British journal of cancer
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British journal of cancer · Aug 2001
Randomized Controlled Trial Multicenter Study Comparative Study Clinical TrialPharmacokinetics of anastrozole and tamoxifen alone, and in combination, during adjuvant endocrine therapy for early breast cancer in postmenopausal women: a sub-protocol of the 'Arimidex and tamoxifen alone or in combination' (ATAC) trial.
The ATAC trial evaluates in a randomized, double-blind design, Arimidextrade mark (anastrozole) alone or in combination with tamoxifen, relative to tamoxifen alone as 5-year adjuvant treatment in postmenopausal women with early breast cancer. Patients included in the pharmacokinetic (PK) sub-protocol had been in ATAC for > or =3 months, taking their medication in the morning and were 100% compliant for the preceding 14 days. Blood samples were collected 24 +/- 4 h after last dose. ⋯ Mean oestradiol levels were 21.3, 19.3, and 21.6 pmol l(-1)prior to treatment and 3.7, 20.9 and 3.6 pmol l(-1)after 3 months in the anastrozole, tamoxifen, and combination groups, respectively (n = 167). On-treatment values were below the detection limit (3 pmol l(-1)) in 43.6 and 38.5% of the anastrozole alone and anastrozole in combination with tamoxifen groups, respectively. As a result of (a) the lack of effect of anastrozole on tamoxifen and DMT levels and (b) the observed fall in blood anastrozole levels having no significant effect on oestradiol suppression by anastrozole, we conclude that the observed reduction in anastrozole levels by tamoxifen is unlikely to be of clinical significance when anastrozole and tamoxifen are administered together.