Aromatt-1 Drug Interactions

Tamoxifen: 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 anastrozole tablets 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. Based on clinical and pharmacokinetic results from the ATAC trial, tamoxifen should not be administered with anastrozole.
Estrogen: Estrogen-containing therapies should not be used with anastrozole tablets as they may diminish its pharmacological action.
Warfarin: In a study conducted in 16 male volunteers, anastrozole did not alter the exposure (as measured by C_max and AUC) and anticoagulant activity (as measured by prothrombin time, activated partial thromboplastin time, and thrombin time) of both R- and S-warfarin.
Cytochrome P450: Based on in vitro and in vivo results, it is unlikely that co-administration of anastrozole tablets 1 mg will affect other drugs as a result inhibition of cytochrome P450 [see Pharmacology under Actions].