Alpha receptor antagonists

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Nonselective alpha receptor antagonists

• Irreversible, noncompetitive: Phenoxybenzamine
  • Indication: pheochromocytoma
    • High doses of norepinephrine can overcome the α-adrenergic inhibition of reversible and competitive Phentolamine
• Reversible, competitive: Phentolamine

Alpha-2 receptor agonists

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Alpha-2 receptor functions

• ↓ Norepinephrine release and synthesis (negative feedback)
• ↓ Insulin release
• ↓ Lipolysis
• ↓ Aqueous humor production
• ↓ salivary secretion
• ↑ Platelet aggregation

Drugs

• Clonidine, Guanfacine
  • Indication
    • Hypertensive urgency
    • ADHD
    • Tourette syndrome
    • Symptomatic control of opioid withdrawal
  • Adverse effects
    • Orthostatic hypotension
    • Sedation and CNS depression
    • Rebound hypertension and headache caused by abrupt discontinuation of medication
    • Respiratory depression
    • Miosis
    • Bradycardia