Nitroprusside

Summary

Nitroprusside is a vasodilating drug that works by causing the direct release of nitric oxide and a subsequent increase in cGMP to lead to smooth muscle relaxation. Nitroprusside is a balanced arterial and venous dilator. Nitroprusside is used first-line in the treatment of hypertensive emergencies, and is associated with dose-dependent cyanide poisoning due to the drug being metabolized to cyanide in the body.

Key Points

• Nitroprusside
  • Mechanism
    • Potent vasodilator
      • Direct release of NO → Increases cGMP
        • Does not depend on intracellular metabolism into NO (I like to think that this is why it affects arteries equally)
        • relaxes vascular smooth muscle
      • Balanced (arteries = veins)
        • Contrast vs. nitrates, which primarily target veins
        • Nitroprusside targets both preload and afterload
  • Indications
    • Hypertensive emergency (1st line)
      • Favored due to its quick onset and short duration of action
    • Acute decompensated heart failure
      • Helps to reduce afterload (and preload), reducing the work on the heart
    • Sodium Cyanide-Nitroprusside test
      • Rapid test to detect cysteine in urine (Cystinuria)
      • not pharmacologic; should be thought of as a separate lab test and not a drug
  • Adverse Effects
    • Cyanide toxicity
      • Metabolized into cyanide and thiocyanate, which limits dosing
        • This is how cyanide toxicity may be tested (script) → check out our other video on this
        • Treatment by thiosulfate, which adds a sulfur group to CN to help it be cleared by the kidneys as thiocyanate
    • Hypotension (obvious)
    • May cause increased intracranial pressure
      • Via vasodilation of cerebral arteries