Pharm 101: Prazosin


Alpha-1 receptor blocker

  • Selective alpha-1 receptor blocker in arterioles and venules
    • Affinity 1000-fold greater than that for alpha-2 receptors
  • Reduces BP by dilating both resistance and capacitance vessels
  • Alpha-1 selectivity allows noradrenaline to exert unopposed negative feedback (mediated by presynaptic alpha-2 receptors) on its own release

  • 50% first pass metabolism
  • Extensive metabolism
  • Half-life 3 hours

Clinical uses
  • Chronic hypertension
  • Benign prostatic hyperplasia
  • Raynaud’s phenomenon (uncommon)

Adverse effects
  • Postural hypotension
  • Headache, lassitude
  • Reduced prostate smooth muscle tone, thus alleviating prostatic urinary obstruction
  • Positive serum antinuclear factor
  • Increased HDL concentration


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MBBS (UWA) CCPU Emergency Medicine Trainee with interests in medical education, ECG interpretation, and the use of point-of-care ultrasound in the undifferentiated patient. Co-author of the LITFL ECG Library | Twitter

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