What is the main MOA of BPH medications such as Prazosin, Terazosin, and Tamsulosin?

• A. Alpha 1 blockers
• B. Beta blockers
• C. PDE-5 inhibitors
• D. Antimuscarinics

Answer: (A)

Blocking alpha-1 adrenergic receptors in the smooth muscle of the prostate and bladder neck is the main action. By inhibiting these receptors, the tonic contraction of prostatic and bladder neck smooth muscle decreases, reducing the resistance to urine flow and easing voiding symptoms. This rapid relief targets the dynamic component of bladder outlet obstruction in BPH, rather than shrinking the enlarged prostate itself (that would be the job of 5-alpha reductase inhibitors). The drugs mentioned—prazosin and terazosin (older, nonselective alpha-1 blockers) and tamsulosin (more uroselective for alpha-1A receptors in the prostate)—all share this mechanism. Other options listed don’t primarily achieve this effect: beta blockers affect heart rate and airways, PDE-5 inhibitors relax smooth muscle via different pathways and are not first-line for BPH, and antimuscarinics reduce bladder overactivity but don’t relieve prostatic outlet resistance.