Tocolytic and Hemodynamic Effects of Nifedipine in the Ewe

The ability of the calcium antagonist nifedipine to inhibit uterine contractions during labor and in the postpartum period was measured in the ewe. The hemodynamic effects of tocolytic doses of this drug were measured and compared with the hemodynamic effects of equivalent doses of ritodrine. Intravenous nifedipine was found to be a potent tocolytic agent that completely inhibited uterine activity even in advanced labor when administered at infusion rates that resulted in only mild hemodynamic effects. At tocolytically similar infusion rates nifedipine produced significantly less increase in maternal heart rate than did ritodrine.