The pharmacokinetics of the beta 2-adrenoceptor agonist fenoterol in healthy women.

We have studied the pharmacokinetics of fenoterol in healthy women during and after a 3 h intravenous infusion of different doses within the therapeutic range for tocolysis (0.5 microgram.min-1, 1.0 micrograms.min-1, and 2.0 micrograms.min-1). A specific and sensitive radioimmunoassay was used for the determination of fenoterol. For compartmental analysis the plasma concentration time data were fitted with the TOPFIT program, assuming two exponentials. The total clearance of fenoterol increased with dose (1299 ml.min-1 at 0.5 microgram.min-1, 1483 ml.min-1 at 1.0 micrograms.min-1, and 1924 ml.min-1 at 2.0 micrograms.min-1), as did the apparent volume of distribution (from 49 l at the lowest to 85 l at the highest dose). In contrast, the apparent half-lives were not dose-dependent, with t1/2.lambda 1 4.8 min and t1/2.lambda z 52 min.