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Selective alpha 1 blocker, causing decrease in TPR and venous return. It has no effects on alpha 2 receptors.


It has a half life of 3 hours. Its bioavailability is 50%.

Adverse Effects

Adverse effects include:

  1. Postural hypotension
  1. Causes first dose response

When administered, causes postural hypotension and the person may collapse. To cope this, first a small dose is administered, which is increased very slowly. It is preferably administered at night, and the patient is advised to stay in bed in lying position. Sudden withdrawal is avoided and other hypertensives are withdrawn. Otherwise severe hypertension might occur. The patient is strictly warned about the side effects.



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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