin, tamsulosin, alfuzosin and silodosin. Yohimbine is an alpha-2-preferring antagonist with limited routine therapeutic use.
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Clinical uses
Clinical uses
Uses include benign prostatic hyperplasia, selected cases of hypertension, preoperative or acute control of catecholamine excess, and a small number of specialist indications such as Raynaud phenomenon or PTSD-associated nightmares.
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Adverse effects
Adverse effects
Orthostatic hypotension, dizziness, syncope and nasal congestion are typical. Reflex tachycardia is more prominent with nonselective blockade; alpha-1A-selective drugs can cause ejaculatory disturbance, and some alpha-1 blockers are associated with intraoperative floppy iris syndrome.
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Contraindications and precautions
Contraindications and precautions
Begin cautiously in patients at risk of falls, volume depletion or hypotension. Pheochromocytoma requires specialist preparation, adequate volume expansion and alpha blockade before any beta blocker is introduced.
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References
- Nachawati D, Patel JB. Alpha-Blockers. NCBI Bookshelf. Updated 2025. SOURCE:NCBI:ALPHA_BLOCKERS:2025