chap 7

• Adrenergic antagonist


  Drugs that have the ability to bind to receptors but do not activate them
• Adrenergic blocker


  Another name for adrenergic antagonist, as they bind to receptors and block the action of the original substance (norepinephrine or epinephrine)
• Sympatholytic


  Another name for adrenergic antagonist, as they mimic the action of norepinephrine
• Receptors blocked by adrenergic antagonists

  • Alpha 1
  • Alpha 2
  • Beta 1
  • Beta 2
  • Beta 3
• Mechanism of action of adrenergic antagonists

  1. Bind to receptors (reversibly or irreversibly)

  2. Prevent binding of norepinephrine/epinephrine to receptors

  3. Block the action of norepinephrine/epinephrine
• Phenoxybenzamine


  • Non-selective alpha blocker
  • Binds irreversibly to alpha 1 and alpha 2 receptors
  • Takes 14-48 hours to reverse the action
• Phenoxybenzamine is used as a treatment for pheochromocytoma
• Pheochromocytoma


  Benign tumor in the adrenal medulla that secretes excess norepinephrine and epinephrine
• Excess norepinephrine in pheochromocytoma

  Binds to alpha 1 receptors in blood vessels, causing vasoconstriction and increased blood pressure
• Orthostatic hypotension


  Sudden drop in blood pressure when changing position from lying/sitting to standing
• Phenoxybenzamine can cause orthostatic hypotension as an adverse effect
• Phentolamine


  • Non-selective alpha blocker
  • Competitive antagonist (can be reversed by increasing agonist concentration)
  • Can cause severe tachycardia or arrhythmia
• Prazosin


  • Selective alpha 1 receptor antagonist
  • Effective for management of hypertension
  • Causes vasodilation of arteries and veins
• Benign prostatic hyperplasia (BPH)


  Non-cancerous enlargement of the prostate gland
• Prazosin and other alpha 1 blockers are also used for the treatment of BPH
• Pharmacokinetic profile


  Duration of action difference
• They have the same mechanism of action
• Reversible alpha one selective antagonist


  Used for hypertension
• Benign prostatic hyperplasia (BPH)


  Enlarged prostate gland
• Benign prostatic hyperplasia


  1. Increase in the number of cells in the prostate

  2. Increase in the size of the prostate

  3. Prostate located beneath the urinary bladder

  4. Causes urinary symptoms
• BPH is not cancerous but can lead to prostate cancer
• BPH causes urinary symptoms like urinary incontinence
• Alpha one receptors


  Found in the prostate
• Alpha one receptor stimulation

  Causes contraction
• Alpha one antagonists


  Can treat urinary symptoms in BPH
• Doxazosin


  Alpha one antagonist with longer half-life, allowing once daily dosing
• Tamsulosin


  Alpha one antagonist with different structure from other zosin drugs
• Finasteride


  Single agent that relaxes prostate smooth muscle
• Combination of tamsulosin and finasteride

  Used for more severe BPH
• Not everyone develops BPH as they age
• BPH is not associated with erectile dysfunction
• Prostate


  Important organ for producing seminal fluid
• Adverse effect of first dose of alpha one antagonists is syncope or hypotension
• Measures to prevent first dose syncope

  • Taper the dose
  • Administer at bedtime
• Indoramin


  Alpha one antagonist used for hypertension, not available in USA
• Urapidil


  Alpha one antagonist, also alpha two agonist and weak beta one antagonist, used for hypertension
• Labetalol


  Beta blocker with some alpha one antagonist activity
• Neuroleptic drugs


  Antipsychotics that also have alpha receptor antagonist activity, explaining adverse effects
• Trazodone


  Antidepressant with alpha receptor antagonist activity, causing hypotension
• Ergot derivatives


  Alkaloids derived from the fungus Claviceps purpurea, with effects on alpha receptors