Mechanism of Action of Endoxifen and Its Clinical Relevance

Clinical Relevance to Tamoxifen Therapy

• Endoxifen is produced through CYP2D6-mediated metabolism of tamoxifen's primary metabolite, N-desmethyltamoxifen, and its levels can be affected by CYP2D6 genetic polymorphisms and drug interactions with CYP2D6 inhibitors, which may impact cancer recurrence risk in patients taking tamoxifen 1, 2
• The American Society of Clinical Oncology recommends that clinicians avoid concurrent use of known CYP2D6 inhibitors when suitable alternatives exist to ensure optimal endoxifen levels for therapeutic effect in patients taking tamoxifen 1, 2
• CYP2D6 poor metabolizers or patients taking strong CYP2D6 inhibitors may have insufficient endoxifen levels for optimal therapeutic effect, highlighting the importance of considering CYP2D6 status in patients taking tamoxifen 1, 2