Nausea, vomiting, headache, and sweating may be caused by excessively rapid lowering of blood pressure.
Cyanide toxicity, manifested by altered mental status and metabolic (lactic) acidosis, may occur with rapid high-dose infusion (10–15 mcg/kg/min) for periods of 1 hour or longer. Patients with depleted thiosulfate stores (eg, malnourished) may have elevated cyanide levels at lower infusion rates. Continuous intravenous infusion of hydroxocobalamin, 25 mg/h (See Hydroxocobalamin), or thiosulfate (See Thiosulfate, Sodium) has been used to limit cyanide toxicity. If severe cyanide toxicity occurs, discontinue the nitroprusside infusion and consider antidotal doses of thiosulfate and sodium nitrite (See Nitrite, Sodium and Amyl) or high-dose hydroxocobalamin (See Hydroxocobalamin).
Thiocyanate intoxication, manifested by disorientation, delirium, muscle twitching, and psychosis, may occur with prolonged high-dose nitroprusside infusions (usually ≥3 mcg/kg/min for ≥48 hours), particularly in patients with renal insufficiency (may occur at rates as low as 1 mcg/kg/min). Thiocyanate production is also enhanced by co-administration of sodium thiosulfate. Monitor thiocyanate levels if the nitroprusside infusion lasts more than 1–2 days; toxicity is associated with thiocyanate levels of 50 mg/L or greater. Usually treat by lowering the infusion rate or discontinuing the use of nitroprusside. Thiocyanate is removed effectively by hemodialysis.
Rebound hypertension may be observed after sudden discontinuance.
Methemoglobinemia may be observed in patients receiving more than 10 mg/kg but is typically not severe.
Use in pregnancy. FDA Category C (indeterminate [See Introduction in Section III]). It may cross the placenta and may affect uterine blood flow; however, it has been used successfully in pregnant women.