Fatal methadone toxicity: potential role of CYP3A4 genetic polymorphism

Pharmacogenetics of Lethal Opioid Overdose: Review of Current Evidence and Preliminary Results from a Pilot Study

There has been a worldwide substantial increase in accidental opioid-overdose deaths. The aim of this review, along with preliminary results from our pilot study, is to highlight the use of pharmacogenetics as a tool to predict causes of accidental opioid-overdose death. For this review, a systematic literature search of PubMed^® between the time period of January 2000 to March 2023 was carried out. We included study cohorts, case-controls, or case reports that investigated the frequency of genetic variants in opioid-related post-mortem samples and the association between these variants and opioid plasma concentrations. A total of 18 studies were included in our systematic review. The systematic review provides evidence of the use of CYP2D6, and to a lower extent, CYP2B6 and CYP3A4/5 genotyping in identifying unexpectedly high or low opioid and metabolite blood concentrations from post-mortem samples. Our own pilot study provides support for an enrichment of the CYP2B6*4-allele in our methadone-overdose sample (n = 41) compared to the anticipated frequency in the general population. The results from our systematic review and the pilot study highlight the potential of pharmacogenetics in determining vulnerability to overdose of opioids.

A Comprehensive Analysis of Human CYP3A4 Crystal Structures as a Potential Tool for Molecular Docking-Based Site of Metabolism and Enzyme Inhibition Studies

The notable ability of human liver cytochrome P450 3A4 (CYP3A4) to metabolize diverse xenobiotics encourages researchers to explore in-depth the mechanism of enzyme action. Numerous CYP3A4 protein crystal structures have been deposited in protein data bank (PDB) and are majorly used in molecular docking analysis. The quality of the molecular docking results depends on the three-dimensional CYP3A4 protein crystal structures from the PDB. Present review endeavors to provide a brief outline of some technical parameters of CYP3A4 PDB entries as valuable information for molecular docking research. PDB entries between 22 April 2004 and 2 June 2021 were compiled and the active sites were thoroughly observed. The present review identified 76 deposited PDB entries and described basic information that includes CYP3A4 from human genetic, Escherichia coli (E. coli) use for protein expression, crystal structure obtained from X-ray diffraction method, taxonomy ID 9606, Uniprot ID P08684, ligand–protein structure description, co-crystal ligand, protein site deposit and resolution ranges between 1.7[Formula: see text]Å and 2.95[Formula: see text]Å. The observation of protein–ligand interactions showed the various residues on the active site depending on the ligand. The residues Ala305, Ser119, Ala370, Phe304, Phe108, Phe213 and Phe215 have been found to frequently interact with ligands from CYP3A4 PDB. Literature surveys of 17 co-crystal ligands reveal multiple mechanisms that include competitive inhibition, noncompetitive inhibition, mixed-mode inhibition, mechanism-based inhibition, substrate with metabolite, inducer, or combination modes of action. This overview may help researchers choose a trustworthy CYP3A4 protein structure from the PDB database to apply the protein in molecular docking analysis for drug discovery.

Pharmacokinetic modeling of R and S-Methadone and their metabolites to study the effects of various covariates in post-operative children

Methadone is a synthetic opioid used as an analgesic and for the treatment of opioid abuse disorder. The analgesic dose in the pediatric population is not well-defined. The pharmacokinetics (PKs) of methadone is highly variable due to the variability in alpha-1 acid glycoprotein (AAG) and genotypic differences in drug-metabolizing enzymes. Additionally, the R and S enantiomers of methadone have unique PK and pharmacodynamic properties. This study aims to describe the PKs of R and S methadone and its metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in pediatric surgical patients and to identify sources of inter- and intra-individual variability. Children aged 8-17.9 years undergoing orthopedic surgeries received intravenous methadone 0.1 mg/kg intra-operatively followed by oral methadone 0.1 mg/kg postoperatively every 12 h. Pharmacokinetics of R and S methadone and EDDP were determined using liquid chromatography tandem mass spectrometry assays and the data were modeled using nonlinear mixed-effects modeling in NONMEM. R and S methadone PKs were well-described by two-compartment disposition models with first-order absorption and elimination. EDDP metabolites were described by one compartment disposition models with first order elimination. Clearance of both R and S methadone were allometrically scaled by bodyweight. CYP2B6 phenotype was a determinant of the clearance of both the enantiomers in an additive gene model. The intronic CYP3A4 single-nucleotide polymorphism (SNP) rs2246709 was associated with decreased clearance of R and S methadone. Concentrations of AAG and the SNP of AAG rs17650 independently increased the volume of distribution of both the enantiomers. The knowledge of these important covariates will aid in the optimal dosing of methadone in children.

Pharmacogenomics in Pain Management: A Review of Relevant Gene-Drug Associations and Clinical Considerations

OBJECTIVE

To provide an overview of clinical recommendations regarding genomic medicine relating to pain management and opioid use disorder.

DATA SOURCES

A literature review was conducted using the search terms pain management, pharmacogenomics, pharmacogenetics, pharmacokinetics, pharmacodynamics, and opioids on PubMed (inception to February 1, 2021), CINAHL (2016 through February 1, 2021), and EMBASE (inception through February 1, 2021).

STUDY SELECTION AND DATA EXTRACTION

All relevant clinical trials, review articles, package inserts, and guidelines evaluating applicable pharmacogenotypes were considered for inclusion.

DATA SYNTHESIS

More than 300 Food and Drug Administration-approved medications contain pharmacogenomic information in their labeling. Genetic variability may alter the therapeutic effects of commonly prescribed pain medications. Pharmacogenomic-guided therapy continues to gain traction in clinical practice, but a multitude of barriers to widespread pharmacogenomic implementation exist.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Pain is notoriously difficult to treat given the need to balance safety and efficacy when selecting pharmacotherapy. Pharmacogenomic data can help optimize outcomes for patients with pain. With improved technological advances, more affordable testing, and a better understanding of genomic variants resulting in treatment disparities, pharmacogenomics continues to gain popularity. Unfortunately, despite these and other advancements, pharmacogenomic testing and implementation remain underutilized and misunderstood in clinical care, in part because of a lack of health care professionals trained in assessing and implementing test results.

CONCLUSIONS

A one-size-fits-all approach to pain management is inadequate and outdated. With increasing genomic data and pharmacogenomic understanding, patient-specific genomic testing offers a comprehensive and personalized treatment alternative worthy of additional research and consideration.

OPRM1 and CYP3A4 association with methadone dose in Iranian patients undergoing methadone maintenance therapy

BACKGROUND

Investigations proposed that genetic polymorphisms within proteins in methadone pharmacokinetic and pharmacodynamics are critical factors in determination of methadone dose in methadone maintenance therapy (MMT).

OBJECTIVE

This study aimed to assess the associations between two polymorphisms, CYP3A4 (rs2740574) and OPRM1 (rs1799971), with dose of methadone in Iranian patients undergoing MMT.

METHODS

A total of 124 Iranian male subjects aged 18-65 years old who were confirmed to be addicted by the addiction diagnostic tests and underwent MMT were assessed. Patients were divided into three groups of low (less than 40 mg/day), moderate (more than 40 mg/day and less than 110 mg/day) and high (more than 110 mg/day) methadone dose consumption. DNAs of included patients were extracted from their blood samples and were assessed for CYP3A4 and OPRM1 polymorphisms.

RESULTS

Results showed that there was no significant association between the studied polymorphisms and methadone dose in Iranian addicted patients underwent MMT (P > 0.05).

CONCLUSIONS

CYP3A4 and OPRM1 single variations cannot explain variability in methadone dosage in MMT. Studying the interactions of more genetic factors in larger samples may elucidate factors influencing the required dose of methadone and better individualized therapy.

ABCB1, CYP2B6, and CYP3A4 genetic polymorphisms do not affect methadone maintenance treatment in HCV-positive patients

The aim of this study was to determine the influence of ABCB1, CYP2B6, and CYP3A4 genetic polymorphisms on methadone metabolism in patients with hepatitis C virus (HCV) undergoing methadone maintenance treatment (MMT). The study included 35 participants undergoing MMT, who were divided in three groups: HCV-positive (N=12), HCV-negative (N=16), and HCV clinical remission (CR) (N=7). The concentrations of methadone and its main metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) were determined with gas chromatography-mass spectrometry. The patients were genotyped for ABCB1 rs1045642, CYP2B6 rs3745274, CYP3A4 rs2242480, and CYP3A4 rs2740574 polymorphisms. Differences between single nucleotide polymorphism (SNP) genotypes and methadone-to-EDDP ratio were analysed with one-way ANOVA, which showed no significant difference between the genes (p=0.3772 for ABCB1 rs1045642, p=0.6909 for CYP2B6 rs3745274, and p=0.6533 for CYP3A4 rs2242480). None of the four analysed SNP genotypes correlated with methadone-to-EDDP concentration ratio. A major influence on it in hepatitis C-positive patients turned out to be the stage of liver damage.

Pharmacogenomics of methadone: a narrative review of the literature

Background: Methadone, a synthetic opioid with longer duration of action and lower abuse potential compared with morphine, is used to prevent opioid withdrawal, as well as to manage chronic and acute surgical pain. The variability in response to methadone has been widely recognized. The purpose of this article is to review the literature on the pharmacogenetic factors underlying this variability. Materials & methods: This is a narrative overview of the literature on the genetic variants affecting pharmacodynamics and pharmacokinetics of methadone, retrieved from searches of databases such as PubMed and google scholar. Discussion: Clinical responses to methadone may be affected by genetic variants in the opioidergic, dopaminergic and neurotrophic pathways. Polymorphisms in genes related to disposition and elimination of methadone alter the pharmacokinetics, and possibly pharmacodynamics of methadone. Cytochrome P450 enzymes and P-glycoprotein variants contribute to the interindividual variability in methadone pharmacokinetics. Evidence for single gene variants affecting methadone response remains weak. Multiple genetic variants must be considered in conjunction to improve predictive ability. Conclusion: Evidence remains scarce at this time, to recommend pharmacogenetic testing before methadone administration. Well-powered clinical studies are needed with population pharmacokinetic-pharmacodynamic modeling and multigenetic signature-based predictions to enable tailored use of methadone in clinical practice.

Characterizing Fentanyl Variability Using Population Pharmacokinetics in Pediatric Burn Patients

Opioids are essential first line analgesics for pain management after burn injury. Opioid dosing remains challenging in burn patients, particularly in children, due to the immense variability in efficacy between patients. Opioid pharmacokinetics are altered in burned children, increasing variability and obviating dosing regimens extrapolated from adult-data. The present study aimed to characterize variability in fentanyl pharmacokinetics and identify significant contributors to variability in children with ≥10% total body surface area burn requiring fentanyl during routine wound care. We recorded patient demographics and clinical data. Blood samples were collected following fentanyl administration for pharmacokinetics at time 0, 30, 60, 120, and 240 minutes on day of admission and repeated on days 3 and 7. Serum fentanyl concentrations were quantified using tandem liquid chromatography mass spectrometry. Population analysis was used to estimate pharmacokinetics parameters. Fourteen patients, 1.2-17 years, with burns from 10-50.5% were included in analysis. A two-compartment model with body weight as a covariate best described fentanyl pharmacokinetics for the overall population. The population clearance and intercompartmental clearance were 7.19 and 2.16 L/hour, respectively, and the volume of distribution for the central and peripheral compartments was 4.01 and 25.1 L, respectively. Individual patient parameter estimates had extensive variability. This study confirmed the high variability in pediatric burn patient fentanyl pharmacokinetics and demonstrates similarities and differences to other populations reported in literature. Further research is needed with a larger number of patients to extensively investigate the impact of burns, genetic polymorphisms, and other factors on fentanyl efficacy and patient outcomes.

Effects of UGT2B7, SCN1A and CYP3A4 on the therapeutic response of sodium valproate treatment in children with generalized seizures

PURPOSE

This study aims to evaluate the associations between genetic polymorphisms and the effect of sodium valproate (VPA) therapy in children with generalized seizures.

METHODS

A total of 174 children with generalized seizures on VPA therapy were enrolled. Steady-state trough plasma concentrations of VPA were analyzed. Seventy-six single nucleotide polymorphisms involved in the absorption, metabolism, transport, and target receptor of VPA were identified, and their associations with the therapeutic effect (seizure reduction) were evaluated using logistic regression adjusted by various influence factors.

RESULTS

rs7668282 (UGT2B7, T > C, OR = 2.67, 95% CI: 1.19 to 5.91, P = 0.017) was more prevalent in drug-resistant patients than drug-responsive patients. rs2242480 (CYP3A4, C > T, OR = 0.27, 95% CI: 0.095 to 0.79, P = 0.017) and rs10188577 (SCN1A, T > C, OR = 0.40, 95% CI: 0.17 to 0.94, P = 0.035) were more prevalent in drug-responsive patients compared to drug-resistant patients.

CONCLUSION

In children with generalized seizures on VPA therapy, polymorphisms of UGT2B7, CYP3A4, and SCN1A genes were associated with seizure reduction. Larger studies are warranted to corroborate the results.

Pharmacogenetics of Opioid Use Disorder Treatment

Opioid use disorder (OUD) is a significant health problem in the United States and many other countries. A combination of issues, most notably increased prescription of opioid analgesics, has resulted in climbing rates of opioid abuse and overdose over the last decade. This ongoing epidemic has produced a growing population of patients requiring treatment for OUD. Medications such as methadone and buprenorphine have well documented success rates in treating the disorder compared with placebo. However, significant percentages of the population still fail to maintain abstinence or reduce illicit opioid use while using such medications. Genetic variation may play a role in this variability in outcome through pharmacokinetic or pharmacodynamic effects on OUD medications, or by affecting the rate of negative side effects and adverse events. This review focuses on the existing literature on the pharmacogenetics of OUD treatment, with specific focus on medication metabolism, treatment outcomes, and adverse events.

Methadone Inpatient and Discharge Prescribing Patterns for Pain at an Academic Health System

BACKGROUND

Methadone is effective for the treatment of chronic pain, but its unique pharmacology requires additional considerations with dosing and monitoring.

OBJECTIVE

The study objective was to evaluate methadone prescribing for pain and subsequent monitoring.

METHODS

This retrospective chart review at a single center reviewed patients who received methadone over a two-year period.

RESULTS

Of the 100 patients, most were noncancer cases (60%) with unspecified pain (50%). The majority of methadone treatments were initiated by medicine service (37%), followed by burn service (27%), and trauma (10%). Forty-two percent of the patients were being followed by the palliative care team, primarily for the medicine patients (80%). Patients on the burn service had significantly higher oral morphine equivalent (χ² = 10.6, p = 0.01) and longest length of stay (χ² = 37.9, p = 0.0001). Patients on medicine service were significantly more likely to have an outpatient discharge plan for methadone starts in the hospital (odds ratio = 3.7, confidence interval: 1.4, 9.7). Only 45% of patients had an electrocardiogram (EKG) checked seven days before methadone start and 37% of those have a measured corrected QT (QTc) of greater than 450 milliseconds. Electrolytes (potassium and magnesium) were not consistently checked and, of those that were evaluated, 15-20% were abnormal. There was an average of 2.6 severe or major drug interactions per patient related to methadone, with the most common being related to concomitant sedatives and other medications that prolonged the QTc.

CONCLUSIONS

Prescribing guidelines for methadone would provide a consistent approach for all practitioners involved in using methadone safely and effectively for chronic pain.

Effects of cytochrome P450 single nucleotide polymorphisms on methadone metabolism and pharmacodynamics

Methadone is a synthetic, long-acting opioid with a single chiral center forming two enantiomers, (R)-methadone and (S)-methadone, each having specific pharmacological actions. Concentrations of (R)- and (S)-methadone above therapeutic levels have the ability to cause serious, life-threatening, and fatal side effects. This toxicity can be due in part to the pharmacogenetics of an individual, which influences the pharmacokinetic and pharmacodynamic properties of the drug. Methadone is primarily metabolized in the liver by cytochrome P450 (CYP) enzymes, predominately by CYP2B6, followed by CYP3A4, 2C19, 2D6, and to a lesser extent, CYP2C18, 3A7, 2C8, 2C9, 3A5, and 1A2. Single nucleotide polymorphisms (SNPs) located within CYPs have the potential to play an important role in altering methadone metabolism and pharmacodynamics. Several SNPs in the CYP2B6, 3A4, 2C19, 2D6, and 3A5 genes result in increases in methadone plasma concentrations, decreased N-demethylation, and decreased methadone clearance. In particular, carriers of CYP2B6*6/*6 may have a greater risk for detrimental adverse effects, as methadone metabolism and clearance are diminished in these individuals. CYP2B6*4, on the other hand, has been observed to decrease plasma concentrations of methadone due to increased methadone clearance. The involvement, contribution, and understanding the role of SNPs in CYP2B6, and other CYP genes, in methadone metabolism can improve the therapeutic uses of methadone in patient outcome and the development of personalized medicine.

The Promise of Molecular Autopsy in Forensic Pathology Practice

Molecular autopsy is changing the practice of forensic pathology. Under some circumstances, one must contemplate the involvement of genetic factors to help explain why someone has died unexpectedly. Such considerations most commonly occur when a young person dies by natural means. However, there are deaths that occur by nonnatural means that the forensic pathologist will be asked to investigate, which could involve natural disease that has a significant genetic underpinning. Elucidation of genetic mutations may not only further an understanding of the pathophysiology at hand, but also speak to underlying susceptibilities in an individual who dies that may not have been recognized. In addition, one may occasionally identify pathological findings that are confused for trauma that may actually be better explained by an underlying disease process. Using molecular medicine as a tool to explore such possibilities can improve the quality of death investigations and provide a new lens to probe challenging and contentious forensic cases that have proved resistant to traditional methods.

Exploring public genomics data for population pharmacogenomics

Racial and ethnic differences in drug responses are now well studied and documented. Pharmacogenomics research seeks to unravel the genetic underpinnings of inter-individual variability with the aim of tailored-made theranostics and therapeutics. Taking into account the differential expression of pharmacogenes coding for key metabolic enzymes and transporters that affect drug pharmacokinetics and pharmacodynamics, we advise that data interpretation and analysis need to occur in light of geographical ancestry, if implications for drug development and global health are to be considered. Herein, we exploit ePGA, a web-based electronic Pharmacogenomics Assistant and publicly available genetic data from the 1000 Genomes Project to explore genotype to phenotype associations among the 1000 Genomes Project populations.

Tell-Tale SNPs: The Role of CYP2B6 in Methadone Fatalities

Cytochrome P450 (CYP) enzyme 2B6 plays a significant role in the stereo-selective metabolism of (S)-methadone to 2-ethyl-1,5-dimethyl-3,3-diphenylpyrrolidine, an inactive methadone metabolite. Elevated (S)-methadone can cause cardiotoxicity by prolonging the QT interval of the heart's electrical cycle. Large inter-individual variability of methadone pharmacokinetics causes discordance in the relationship between dose, plasma concentrations and side effects. The purpose of this study was to determine if one or more single nucleotide polymorphisms (SNPs) located within the CYP2B6 gene contributes to a poor metabolizer phenotype for methadone in these fatal cases. The genetic analysis was conducted on 125 Caucasian methadone-only fatalities obtained from the West Virginia and Kentucky Offices of the Chief Medical Examiner. The frequency of eight exonic and intronic SNPs (rs2279344, rs3211371, rs3745274, rs4803419, rs8192709, rs8192719, rs12721655 and rs35979566) was determined. The frequencies of SNPs rs3745274 (*9, c516G > T, Q172H), and rs8192719 (21563 C > T) were enhanced in the methadone-only group. Higher blood methadone concentrations were observed in individuals who were genotyped homozygous for SNP rs3211371 (*5, c1459C > T, R487C). These results indicate that these three CYP2B6 SNPs are associated with methadone fatalities.

CYP gene family variants as potential protective factors in drug addiction in Han Chinese

BACKGROUND

There is growing evidence that genetic factors also contribute to drug addiction. The human cytochrome P450 has shown special interest because of pharmacokinetic variation in different individuals and populations, which is largely determined by the relevant genes. The present study aimed to investigate the polymorphism of the CYP/addicts relationship.

METHODS

We genotyped 13 tag single-nucleotide polymorphisms (tSNPs) from three genes, including 692 cases and 700 controls. Sequenom MassARRAY RS1000 (Sequenom, Inc., San Diego, CA, USA) was used for SNP genotyping. Statistical analysis of the association between tSNPs and drug addiction was performed using the chi-squared test and SNP Stats software (http://bioinfo.iconcologia.net).

RESULTS

The T/T genotype of rs2242480 in CYP3A4 was associated with decreased risk in the recessive model (p = 0.0002). Allele frequency at rs3743484 in CYP1A2 showed significant differences between addicts and controls (p = 0.046; odds ratio = 0.80; 95% confidence interval = 0.65-1.00). In genetic model analyses, the minor C allele of rs3743484 in CYP1A2 was associated with a reduced risk of drug addiction based on analysis using codominant and additive models (p = 0.027 dominant model; p =0.038 additive model).

CONCLUSIONS

Our findings show that at allelic and genotypic level polymorphisms in CYP3A4 and CYP1A2 are significantly associated with a reduced risk of drug addiction in X'ian Han Chinese individuals. However, this result needs to be confirmed in additional studies. Copyright © 2016 John Wiley & Sons, Ltd.

Clinical Presentation and the Outcome of Therapy in a Cohort of Patients with Methadone Toxicity in Iran

Background:

Agonist maintenance therapy with methadone is amongst the preferred remedies for treating opioid dependence and is increasingly supported by the regional governments in this part of the world. In this study we have investigated the clinical manifestations and factors affecting the outcome of therapy in patients with methadone poisoning in a Middle-Eastern (Iranian) referral tertiary care University hospital.

Methods:

In this prospective and descriptive-analytic study which was done in a tertiary care and referral University hospital in Iran (2012-2013) all of the admitted patients with a clear and reliable history of methadone poisoning (n=433) were included and demographic data, Clinical status on admission including Glasgow Coma Scale (GCS) score, time elapsed from ingestion to hospital admission, average dose of naloxone used, any history of psychiatric disorder, type of toxic exposure, co ingestion of other medication, hospitalization time and the outcome were recorded and statistically analyzed.

Results:

The average length of hospital stay was 33 ± 26 hours. 80.1% of patients had ingested methadone alone, and 90.3% survived. Complications were pulmonary edema (7%), aspiration pneumonia (1.4%), generalized tonic colonic seizure (0.9%), and renal failure (0.5%). GCS, systolic blood pressure and respiratory rate were lower in fatal cases and GCS had prognostic value for the outcome of therapy in methadone intoxicated patients. Patients with higher GCS on admission had better outcome [OR =0.47 (95% CI: 0.38-0.580); P value< 0.0001].

Conclusion:

Admission time GCS score maybe considered as an important predictor for the outcome of therapy in methadone poisoning.