Relaxing effects of Nifedipine on the nonpregnant human uterus in vitro and in vivo

The effects of the calcium antagonist Nifedipine were investigated on isolated human myometrium and on uterine activity in healthy women during their first menstrual days. Nifedipine (0.01-1.0 microgram/ml) had a concentration-related inhibiting effect on spontaneous activity of the myometrial strips, and relaxed preparations contracted by potassium. In vivo, Nifedipine (20-30 mg) given orally, effectively and rapidly reduced uterine activity, decreasing both amplitude and frequency of uterine contractions, and reduced basal tone. A moderate increase in heart rate and a transient facial flushing were noted, but otherwise no side effects were observed. Calcium antagonists like Nifedipine represent a new approach to the problem of relaxing the myometrium, and might be an interesting therapeutic alternative in situations where inhibition of unwanted uterine activity is desirable.