Simvastatin ammonium is an active metabolite of simvastatin lactone mediated by CYP3A4/5 in the intestinal wall and liver (pKa=5.5). Simvastatin ammonium reduces indoxyl sulfate-mediated reactive oxygen species and modulates OATP3A1 expression in cardiomyocytes and HEK293 cells transfected with the OATP3A1 gene^[1]. In Vitro: There is a pH-dependent effect on organic anion transporting polypeptide 3A1 (OATP3A1) uptake, with more efficient simvastatin acid uptake at pH5.5 in HEK293 cells transfected with the OATP3A1 gene. The Michaelis-Menten constant (Km) for simvastatin acid uptake by OATP3A1 was 0.017 μM and the Vmax was 0.995 fmol/min/105 cells^[1].