minoxidil

Minoxidil is a prodrug activated to minoxidil sulfate, which opens vascular smooth muscle K-ATP channels, hyperpolarizing the cell and relaxing arterioles (not veins), causing marked afterload reduction. Reflex sympathetic activation triggers tachycardia and sodium/water retention, so it must be co-administered with a beta-blocker and a loop diuretic. Indications: severe refractory hypertension; topical form (Rogaine) for male/female pattern baldness. Key adverse effects: hypertrichosis (hair growth — boards buzz), pericardial effusion, reflex tachycardia, fluid retention. Mechanism mnemonic: 'opens K+ channels' shared with diazoxide.