A 45-year-old man with severe resistant hypertension is started on oral minoxidil along with a beta-blocker and a loop diuretic. Why must minoxidil always be co-prescribed with these two classes?

• A To prevent reflex bradycardia and hyperkalemia
• B To counter reflex tachycardia, fluid retention, and pericardial effusion risk ✓
• C To prevent first-dose syncope and orthostatic hypotension
• D To reduce the risk of hypertrichosis and hirsutism

Explanation

Minoxidil opens ATP-sensitive potassium channels in vascular smooth muscle, producing powerful arteriolar vasodilation. This triggers intense reflex sympathetic stimulation causing tachycardia and increased myocardial oxygen demand, countered by a beta-blocker. It also activates the renin-angiotensin-aldosterone axis causing marked sodium and water retention, countered by a loop diuretic, since thiazides are inadequate at these doses. Pericardial effusion and rarely tamponade are reported complications. Hypertrichosis is cosmetic and unaffected by co-medication.

Reference: Katzung Basic and Clinical Pharmacology, 16th ed.

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