EXPLORING THE INHIBITION POTENTIAL OF CYP2C9 ENZYME: IN VITRO ASSESSMENT AND PREDICTION OF GLIMEPIRIDE-SULFAMETHOXAZOLE INTERACTIONS.

Abstract

CYP2C9 represents a genetically diverse enzyme that plays a crucial role in the oxidative transformation of nearly 15% of drugs subject to initial phase I metabolism. Given its integral involvement in drug metabolism, it becomes imperative to assess the dynamic attributes of CYP2C9 substrates, particularly in tandem with co-administered drugs that could potentially instigate inhibition. An example of a well-acknowledged drug interaction is the occurrence of hypoglycemia stemming from the concurrent use of sulfonylurea and sulfonamide drugs. Therefore, the focal point of this investigation encompassed a comprehensive exploration into the repercussions of CYP2C9 inhibition on the pharmacokinetics of glimepiride (GLM), employing sulfamethoxazole (SMZ) as a representative in vitro inhibitor of CYP2C9. This inquiry primarily utilized human liver microsomes (HLM) to shed light on the intricate interplay between GLM and SMZ by evaluating key kinetic parameters such as Km, Vmax, IC50, and Ki. The aspiration extended to predictive efforts aimed at deciphering potential in vivo drug interactions leveraging in vitro findings.

Within the concentration range of 30 to 1100 µMole, SMZ exhibited a discernible inhibitory effect specifically targeting CYP2C9-mediated GLM hydroxylation. Evident from an apparent IC50 (Ki) value of 400 µMole and an intrinsic Ki value of 290 µMole, this inhibition demonstrated a competitive pattern as showcased by the discernible increase in Km, while Vmax remained relatively stable. This outcome, consistent with predictions derived from Michaelis-Menten and LineweaverBurk plots, found further substantiation through the leftward positioning of the Ki value according to the Dixon plot, indicative of competitive inhibition. Importantly, the outcomes underscored that SMZ, when employed at concentrations below 500 µMole, could effectively serve as a specific CYP2C9 inhibitor for in vitro inquiries.

Insights garnered from the in vitro-in vivo correlation (IVIVC) analyses pointed towards a 1.5-fold escalation in the AUC of GLM when influenced by SMZ. This meticulous exploration delved into the inhibitory impact of SMZ on CYP2C9-mediated GLM metabolism, with the projected surge in GLM plasma concentrations warranting vigilance due to the associated risk of hypoglycemia upon concurrent administration of SMZ and GLM.