Alpha adrenergic blockers, or alpha adrenergic antagonists, affect the alpha receptors of the sympathetic nervous system. There are two types of alpha-adrenergic receptors: alpha-1 and alpha-2. Alpha-1 adrenergic receptors are found in the vascular smooth muscles such as the skin, sphincters of the gastrointestinal system, kidneys, and brain and cause vasoconstriction when activated by catecholamines (Nachawati & Patel, 2021). Alpha-2 adrenergic receptors are found in the peripheral nerve endings and inhibit the release of norepinephrine when activated. Nonselective alpha-adrenergic antagonists cause vasodilation by blocking both alpha-1 and alpha-2 receptors.
How do they work?
By occupying alpha receptor sites, alpha-adrenergic blocking drugs cause the blood vessel walls to relax. This leads to dilation of the blood vessels and reduced peripheral vascular resistance (the pressure that blood must overcome as it flows in a vessel). This action can result in orthostatic hypotension, a drop in blood pressure that occurs when changing position from lying down to standing. Redistribution of blood to the dilated blood vessels of the legs causes hypotension.
Nonselective alpha-antagonists (block both alpha-1 and alpha-2)
- Phenoxybenzamine (Dibenzyline): treats perspiration and hypertension (HTN) associated with pheochromocytoma.
- Phentolamine: treats hypertensive episodes in patients with pheochromocytoma during preoperative preparation and surgical excision.
Selective alpha-1 adrenergic antagonists cause vasodilation resulting in a decrease in blood pressure and thus is used to treat hypertension. Alpha-1 blockers also relax smooth muscles in the prostate and are used to treat benign prostatic hyperplasia (BPH).
Alpha-1 Adrenergic Blockers
(Facts & Comparisons, 2022) |
Generic Name |
Alfuzosin |
Doxazosin |
Prazosin |
Silodosin |
Tamsulosin |
Terazosin |
Trade Name |
Uroxatral |
Cardura |
Minipress |
Rapaflo |
Flomax |
N/A |
Receptor Blockade Location |
Lower urinary track |
Systemic |
Postsynaptic |
Lower urinary track |
Prostate |
Systemic |
Indication |
BPH |
BPH
HTN |
HTN |
BPH |
BPH |
BPH
HTN |
Selective alpha-2 blockers are currently under investigation and have not received Federal Drug Administration (FDA) approval.
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