Updated: 3/13/2019

Alpha-Blockers

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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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