A 70-year-old man with BPH is started on tamsulosin. Compared to prazosin, tamsulosin is preferred because it:

• A Has a longer duration of action requiring weekly dosing
• B Also inhibits 5-alpha reductase, reducing prostate size
• C Crosses the blood-brain barrier to reduce sympathetic outflow
• D Selectively blocks alpha-1A and alpha-1D receptors, causing less orthostatic hypotension ✓

Explanation

Tamsulosin is subtype-selective for alpha-1A (predominant in prostate, bladder neck) and alpha-1D (bladder body) receptors over alpha-1B (predominant in vascular smooth muscle). This selectivity produces effective prostatic relaxation with significantly less vascular effect and therefore less orthostatic hypotension compared to non-selective alpha-1 blockers like prazosin or doxazosin. It does not inhibit 5-alpha reductase; that is finasteride's mechanism.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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