Terbutaline in the treatment of preterm labour.

Continuous terbutaline infusion in 8 women with premature labour arrested the uterine contractions within 1.5 h in 7 of them when an infusion rate of 10 micrograms/min was used. The plasma concentrations of terbutaline were in the range 10-14 micrograms/L after 1 h. In 4 other women with less severe contractions, labour could be stopped with infusion rates of 5 or 7.5 micrograms/min. A condition approaching steady state seemed to be attained after infusion at a constant rate of 2.5 micrograms/min for 17-34 h with a mean plasma concentration of 6.7 micrograms/L. This value would give a mean total body clearance of 0.30 L/min which is about one third higher than that previously found in healthy men. The terbutaline plasma concentrations determined in this study were compared with simulated curves based on pharmacokinetic parameters obtained in healthy male volunteers. The data correlated well during the first 3 h of infusion, indicating similar distribution kinetics in the patients and the volunteers. After infusion for a longer period (greater than 10 h), the measured plasma concentrations were generally lower than those predicted by the simulation. Treatment of 10 women (7 initially treated intravenously) with terbutaline tablets 5 mg three times daily postponed delivery for more than 7 days in 9 of the patients. The mean plasma concentrations of terbutaline during repeated tablet treatment were 3.4, 4.1 and 4.1 micrograms/L at 1, 2 and 4 h after administration, respectively. No serious side-effects occurred.