Tamoxen Drug Interactions

When Tamoxifen (TAMOXEN) is used in combination with coumarin-type anticoagulants, a significant increase in anticoagulant effect may occur. Where such coadministration is initiated, careful monitoring of the patient is recommended.
When Tamoxifen (TAMOXEN) is used in combination with cytotoxic agents, there is increased risk of thromboembolic events occurring.
The use of Tamoxifen (TAMOXEN) in combination with anastrozole as adjuvant therapy has not shown improved efficacy compared with Tamoxifen (TAMOXEN) alone.
The known principal pathway for Tamoxifen (TAMOXEN) metabolism in humans is demethylation, catalysed by CYP3A4 enzymes. Pharmacokinetic interaction with the CYP3A4 inducing agent rifampicin, showing a reduction in Tamoxifen (TAMOXEN) in plasma levels have been reported in the literature. The relevance of this finding is not known.
Pharmacokinetic interaction with CYP2D6 inhibitors, showing a reduction in plasma level of an active Tamoxifen (TAMOXEN) metabolite, 4-hydroxy-Ndesmethyltamoxifen (endoxifen), has been reported in the literature.
Pharmacokinetic interaction with CYP2D6 inhibitors, showing a 65-75% reduction in plasma levels of one of the more active forms of the drug, i.e. endoxifen, has been reported in the literature. Reduced efficacy of Tamoxifen (TAMOXEN) has been reported with concomitant usage of some SSRI antidepressants (e.g. paroxetine) in some studies. As a reduced effect of Tamoxifen (TAMOXEN) cannot be excluded, co-administration with potent CYP2D6 inhibitors (e.g. paroxetine, fluoxetine, quinidine, cinacalcet or bupropion) should whenever possible be avoided.