Indication:
adjuvant for breast cancer treatment
Mechanism:
Tamoxifen is a prodrug which is converted to the active metabolite endoxifen via CYP 2D6 metabolism. Endoxifen blocks the receptor site for estrogen to exert its effects on breast cancer tissue.
Usual Dosing:
20 mg once daily for 10 years (extended treatment) *use in premenopausal patients (if post menopausal, use aromatase inhibitors)
Adverse Effects: LOTS!
-GI upset
-hot flashes (related to anti-estrogen mechanism)
-increased risk of clots (stroke, deep vein thrombosis, pulmonary embolism)
-increased risk of endometrial cancer
-bone and muscle pain
-platelet reduction
-parasthesia
-altered lipid profile
-vaginal bleeding
Drug Interactions:
CYP 2D6 inhibitors (terbinafine, fluoxetine, paroxetine, bupropion): reduced tamoxifen activation --> failure of tamoxifen