Impact of CYP2A6 gene polymorphism on the pharmacokinetics of dexmedetomidine for premedication

Pharmacogenetic and pharmacokinetic factors for dexmedetomidine-associated hemodynamic instability in pediatric patients

Purpose

The incidence of hemodynamic instability associated with dexmedetomidine (DEX) sedation has been reported to exceed 50%, with substantial inter-individual variability in response. Genetic factors have been suggested to contribute significantly to such variation. The aim of this study was to identify the clinical, pharmacokinetic, and genetic factors associated with DEX-induced hemodynamic instability in pediatric anesthesia patients.

Methods

A cohort of 270 pediatric patients scheduled for elective interventional surgery received an intranasal dose of 3 mcg·kg-1 of dexmedetomidine, and subsequent propofol induction was conducted when patients had a UMSS of 2-4. The primary endpoint was hemodynamic instability-defined as a composite of hypotension and/or bradycardia, which is characterized by a 20% reduction from age-specific baseline values. Plasma concentrations of dexmedetomidine were determined, and single-nucleotide polymorphisms (SNPs) were genotyped. A validated population pharmacokinetic model was used to estimate pharmacokinetic parameters. LASSO regression was used to identify significant factors, and a Cox's proportional hazards model-derived nomogram for hemodynamic instability was developed.

Results

Hemodynamic instability was observed in 52 out of 270 patients (209 events), resulting in a cumulative incidence of 16.30% at 90 min, as estimated by Kaplan-Meier estimation, and it was associated with a median time to event of 35 min. The interval time between DEX initiation and propofol induction was 16 min (IQR: 12-22 min). The cumulative incidence was 8.2% within 22 min after DEX initiation. The identified significant risk factors for DEX-associated hemodynamic instability included weight, DEX clearance, concomitant propofol use, and the following gene variants UGT2B10 rs1841042 (hazard ratio (HR):1.41, 95% confidence interval (CI): 1.12-1.79), CYP2A6 rs8192733 (HR:0.28, 95%CI:0.09-0.88), ADRA2B rs3813662 (HR:1.39,95%CI:1.02-1.89), CACNA2D2 rs2236957 (HR:1.46, 95%CI:1.09-1.96), NR1I2 rs3814057 (HR:0.64, 95%CI:0.43-0.95), and CACNB2 rs10764319 (HR:1.40,95%CI:1.05-1.87). The areas under the curve for the training and test cohorts were 0.881 and 0.762, respectively. The calibration curve indicated excellent agreement.

Conclusion

The predictive nomogram, which incorporates genetic variants (UGT2B10, CYP2A6, ADRA2B, CACNA2D2, NR1I2, and CACNB2) along with clinical factors such as weight, DEX clearance, and propofol use, may help prevent DEX-associated hemodynamic instability. Delayed hemodynamic instability is likely to occur after 35-min DEX initiation in patients with lower DEX clearance after propofol induction.

Pharmacokinetics, pharmacodynamics and bioavailability of dexmedetomidine nasal spray in healthy Chinese adults: A phase I clinical trial

Background

Intranasal administration is a convenient route for drug delivery that can be applied for procedural sedation. However, there is currently limited exploration into fixed dosing regimens. This study was to investigate the pharmacokinetics (PK), pharmacodynamics (PD), bioavailability (BA) and safety of dexmedetomidine after fixed doses of intranasal and intravenous administration in healthy male and female subjects.

Methods

Group A subjects received intranasal or intravenous administration in two periods (12 subjects received intranasal dexmedetomidine (Dex) or the intravenous formulation, and four received the corresponding placebo). Groups B to F underwent single-period dose ascending, receiving only the intranasal Dex formulation or the corresponding placebo (the number of subjects receiving the drug/placebo in groups B to F were 12/2, 12/2, 12/2, 10/2, 10/2, respectively), with doses of 75 μg, 125 μg, 150 μg, 175 μg, and 200 μg, respectively. After administration of each group, blood samples were collected to investigate the plasma concentration of dexmedetomidine, adrenaline and noradrenaline using a HPLC-MS/MS method. Ramsay score, blood pressure and heart rate were collected for safety evaluation. Pharmacokinetic parameters (Cmax, Tmax, AUC0-24h,AUC 0 - ∞ , and t1/2) of dexmedetomidine were calculated.

Results

A total of 82 subjects were randomized. One subject withdrew for personal reasons before administration and the other subjects completed the entire study process. At a dose of 25 μg, the absolute bioavailability was 59%. Across the dose range of 25 to 200 μg, the median Tmax was similar (0.5-1 h), and the mean elimination half-life was comparable (3.09-4.28 h), with exposure (Cmax and AUC0-t) increasing with dose. The pharmacokinetics after intranasal spray administration exhibited linear characteristics, although Cmax was similar in the higher dose groups (175 μg and 200 μg). PD results showed that ideal sedation effects (Ramsay score of 3 or higher in at least 90% of subjects) could be achieved within 30 min following intranasal administration of 75 μg or higher doses. All the subjects were well tolerated without any serious adverse events (SAEs).

Conclusion

Dexmedetomidine nasal spray was well tolerated and achieved satisfactory sedation in the dose range of 25-200 μg in Chinese healthy male and female subjects.

Clinical Trial Registration

http://www.chinadrugtrials.org.cn/, identifier CTR20201650.

CYP2A6 and GABRA2 Gene Polymorphisms are Associated With Dexmedetomidine Drug Response

Background: Dexmedetomidine is a commonly used clinical sedative; however, the drug response varies among individuals. Thus, the purpose of this study was to explore the association between dexmedetomidine response and gene polymorphisms related to drug-metabolizing enzymes and drug response (CYP2A6, UGT2B10, UGT1A4, ADRA2A, ADRA2B, ADRA2C, GABRA1, GABRB2, and GLRA1).

Methods: This study was a prospective cohort study. A total of 194 female patients aged 18–60 years, American Society of Anesthesiologists (ASA) score I-II, who underwent laparoscopy at the Third Xiangya Hospital of Central South University, were included. The sedative effect was assessed every 2 min using the Ramsay score, and the patient’s heart rate decrease within 20 min was recorded. Peripheral blood was collected from each participant to identify genetic variants in the candidate genes of metabolic and drug effects using the Sequenom MassARRAY^® platform. Furthermore, additional peripheral blood samples were collected from the first 99 participants at multiple time points after dexmedetomidine infusion to perform dexmedetomidine pharmacokinetic analysis by Phoenix^® WinNonlin 7.0 software.

Results: Carriers of the minor allele (C) of CYP2A6 rs28399433 had lower metabolic enzyme efficiency and higher plasma concentrations of dexmedetomidine. In addition, the participants were divided into dexmedetomidine sensitive or dexmedetomidine tolerant groups based on whether they had a Ramsay score of at least four within 20 min, and CYP2A6 rs28399433 was identified to have a significant influence on the dexmedetomidine sedation sensitivity by logistic regression with Plink software [p = 0.003, OR (95% CI): 0.27 (0.11–0.65)]. C allele carriers were more sensitive to the sedative effects of dexmedetomidine than A allele carriers. GABRA2 rs279847 polymorphism was significantly associated with the degree of the heart rate decrease. In particular, individuals with the GG genotype had a 4-fold higher risk of heart rate abnormality than carriers of the T allele (OR = 4.32, 95% CI: 1.96–9.50, p = 0.00027).

Conclusion:CYP2A6 rs28399433 polymorphism affects the metabolic rate of dexmedetomidine and is associated with susceptibility to the sedative effects of dexmedetomidine; GABRA2 rs279847 polymorphism is significantly associated with the degree of the heart rate decrease.

The Role of Cytochrome P450 Enzymes in COVID-19 Pathogenesis and Therapy

Coronavirus disease 2019 (COVID-19) has become a new public health crisis threatening the world. Dysregulated immune responses are the most striking pathophysiological features of patients with severe COVID-19, which can result in multiple-organ failure and death. The cytochrome P450 (CYP) system is the most important drug metabolizing enzyme family, which plays a significant role in the metabolism of endogenous or exogenous substances. Endogenous CYPs participate in the biosynthesis or catabolism of endogenous substances, including steroids, vitamins, eicosanoids, and fatty acids, whilst xenobiotic CYPs are associated with the metabolism of environmental toxins, drugs, and carcinogens. CYP expression and activity are greatly affected by immune response. However, changes in CYP expression and/or function in COVID-19 and their impact on COVID-19 pathophysiology and the metabolism of therapeutic agents in COVID-19, remain unclear. In this analysis, we review current evidence predominantly in the following areas: firstly, the possible changes in CYP expression and/or function in COVID-19; secondly, the effects of CYPs on the metabolism of arachidonic acid, vitamins, and steroid hormones in COVID-19; and thirdly, the effects of CYPs on the metabolism of therapeutic COVID-19 drugs.

Dexmedetomidine Clearance Decreases with Increasing Drug Exposure: Implications for Current Dosing Regimens and Target-controlled Infusion Models Assuming Linear Pharmacokinetics

BACKGROUND

Numerous pharmacokinetic models have been published aiming at more accurate and safer dosing of dexmedetomidine. The vast majority of the developed models underpredict the measured plasma concentrations with respect to the target concentration, especially at plasma concentrations higher than those used in the original studies. The aim of this article was to develop a dexmedetomidine pharmacokinetic model in healthy adults emphasizing linear versus nonlinear kinetics.

METHODS

The data of two previously published clinical trials with stepwise increasing dexmedetomidine target-controlled infusion were pooled to build a pharmacokinetic model using the NONMEM software package (ICON Development Solutions, USA). Data from 48 healthy subjects, included in a stratified manner, were utilized to build the model.

RESULTS

A three-compartment mamillary model with nonlinear elimination from the central compartment was superior to a model assuming linear pharmacokinetics. Covariates included in the final model were age, sex, and total body weight. Cardiac output did not explain between-subject or within-subject variability in dexmedetomidine clearance. The results of a simulation study based on the final model showed that at concentrations up to 2 ng · ml-1, the predicted dexmedetomidine plasma concentrations were similar between the currently available Hannivoort model assuming linear pharmacokinetics and the nonlinear model developed in this study. At higher simulated plasma concentrations, exposure increased nonlinearly with target concentration due to the decreasing dexmedetomidine clearance with increasing plasma concentrations. Simulations also show that currently approved dosing regimens in the intensive care unit may potentially lead to higher-than-expected dexmedetomidine plasma concentrations.

CONCLUSIONS

This study developed a nonlinear three-compartment pharmacokinetic model that accurately described dexmedetomidine plasma concentrations. Dexmedetomidine may be safely administered up to target-controlled infusion targets under 2 ng · ml-1 using the Hannivoort model, which assumed linear pharmacokinetics. Consideration should be taken during long-term administration and during an initial loading dose when following the dosing strategies of the current guidelines.

EDITOR’S PERSPECTIVE

Sedative and Immunosuppressive Effects of Dexmedetomidine in Transplantation

Dexmedetomidine, an α2-adrenergic receptor agonist, is used as an anti-anxiety medication. It exerts a cholinergic effect, thereby reducing the release of tumor necrosis factor alpha (TNF-α). We hypothesized that the use of dexmedetomidine as a sedative agent in transplantation would also protect allografts. We examined our patients who underwent living donor liver transplantation. Subsequently, we generated a series of mouse models to investigate the effect of dexmedetomidine on sedation-based tolerance post transplantation. A total of 49 liver recipients were enrolled in this study, of which 23 (47%) were administered dexmedetomidine through 24 h infusion on postoperative day 1. A trend toward the improvement of hepatocyte injury along with better liver function was observed in the dexmedetomidine-treated group during the first postoperative week. In animal models, dexmedetomidine inhibited the proliferation of CD4+ and CD8+ T cells and TNF-α production in a dose-dependent manner. We used dexmedetomidine to treat skin-transplanted mice and observed a significantly prolonged graft survival in mice that were administered a higher dose of dexmedetomidine. Our results revealed that dexmedetomidine exerts a dual effect of sedation and immunosuppression. This light-sedation approach will not only make patients calmer in the intensive care unit but also protect allografts from injury.

Human total clearance values and volumes of distribution of typical human cytochrome P450 2C9/19 substrates predicted by single-species allometric scaling using pharmacokinetic data sets from common marmosets genotyped for P450 2C19

Common marmosets (Callithrix jacchus) are small non-human primates that genetically lack cytochrome P450 2C9 (CYP2C9). Polymorphic marmoset CYP2C19 compensates by mediating oxidations of typical human CYP2C9/19 substrates.Twenty-four probe substrates were intravenously administered in combinations to marmosets assigned to extensive or poor metaboliser (PM) groups by CYP2C19 genotyping. Eliminations from plasma of cilomilast, phenytoin, repaglinide, tolbutamide, and S-warfarin in the CYP2C19 PM group were significantly slow; these drugs are known substrates of human CYP2C8/9/19.Human total clearance values and volumes of distribution of the 24 test compounds were extrapolated using single-species allometric scaling with experimental data from marmosets and found to be mostly comparable with the reported values.Human total clearance values and volumes of distribution of 15 of the 24 test compounds similarly extrapolated using reported data sets from cynomolgus or rhesus monkeys were comparable to the present predicted results, especially to those based on data from PM marmosets.These results suggest that single-species allometric scaling using marmosets, being small, has advantages over multiple-species-based allometry and could be applicable for pharmacokinetic predictions at the discovery stage of drug development.