Dose proportionality and population characteristics of oral fadrozole hydrochloride, an aromatase inhibitor, in postmenopausal women.

The dose proportionality of the pharmacokinetics of fadrozole was investigated in 18 healthy postmenopausal women. Fadrozole hydrochloride was administered as 0.3-, 1.0-, and 2.0-mg oral doses continuously every 12 hr for 5 days each in a Latin square design. At steady state, the dose-normalized pharmacokinetic parameters AUC and Cmax were found to be independent of the dose. In addition, no statistically significant differences in tmax were detected. It was concluded that the pharmacokinetics of fadrozole were dose proportional in the projected therapeutic dose range. The relationship between oral clearance and the demographic factors, age, weight, and height, was assessed. Oral clearance was related to total body weight but not age or height. Prospective estimates of the population components of variance showed that intersubject variance accounted for 91.7% of the total random variance. Weight variance accounted for 36.1% of the intersubject variance.

The pharmacodynamic inhibition of estrogen synthesis by fadrozole, an aromatase inhibitor, and its pharmacokinetic disposition.

In this dose-ranging phase I study, the relationship between in vivo androgen to estrogen conversion kinetics and plasma concentrations of fadrozole was investigated in postmenopausal women receiving therapy with this aromatase inhibitor. Patients received ascending doses, ranging from 0.3-8 mg fadrozole twice daily, each for a period of 2 weeks. Drug kinetics and endocrine effects were evaluated specifically for the 2- and 8-mg twice daily treatment regimens. The in vivo activity of the drug was demonstrated by the suppression of estrone and estradiol biosynthesis from testosterone and androstenedione, respectively. The drug inhibitory constant, KI, for the estrone synthetic pathway, was 3.0 ng/mL (13.4 nmol/L) and was of similar magnitude as that determined under in vitro conditions. The KI for the estradiol synthetic pathway was 5.3 ng/mL (23.7 nmol/L). The disparity between KI values may indicate that the two pathways are not equivalent in terms of their inhibition by fadrozole. Pharmacokinetic data demonstrated tha the drug was rapidly absorbed after oral dosing, with peak plasma concentrations achieved in median times of 1 and 2 h, respectively, for the 2- and 8-mg twice daily treatment regimens. The average half-life and oral clearance values were 10.5 h and 621 mL/min, respectively. Oral clearance was independent of dose.