Fulvestrant Injection 250 mg per 5 mL, 50 mg per mL Single-Dose Prefilled Syringe (2 Syringe Kit)Fulvestrant Injection 250 mg 5 mL (50 mg mL) Prefilled Syringe Fulvestrant (brand: Faslodex) is a selective estrogen receptor downregulator (SERD) used in postmenopausal women with advanced or metastatic hormone receptorpositive (ER+) breast cancer. It binds estrogen receptors and accelerates their degradation, acting as a pure antiestrogen (no agonist effects). By downregulating ER, fulvestrant deprives ER+ tumor cells of estrogen driven growth.