Dose-response study of fenoterol on uterine activity in labor at term.

Uterine hyperactivity can be treated with uterine relaxants. In order to establish the most satisfactory dosage for Fenoterol, several doses were administered intravenously to pregnant women during birth and the actions on uterine relaxation and on side effects were examined. Saline was injected in a group of patients as control. With doses of 20 and 40 micrograms Fenoterol, submaximal uterine relaxation times of 7.3 and 7.9 min were obtained. Subjective side effects were observed, such as palpitations and restlessness; maternal blood pressure was unchanged. The pulse rate increased significantly only after 40 micrograms. 10 micrograms Fenoterol induced a uterine relaxation time of 5.6 min, was without side effects and was therefore regarded as the most satisfactory dosage. With 5 micrograms Fenoterol a relaxation time of only 3.2 min was observed. In the control group, administration of saline was without any observable effect.