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Alpha Adrenergic Antagonist

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Alpha Adrenergic Antagonist, Selective Alpha-1a Antagonist, Prazosin, Minipress, Terazosin, Hytrin, Doxazosin, Cardura, Tamsulosin, Flomax, Alfuzosin, Uroxatral, Silodosin, Rapaflo

  • Indications
  1. See Alpha Adrenergic Receptor (Alpha-1 antagonist)
  1. Preparations used in Benign Prostatic Hypertrophy
    1. Terazosin (Hytrin)
    2. Doxazosin (Cardura)
    3. Tamsulosin (Flomax)
    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. Prazosin (Minipress)
    1. Dose: 1 mg PO bid-tid (Maximum 40 mg/day)
    2. Less expensive but not available for once daily dose
  2. Terazosin (Hytrin)
    1. Dose: 1 mg PO qhs (Maximum 20 mg/day)
  3. Doxazosin (Cardura)
    1. Dose: 1 mg PO qd (Maximum 16 mg/day)
  4. Phenoxybenzamine (Dibenzyline)
    1. Dose: 10 mg PO bid (Maximum 120 mg/day)
  • Preparations
  • Selective Alpha-1a Antagonists (Prostate specific agents)
  1. Precautions
    1. Still cause Orthostatic Hypotension, fall risk, Head Trauma and Fractures, despite selective nature
    2. Number needed to harm (NNH): 600 for fall-related hospitalizations, and 1600 for fall-related Fractures
    3. Welk (2015) BMJ 351:h5398 +PMID:26502947 [PubMed]
  2. Alfuzosin (Uroxatral, generic)
    1. Dose: 10 mg once daily
    2. Contraindicated in moderate to severe liver disease (and Exercise caution in renal disease)
  3. Silodosin (Rapaflo)
    1. Dose: 8 mg daily with food (4 mg daily if GFR 30-50 ml/min)
    2. Contraindicated when GFR <30 ml/min or severe liver disease (Child-Pugh Score 10 or more)
  4. Tamsulosin (Flomax, generic)
    1. Dose 0.4 mg orally daily (maximum 0.8 mg/day)
  • Combination Alpha-Beta Antagonist (Labetalol or Trandate)
  1. Oral: 100 mg PO bid (Maximum: 2400 mg/day)
  2. Intravenous: 20 mg IV q10 minutes (Maximum: 200 mg)
  • Adverse effects (Incidence
  • 7 to 9%)
  1. Dose at bed and slowly titrate to reduce side effects
  2. Cardiovascular adverse effects (also occurs with selective agents, albeit less often)
    1. Dizziness
    2. Postural Hypotension
    3. Associated with fall risk and secondary Fracture risk
  3. Other adverse effects
    1. Fatigue
    2. Asthenia
  • 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]