Effects of isradipine, a new calcium antagonist, on maternal cardiovascular system and uterine activity in labour.

The effects of isradipine (a new calcium antagonist of the dihydropyridine type) on maternal blood pressure and heart rate, fetal heart rate, and uterine activity in labour were measured. Uterine activity was recorded by an intrauterine microtip transducer catheter connected to a fetal monitor. Isradipine was given as a slow injection in doses of 0.5 mg (10 women), 1 mg (11 women), and 1.5 mg (6 women). A reduction of systolic (6-16%) and diastolic (19-22%) blood pressure was seen, and concomitantly there was an increase in maternal (29-34%) and fetal (3-10%) heart rates. Reduction in uterine activity was not dose-related (maximum reduction 17%). Side effects (headache, palpitations) were minor and well tolerated. One women in the high-dose group had a shortlasting episode of hypotension. The results suggest that isradipine given as a bolus dose decreases blood pressure in pregnant women with little effects on uterine activity and fetal heart rate.