Nitroprusside

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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