II. Indications

  1. Non-selective agents
    1. Hypertension (non-selective agents)
      1. Not first-line antihypertensives, and avoid using as monotherapy (higher risk of CVA and CHF)
    2. Pheochromocytoma Hypertensive Crisis (Phentolamine, Phenoxybenzamine)
  2. Selective Alpha-1a Antagonists (e.g. Tamsulosin)
    1. Benign Prostatic Hypertrophy (Selective )
    2. Medical Expulsive Therapy for Ureteral Stone

III. Pharmacokinetics

  1. Agents are highly Protein bound (>90%)

IV. Mechanism: General and Antihypertensive Effects

  1. See Alpha Adrenergic Receptor (Alpha-1 Antagonist)
  2. Peripheral Alpha-1 Adrenergic Antagonists
    1. Arterial and Venous Vasodilation

V. Mechanism: Benign Prostatic Hypertrophy

  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)

VI. Preparations: Non-Selective Agents

  1. Terazosin (Hytrin)
    1. Hypertension
      1. Start 1 mg orally at bedtime
      2. Titrate to effective dose 1 to 5 mg daily or in divided doses (Maximum 20 mg/day)
    2. Benign Prostatic Hypertrophy (replaced by Selective Alpha-1a Antagonists)
      1. Start 1 mg orally at bedtime
      2. Titrate to effect by doubling dose every 1-2 weeks (to 2, 5 and 10 mg, maximum of 20 mg/day)
      3. Observe for effects after 4 to 6 weeks on optimal dose (typically 10 mg)
  2. Doxazosin (Cardura)
    1. Hypertension
      1. Start: 1 mg orally at bedtime and titrate dose (Maximum 16 mg/day)
    2. Benign Prostatic Hypertrophy (replaced by Selective Alpha-1a Antagonists)
      1. Start: 1 mg orally at bedtime and titrate every 1-2 weeks doubling dose, to a maximum of 8 mg at bedtime
      2. Extended release formulation (e.g. Cardura XL) 4 mg in am daily (may increase to 8 mg daily after 3-4 weeks)
    3. Medical Expulsive Therapy for Ureteral Stone (replaced by Selective Alpha-1a Antagonists)
      1. Extended release formulation (e.g. Cardura XL) 4 mg orally daily (not FDA approved)
  3. Prazosin (Minipress)
    1. Terazosin and Doxazosin are preferred instead (once daily dosing at similar cost)
    2. Hypertension
      1. Start 1 mg orally twice daily to three times daily
      2. Titrate to usual daily total dose 20 mg divided two to three times daily
      3. Maximum total daily dose: 40 mg/day (but doses above 20 mg/day offer little additional benefit)

VII. Preparations: Unique Non-Selective Agents Indicated in Pheochromocytoma Hypertensive Crisis

  1. Phenoxybenzamine (Dibenzyline)
    1. Indicated in the Hypertensive Crisis of Pheochromocytoma
      1. Terazosin and Doxazosin are preferred as routine antihypertensive agents instead (once daily dosing at similar cost)
    2. Irreversible alkylation of the Alpha Adrenergic Receptor
    3. Start 10 mg orally twice daily
      1. Titrate to typical dose 20 to 40 mg orally twice daily
      2. Maximum daily dose: 120 mg/day
  2. Phentolamine (Rogatine)
    1. Hypertensive Crisis in Pheochromocytoma
      1. Dose: 5 mg IV/IM for one dose (results in profound drop in BP, e.g. 60/25 mmHg decrease in BP)
    2. IV extravasation of Catecholamines (e.g. Norepinephrine)
      1. Prepare 5-10 mg in 10 ml Normal Saline, and inject 1 ml around extravasation site
      2. In adults may repeat dose up to a total of 5 ml injected around extravasation site

VIII. Preparations: Selective Alpha-1a Antagonists (Prostate specific agents)

IX. Preparations: Combination Alpha-Beta Antagonists

X. Adverse Effects (Incidence: 7 to 9%)

  1. Dose at bedtime
    1. Slowly titrate to reduce side effects (esp. Orthostatic Hypotension, Dizziness, drowsiness)
  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 or light headedness
    3. Associated with Fall Risk and secondary Fracture risk
  3. Other adverse effects
    1. Drowsiness
    2. Fatigue
    3. Asthenia
    4. Xerostomia
    5. Headache
    6. Nightmares
    7. Sexual Dysfunction

XI. Precautions

  1. Pregnancy Category C
  2. Avoid using as monotherapy for Hypertension
    1. Higher risk of CVA and CHF compared with other agents
    2. (2000) JAMA 283:1967-75 [PubMed]

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Cost: Medications

prazosin (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing)
PRAZOSIN 1 MG CAPSULE Generic $0.18 each
PRAZOSIN 2 MG CAPSULE Generic $0.26 each
PRAZOSIN 5 MG CAPSULE Generic $0.50 each
terazosin (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing)
TERAZOSIN 1 MG CAPSULE Generic $0.14 each
TERAZOSIN 10 MG CAPSULE Generic $0.16 each
TERAZOSIN 2 MG CAPSULE Generic $0.14 each
TERAZOSIN 5 MG CAPSULE Generic $0.16 each
doxazosin (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing)
DOXAZOSIN MESYLATE 1 MG TAB Generic $0.09 each
DOXAZOSIN MESYLATE 2 MG TAB Generic $0.07 each
DOXAZOSIN MESYLATE 4 MG TAB Generic $0.09 each
DOXAZOSIN MESYLATE 8 MG TAB Generic $0.11 each