Citation: Sridharan, K.; Qader, A.M.; Hammad, M.; Jassim, A.; Diab, D.E.; Abraham, B.; Hasan, H.M.S.N.; Pasha, S.A.A.; Shah, S. Evaluation of the Association between Single Nucleotide Polymorphisms of Metabolizing Enzymes with the Serum Concentration of Paracetamol and Its Metabolites. Metabolites 2022, 12, 1235. https://doi.org/10.3390/ metabo12121235 Academic Editors: Muhammad Sajid Hamid Akash and Kanwal Rehman Received: 24 October 2022 Accepted: 7 December 2022 Published: 9 December 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). metabolites H OH OH Article Evaluation of the Association between Single Nucleotide Polymorphisms of Metabolizing Enzymes with the Serum Concentration of Paracetamol and Its Metabolites Kannan Sridharan 1, * , Ali Mohamed Qader 2 , Mustafa Hammad 2 , Anfal Jassim 3 , Diab Eltayeb Diab 3 , Betsy Abraham 4 , Hasan M. S. N. Hasan 4 , Sheikh Abdul Azeez Pasha 4 and Shamik Shah 5 1 Department of Pharmacology & Therapeutics, College of Medicine and Medical Sciences, Arabian Gulf University, Manama P.O. Box 26671,Bahrain 2 Salmaniya Medical Complex, Manama P.O. Box 26671, Bahrain 3 Department of Molecular Medicine, College of Medicine and Medical Sciences, Al-Jawhara Center, Arabian Gulf University, Manama P.O. Box 26671,Bahrain 4 Intensive Care Unit, Salmaniya Medical Complex, Manama P.O. Box 26671, Bahrain 5 Department of Nephrology, Salmaniya Medical Complex, Manama P.O. Box 26671, Bahrain * Correspondence: kannans@agu.edu.bh; Tel.: +973-17239794 Abstract: Intravenous paracetamol is a commonly administered analgesic and antipyretic in inpatient settings. Paracetamol is metabolized by cytochrome P450 (CYP) enzymes followed by conjugating enzymes to mainly glucuronide but to a lesser extent, sulphate metabolites, and oxidative metabo- lites. Single nucleotide polymorphisms (SNPs) in the CYP enzymes result in modified enzymatic activity. The present study was carried out to evaluate the prevalence of SNPs related to paracetamol metabolism and principal metabolites in critically ill patients, and those with chronic kidney disease. The present study is a cross-sectional study carried out in adults (>21 years) requiring intravenous paracetamol as part of their standard of care. Details regarding their demographics, and renal and liver function tests were collected. Blood was withdrawn for the analysis of paracetamol and their metabolites, and the SNPs of key CYP enzymes. Paracetamol/paracetamol glucuronide (P/PG), paracetamol/paracetamol sulphate (P/PS) and PG/PS were estimated. Acute liver injury (ALI) and renal dysfunction were defined using standard definitions. We observed a significant prevalence of SNPs in CYP1A2*1C, CYP3A4*3, CYP1A2*1K, CYP1A2*6, CYP2D6*10, and CYP2E1*2 amongst the 150 study participants. Those with CYP1A2*6 (CC genotype) were observed with significantly lower PG and PS concentrations, and a higher P/PS ratio; CYP2D6*10 (1/1 genotype) with a significantly lower PG concentration and a higher P/PG ratio; and CYP1A2*1K (CC genotype) was observed with a significantly higher PG/PS ratio. Good predictive accuracies were observed for determining the SNPs with the cut-off concentration of 0.29 μM for PS in determining CYP1A2*1K, 0.39 μM for PG and 0.32 μM for PS in determining CYP1A2*6 genotype, and 0.29 μM for PG in determining the CYP2D6*10 genotype. Patients with renal dysfunction were observed with significantly greater concentrations of paracetamol, PG and P/PS, and PG/PS ratios, with a lower concentration of PS. No significant differences were observed in any of the metabolites or metabolite ratios in patients with ALI. We have elucidated the prevalence of key CYP enzymes involved in acetaminophen metabolism in our population. Alterations in the metabolite concentrations and metabolic ratios were observed with SNPs, and in patients with renal dysfunction. Population toxicokinetic studies elucidating the dose-response relationship are essential to understand the optimized dose in this sub-population. Keywords: paracetamol; acetaminophen; paracetamol sulphate; paracetamol glucuronide; pharmacogenetics 1. Introduction Paracetamol is the commonly administered analgesic and antipyretic accounting for use in around 65% of critically ill patients [1]. Paracetamol use has been associated with Metabolites 2022, 12, 1235. https://doi.org/10.3390/metabo12121235 https://www.mdpi.com/journal/metabolites