Recovery of reproductive function in rats treated with the aromatase inhibitor fadrozole.

The aromatase inhibitor, fadrozole hydrochloride (CGS 16949A), was developed for the treatment of breast cancer, and has not been available for pediatric use because of the lack of information about potential reproductive toxicology. To determine the effect of fadrozole on subsequent fertility and reproductive performance in rats, peripubertal male and female Sprague-Dawley rats (10/group) were given fadrozole by oral gavage once a day for 60 consecutive days (age 21 through 80 d) at a dose of 0, 1200, or 6000 micrograms/kg/d (dose range in women with breast cancer: 60 to 240 micrograms/kg/d). Following a 30-d recovery period (days 81 through 111 of age), cohabitation with untreated rats of the opposite sex was accomplished for 30 d or until positive evidence of mating was obtained (daily vaginal smears). The nonfadrozole-treated males used for cohabitation were proven fertile breeders; the females were virgin with proven 4-d estrous cycles. The duration of pregnancy, number, sex, condition, and body weight of pups were determined. Pregnant rats were weighed on gestational days 7, 14, and 20. There was a profound decrease in the number of estrous cycles at both dose levels of fadrozole compared to the control (P < 0.001). During the 30-d recovery period, estrous cycles were reestablished within a few days in the treated rats and the number and length of estrous cycles were not statistically different between fadrozole-treated and control rats. The gestational body weights of fadrozole-treated and untreated females did not differ significantly. There were no statistically significant differences in the number of matings/number of pairings, gestational length, mean live pups/litter, % pups born alive/litter, and % male pups/litter in the three groups (vehicle-, low-, and high-dose fadrozole-treated females, cohabited with untreated males and fadrozole-treated males, cohabited with untreated females). Thus, young male and female rats treated for 60 d with large doses of fadrozole had no detectable adverse effect on subsequent reproductive function.