Minoxidil is reserved for severe, refractory hypertension. Why must it almost always be co-prescribed with a beta-blocker and a loop diuretic?

• A To prevent its conversion to inactive metabolites in the liver
• B To counteract reflex sympathetic tachycardia and sodium and fluid retention caused by intense arteriolar vasodilation ✓
• C To reduce the risk of hyperkalemia from its aldosterone-like action
• D To enhance its absorption, which is otherwise poor without food

Explanation

Minoxidil, a prodrug activated by hepatic sulfotransferase to minoxidil sulfate, opens ATP-sensitive potassium channels in vascular smooth muscle, producing profound arteriolar dilation. This triggers baroreceptor-mediated reflex tachycardia and stimulates renin release with marked salt and water retention, so a beta-blocker and loop diuretic are mandatory companions. It causes fluid retention rather than hyperkalemia (option C). Pericardial effusion and hypertrichosis are additional limiting toxicities.

Reference: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

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