Topiroxostat-d 4 is deuterium labeled Topiroxostat. Topiroxostat (FYX-051) is a potent and orally active xanthine oxidoreductase (XOR) inhibitor with an IC50 value of 5.3 nM and a Ki value of 5.7 nM. Topiroxostat exhibits weak CYP3A4-inhibitory activity (18.6%). Topiroxostat has the potential for hyperuricemia treatment.