Evaluation of the Association between Single Nucleotide Polymorphisms of Metabolizing Enzymes with the Serum Concentration of Paracetamol and Its Metabolites

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 metabolites. 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 Blood was withdrawn for the analysis of paracetamol and their metabolites, and the SNPs of key CYP enzymes.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: acetaminophen; paracetamol; paracetamol glucuronide; paracetamol sulphate; pharmacogenetics.

Figure 1

Prevalence of SNPs amongst the study participants. The inner circles represent the CYP enzymes evaluated in this study. The specific SNPs for each of the CYP enzymes are mentioned in the outer circles including the number of patients observed with each polymorphism.

Figure 2

ROC plot for paracetamol metabolites with CYP1A2*1K. This is a ROC plot where the diagonal green line indicates the reference line. The brown line above the reference line represents the predictive ability of paracetamol sulphate. All other metabolites were observed with their lines falling below the reference line thereby they do not significantly predict the SNP. PGPS—Paracetamol glucuronide/Paracetamol sulphate ratio; PG—Paracetamol glucuronide; PPG—Paracetamol/Paracetamol glucuronide ratio; PPS—Paracetamol/Paracetamol sulphate ratio; PS—Paracetamol sulphate.

Figure 3

ROC plot for paracetamol metabolites with CYP1A2*6. This is a ROC plot where the diagonal green line indicates the reference line. The brown line above the reference line represents the predictive ability of paracetamol sulphate as like the dark green line that indicates paracetamol glucuronide metabolite. All other metabolite ratios were observed with their lines falling below the reference line thereby they do not significantly predict the SNP. PGPS—Paracetamol glucuronide/Paracetamol sulphate ratio; PG—Paracetamol glucuronide; PPG—Paracetamol/Paracetamol glucuronide ratio; PPS—Paracetamol/Paracetamol sulphate ratio; PS—Paracetamol sulphate.

Figure 4

ROC plot for paracetamol metabolites with CYP2D6*10. This is a ROC curve where the diagonal green line indicates the reference line. The dark green line above the reference line represents the predictive ability of paracetamol glucuronide. All other metabolites/metabolite ratios were observed with their lines falling below the reference line thereby they do not significantly predict the SNP. PGPS—Paracetamol glucuronide/Paracetamol sulphate ratio; PG—Paracetamol glucuronide; PPG—Paracetamol/Paracetamol glucuronide ratio; PPS—Paracetamol/Paracetamol sulphate ratio; PS—Paracetamol sulphate.

Figure 5

Frequency histogram of the metabolite ratios in the study population. These figures are the frequency histograms of log paracetamol upon paracetamol glucuronide (top left), log paracetamol upon paracetamol sulphate (top right), and log paracetamol glucuronide upon paracetamol sulphate (bottom). The vertical bars indicate the number of individuals observed with the specified log values of the ratios. The distribution looks similar for both paracetamol upon their metabolites while a bimodal distribution was observed for paracetamol glucuronide upon paracetamol sulphate.