Effect of iguratimod on diclofenac metabolism by CYP2C9 in rats and human recombinant CYP2C9 yeast cells

Iguratimod (IGU, also known as T-614), a novel disease modifying antirheumatic drug intended to cure patients with rheumatoid arthritis (RA). The purpose of this study is to evaluate the effect of IGU on the pharmacokinetics of CYP2C9 probe drug diclofenac and its metabolite 4′-hydroxy diclofenac in vivo and in vitro. In in vivo experiments, 24 rats were randomly assigned to three groups consisting of the control group (Normal saline), low dose IGU group (10 mg/kg) and high dose IGU group (30 mg/kg). Blood samples were collected from orbital sinuses vein before 1 hour and serial times of giving diclofenac (15 mg/kg) to all the rats. Plasma concentration of diclofenac and its metabolite 4´-hydroxy diclofenac were assayed by high performance liquid chromatography. Pharmacokinetic parameters were assessed by Winnonlin 6.4 pharmacokinetic software. Moreover, in vitro studies were performed in recombinant human CYP2C9 yeast cell system. IGU at low dose showed no significant differences in the pharmacokinetic parameters of diclofenac and 4-hydroxy diclofenac in vivo when compared with control group (p>0.005). However, at the high dose of IGU, the pharmacokinetic parameters of 4´-hydroxy metabolite of diclofenac increase in half-life (T1/2) and mean area under the curve (AUC0→24), while a decrease in mean clearance (CL, mL/h/kg) and volume of distribution Vz (mL/kg). In addition, in in vitro study, high doses of IGU reduces the metabolism rate of diclofenac. IGU at high dose significantly increase the pharmacokinetics parameters of 4´-hydroxy diclofenac in rats. Additionally, it also showed the potent inhibitory effect on diclofenac metabolism in recombinant human CYP2C9 yeast cells.