Alpha-Blockers

α-Blockers

Drug Clinical Applications Toxicity Nonselective α-Blockers Phenoxybenzamine (irreversible, preferred)   • Pheochromocytoma  • High catecholamine states • Orthostatic hypotension • Reflex tachycardia Phentolamine (reversible)  Selective α1-blockers (-zosin) Prazosin  • Hypertension • Urinary retention in benign prostatic hyperplasia (tamulosin is the most specific for urinary symptoms) • First dose orthostatic hypotension  • Headache and dizziness Doxazosin Terazosin Tamulosin Selective α2 blockers Mirtazapine • Depression • Sedation • Xerostomia • ↑ serum cholesterol • ↑ appetite Yohimbine • Male erectile dysfunction • Hypotension • Anxiety

α-Blockers + Sympathomimetics effects

Epi + α-blocker  before non selective α-blocker is given, epi's net effect is to increase heart rate, contractility, and vasoconstriction leading a net pressor effect on blood pressure after α-blocker is given, epi's α response is blocked while its β2 response remains leading to net depressor effect on blood pressure (top of image) β2 is Gs coupled, increases cAMP, causes vasodilation α is Gq coupled, increases calcium causes vasoconstriction Epi + β-blocker  before nonselective α-blocker is given, epi's net effect is to increase heart rate, contractility, and vasoconstriction leading a net pressor effect on blood pressure after β-blocker given, epi's β response is blocked, while α response remains leading to net pressor effect (bottom of image) Phenylephrine + α-blocker  phenylephrine (α1 > α2 agonist) leads to a net pressor effect on blood pressure administration of a nonselective α-blocker leads a net zero effect on blood pressure

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