Fetal toxicity of nitroprusside in the pregnant ewe.

Sodium nitroprusside, a direct-acting vasodilator, has been used to treat the hypertension associated with preeclampsia and eclampsia. Fatal cyanide intoxication has been reported during infusion of nitroprusside. We have investigated placental transfer and fetal toxicity of nitroprusside in the acute pregnant ewe model. A maternal intravenous infusion of nitroprusside solution was maintained at a rate sufficient to decrease mean maternal arterial pressure by 20% for 1 hour. Maternal and fetal levels of nitroprusside were in equilibrium at the 20 minute sample. Five of the eight animals exhibited tachyphylaxis to nitroprusside, and their fetuses died in utero with lethal levels of cyanide. No significant changes were observed in uterine blood flow.