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Selective alpha 1 blocker, causing decrease in TPR and venous return. It has no effects on alpha 2 receptors.
Pharmacokinetics
It has a half life of 3 hours. Its bioavailability is 50%.
Adverse Effects
Adverse effects include:
- Postural hypotension
- 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 Sudden withdrawal is avoided and other hypertensives are withdrawn.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.
|
Phenoxybenzamine |
Prazosin |
| 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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Terazosin, Tamsulosin and Yohimbine
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