Question
Sodium nitroprusside.
Answer
Sodium nitroprusside is a direct-acting arteriolar and venous vasodilator, given by IV infusion.
MOA: nitroprusside → releases nitric oxide (spontaneously, non-enzymatically) → activates guanylyl cyclase → ↑cGMP → smooth muscle relaxation in both arterioles and veins, reducing afterload and preload simultaneously.
Uses: hypertensive emergencies (rapid, titratable BP control), acute severe heart failure (reduces both preload and afterload), controlled hypotension during surgery.
Adverse effects: cyanide toxicity with prolonged use or high doses (nitroprusside metabolism releases cyanide, which accumulates faster than the body’s thiosulfate-dependent detoxification capacity — monitored and managed with co-administered sodium thiosulfate), excessive hypotension, thiocyanate toxicity in renal impairment. Requires continuous BP monitoring and protection from light (photodegradation).