Pharmacogenetics of Opioid Use Disorder Treatment

OPRM1 rs2075572 has potential to affect plasma buprenorphine level in opioid users, but not OPRM1 rs562859

OPRM1 gene encoding mu-opioid receptor (MOR) is the primary candidate gene for buprenorphine (BUP) pharmacogenetics. OPRM1 undergoes alternative splicing leading to multiple MOR subtypes. Thus, in the current study 2 SNPs (rs1799972 and rs562859) were selected due to evidence for their contribution to alternative splicing of OPRM1. The effects of 2 SNPs of OPRM1 gene on plasma buprenorphine and norbuprenorphine levels in a sample of 233 OUD patients receiving BUP/naloxone were examined. Polymorphisms were analyzed by PCR and RFLP. BUP and norbuprenorphine concentrations in plasma were measured by LC-MS/MS. OPRM1 rs2075572 GC + CC (0.12 ng/ml) had significantly higher plasma BUP level compared to GG (0.084 ng/ml) (p = 0.043). Although there was not a statistically significant difference between OPRM1 rs562859 genotypes (p = 0.46), patients with OPRM1 rs562859 CT + TT had higher plasma BUP and BUP-related values as compared to those with CC. In conclusion, the effect of OPRM1 rs2075572 on BUP levels in opioid users' plasma was shown in a Caucasian population for the first time. On the other hand, OPRM1 rs562859 seems not to influence the BUP pharmacology.

The genetic landscape of substance use disorders

Substance use disorders represent a significant public health concern with considerable socioeconomic implications worldwide. Twin and family-based studies have long established a heritable component underlying these disorders. In recent years, genome-wide association studies of large, broadly phenotyped samples have identified regions of the genome that harbour genetic risk variants associated with substance use disorders. These regions have enabled the discovery of putative causal genes and improved our understanding of genetic relationships among substance use disorders and other traits. Furthermore, the integration of these data with clinical information has yielded promising insights into how individuals respond to medications, allowing for the development of personalized treatment approaches based on an individual's genetic profile. This review article provides an overview of recent advances in the genetics of substance use disorders and demonstrates how genetic data may be used to reduce the burden of disease and improve public health outcomes.

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.

Association between NTRK2 Polymorphisms, Hippocampal Volumes and Treatment Resistance in Major Depressive Disorder

Despite the increasing availability of antidepressant drugs, a high rate of patients with major depression (MDD) does not respond to pharmacological treatments. Brain-derived neurotrophic factor (BDNF)-tyrosine receptor kinase B (TrkB) signaling is thought to influence antidepressant efficacy and hippocampal volumes, robust predictors of treatment resistance. We therefore hypothesized the possible role of BDNF and neurotrophic receptor tyrosine kinase 2 (NTRK2)-related polymorphisms in affecting both hippocampal volumes and treatment resistance in MDD. A total of 121 MDD inpatients underwent 3T structural MRI scanning and blood sampling to obtain genotype information. General linear models and binary logistic regressions were employed to test the effect of genetic variations related to BDNF and NTRK2 on bilateral hippocampal volumes and treatment resistance, respectively. Finally, the possible mediating role of hippocampal volumes on the relationship between genetic markers and treatment response was investigated. A significant association between one NTRK2 polymorphism with hippocampal volumes and antidepressant response was found, with significant indirect effects. Our results highlight a possible mechanistic explanation of antidepressant action, possibly contributing to the understanding of MDD pathophysiology.

Influence of CYP2B6 Genotype on Methadone Dosage in Patients from the Methadone Maintenance Treatment (MMT) Program in Pereira, Colombia

Methadone treatment reduces the use of heroin and withdrawal symptoms; however, methadone is an expensive medication with a narrow safety margin. We compared the retention rates, persistence of heroin use, and quality of life of a group of patients undergoing conventional Methadone Maintenance Treatment (MMT) with a group for whom the CYP2B6 516G>T polymorphism was used in addition to the MMT to calculate the required methadone dose. Over 12 weeks, the retention rate, heroin usage, and quality of life of patients under conventional treatment (n = 34) were compared with those of patients for whom we used genetic markers to calculate methadone dosage (n = 38). At the end of the study, 26.4% of patients abandoned the program, and neither demographic nor clinical variables were associated with treatment adherence. Of the remaining patients, 16% of the control group and 8% of patients in the pharmacogenetic group reported heroin use, while both groups showed a 64% reduction in the use of cocaine/crack (no significant differences between the groups were found). Starting in the second week, the methadone dosage was lower among the patients for whom methadone was prescribed based on genotype. Although there were six individuals in the control group and three in the pharmacogenetic group with QTc intervals > 450 ms (a threshold that is considered dangerous), we did not find a relationship between the QTc interval and methadone dosage. There were no differences in the perception of quality of life between the two groups. The results of this pilot study suggest that concerning methadone therapy, the CYP2B6 genotype contributes to reduced effective doses and treatment costs.

Effects of UGT2B7 rs7662029 and rs7439366 polymorphisms on sublingual buprenorphine metabolism in heroin addicts: An improved PCR-RFLP assay for the detection of rs7662029 polymorphism

This study aimed to determine the effects of UGT2B7 rs7662029 and rs7439366 polymorphisms on plasma buprenorphine (BUP) concentration and different treatment responses in a sample of 109 patients with opioid use disorder (OUD) treated with sublingual BUP/naloxone. Polymorphisms were analysed by PCR-RFLP. Plasma concentrations of BUP and its metabolite norbuprenorphine were detected by LC-MS/MS. Craving, withdrawal, depression and anxiety were measured by appropriate scales. OUD patients with rs7439366 CC or rs7662029 GG genotypes had significantly lower dose-normalized (BUP/D) and dose/kg-normalized BUP (BUP/D.kg^-1) levels than those who were CT or AA carriers. Significant associations between UGT2B7 rs7662029 and increased craving (p = 0.037) and withdrawal symptoms (p = 0.029) were detected. Our findings were pointing to an important role of UGT2B7 in the metabolism of sublingual BUP/naloxone in the heroin addicts for the first time. A novel PCR-RFLP assay was developed for the determination of UGT2B7 rs7662029 polymorphism, based on utilizing novel restriction enzyme.

Implications of OPRM1 and CYP2B6 variants on treatment outcomes in methadone-maintained patients in Ontario: Exploring sex differences

Genetic variants in the OPRM1 and CYP2B6 genes, respectively coding for an opioid receptor and methadone metabolizers, have been linked to negative treatment outcomes in patients undergoing methadone maintenance treatment, with little consensus on their effect. This study aims to test the associations between pre-selected SNPs of OPRM1 and CYP2B6 and outcomes of continued opioid use, relapse, and methadone dose. It also aims to observe differences in associations within the sexes. 1,172 participants treated with methadone (nMale = 666, nFemale = 506) were included in this study. SNPs rs73568641 and rs7451325 from OPRM1 and all the tested CYP2B6 SNPs were detected to be in high linkage disequilibrium. Though no associations were found to be significant, noteworthy differences were observed in associations of OPRM1 rs73568641 and CYP2B6 rs3745274 with treatment outcomes between males and females. Further research is needed to determine if sex-specific differences are present.

A systematic review of GWAS identified SNPs associated with outcomes of medications for opioid use disorder

BACKGROUND

Patients with opioid use disorder (OUD) display an interindividual variability in their response to medications for opioid use disorder (MOUD). A genetic basis may explain the variability in this response. However, no consensus has been reached regarding which genetic variants significantly contribute to MOUD outcomes.

OBJECTIVES

This systematic review aims to summarize genome-wide significant findings on MOUD outcomes and critically appraise the quality of the studies involved.

METHODS

Databases searched from inception until August 21st, 2020 include: MEDLINE, Web of Science, EMBASE, CINAHL and Pre-CINAHL, GWAS Catalog and GWAS Central. The included studies had to be GWASs that assessed MOUD in an OUD population. All studies were screened in duplicate. The quality of the included studies was scored and assessed using the Q-Genie tool. Quantitative analysis, as planned in the protocol, was not feasible, so the studies were analyzed qualitatively.

RESULTS

Our search identified 7292 studies. Five studies meeting the eligibility criteria were included. However, only three studies reported results that met our significance threshold of p ≤ 1.0 × 10-7. In total, 43 genetic variants were identified. Variants corresponding to CNIH3 were reported to be associated with daily heroin injection in Europeans, OPRM1, TRIB2, and ZNF146 with methadone dose in African Americans, EYS with methadone dose in Europeans, and SPON1 and intergenic regions in chromosomes 9 and 3 with plasma concentrations of S-methadone, R-methadone, and R-EDDP, respectively, in Han Chinese.

LIMITATIONS

The limitations of this study include not being able to synthesize the data in a quantitative way and a conservative eligibility and data collection model.

CONCLUSION

The results from this systematic review will aid in highlighting significant genetic variants that can be replicated in future OUD pharmacogenetics research to ascertain their role in patient-specific MOUD outcomes. Systematic review registration number CRD42020169121.

Untangling the Complexities of Substance Use Initiation and Recovery: Client Reflections on Opioid Use Prevention and Recovery From a Social-Ecological Perspective

Background:

In Canada, the rate of opioid use, opioid use disorder (OUD), and associated mortality and morbidity are higher among Indigenous Peoples than the general population. Indigenous Peoples on medications for opioid use disorders (MOUD) often face distinct barriers that hinder their clinical progress, leading to treatment attrition.

Methods:

We used a social-ecological model to inquire into clients’ experiences with a history of treatment failure for OUD. We used exploratory qualitative research to engage 22 clients with a history of OUD treatment dropouts and who are currently on MOUD. In-depth, semi-structured interviews lasting an average of 30 minutes were conducted on-site.

Results:

We identified 4 themes from the study: (a) risk for substance use; (b) factors sustaining substance use; (c) factors leading to treatment, and (d) treatment failure and re-enrollment.

Conclusion:

Using a socio-ecological model helps to understand factors that influence an individual’s risk for OUD, decision to pursue treatment, and treatment outcomes. Furthermore, social ecological model also creates possibilities to develop supportive, multilevel interventions to prevent OUD risks and support for clients on MOUD. Such interventions include mitigating adverse childhood experiences, supporting families, and creating safe community environments.

Neurocognitive Empowerment for Addiction Treatment (NEAT): study protocol for a randomized controlled trial

BACKGROUND

Neurocognitive deficits (NCDs) and associated meta-cognition difficulties associated with chronic substance use often delay the learning and change process necessary for addiction recovery and relapse prevention. However, very few cognitive remediation programs have been developed to target NCDs and meta-cognition for substance users. The study described herein aims to investigate the efficacy of a multi-component neurocognitive rehabilitation and awareness program termed "Neurocognitive Empowerment for Addiction Treatment" (NEAT). NEAT is a fully manualized, cartoon-based intervention involving psychoeducation, cognitive practice, and compensatory strategies relevant across 10 major cognitive domains, including aspects of attention, memory, executive functions, and decision-making.

METHOD/DESIGN

In a single-blind randomized controlled trial (RCT), 80 female opioid and/or methamphetamine users will be recruited from an addiction recovery program providing an alternative to incarceration for women with substance use-related offenses. Eight groups of 9-12 participants will be randomized into NEAT or treatment-as-usual (TAU). NEAT involves 14 90-min sessions, delivered twice weekly. The primary outcome is change in self-reported drug craving from before to after intervention using Obsessive Compulsive Drug Use Scale. Secondary and exploratory outcomes include additional psychological, neurocognitive, and structural and functional neuroimaging measures. Clinical measures will be performed at five time points (pre- and post-intervention, 3-, 6-, and 12-month follow-up); neuroimaging measures will be completed at pre- and post-intervention.

DISCUSSION

The present RCT is the first study to examine the efficacy of an adjunctive neurocognitive rehabilitation and awareness program for addiction. Results from this study will provide initial information concerning potential clinical efficacy of the treatment, as well as delineate neural mechanisms potentially targeted by this novel intervention.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03922646 . Registered on 22 April 2019.

Factors mediating pain-related risk for opioid use disorder

Pain is a complex experience with far-reaching organismal influences ranging from biological factors to those that are psychological and social. Such influences can serve as pain-related risk factors that represent susceptibilities to opioid use disorder. This review evaluates various pain-related risk factors to form a consensus on those that facilitate opioid abuse. Epidemiological findings represent a high degree of co-occurrence between chronic pain and opioid use disorder that is, in part, driven by an increase in the availability of opioid analgesics and the diversion of their use in a non-medical context. Brain imaging studies in individuals with chronic pain that use/abuse opioids suggest abuse-related mechanisms that are rooted within mesocorticolimbic processing. Preclinical studies suggest that pain states have a limited impact on increasing the rewarding effects of opioids. Indeed, many findings indicate a reduction in the rewarding and reinforcing effects of opioids during pain states. An increase in opioid use may be facilitated by an increase in the availability of opioids and a decrease in access to non-opioid reinforcers that require mobility or social interaction. Moreover, chronic pain and substance abuse conditions are known to impair cognitive function, resulting in deficits in attention and decision making that may promote opioid abuse. A better understanding of pain-related risk factors can improve our knowledge in the development of OUD in persons with pain conditions and can help identify appropriate treatment strategies. This article is part of the special issue on 'Vulnerabilities to Substance Abuse.'.

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.

Buprenorphine dosing for the treatment of opioid use disorder through pregnancy and postpartum

PURPOSE OF REVIEW

Opioid-related deaths are a leading cause of mortality during pregnancy through 12 months postpartum. Buprenorphine use during pregnancy is increasing, yet expert opinion on its dosing through the perinatal period is limited. We provide a review of the current clinical literature on buprenorphine dosing during pregnancy through 12 months postpartum. and present data from a retrospective chart review of patients at our institution describing trends in buprenorphine dosing during pregnancy and postpartum. Utilizing this information, we synthesize findings to provide clinical recommendations for providers.

RECENT FINDINGS

Existing literature during pregnancy reflects how many women increase and split total daily buprenorphine doses as gestational age advances.

SUMMARY

We present data from a retrospective chart review of patients at our institution describing trends in buprenorphine dosing during pregnancy and postpartum. Utilizing this information, we synthesize findings to provide clinical recommendations for providers. Changes in the total daily dose of buprenorphine used across pregnancy and through 12 months postpartum at the individual level do not follow consistent patterns, highlighting substantial individual variability. Altogether, buprenorphine dosing should be individualized through pregnancy and postpartum with frequent evaluations by providers and solicited input from patients.

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.

Four single nucleotide polymorphisms in genes involved in neuronal signaling are associated with Opioid Use Disorder in West Virginia

Objective

Pilot study to assess utility in opioid use disorder (OUD) of a panel of single nucleotide polymorphisms in genes previously related to substance use disorder (SUD) and/or phenotypes that predispose individuals to OUD/SUD.

Design

Genetic association study.

Setting

West Virginia University's Chestnut Ridge Center Comprehensive Opioid Abuse Treatment (COAT) clinic for individuals diagnosed with OUD.

Patients

Sixty patients 18 years of age or older with OUD undergoing medication (buprenorphine/naloxone)-assisted treatment (MAT); all sixty patients recruited contributed samples for genetic analysis.

Outcome Measures

Minor allele frequencies for single nucleotide polymorphisms.

Results

Four of the fourteen single nucleotide polymorphisms examined were present at frequencies that are statistically significantly different than in a demographically-matched general population.

Conclusions

For the purposes of testing WV individuals via genetic means for predisposition to OUD, at least four single nucleotide polymorphisms in three genes are likely to have utility in predicting susceptibility. Additional studies with larger populations will need to be conducted to confirm these results before use in a clinical setting.

Pharmacogenomics: What the Doctor Ordered?

About half a million adverse drug reactions are reported in the US each year that result in disability, hospitalization or death. The efficacy or toxicity of a drug in a patient can be strongly influenced by their genetics as well as environment. Application of genomics to clinical pharmacology, "pharmacogenomics," promises to transform patient care and health resource utilization in the coming decade.

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.

Management of opioid use disorder in the USA: present status and future directions

Opioid use disorder is characterised by the persistent use of opioids despite the adverse consequences of its use. The disorder is associated with a range of mental and general medical comorbid disorders, and with increased mortality. Although genetics are important in opioid use disorder, younger age, male sex, and lower educational attainment level and income, increase the risk of opioid use disorder, as do certain psychiatric disorders (eg, other substance use disorders and mood disorders). The medications for opioid use disorder, which include methadone, buprenorphine, and extended-release naltrexone, significantly improve opioid use disorder outcomes. However, the effectiveness of medications for opioid use disorder is limited by problems at all levels of the care cascade, including diagnosis, entry into treatment, and retention in treatment. There is an urgent need for expanding the use of medications for opioid use disorder, including training of health-care professionals in the treatment and prevention of opioid use disorder, and for development of alternative medications and new models of care to expand capabilities for personalised interventions.

Third-Year Medical Students' Reactions to Surgical Patients in Pain: Doubt, Distress, and Depersonalization

CONTEXT

Medical students have limited instruction about how to manage the interpersonal relationships required to care for patients in pain.

OBJECTIVES

The objective of this study was to characterize the experiences of medical students as they encounter pain, suffering, and the emotional experiences of doctoring.

METHODS

We used qualitative analysis to explore the content of 341 essays written by third-year medical students who described their experiences with surgical patients in pain. We used an inductive process to develop a coding taxonomy and then characterized the content of these essays related to empathy, patient-clinician interaction, and descriptions of clinical norms.

RESULTS

Students found it difficult to reconcile patient suffering with the therapeutic objective of treatment. They feared an empathic response to pain might compromise the fortitude and efficiency required to be a doctor and they pursued strategies to distance themselves from these feelings. Students described tension around prescription of pain medications and worried about the side effects of medications used to treat pain. Students felt disillusioned when operations caused suffering without therapeutic benefit or were associated with unexpected complications. Although patients had expressed a desire for intervention, students worried that the burdens of treatment and long-term consequences were beyond patient imagination.

CONCLUSION

These observations about patient-doctor relationships suggest that there is a larger problem among clinicians relating to patient distress and personal processing of the emotional nature of patient care. Efforts to address this problem will require explicit instruction in skills to develop a personal strategy for managing the emotionally challenging aspects of clinical work.

The Cholinergic System as a Treatment Target for Opioid Use Disorder

Opioid overdoses recently became the leading cause of accidental death in the US, marking an increase in the severity of the opioid use disorder (OUD) epidemic that is impacting global health. Current treatment protocols for OUD are limited to opioid medications, including methadone, buprenorphine, and naltrexone. While these medications are effective in many cases, new treatments are required to more effectively address the rising societal and interpersonal costs associated with OUD. In this article, we review the opioid and cholinergic systems, and examine the potential of acetylcholine (ACh) as a treatment target for OUD. The cholinergic system includes enzymes that synthesize and degrade ACh and receptors that mediate the effects of ACh. ACh is involved in many central nervous system functions that are critical to the development and maintenance of OUD, such as reward and cognition. Medications that target the cholinergic system have been approved for the treatment of Alzheimer's disease, tobacco use disorder, and nausea. Clinical and preclinical studies suggest that medications such as cholinesterase inhibitors and scopolamine, which target components of the cholinergic system, show promise for the treatment of OUD and further investigations are warranted.