Abstract Body: Human cytochrome P450 (CYP) enzymes are a superfamily of heme-containing oxidoreductases essential in the metabolism of various xenobiotics. CYP2C8 is responsible for the oxidative metabolism of many important drugs including cerivastatin, repaglinide, pioglitazone, enzalutamide, dasabuvir, imatinib, etc. and has generated research interest due to its involvement in drug-drug interactions (DDI). The glucuronide metabolites of the antilipemic drug gemfibrozil and the antiplatelet drug clopidogrel are known as strong inhibitors of CYP2C8 leading to several DDIs. Most of the gemfibrozil dose is primarily metabolized as glucuronide conjugate or gemfibrozil acyl-glucuronide, which is a known mechanism-based inhibitor of CYP2C8 that leads to clinical DDIs with the substrates of CYP2C8. For example, the co-administration of gemfibrozil with the CYP2C8 substrate pioglitazone inhibited the metabolism and increased the concentration of pioglitazone leading to DDIs. In addition, the clopidogrel acyl-glucuronide metabolite is a known strong time-dependent inhibitor of CYP2C8 leading to marked clinical DDIs with the substrates of this enzyme. Patients on clopidogrel and concurrently taking cerivastatin, or the anti-diabetic repaglinide, are at increased risk of rhabdomyolysis. It is not clear how a glucuronide metabolite of these drugs binds in the active site of CYP2C8 and inhibit the enzyme. CYP2C8 enzyme was recombinantly expressed and purified. A biophysical method Surface Plasmon Resonance (SPR) was used to elucidate the binding of the acyl-glucuronide metabolites of gemfibrozil and clopidogrel with CYP2C8. The representative dissociation constant (K_D) of CYP2C8 binding with gemfibrozil acyl-glucuronide was 227.5 ± 38.5 µM, whereas the K_D of CYP2C8 binding with clopidogrel acyl-glucuronide was ten-fold lower, in the range of 3 to 25 µM indicative of higher affinity. The purified protein was also used for crystallization with these acyl glucuronides of gemfibrozil and clopidogrel with an aim to determine the three-dimensional structure. Overall, the characterization of CYP2C8 with gemfibrozil acyl-glucuronide and clopidogrel acyl-glucuronide yielded insights into the binding and inhibition of an important drug metabolizing enzyme.