Arimidex (ZD1033): A selective, potent inhibitor of aromatase in postmenopausal female volunteers

Two multiple-dose studies were conducted in healthy post-menopausal female volunteers to investigate the pharmacokinetics and effects on endocrinology of Arimidex (ZD1033). Volunteers in the first trial were dosed with 3 mg of ZD1033 daily over 10 days to assess the effects on endocrinology of ZD1033 and establish the pharmacokinetic profile. In the second trial volunteers received 14 daily doses of either 0.5 or 1.0 mg of ZD1033 to assess the pharmacokinetics of ZD1033 and the effects of low doses of ZD1033 on serum oestradiol concentrations. Following multiple dosing a significant reduction in the concentration of serum oestradiol of approximately 80% of baseline was obtained with all three doses; no recovery in oestradiol was apparent for up to 144 h after the last dose. There was no overall difference in the level of oestradiol suppression between the 0.5 or 1.0 mg doses of ZD1033. However, comparison of the number of volunteers with oestradiol concentrations below the limits of detection of the assay, 24 h after the last dose of ZD1033, suggested that 1.0 mg was the minimal dose required for maximal suppression of oestradiol. No significant effect was recorded on serum concentrations of gonadotrophins over the dosing period. Serum concentrations of a range of adrenal steroids were not affected by administration of ZD1033; furthermore, steroid response to standard adrenocorticotrophic hormone (ACTH) challenge was unimpaired by ZD1033. Together these data demonstrate the potency, tolerability and selectivity of ZD1033. The pharmacokinetic profile of ZD1033 supports its use as a once-daily treatment given orally.