Prazosin causes a characteristic 'first-dose hypotension' unlike tamsulosin. The pharmacological basis for this difference is:
- A Tamsulosin is uroselective (alpha-1A subtype preferring), causing less vascular alpha-1B blockade ✓
- B Prazosin blocks alpha-2 receptors peripherally, causing excess norepinephrine release
- C Prazosin has a longer plasma half-life than tamsulosin
- D Tamsulosin activates beta-2 receptors to counter the hypotensive effect
Correct answer: A. Tamsulosin is uroselective (alpha-1A subtype preferring), causing less vascular alpha-1B blockade
Explanation
Tamsulosin is selective for the alpha-1A subtype predominant in the prostate and bladder neck, producing minimal blockade of vascular alpha-1B receptors; this uroselectivity sharply reduces the orthostatic hypotension seen with non-selective alpha-1 blockers like prazosin. Prazosin blocks all alpha-1 subtypes equally, leading to pronounced venous dilation and postural hypotension with the first dose. There is no interaction with beta-2 or alpha-2 receptors in tamsulosin's mechanism.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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