Maternal plasma concentrations in multiple oral fenoterol treatment

Abstract

Reports on the clinical effectiveness of oral treatment with beta-sympathomimetic fenoterol are quite divergent in their conclusions. The aim of this study was to determine the plasma levels of fenoterol in steady state during tocolytic treatment with high oral doses. Nine pregnant women with clinically indicated tocolysis were given a 5 mg dose of fenoterol in tablet form eight times per day at prescribed hours. During the first four days, in the late afternoon just before and again one hour after the intake, a blood sample was taken to determine the fenoterol concentration by radioimmunoassay. In addition, uterine activity, blood pressure, heart rate, and tremor were periodically checked while the patient was under observation. The fenoterol levels in the plasma ranged from 130 to 200 pg/ml; the steady state concentration remained relatively constant throughout the observation period. It is not certain, that by taking the blood sample one hour after the tablet was swallowed, the maximal concentration was found. However, with the given doses, nearly the same fenoterol levels were measured in the blood as with low doses of intravenously administered fenoterol.