Raloxifene 4'-glucuronide is a primary metabolite of Raloxifene. Raloxifene 4'-glucuronide formation is mediated mostly by UGT1A10 and UGT1A8. Raloxifene 4'-glucuronide binds to estrogen receptor with an IC₅₀ of 370 μM. ^[1][2]. Raloxifene is a selective estrogen receptor modulator. Raloxifene activates TGFβ3 promoter as a full agonist at nanomolar concentrations, and inhibits the estrogen response element-containing vitellogenin promoter expression^[3]. IC50 & Target: IC50: 370 μM (Estrogen receptor)^[2] In Vitro: Expressed UGT1A8 catalyzes Raloxifene 4'-glucuronide with an apparent K_m of 59 μM and a V_max of 2.0 nmol/min/mg. Based on rates of Raloxifene glucuronidation and known extrahepatic expression, UGT1A8 and 1A10 appear to be primary contributors to Raloxifene glucuronidation in human jejunum microsomes. For human liver microsomes, the variability of Raloxifene 4'-glucuronide formation is 4-fold. Treatment of expressed UGTs with alamethicin results in minor increases in enzyme activity, whereas in human intestinal microsomes, maximal increases of 9-fold for the Raloxifene 4'-glucuronide are observed. Intrinsic clearance values in intestinal microsomes are 95 μl/min/mg for the Raloxifene 4'-glucuronide^[2].