Prazosin, Terazosin, and Tamsulosin are primarily what type of drug mechanism?

• A. Alpha-1 blockers
• B. Alpha-2 blockers
• C. Beta-1 blockers
• D. Beta-2 blockers

Answer: (A)

These drugs work by blocking alpha-1 adrenergic receptors. When alpha-1 receptors on vascular smooth muscle are blocked, the vessels dilate, reducing systemic vascular resistance and lowering blood pressure. In the urinary tract, alpha-1 receptors mediate contraction of the smooth muscle in the bladder neck and prostatic urethra; blocking these receptors relaxes that tissue and improves urine flow, which is especially helpful in benign prostatic hyperplasia.

Prazosin and terazosin are traditional alpha-1 blockers that affect both vascular and urinary smooth muscle, so they can lower blood pressure in addition to easing BPH symptoms (with a higher risk of orthostatic dizziness). Tamsulosin is more selective for the alpha-1A subtype predominant in the prostate and bladder, so it relieves BPH symptoms with less impact on blood pressure. This mechanism is different from alpha-2 blockade (which would alter norepinephrine release) and from beta blockade (which mainly affects heart rate, contractility, and bronchodilation).