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Phenoxy benzamine

Irreversible alpha blocker, forms covalent bonds. Although being non selective, it is more selective for alpha 1 than alpha 2 receptors. It forms ethylene ammonium metabolite, making strong bond with alpha receptors.


It has a very long half life of about 14-48 hours. It is lipid soluble and can cross the blood brain barrier to cause sedation, fatigue, nausea, decreased TPR, postural hypertension, reflex tachycardia. It has lesser intensity than phentolamine. It also inhibits the reuptake of nor adrenaline.


It has a role in management of pheochromocytoma.



Irreversible antagonism Reversible antagonism
Alpha 1 and 2 selective Alpha 1 selective blockers
Decrease TPR and B.P, produce vasodilatation and reflex tachycardia Veins are less affected, less reflex tachycardia and less decrease in TPR and B.P
May cause sedation, nausea and fatigue May cause 1st dose phenomenon
Used in pheochromocytoma Used in HTN and BPH
Can cross blood brain barrier (Antihistamine in nature) Cannot cross blood brain barrier
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