Main Article Content

Dipti B. Ruikar
Gajanan J Deshmukh
Sadhana J Rajput
Aarti S Zanwar
Deepak S. Mohale


Glimepiride, Sulfamethoxazole, Human liver microsomes, CYP2C9, IC50


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.

Abstract 45 | pdf Downloads 45


1. Vikas K, Dan R, Chad W, Timothy T, Jan L. W: Enzyme source effects on CYP2C9 kinetics and inhibition. Drug metab Dispos 2006, 34: 1903-1908.
2. Dermot F, James T Steve T, Robert J: Prediction of CYP2C9-mediated drug-drug interactions: a comparison using data from recombinant enzymes and human hepatocytes. Drug metab Dispos 2005, 33: 1700-1707.
3. Dayong Si, Ying W, Yi-Han Zhou, Yingjie G, Juan W, Hui Z, Ze-Sheng Li, and J. Paul F: Mechanism of CYP2C9 Inhibition by flavones and flavonols. Drug metab Dispos 2009, 37: 629-634. 4. Vikas K, Jan W, Dan R, Chad J, Lee A, Timothy T: CYP2C9 Inhibition: Impact of probe selection and pharmacogenetics on in vitro inhibition profiles. Drug metab Dispos 2006, 37: 1966-1975.
4. Ruikar D and Rajput S: Optimization of the in vitro oxidative biotransformation of glimepiride as a model substrate for cytochrome P450 using factorial design. DARU Journal of Pharmaceutical Sciences 2012, 20:1-8.
5. Kirchheiner J, Roots I, Goldammer M, Rosenkranz B, Brockmöller J: Effect of genetic polymorphisms in cytochrome p450 CYP2C9 and CYP2C8 on the pharmacokinetics of oral antidiabetic drugs. Clinical Relevance Clin Pharmacokinet 2005, 44: 1209-1225.
6. Suzuki K,Yanagawa T,Shibasaki T,Kaniwa N,Hasegawa R,Tohkin M: Effect of CYP2C9 genetic polymorphisms on the efficacy and pharmacokinetics of glimepiride in subjects with type 2 diabetes. Diabetes Res Clin Pract 2006, 72: 148-54.
7. Keiko M, Noriko H, Emiko S, Masahiro T, Su-Ryang K, Nahoko K, Noriko K, Ryuichi H, Kazuki Y, Kei K, Toshiyuki M, Yoshiro S, and Jun-ichi S: Substrate-Dependent Functional Alterations of Seven CYP2C9 Variants Found in Japanese Subjects. Drug metab Dispos 2009, 37: 1895-1903.
8. Tirkkonen T, Heikkila P, Huupponen R, Laine K: Potential CYP2C9-mediated drug–drug interactions in hospitalized type 2 diabetesmellitus patients treated with the sulphonylureas glibenclamide, glimepiride or glipizide. J Intern Med2010, 268; 359–366.
9. Xia W, Jun-Sheng W, Janne T, Jouko L, Pertti J: Trimethoprim and sulfamethoxazole are selective inhibitors of CYP2C8 and CYP2C9, respectively. Drug metab Dispos 2002, 30: 631-635. 11. Kanji K, Kiyomi I, Yukiko N, Shin-Ichi K, Susumu I, Yoshihiko F, Carol E, Charles A , Noriaki S, Yuichi S: Prediction of in vivo drug-drug interactions between tolbutamide and various sulfonamides in humans based on in vitro experiments. Drug metab Dispos 2000, 28: 475-481.
10. Tianyi Z, Yongxin Z, Chandrani G: Simultaneous determination of metabolites from multiple cytochrome P450 probe substrates by gradient liquid chromatography with UV detection. Current. Separations 2003, 20: 87-91.
11. Khan U, Aslam F, Ashfaq M, Asghar N: Determination of glimepiride in pharmaceutical formulations using HPLC and first-derivative spectrophotometric methods. J. Anal. Chem 2009, 64: 171–175.
12. Tarundeep K, Harold B, Michael M: Estimation of ki in a competitive enzyme-inhibition model:
13. Comparisons among three methods of data analysis. Drug metab Dispos 1999, 27: 756-762. 15 M. Dixon: The determination of enzyme inhibitor constants. Biochem. J. 1953, 55: 170-171.
14. Hayley S. , Kiyomi I, Aleksandra G, Brian J: Prediction of in vivo drug–drug interactions from in vitro data: impact of incorporating parallel pathways of drug elimination and inhibitor absorption rate constant. Br J Clin Pharmacol2005 , 60: 508–518.
15. Larry C, Timothy G: Predicting in vivo drug interactions from in vitro Drug discovery data. Drug Discov2005, 4: 825-833