- Vasodilators used for acute
management of hypertensive crisis or malignant
hypertension include sodium nitroprusside and diazoxide.
- Nitroprusside sodium (Nipride) is
the agent of choice.
- Administered by a
continuously variable rate i.v. infusion
pump, precise blood pressure control can
be obtained.
- Nitroprusside sodium
(Nipride), a nitrovasodilator, is
metabolized by smooth muscle cells to
nitric oxide which dilates both
arterioles and venules.
- 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
sodium (Nipride) 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.
- Diazoxide (Hyperstat) is
infrequently used unless accurate infusion pumps
are unavailable.
- The mechanism of action
involves activation of ATP-sensitive
potassium channels, hyperpolarization of
arteriolar smooth muscle, relaxation and dilation.
- Adverse effects
include salt and water retention and
hyperglycemia. Diazoxide inhibits insulin
release.
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