Flutamide-d7 is intended for use as an internal standard for the quantification of flutamide by GC- or LC-MS. Flutamide is an androgen receptor antagonist and prodrug form of 2-hydroxy flutamide. Flutamide is converted to 2-hydroxy flutamide by the cytochrome P450 (CYP) isoform CYP1A2 in human liver microsomes. It is cytotoxic to PC3 and LNCaP prostate cancer cells with IC50 values of 98.8 and 81.8 µM, respectively. Flutamide (50 mg/kg per day) reduces tumor growth in a PC-82 mouse xenograft model. Formulations containing flutamide have been used in the treatment of prostate cancer.