Pharm 101: Prazosin

Class

Alpha-1 receptor blocker

Pharmacodynamics

• 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

Pharmacokinetics

• 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

References

• Katzung BG. Basic and Clinical Pharmacology. 14e. 2018: 159-171