Ovine fetal cardiorespiratory response to nicardipine

Nicardipine, a calcium antagonist associated with decreased uterine blood flow in near-term pregnant rabbits and fetal asphyxia after maternal administration in the rhesus monkey and sheep, was infused directly to the fetus in six chronically prepared pregnant ewes at 128 days' gestation. Changes in fetal mean arterial and diastolic blood pressure levels at 2 and 30 minutes after bolus injection of 50 micrograms were minimal; by 60 minutes these values had returned to preinfusion levels. No significant changes were observed after infusion of 100 micrograms of nicardipine. Fetal heart rate, fetal arterial blood gas values, and maternal cardiovascular variables did not change at either dose. Fetal plasma concentrations of nicardipine were 78 +/- 28 ng/ml and 114 +/- 48 ng/ml at 30 minutes after infusion of 50 micrograms and 100 micrograms, respectively, well within the range previously reported to be associated with fetal asphyxia. These data suggest that the previously reported fetal acidosis from maternal infusion of nicardipine may be primarily due to a decrease in maternal uterine blood flow rather than a direct fetal effect of the drug.