Vasodilators used for acute management of hypertensive crisis or malignant hypertension include sodium nitroprusside and diazoxide. Sodium nitroprusside is the agent of choice.

Administered by a continuously variable rate i.v. infusion pump, precise blood pressure control can be obtained.

Nitroprusside, a nitrovasodilator, is metabolized by smooth muscle cells to nitric oxide which dilates both arterioles and venules.

Diazoxide is infrequently used unless accurate infusion pumps are unavailable.

• The mechanism of action involves activation of ATP-sensitive potassium channels, depolarization of arteriolar smooth muscle, relaxation and dilation.

• Adverse effects include salt and water retention and hyperglycemia. Diazoxide inhibits insulin release.

  • Side effects are mainly due to excessive vasodilation.

  • Much less commonly, toxicity may result from conversion of nitroprusside to cyanide and thiocyanate. Risk of toxicity due to thiocyanate increases after 24 to 48 hours.

  • Nitroprusside can worsen arterial hypoxemia in patients with obstructive pulmonary airway disease since nitroprusside will interfere with hypoxic pulmonary vasoconstriction. A result is increasing ventilation-perfusion mismatching.