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Alpha Adrenergic Antagonist

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Alpha Adrenergic Antagonist, Peripheral Alpha-1 Adrenergic Antagonist, Postsynaptic Alpha Adrenergic Antagonist, Alpha Adrenergic Receptor Blocker, Prazosin, Minipress, Terazosin, Hytrin, Doxazosin, Cardura

  • Indications
  • Pharmacokinetics
  1. Agents are highly protein bound (>90%)
  • Mechanism
  • General and Antihypertensive Effects
  1. See Alpha Adrenergic Receptor (Alpha-1 antagonist)
  2. Peripheral Alpha-1 Adrenergic Antagonists
    1. Arterial and Venous Vasodilation
  1. Preparations used in Benign Prostatic Hypertrophy
    1. See Selective Alpha-1a Antagonist (Tamsulosin, Alfuzosin, Silodosin)
    2. Terazosin (Hytrin)
    3. Doxazosin (Cardura)
    4. Prazosin (Minipress)
  2. Rapid relaxation of Smooth Muscle tone
    1. Bladder neck
    2. Prostate Capsule
    3. Prostatic Urethra
  3. Relieves symptoms of urinary obstruction
    1. May see full effect within 2 weeks
  4. Does not effect size of Prostate (unlike Proscar)
  • Preparations
  • Non-Selective Agents
  1. Terazosin (Hytrin)
    1. Dose: 1 mg orally at bedtime (Maximum 20 mg/day)
  2. Doxazosin (Cardura)
    1. Dose: 1 mg orally at bedtime (Maximum 16 mg/day)
  3. Prazosin (Minipress)
    1. Dose: 1 mg PO bid-tid (Maximum 40 mg/day)
    2. Terazosin and Doxazosin are preferred instead (once daily dosing at similar cost)
  4. Phenoxybenzamine (Dibenzyline)
    1. Dose: 10 mg PO bid (Maximum 120 mg/day)
    2. Terazosin and Doxazosin are preferred instead (once daily dosing at similar cost)
  • Preparations
  • Combination Alpha-Beta Antagonists
  • Adverse Effects (Incidence
  • 7 to 9%)
  1. Dose at bedtime
    1. Slowly titrate to reduce side effects (esp. Orthostatic Hypotension)
  2. Cardiovascular adverse effects (also occurs with selective agents, albeit less often)
    1. Postural or Orthostatic Hypotension
      1. Common with first dose (may be severe)
      2. Exacerbated by Hyponatremia
    2. Dizziness
    3. Associated with fall risk and secondary Fracture risk
  3. Other adverse effects
    1. Fatigue
    2. Asthenia
    3. Xerostomia
    4. Headache
    5. Nightmares
    6. Sexual Dysfunction
  • Precautions
  1. Avoid using as monotherapy for Hypertension
    1. Higher risk of CVA and CHF compared with other agents
    2. (2000) JAMA 283:1967-75 [PubMed]