Co-administration of anastrozole and tamoxifen in breast cancer patients reduced anastrozole plasma concentration by 27%. However, the co-administration of anastrozole and tamoxifen did not affect the pharmacokinetics of tamoxifen or N-desmethyltamoxifen. At a median follow-up of 33 months, the combination of ARIMIDEX and tamoxifen did not demonstrate any efficacy benefit when compared with tamoxifen in all patients as well as in the hormone receptor-positive subpopulation. This treatment arm was discontinued from the trial [see
]. Based on clinical and pharmacokinetic results from the ATAC trial, tamoxifen should not be administered with anastrozole.
Estrogen-containing therapies should not be used with ARIMIDEX as they may diminish its pharmacological action.
In a study conducted in 16 male volunteers, anastrozole did not alter the exposure (as measured by Cmax and AUC) and anticoagulant activity (as measured by prothrombin time, activated partial thromboplastin time, and thrombin time) of both R- and S-warfarin.
Based on in vitro and in vivo results, it is unlikely that co-administration of ARIMIDEX 1 mg will affect other drugs as a result of inhibition of cytochrome P450 [see