Which drug is an alpha-1 antagonist used as a hypotensive agent?

• A. Glycopyrrolate
• B. Detomidine
• C. Romifidine
• D. Prazosin

Answer: (D)

The key idea is that blocking alpha-1 receptors on vascular smooth muscle prevents norepinephrine-induced vasoconstriction, leading to vasodilation and a drop in blood pressure. Prazosin is a selective alpha-1 adrenergic receptor antagonist, so it directly lowers vascular tone and acts as a hypotensive agent. This makes it useful for conditions like systemic hypertension or heart failure in dogs by reducing afterload. The other drugs don’t fit this role: glycopyrrolate is an antimuscarinic that affects secretions and GI motility rather than vascular tone; detomidine and romifidine are alpha-2 adrenergic agonists used for sedation, which can increase blood pressure initially and are not alpha-1 blockers.