Pharmacogenetic analysis of opioid dependence treatment dose and dropout rate

Opioid Monitoring in Clinical Settings: Strategies and Implications of Tailored Approaches for Therapy

This review emphasises the importance of opioid monitoring in clinical practice and advocates for a personalised approach based on pharmacogenetics. Beyond effectively managing pain, meticulous oversight is required to address concerns about side effects, specially due to opioid-crisis-related abuse and dependence. Various monitoring techniques, along with pharmacogenetic considerations, are critical for personalising treatment and optimising pain relief while reducing misuse and addiction risks. Future perspectives reveal both opportunities and challenges, with advances in analytical technologies holding promise for increasing monitoring efficiency. The integration of pharmacogenetics has the potential to transform pain management by allowing for a precise prediction of drug responses. Nevertheless, challenges such as prominent pharmacogenetic testing and guideline standardisation persist. Collaborative efforts are critical for transforming scientific advances into tangible improvements in patient care. Standardised protocols and interdisciplinary collaboration are required to ensure consistent and evidence-based opioid monitoring. Future research should look into the long-term effects of opioid therapy, as well as the impact of genetic factors on individual responses, to help guide personalised treatment plans and reduce adverse events. Lastly, embracing innovation and collaboration can improve the standard of care in chronic pain management by striking a balance between pain relief and patient safety.

Clinical prediction of opioid use disorder in chronic pain patients: a cohort-retrospective study with a pharmacogenetic approach

BACKGROUND

Opioids are widely used in chronic non-cancer pain (CNCP) management. However, they remain controversial due to serious risk of causing opioid use disorder (OUD). Our main aim was to develop a predictive model for future clinical translation that include pharmacogenetic markers.

METHODS

An observational study was conducted in 806 pre-screened Spanish CNCP patients, under long-term use of opioids, to compare cases (with OUD, N.=137) with controls (without OUD, N.=669). Mu-opioid receptor 1 (OPRM1, A118G, rs1799971) and catechol-O-methyltransferase (COMT, G472A, rs4680) genetic variants plus cytochrome P450 2D6 (CYP2D6) liver enzyme phenotypes were analyzed. Socio-demographic, clinical and pharmacological outcomes were also registered. A logistic regression model was performed. The model performance and diagnostic accuracy were calculated.

RESULTS

OPRM1-AA genotype and CYP2D6 poor and ultrarapid metabolizers together with three other potential predictors: 1) age; 2) work disability; 3) oral morphine equivalent daily dose (MEDD), were selected with a satisfactory diagnostic accuracy (sensitivity: 0.82 and specificity: 0.85), goodness of fit (P=0.87) and discrimination (0.89). Cases were ten-year younger with lower incomes, more sleep disturbances, benzodiazepines use, and history of substance use disorder in front of controls.

CONCLUSIONS

Functional polymorphisms related to OPRM1 variant and CYP2D6 phenotypes may predict a higher OUD risk. Established risk factors such as young age, elevated MEDD and lower incomes were identified. A predictive model is expected to be implemented in clinical setting among CNCP patients under long-term opioids use.

Pharmacogenetics of Biochemically Verified Abstinence in an Opioid Agonist Therapy Randomized Clinical Trial of Methadone and Buprenorphine/Naloxone

Methadone and buprenorphine/naloxone are opioid agonist therapies for opioid use disorder treatment. Genetic factors contribute to individual differences in opioid response; however, little is known regarding genetic associations with clinical outcomes in people receiving opioid agonist therapies. Participants diagnosed with opioid use disorder, principally consisting of prescription opioids (licit or illicit), were randomized to methadone or buprenorphine/naloxone for 24 weeks of daily treatment (NCT03033732). Urine was collected at 12 biweekly study visits and analyzed for non-treatment opioids. Variants in genes involved in methadone metabolism (CYP2B6, CYP2C19, and CYP3A4), buprenorphine metabolism (CYP3A4 and UGT2B7), and μ-opioid receptor function (OPRM1) were genotyped and analyzed for their association with the number of non-treatment opioid-free urine screens. Primary analyses focused on the last 12 weeks (6 study visits, post-titration) of treatment among those reporting White ethnicity. Additional sensitivity and exploratory analyses were performed. Among methadone-treated participants (n = 52), the OPRM1 rs1799971 AA genotype (vs. G-genotypes, i.e., having one or two G alleles) was associated with greater opioid-free urine screens (incidence rate ratio = 5.24, 95% confidence interval (CI) = 2.43-11.26, P = 0.000023); longitudinal analyses showed a significant genotype-by-time interaction over the full 24 weeks (12 study visits, β = -0.28, 95% CI = -0.45 to -0.11, P = 0.0015). Exploratory analyses suggest an OPRM1 rs1799971 genotype effect on retention. No evidence of association was found between other genetic variants, including in metabolic variants, and non-treatment opioid-free urine screens in the methadone or buprenorphine/naloxone arms. Those with the OPRM1 rs1799971 G-genotypes may have a poorer response to methadone maintenance treatment, an effect that persisted through 24 weeks of treatment.

Evaluation of adherence monitoring in buprenorphine treatment: A pilot study using timed drug assays to determine accuracy of testing

AIMS

Buprenorphine is effective at reducing relapse to opioid misuse, morbidity and mortality in opioid-dependent patients. Urine drug screening (UDS) to assess adherence is used routinely in opioid agonist treatment (OAT). The primary aim of this study was to determine factors which may be associated with a negative qualitative urine drug screen for buprenorphine in OAT patients.

METHODS

This prospective pilot study was conducted at a tertiary addiction medicine centre. Twenty participants on stable treatment underwent supervised administration of sublingual buprenorphine. Matched urine and blood samples were collected prior to and 2, 4 and 6 hours after buprenorphine administration. Qualitative urine drug screen results were obtained using gas chromatography-mass spectrometry (GC-MS), while quantitative blood and urine results were obtained using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS).

RESULTS

Qualitative urine assay yielded a negative result for buprenorphine in 57% of tested samples. The median concentration of urinary buprenorphine was 167 mcg/L (range: 2-1730 mcg/L). Thirty percent of all blood samples did not detect buprenorphine (range 0-18 mcg/L). Positive qualitative urine drug screen results were associated with higher urine (343 mcg/L compared with 75 mcg/L; P < .05) and blood (4 mcg/L compared with 2 mcg/L; P < .05) buprenorphine concentrations. Median urine concentrations of buprenorphine were highest at 2 hours and were higher in participants receiving CYP3A4 inhibitors.

CONCLUSION

Interpretation of qualitative urine drug screens to assess adherence in OAT is complex. Poor adherence with treatment cannot be assumed in patients returning a negative qualitative GC-MS urine drug screen.

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.

Validation of Pharmacogenomic Interaction Probability (PIP) Scores in Predicting Drug-Gene, Drug-Drug-Gene, and Drug-Gene-Gene Interaction Risks in a Large Patient Population

Utilizing pharmacogenomic (PGx) testing and integrating evidence-based guidance in drug therapy enables an improved treatment response and decreases the occurrence of adverse drug events. We conducted a retrospective analysis to validate the YouScript^® PGx interaction probability (PIP) algorithm, which predicts patients for whom PGx testing would identify one or more evidence-based, actionable drug-gene, drug-drug-gene, or drug-gene-gene interactions (EADGIs). PIP scores generated for 36,511 patients were assessed according to the results of PGx multigene panel testing. PIP scores versus the proportion of patients in whom at least one EADGI was found were 22.4% vs. 22.4% (p = 1.000), 23.5% vs. 23.4% (p = 0.6895), 30.9% vs. 29.4% (p = 0.0667), and 27.3% vs. 26.4% (p = 0.3583) for patients tested with a minimum of 3-, 5-, 14-, and 25-gene panels, respectively. These data suggest a striking concordance between the PIP scores and the EAGDIs found by gene panel testing. The ability to identify patients most likely to benefit from PGx testing has the potential to reduce health care costs, enable patient access to personalized medicine, and ultimately improve drug efficacy and safety.

Association between rs1799971 in the mu opioid receptor gene and methadone maintenance treatment response

OBJECTIVE

Genetic variations can affect individual response to methadone maintenance treatment (MMT) for heroin addiction. The A118G variant (rs1799971) in the mu opioid receptor gene (OPRM1) is a potential candidate single nucleotide polymorphism (SNP) for personalized MMT. This study determined whether rs1799971 is related to MMT response or dose.

METHODS

We recruited 286 MMT patients from a Han Chinese population. The rs1799971 genotype was determined via TaqMan genotyping assay. The genetic effect of this SNP on MMT response or dose was evaluated using logistic regression. A meta-analysis was performed to merge all available data to evaluate the role of rs1799971 in MMT using RevMan 5.3 software.

RESULTS

No statistical significance was observed in the association between the OPRM1 rs1799971 and MMT response or dose in our Chinese cohort. Meta-analysis indicated that the OPRM1 A118G variation was not significantly associated with MMT response or dose requirement.

CONCLUSION

The results suggest that rs1799971 in OPRM1 might not play a critical role alone in influencing MMT response or dose.

Sublingual buprenorphine/naloxone treatment is not affected by OPRM1 A118G and BDNF Va66Met polymorphisms, but alters the plasma beta-endorphin and BDNF levels in individuals with opioid use disorder

The study aimed to examine the genetic contribution to buprenorphine (BUP) treatment in individuals with opioid use disorder (OUD), with a specific focus on BDNF and OPRM1 genes. A total of 113 controls and 111 OUD patients receiving sublingual BUP/naloxone were enrolled. OPRM1 A118G and BDNF Val66Met polymorphisms were investigated by PCR-FRLP. Plasma BDNF and beta-endorphin levels were assessed by ELISA kits in both groups. Blood BUP levels were measured by LC-MS/MS and normalized with daily BUP dose (BUP/D). OPRM1 A118G and BDNF Val66Met polymorphisms didn't have an effect on plasma beta-endorphin and BDNF levels in OUD patients, respectively. Interestingly, OUD patients had significantly higher plasma BDNF and lower beta-endorphin levels compared to the controls (p < 0.001). A negative and significant correlation between plasma BUP/D and BDNF levels was found. Age onset of first use was associated with OPRM1 A118G polymorphism. The findings indicated that sublingual BUP/naloxone may increase plasma BDNF levels, but may decrease beta-endorphin levels in individuals with OUD. Plasma BDNF level seemed to be decreased in a BUP/D concentration-dependent manner.

Opioid agonist treatment for people who are dependent on pharmaceutical opioids

BACKGROUND

There are ongoing concerns regarding pharmaceutical opioid-related harms, including overdose and dependence, with an associated increase in treatment demand. People dependent on pharmaceutical opioids appear to differ in important ways from people who use heroin, yet most opioid agonist treatment research has been conducted in people who use heroin.  OBJECTIVES: To assess the effects of maintenance opioid agonist pharmacotherapy for the treatment of pharmaceutical opioid dependence.

SEARCH METHODS

We updated our searches of the following databases to January 2022: the Cochrane Drugs and Alcohol Group Specialised Register, CENTRAL, MEDLINE, four other databases, and two trial registers. We checked the reference lists of included studies for further references to relevant randomised controlled trials (RCTs).

SELECTION CRITERIA

We included RCTs with adults and adolescents examining maintenance opioid agonist treatments that made the following two comparisons. 1. Full opioid agonists (methadone, morphine, oxycodone, levo-alpha-acetylmethadol (LAAM), or codeine) versus different full opioid agonists or partial opioid agonists (buprenorphine) for maintenance treatment. 2. Full or partial opioid agonist maintenance versus non-opioid agonist treatments (detoxification, opioid antagonist, or psychological treatment without opioid agonist treatment).

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods.

MAIN RESULTS

We identified eight RCTs that met inclusion criteria (709 participants). We found four studies that compared methadone and buprenorphine maintenance treatment, and four studies that compared buprenorphine maintenance to either buprenorphine taper (in addition to psychological treatment) or a non-opioid maintenance treatment comparison. We found low-certainty evidence from three studies of a difference between methadone and buprenorphine in favour of methadone on self-reported opioid use at end of treatment (risk ratio (RR) 0.49, 95% confidence interval (CI) 0.28 to 0.86; 165 participants), and low-certainty evidence from four studies finding a difference in favour of methadone for retention in treatment (RR 1.21, 95% CI 1.02 to 1.43; 379 participants). We found low-certainty evidence from three studies showing no difference between methadone and buprenorphine on substance use measured with urine drug screens at end of treatment (RR 0.81, 95% CI 0.57 to 1.17; 206 participants), and moderate-certainty evidence from one study of no difference in days of self-reported opioid use (mean difference 1.41 days, 95% CI 3.37 lower to 0.55 days higher; 129 participants). There was low-certainty evidence from three studies of no difference between methadone and buprenorphine on adverse events (RR 1.13, 95% CI 0.66 to 1.93; 206 participants). We found low-certainty evidence from four studies favouring maintenance buprenorphine treatment over non-opioid treatments in terms of fewer opioid positive urine drug tests at end of treatment (RR 0.66, 95% CI 0.52 to 0.84; 270 participants), and very low-certainty evidence from four studies finding no difference on self-reported opioid use in the past 30 days at end of treatment (RR 0.63, 95% CI 0.39 to 1.01; 276 participants). There was low-certainty evidence from three studies of no difference in the number of days of unsanctioned opioid use (standardised mean difference (SMD) -0.19, 95% CI -0.47 to 0.09; 205 participants). There was moderate-certainty evidence from four studies favouring buprenorphine maintenance over non-opioid treatments on retention in treatment (RR 3.02, 95% CI 1.73 to 5.27; 333 participants). There was moderate-certainty evidence from three studies of no difference in adverse effects between buprenorphine maintenance and non-opioid treatments (RR 0.50, 95% CI 0.07 to 3.48; 252 participants). The main weaknesses in the quality of the data was the use of open-label study designs, and difference in follow-up rates between treatment arms.

AUTHORS' CONCLUSIONS

There is  very low- to moderate-certainty evidence supporting the use of maintenance agonist pharmacotherapy for pharmaceutical opioid dependence. Methadone or buprenorphine did not differ on some outcomes, although on the outcomes of retention and self-reported substance use some results favoured methadone. Maintenance treatment with buprenorphine appears more effective than non-opioid treatments. Due to the overall very low- to moderate-certainty evidence and small sample sizes, there is the possibility that the further research may change these findings.

A potential paradigm shift in opioid crisis management: The role of pharmacogenomics

Pharmacogenetic investigations into the opioid crisis suggest genetic variation could be a significant cause of opioid-related morbidity and mortality. Variability in opioid system genes, including single nucleotide polymorphisms, manifest after pharmacogenetic testing, as previously invisible risk factors for addiction and overdose. Pharmacodynamic genes regulate opioid-sensitive brain networks and neural reward circuitry. Pharmacokinetic genes expressed in drug metabolic pathways regulate blood levels of active vs. inactive opioid metabolites. Elucidating the complex interplay of genetic variations in pharmacokinetic and pharmacodynamic pathways will shed new light on the addictive and toxic properties of opioids. This narrative review serves to promote understanding of key genetic mechanisms affecting the metabolism and actions of opioids, and to explore causes of the recent surge in opioid-related mortality associated with COVID-19. Personalised treatment plans centred around an individual's genetic makeup could make opioid-based pain management and opioid use disorder (OUD) treatments safer and more effective at both the individual and system levels.

Goofballing of Opioid and Methamphetamine: The Science Behind the Deadly Cocktail

Globally, millions of people suffer from various substance use disorders (SUD), including mono-and polydrug use of opioids and methamphetamine. Brain regions such as the cingulate cortex, infralimbic cortex, dorsal striatum, nucleus accumbens, basolateral and central amygdala have been shown to play important roles in addiction-related behavioral changes. Clinical and pre-clinical studies have characterized these brain regions and their corresponding neurochemical changes in numerous phases of drug dependence such as acute drug use, intoxication, craving, withdrawal, and relapse. At present, many studies have reported the individual effects of opioids and methamphetamine. However, little is known about their combined effects. Co-use of these drugs produces effects greater than either drug alone, where one decreases the side effects of the other, and the combination produces a prolonged intoxication period or a more desirable intoxication effect. An increasing number of studies have associated polydrug abuse with poorer treatment outcomes, drug-related deaths, and more severe psychopathologies. To date, the pharmacological treatment efficacy for polydrug abuse is vague, and still at the experimental stage. This present review discusses the human and animal behavioral, neuroanatomical, and neurochemical changes underlying both morphine and methamphetamine dependence separately, as well as its combination. This narrative review also delineates the recent advances in the pharmacotherapy of mono- and poly drug-use of opioids and methamphetamine at clinical and preclinical stages.

Pharmacogenetics of Addiction Therapy

Drug addiction is a serious relapsing disease that has high costs to society and to the individual addicts. Treatment of these addictions is still in its nascency, with only a few examples of successful therapies. Therapeutic response depends upon genetic, biological, social, and environmental components. A role for genetic makeup in the response to treatment has been shown for several addiction pharmacotherapies with response to treatment based on individual genetic makeup. In this chapter, we will discuss the role of genetics in pharmacotherapies, specifically for cocaine, alcohol, and opioid dependences. The continued elucidation of the role of genetics should aid in the development of new treatments and increase the efficacy of existing treatments.

Biomarkers to predict staging and treatment response in opioid dependence: A narrative review

Opioid use disorder is a devastating disorder with a high burden in terms of overdose mortality, with an urgent need for more personalized prevention or therapeutic interventions. For this purpose, the description and validation of biological measures of staging or treatment response is a highly active research field. We conducted a narrative review on the pathophysiology of opioid use disorder to propose staging of the disease and search for research studies proposing or demonstrating the predictive value of biomarkers. We propose a IV stage description of opioid use disorder, from (I) vulnerability stage to (II) disease progression, (III) constituted opioid dependence and were several type of treatments can be applied, to the reach a (IV) modified health state. We classified biomarkers studies according to the stage of the disorder they were intended to predict, and to the three categories of methods they used: anatomical and functional aspects of the brain, genetic/transcriptomic/epigenetic studies, and lastly biomarkers of systemic modifications associated with opioid use disorder, especially regarding the immune system. Most studies predicting Stage III that we reviewed collected data from small samples sizes and were cross-sectional association studies comparing opioid dependent patients and control groups. Pharmacogenetic biomarkers are proposed to predict treatment response. Future research should now emphasize prospective studies, replication in independent samples, and predictive value calculation of each biomarker. The most promising results are multimodal evaluations to be able to measure the state of the brain reward system in living individuals.

A review of the existing literature on buprenorphine pharmacogenomics

Buprenorphine is an effective treatment for opioid dependence; however, it demonstrates individual variability in efficacy. Pharmacogenomics may explain this drug response variability and could allow for tailored therapy on an individual basis. The Food and Drug Administration and the Clinical Pharmacogenomics Implementation Consortium have guidelines on pharmacogenomic testing for some opioids (e.g., codeine); however, no guidelines exist for the partial opioid agonist buprenorphine. Pharmacogenomic testing targets for buprenorphine include pharmacodynamic genes like the mu-opioid receptor (MOP receptor) and catechol-O-methyltransferase (COMT), as well as the pharmacokinetic genes like the CYP enzymes. In this review we identified genotypes in patients with opioid addiction receiving buprenorphine that may result in altered therapeutic dosing and increased rate of relapse. The OPRM1 A118G single nucleotide polymorphism (SNP rs1799971) gene variant encoding the N40D MOP receptor has been associated with variable efficacy and response to treatment in both adult and neonatal patients receiving buprenorphine for treatment of opioid withdrawal. An SNP associated with rs678849 of OPRD1, coding for the delta opioid receptor, was associated with opioid relapse as indicated by opioid positive urine drug screens; there was also sex specific SNP identified at rs581111 and rs529520 in the European American population. COMT variability, particularly in rs4680, has been associated with length of stay and need for opioid treatment in patients with neonatal abstinence syndrome. Variations of the pharmacokinetic gene for CYP3A4 showed that the ultrarapid metabolizer phenotype required higher doses of buprenorphine. Genotyping of patients may allow us to appropriately tailor buprenorphine therapy to individual patients and lead to improved patient outcomes; however, further research on the pharmacogenomics of buprenorphine is needed.

Evaluation of Phenotypic and Genotypic Variations of Drug Metabolising Enzymes and Transporters in Chronic Pain Patients Facing Adverse Drug Reactions or Non-Response to Analgesics: A Retrospective Study

This retrospective study evaluates the link between an adverse drug reaction (ADR) or a non-response to treatment and cytochromes P450 (CYP), P-glycoprotein (P-gp) or catechol-O-methyltransferase (COMT) activity in patients taking analgesic drugs for chronic pain. Patients referred to a pain center for an ADR or a non-response to an analgesic drug between January 2005 and November 2014 were included. The genotype and/or phenotype was obtained for assessment of the CYPs, P-gp or COMT activities. The relation between the event and the result of the genotype and/or phenotype was evaluated using a semi-quantitative scale. Our analysis included 243 individual genotypic and/or phenotypic explorations. Genotypes/phenotypes were mainly assessed because of an ADR (n = 145, 59.7%), and the majority of clinical situations were observed with prodrug opioids (n = 148, 60.9%). The probability of a link between an ADR or a non-response and the genotypic/phenotypic status of the patient was evaluated as intermediate to high in 40% and 28.2% of all cases, respectively. The drugs in which the probability of an association was the strongest were the prodrug opioids, with an intermediate to high link in 45.6% of the cases for occurrence of ADRs and 36.0% of the cases for non-response. This study shows that the genotypic and phenotypic approach is useful to understand ADRs or therapeutic resistance to a usual therapeutic dosage, and can be part of the evaluation of chronic pain patients.

Endogenous Opiates and Behavior: 2018

This paper is the forty-first consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2018 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (2), the roles of these opioid peptides and receptors in pain and analgesia in animals (3) and humans (4), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (5), opioid peptide and receptor involvement in tolerance and dependence (6), stress and social status (7), learning and memory (8), eating and drinking (9), drug abuse and alcohol (10), sexual activity and hormones, pregnancy, development and endocrinology (11), mental illness and mood (12), seizures and neurologic disorders (13), electrical-related activity and neurophysiology (14), general activity and locomotion (15), gastrointestinal, renal and hepatic functions (16), cardiovascular responses (17), respiration and thermoregulation (18), and immunological responses (19).

A review of the pharmacogenomics of buprenorphine for the treatment of opioid use disorder

As the opioid epidemic continues to grow across the United States, the number of patients requiring treatment for opioid use disorder continues to climb. Although medication-assisted treatment presents a highly effective tool that can help address this epidemic, its use has been limited. Nonetheless, with easier dosing protocols (compared to the more complex dosing required of methadone due to its long and variable half-life) and fewer prescribing limitations (may be prescribed outside the setting of federally approved clinics), the increase in buprenorphine use in the United States has been dramatic in recent years. Despite buprenorphine's demonstrated efficacy, patient-specific factors can alter the response to the medications, which may lead to treatment failure in some patients. Clinical characteristics (sex, concurrent medications, and mental health comorbidities) as well as social determinants of health (housing status, involvement with the criminal justice system, and socioeconomic status) may impact treatment outcomes. Furthermore, a growing body of data suggests that genetic variations can alter pharmacological effects and influence therapeutic response. This review will cover the available pharmacogenomic data for the use of buprenorphine in the management of opioid use disorders. Pharmacogenomic determinants that affect opioid receptors, the dopaminergic system, metabolism of buprenorphine, and adverse events are discussed. Although much of the existing data comes from observational studies, clinical research is ongoing. Nevertheless, the development of pharmacogenomic-guided strategies has the potential to reduce opioid misuse, improve clinical outcomes, and save healthcare resources.

Treatment resistant opioid use disorder (TROUD): Definition, rationale, and recommendations

The opioid overdose epidemic kills about 130 people a day in the United States and it is estimated that there are about 2.1 million people who suffer from an opioid use disorder (OUD). Academic neuroscientists, psychiatrists and the National Institute of Drug Abuse have spent the last forty-years establishing the foundation of addiction as a brain disorder. It is now clear that extended opioid use causes multiple important and at times, irreversible changes to the brain, especially to its dopamine and opioid systems. With our recognized criteria for diagnosis and the accepted multifaceted treatment approach of both professional psychotherapy and medications that assist treatments, treatment failures should be limited. Unfortunately, this is not the case. Slips, relapses, overdose and multiple failures are all too common. Similar to treatment resistant depression there is a subpopulation who do not respond to standard OUD treatments. However, the field has suggested that if a treatment does not work, it is either the patients fault, they have not hit bottom or simply we need to try the same treatment again. There is a rational to consider this a new category of OUD, treatment resistant opioid use disorder (TROUD). This paper explores past treatment attempts data from OUD patients entering traditional outpatient treatment and makes recommendations how TROUD can be defined. It challenges the addiction research and treatment providers to change its focus from individuals being resistant to the unique conditions associated with this brain disorder as being resistant to treatment as usual.

Assessing the contribution of opioid- and dopamine-related genetic polymorphisms to the abuse liability of oxycodone

BACKGROUND

Attempts to identify opioid users at increased risk of escalating to opioid use disorder have had limited success. Data from a variety of sources suggest that genetic variation may mediate the subjective response to opioid drugs, and therefore contribute to their abuse potential. The goal of the current study was to observe the relationship between select genetic polymorphisms and the subjective effects of oxycodone under controlled clinical laboratory conditions.

METHODS

Non-dependent, volunteers with some history of prescription opioid exposure (N = 36) provided a blood sample for analyses of variations in the genes that encode for the μ-, κ- and δ-opioid receptors, and the dopamine metabolizing enzyme, catechol-O-methyltransferase (COMT). Participants then completed a single laboratory test session to evaluate the subjective and analgesic effects of oral oxycodone (0, 10, and 20 mg, cumulative dose = 30 mg).

RESULTS

Oxycodone produced typical μ-opioid receptor agonist effects, such as miosis, and decreased pain perception. Oxycodone also produced dose-dependent increases in positive subjective responses such as: drug "Liking" and "Good Effect." Genetic variants in the μ- (rs6848893) and δ-opioid receptor (rs581111) influenced the responses to oxycodone administration. Additionally, self-reported "Stimulated" effects of oxycodone varied significantly as a function of COMT rs4680 genotype.

DISCUSSION

The current study shows that the euphoric and stimulating effects of oxycodone can vary as a function of genetic variation. Though the relationship between the stimulating effects of opioids and their abuse liability is not well established, we know that the ability of opioids to provide intense feelings of pleasure is a significant motivator for continued use. If replicated, specific genetic variants may be useful in predicting who is at increased risk of developing maladaptive patterns of use following medical exposure to opioid analgesics.

Relevance of CYP2B6 and CYP2D6 genotypes to methadone pharmacokinetics and response in the OPAL study

AIMS

Our study aimed to evaluate the impacts of the cytochrome P450 (CYP) 2B6-G516T and CYP2D6 genetic polymorphisms on pharmacokinetic and clinical parameters in patients receiving methadone maintenance treatment.

METHODS

Opioid PhArmacoLogy (OPAL) was a clinical survey of the sociodemographic characteristics, history and consequences of pathology associated with methadone maintenance treatment response and current addictive comorbidities. A subgroup of 72 methadone patients was genotyped.

RESULTS

When comparing the three CYP2B6 genotype groups, the methadone (R)- and (S)-methadone enantiomer concentrations/doses (concentrations relative to doses) were different (P = .029, P = .0019). The CYP2D6 phenotypes did not seem to be relevant with regard to methadone levels. On multivariate analysis, neither the CYP2B6 genotype nor the CYP2D6 phenotype explained the (R)-methadone concentration/dose values (P = .92; P = .86); the (S)-methadone concentration/dose values (P = .052; P = .95 [although there was a difference between the TT group and GT and GG groups {P = .019}]); or opiate cessation (P = .12; P = .90).

CONCLUSION

The genotyping of CYP2B6 G516T could be an interesting tool to explore methadone intervariability.

The importance of buprenorphine research in the opioid crisis

With the urgency to treat patients more effectively for opioid use disorder in the midst of the opioid epidemic, a key area for precision medicine is to improve individualized medication-assisted treatment for opioid use disorder. The expansion of medication-assisted treatment is a key to reducing illicit opioid use, preventing opioid overdose deaths, and reducing the comorbidities and societal impacts of opioid use disorder. The most common medication for opioid use disorder will soon be buprenorphine. Research to date shows the successful impact of buprenorphine treatment, including the pharmacogenomics of buprenorphine response and treatment efficacy. Buprenorphine is also a promising treatment for depression and anxiety, and neonatal opioid withdrawal syndrome (NOWS). However, the rates of success with medication-assisted treatment for opioid use disorder, particularly at the beginning of treatment, still show many individuals relapsing to illicit opioid use. With the scope of the opioid crisis, there is an urgent need for expansion of buprenorphine treatment research to provide critical information for improving outcomes of opioid use disorder. Implementing the best strategies for opioid use disorder treatment is of dire urgency and will save lives.