Use and Misuse of Opioids in Chronic Pain

Pain medication tapering for patients with Persistent Spinal Pain Syndrome Type II, treated with Spinal Cord Stimulation: A RCT-study protocol of the PIANISSIMO study

BACKGROUND

Spinal Cord Stimulation (SCS) may provide pain relief in patients with therapy-refractory Persistent Spinal Pain Syndrome Type II (PSPS-T2). Despite the evidence that SCS can reduce disability and reduce pain medication usage, only 25% of the patients is able to completely omit pain medication usage after 12 months of SCS. To tackle the high burden of patients who consume a lot of pain medication, tapering programs could be initiated before starting a trajectory with SCS. The current objective is to examine whether a pain medication tapering program before SCS alters disability in PSPS-T2 patients compared to no tapering program.

METHODS AND DESIGN

A three-arm, parallel-group multicenter randomized controlled trial will be conducted including 195 patients who will be randomized (1:1:1) to either (a) a standardized pain medication tapering program, (b) a personalized pain medication tapering program, or (c) no tapering program before SCS implantation, all with a follow-up period until 12 months after implantation. The primary outcome is disability. The secondary outcomes are pain intensity, health-related quality of life, participation, domains affected by substance use, anxiety and depression, medication usage, psychological constructs, sleep, symptoms of central sensitization, and healthcare expenditure.

DISCUSSION

Within the PIANISSIMO project we propose a way to reduce the risks of adverse events, medication-induced hyperalgesia, tolerance, and dependence by providing pain medication tapering before SCS. Due to the lack of a commonly accepted in-hospital tapering approach, two different tapering programs will be evaluated in this study. If pain medication tapering programs are deemed to be more effective than no tapering on disability, this would add to the evidence towards an improved patient-centered care model in this patient group and set a clear path to advocate for pain medication tapering before SCS as the new standard treatment guideline for these patients.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05861609. Registered on May 17, 2023.

A Conceptual Analysis of Opioid Use Disorder in Chronic Noncancer Pain Using Rodger's Evolutionary Approach

OBJECTIVE

This study aims to examine the complex nature of opioid use disorder (OUD) in chronic noncancer pain (CNCP) by exploring its antecedents, attributes, consequences, and interrelated concepts.

DESIGN

A systematic literature review was conducted to gather relevant studies published between 2015 and 2022, utilizing the CINAHL, MEDLINE, PsycINFO, and PubMed databases.

DATA SOURCES

The selected databases provided a comprehensive range of articles related to OUD in CNCP, ensuring a comprehensive topic analysis.

METHODS

Twenty-two articles meeting the inclusion criteria were included in the analysis. These articles were critically reviewed and analyzed to identify key themes and concepts related to OUD in CNCP.

RESULTS

The findings of this study shed light on the multifaceted aspects of OUD in CNCP, including its antecedents, such as goals of physical function improvement, prescription of opioids for CNCP, social influences, and mental health dynamics. The attributes of OUD in CNCP were identified as chronic pain, noncancer pain, opioid use, misuse, and abuse. OUD's consequences in CNCP include impaired functioning, increased health risks, psychological distress, social challenges, and economic burden.

CONCLUSION

Understanding the complexity of OUD in CNCP is crucial for improving patient outcomes. Collaborative efforts among healthcare systems, regulatory bodies, and professional organizations are needed to develop policies promoting safe and effective pain management while mitigating risks associated with opioid use in CNCP.

IMPLICATIONS FOR PRACTICE

Implementing policy recommendations derived from this study enhances care and outcomes for individuals with CNCP. By addressing complex issues of OUD in CNCP and adopting evidence-based practices, healthcare providers can optimize pain management and promote well-being in CNCP patients.

Prediction of sustained opioid use in children and adolescents using machine learning

BACKGROUND

Opioid misuse in the paediatric population is understudied. This study aimed to develop a machine learning classifier to differentiate between occasional and sustained opioid users among children and adolescents in outpatient settings.

METHODS

Data for 29,335 patients under 19 yr with recorded opioid purchases were collected from medical records. Machine learning methods were applied to predict sustained opioid use within 1, 2, or 3 yr after first opioid use, using sociodemographic information, medical history, and healthcare usage variables collected near the time of first prescription fulfilment. The models' performance was evaluated with classification and calibration metrics, and a decision curve analysis. An online tool was deployed for model self-exploration and visualisation.

RESULTS

The models demonstrated good performance, with a 1-yr follow-up model achieving a sensitivity of 0.772, a specificity of 0.703, and an ROC-AUC of 0.792 on an independent test set, with calibration intercept and slope of 0.00 and 1.02, respectively. Decision curve analysis revealed the clinical benefit of using the model relative to other strategies. SHAP analysis (SHapley Additive exPlanations) identified influential variables, including the number of diagnoses, medical images, laboratory tests, and type of opioid used.

CONCLUSIONS

Our model showed promising performance in predicting sustained opioid use among paediatric patients. The online risk prediction tool can facilitate compliance to such tools by clinicians. This study presents the potential of machine learning in identifying at-risk paediatric populations for sustained opioid use, potentially contributing to secondary prevention of opioid abuse.

Implementing a pragmatic clinical trial to tailor opioids for chronic pain on behalf of the IGNITE ADOPT PGx investigators

Chronic pain is a prevalent condition with enormous economic burden. Opioids such as tramadol, codeine, and hydrocodone are commonly used to treat chronic pain; these drugs are activated to more potent opioid receptor agonists by the hepatic CYP2D6 enzyme. Results from clinical studies and mechanistic understandings suggest that CYP2D6-guided therapy will improve pain control and reduce adverse drug events. However, CYP2D6 is rarely used in clinical practice due in part to the demand for additional clinical trial evidence. Thus, we designed the ADOPT-PGx (A Depression and Opioid Pragmatic Trial in Pharmacogenetics) chronic pain study, a multicenter, pragmatic, randomized controlled clinical trial, to assess the effect of CYP2D6 testing on pain management. The study enrolled 1048 participants who are taking or being considered for treatment with CYP2D6-impacted opioids for their chronic pain. Participants were randomized to receive immediate or delayed (by 6 months) genotyping of CYP2D6 with clinical decision support (CDS). CDS encouraged the providers to follow the CYP2D6-guided trial recommendations. The primary study outcome is the 3-month absolute change in the composite pain intensity score assessed using Patient-Reported Outcomes Measurement Information System (PROMIS) measures. Follow-up will be completed in July 2024. Herein, we describe the design of this trial along with challenges encountered during enrollment.

Indirect effects of emotion regulation in the relationship between pain and cannabis use in adults 18-64 years

INTRODUCTION

Individuals with chronic pain often receive prescription opioid medication, and they may use cannabis to treat pain as well, although the risks of cannabis-opioid co-use are significant. This study aimed to investigate whether two transdiagnostic factors, emotion regulation and distress tolerance, had significant indirect effects in the relationship between pain and cannabis use in adults with chronic pain and an opioid prescription.

METHODS

Participants (n = 450; mean age = 38.6 ± 11.09) were recruited using Qualtrics panel service and were 75 % female and 79 % White, non-Hispanic. Participants completed a 30-minute self-report survey capturing three-month cannabis use, the Difficulties in Emotional Regulation Scale (DERS), and the Distress Tolerance Scale (DTS). The Graded Pain Scale (GCPS) assessed pain severity/intensity and disability. Analyses used the SPSS PROCESS macro, with both single (i.e., one transdiagnostic factor) and parallel indirect effects (i.e., both the DERS and DTS) examined.

RESULTS

There were statistically significant indirect effects for both the DERS and DTS in the relationship between pain intensity or disability and three-month cannabis use in single factor models. In the parallel indirect effect model, only the DERS was statistically significant (intensity indirect effect coefficient = 0.0195 % confidence interval [95 %CI] = 0.0065, 0.390; disability indirect effect coefficient = 0.0147, 95 %CI = 0.0055, 0.0274).

CONCLUSIONS

When examining parallel indirect effects, only emotional regulation and not distress tolerance mediated the relationship between chronic pain and cannabis use among those with an opioid prescription. Clinically, interventions aimed at improving emotional regulation in individuals with chronic pain can help limit cannabis and opioid co-use.

Opioid use surrounding diagnosis and follow-up in patients with ankylosing spondylitis, psoriatic arthritis, and rheumatoid arthritis: Results from US claims databases

OBJECTIVE

To describe patients' use of opioids in the year preceding and year following new diagnosis of ankylosing spondylitis (AS), psoriatic arthritis (PsA), or rheumatoid arthritis (RA), compared with patients without the/se diseases.

METHODS

This study used US IBM® MarketScan® Commercial Claims and Encounters (CCAE) and Medicaid data and included three cohorts, comprised of incident cases of AS, PsA, or RA (2010-2017). Three matched comparator patients (without the incident disease) were selected for each patient within the disease cohort. Opioid use and appropriate treatment exposure (as defined by US guideline recommendations) in the 12-month baseline and follow-up periods were evaluated using descriptive analyses.

RESULTS

Prevalence of claims for opioids was higher for disease cohorts vs. comparators in CCAE; 36.4% of patients with AS, 29.5% with PsA, and 44.4% with RA did not have any claim for guideline-appropriate therapy in follow-up. Prevalence of claims for opioids was also higher for disease cohorts vs. comparators in Medicaid; 30.6% of patients with AS, 36.6% with PsA, and 65.4% with RA did not have any claim for guideline-appropriate therapy in follow-up.

CONCLUSIONS

In patients with AS, PsA, or RA, there was high reliance on opioids at and around the time of diagnosis. Significant proportions of patients were not on appropriate treatment as defined by professional society post-diagnosis guidelines; this discordance between actual patient therapies and treatment recommendations may suggest a need for better awareness of appropriate pain management and treatment strategies in rheumatic diseases. Key Points • This study analysed opioid use among patients with ankylosing spondylitis (AS), psoriatic arthritis (PsA), or rheumatoid arthritis (RA), and adds to current knowledge by expanding beyond assessment of opioid use at diagnosis, to the year before and after diagnosis. • Opioid use was found to be highly prevalent in AS, PsA, and RA in the year prior to diagnosis and, interestingly, was still seen during the year after diagnosis. • Opioids are neither disease modifying, nor a targeted/recommended treatment for chronic autoimmune diseases. In addition to their association with significant economic costs, opioids are potentially hazardous and are not better than alternative treatments with superior safety profiles. • The reasons behind opioid prescribing patterns should be explored further to support movement to targeted therapies.

A synthetic peptide exerts nontolerance-forming antihyperalgesic and antidepressant effects in mice

Chronic pain is a prevalent and persistent ailment that affects individuals worldwide. Conventional medications employed in the treatment of chronic pain typically demonstrate limited analgesic effectiveness and frequently give rise to debilitating side effects, such as tolerance and addiction, thereby diminishing patient compliance with medication. Consequently, there is an urgent need for the development of efficacious novel analgesics and innovative methodologies to address chronic pain. Recently, a growing body of evidence has suggested that multireceptor ligands targeting opioid receptors (ORs) are favorable for improving analgesic efficacy, decreasing the risk of adverse effects, and occasionally yielding additional advantages. In this study, the intrathecal injection of a recently developed peptide (VYWEMEDKN) at nanomolar concentrations decreased pain sensitivity in naïve mice and effectively reduced pain-related behaviors in nociceptive pain model mice with minimal opioid-related side effects. Importantly, the compound exerted significant rapid-acting antidepressant effects in both the forced swim test and tail suspension test. It is possible that the rapid antihyperalgesic and antidepressant effects of the peptide are mediated through the OR pathway. Overall, this peptide could both effectively provide pain relief and alleviate depression with fewer side effects, suggesting that it is a potential agent for chronic pain and depression comorbidities from the perspective of pharmaceutical development.

L-NAC and L-NAC methyl ester prevent and overcome physical dependence to fentanyl in male rats

N-acetyl-L-cysteine (L-NAC) is a proposed therapeutic for opioid use disorder. This study determined whether co-injections of L-NAC (500 μmol/kg, IV) or its highly cell-penetrant analogue, L-NAC methyl ester (L-NACme, 500 μmol/kg, IV), prevent acquisition of acute physical dependence induced by twice-daily injections of fentanyl (125 μg/kg, IV), and overcome acquired dependence to these injections in freely-moving male Sprague Dawley rats. The injection of the opioid receptor antagonist, naloxone HCl (NLX; 1.5 mg/kg, IV), elicited a series of withdrawal phenomena (i.e. behavioral and cardiorespiratory responses, hypothermia and body weight loss) in rats that received 5 or 10 injections of fentanyl and similar numbers of vehicle co-injections. With respect to the development of dependence, the NLX-precipitated withdrawal phenomena were reduced in rats that received had co-injections of L-NAC, and more greatly reduced in rats that received co-injections of L-NACme. In regard to overcoming established dependence, the NLX-precipitated withdrawal phenomena in rats that had received 10 injections of fentanyl (125 μg/kg, IV) were reduced in rats that had received co-injections of L-NAC, and more greatly reduced in rats that received co-injections of L-NACme beginning with injection 6 of fentanyl. This study provides compelling evidence that co-injections of L-NAC and L-NACme prevent the acquisition of physical dependence and overcome acquired dependence to fentanyl in male rats. The higher efficacy of L-NACme is likely due to its greater cell penetrability in brain regions mediating dependence to fentanyl and interaction with intracellular signaling cascades, including redox-dependent processes, responsible for the acquisition of physical dependence to fentanyl.

Lipophilic analogues of D-cysteine prevent and reverse physical dependence to fentanyl in male rats

We examined whether co-injections of the cell-permeant D-cysteine analogues, D-cysteine ethyl ester (D-CYSee) and D-cysteine ethyl amide (D-CYSea), prevent acquisition of physical dependence induced by twice-daily injections of fentanyl, and reverse acquired dependence to these injections in freely-moving male Sprague Dawley rats. Injection of the opioid receptor antagonist, naloxone HCl (NLX, 1.5 mg/kg, IV), elicited a series of withdrawal phenomena that included cardiorespiratory and behavioral responses, and falls in body weight and body temperature, in rats that received 5 or 10 injections of fentanyl (125 μg/kg, IV), and the same number of vehicle co-injections. Regarding the development of physical dependence, the NLX-precipitated withdrawal phenomena were markedly reduced in fentanyl-injected rats that had received co-injections of D-CYSee (250 μmol/kg, IV) or D-CYSea (100 μmol/kg, IV), but not D-cysteine (250 μmol/kg, IV). Regarding reversal of established dependence to fentanyl, the NLX-precipitated withdrawal phenomena in rats that had received 10 injections of fentanyl (125 μg/kg, IV) was markedly reduced in rats that received co-injections of D-CYSee (250 μmol/kg, IV) or D-CYSea (100 μmol/kg, IV), but not D-cysteine (250 μmol/kg, IV), starting with injection 6 of fentanyl. This study provides evidence that co-injections of D-CYSee and D-CYSea prevent the acquisition of physical dependence, and reverse acquired dependence to fentanyl in male rats. The lack of effect of D-cysteine suggests that the enhanced cell-penetrability of D-CYSee and D-CYSea into cells, particularly within the brain, is key to their ability to interact with intracellular signaling events involved in acquisition to physical dependence to fentanyl.

Telling the story of the opioid crisis: A narrative analysis of the TV series Dopesick

Dopesick (2021) is the first TV series whose plot deals exclusively with the opioid crisis in the United States. The current study uses narrative analysis and framing theory to explore this series, discussing its portrayal of the people and themes involved in the opioid crisis. Our analysis found that although Dopesick attempts to portray multiple dimensions of the opioid crisis, its narrative oversimplifies the story in attributing the cause of the problem almost exclusively to Purdue Pharma and its director Richard Sackler, while downplaying other factors that contributed to the opioid crisis. Thus, the narrative in this TV series tends to offer simple explanations to a complex problem for which simple solutions are likely to be inadequate.

In Vitro and In Vivo Pharmacological Profiles of LENART01, a Dermorphin-Ranatensin Hybrid Peptide

Diverse chemical and pharmacological strategies are currently being explored to minimize the unwanted side effects of currently used opioid analgesics while achieving effective pain relief. The use of multitarget ligands with activity at more than one receptor represents a promising therapeutic approach. We recently reported a bifunctional peptide-based hybrid LENART01 combining dermorphin and ranatensin pharmacophores, which displays activity to the mu-opioid receptor (MOR) and dopamine D2 receptor (D2R) in rat brains and spinal cords. In this study, we investigated the in vitro binding and functional activities to the human MOR and the in vivo pharmacology of LENART01 in mice after subcutaneous administration. In vitro binding assays showed LENART01 to bind and be selective to the human MOR over the other opioid receptor subtypes and delta, kappa and nociceptin receptors. In the [35S]GTPγS binding assay, LENART01 acted as a potent and full agonist to the human MOR. In mice, LENART01 produced dose-dependent antinociceptive effects in formalin-induced inflammatory pain, with increased potency than morphine. Antinociceptive effects were reversed by naloxone, indicating MOR activation in vivo. Behavioral studies also demonstrated LENART01's properties to induce less adverse effects without locomotor dysfunction and withdrawal syndrome compared to conventional opioid analgesics, such as morphine. LENART01 is the first peptide-based MOR-D2R ligand known to date and the first dual MOR-dopamine D2R ligand for which in vivo pharmacology is reported with antinociceptive efficacy and reduced opioid-related side effects. Our current findings may pave the way to new pain therapeutics with limited side effects in acute and chronic use.

Inflammation, lipid dysregulation, and transient receptor potential cation channel subfamily V member 4 signaling perpetuate chronic vulvar pain

ABSTRACT

Localized provoked vulvodynia is characterized by chronic vulvar pain that disrupts every aspect of the patient's life. Pain is localized to the vulvar vestibule, a specialized ring of tissue immediately surrounding the vaginal opening involved in immune defense. In this article, we show inflammation is the critical first step necessary for the generation of pain signals in the vulva. Inflammatory stimuli alone or combined with the transient receptor potential cation channel subfamily V member 4 (TRPV4) agonist 4α-phorbol 12,13-didecanoate stimulate calcium flux into vulvar fibroblast cells. Activity is blocked by the TRPV4 antagonist HC067047, denoting specificity to TRPV4. Using lipidomics, we found pro-resolving lipids in the vulvar vestibule were dysregulated, characterized by a reduction in pro-resolving mediators and heightened production of inflammatory mediators. We demonstrate specialized pro-resolving mediators represent a potential new therapy for vulvar pain, acting on 2 key parts of the disease mechanism by limiting inflammation and acutely inhibiting TRPV4 signaling.

Incidence and Prevalence of Pain Medication Prescriptions in Pathologies with a Potential for Chronic Pain

BACKGROUND

Heightened risks of dependence, addiction, anxiolytic effects, or prescription overdose death due to long-term use of pain medication have increased awareness about extended pain medication use in chronic pain populations. The goal of this study was to evaluate the incidence and prevalence of pain medication prescriptions from 2012 to 2022 in common pathologies with a potential for chronic pain.

METHODS

A retrospective cohort study was conducted using electronic health records from TriNetX (Cambridge, Massachusetts) Global Collaborative Network. For 10 distinct cohorts (total n = 9,357,584 patients), pain medication prescriptions were extracted for five classes, namely nonsteroidal anti-inflammatory drug (NSAIDs) and acetaminophen, opioids, gabapentinoids, neuropathic mood agents, and muscle relaxants. Annual incidence and prevalence of each class of medication were evaluated for the past 11 yr.

RESULTS

From 2012 to 2022, there was a significant increase in prescriptions of NSAIDs, except for patients with fibromyalgia, and persistent spinal pain syndrome (PSPS) type 2. Interestingly, over time, prescriptions of opioids in patients with complex regional pain syndrome, endometriosis, osteoarthritis, and PSPS type 2 increased, as did prescriptions of muscle relaxants for all cohorts except those with fibromyalgia. Incidence of prescriptions of neuropathic mood agents is high for patients with complex regional pain syndrome (both types) and PSPS type 2. Only for benzodiazepines did there seem to be a decline over the years, with a significantly decreased time trend in patients with complex regional pain syndrome type 1, fibromyalgia, and PSPS type 2.

CONCLUSIONS

During the last 11 yr, an increase in incidence of NSAIDs and acetaminophen, opioids, neuropathic agents, and muscle relaxants was observed. Only prescriptions of benzodiazepines significantly decreased over time in specific cohorts. Overall, patients with PSPS type 2 and complex regional pain syndrome (both types) consume a broad variety of pain medication classes.

EDITOR’S PERSPECTIVE

Efficacy of interventions targeted at physician prescribers of opioids for chronic non-cancer pain: an overview of systematic reviews

BACKGROUND

To combat the opioid crisis, interventions targeting the opioid prescribing behaviour of physicians involved in the management of patients with chronic non-cancer pain (CNCP) have been introduced in clinical settings. An integrative synthesis of systematic review evidence is required to better understand the effects of these interventions. Our objective was to synthesize the systematic review evidence on the effect of interventions targeting the behaviours of physician opioid prescribers for CNCP among adults on patient and population health and prescriber behaviour.

METHODS

We searched MEDLINE, Embase, and PsycInfo via Ovid; the Cochrane Database of Systematic Reviews; and Epistemonikos. We included systematic reviews that evaluate any type of intervention aimed at impacting opioid prescriber behaviour for adult CNCP in an outpatient setting.

RESULTS

We identified three full texts for our review that contained 68 unique primary studies. The main interventions we evaluated were structured prescriber education (one review) and prescription drug monitoring programmes (PDMPs) (two reviews). Due to the paucity of data available, we could not determine with certainty that education interventions improved outcomes in deprescribing. There is some evidence that PDMPs decrease the number of adverse opioid-related events, increase communication among healthcare workers and patients, modify healthcare practitioners' approach towards their opioid prescribed patients, and offer more chances for education and counselling.

CONCLUSIONS

Our overview explores the possibility of PDMPs as an opioid deprescribing intervention and highlights the need for more high-quality primary research on this topic.

Methadone Requires the Co-Activation of μ-Opioid and Toll-Like-4 Receptors to Produce Extracellular DNA Traps in Bone-Marrow-Derived Mast Cells

Methadone is an effective and long-lasting analgesic drug that is also used in medication-assisted treatment for people with opioid use disorders. Although there is evidence that methadone activates μ-opioid and Toll-like-4 receptors (TLR-4s), its effects on distinct immune cells, including mast cells (MCs), are not well characterized. MCs express μ-opioid and Toll-like receptors (TLRs) and constitute an important cell lineage involved in allergy and effective innate immunity responses. In the present study, murine bone-marrow-derived mast cells (BMMCs) were treated with methadone to evaluate cell viability by flow cytometry, cell morphology with immunofluorescence and scanning electron microscopy, reactive oxygen species (ROS) production, and intracellular calcium concentration ([Ca2+]i) increase. We found that exposure of BMMCs to 0.5 mM or 1 mM methadone rapidly induced cell death by forming extracellular DNA traps (ETosis). Methadone-induced cell death depended on ROS formation and [Ca2+]i. Using pharmacological approaches and TLR4-defective BMMC cultures, we found that µ-opioid receptors were necessary for both methadone-induced ROS production and intracellular calcium increase. Remarkably, TLR4 receptors were also involved in methadone-induced ROS production as it did not occur in BMMCs obtained from TLR4-deficient mice. Finally, confocal microscopy images showed a significant co-localization of μ-opioid and TLR4 receptors that increased after methadone treatment. Our results suggest that methadone produces MCETosis by a mechanism requiring a novel crosstalk pathway between μ-opioid and TLR4 receptors.

Association of initial opioid prescription duration and an opioid refill by pain diagnosis: Evidence from outpatient settings in ten US health systems

OBJECTIVE

The Centers for Disease Control and Prevention's 2022 Clinical Practice Guideline for Prescribing Opioids for Pain cautioned that inflexible opioid prescription duration limits may harm patients. Information about the relationship between initial opioid prescription duration and a subsequent refill could inform prescribing policies and practices to optimize patient outcomes. We assessed the association between initial opioid duration and an opioid refill prescription.

METHODS

We conducted a retrospective cohort study of adults ≥19 years of age in 10 US health systems between 2013 and 2018 from outpatient care with a diagnosis for back pain without radiculopathy, back pain with radiculopathy, neck pain, joint pain, tendonitis/bursitis, mild musculoskeletal pain, severe musculoskeletal pain, urinary calculus, or headache. Generalized additive models were used to estimate the association between opioid days' supply and a refill prescription.

RESULTS

Overall, 220,797 patients were prescribed opioid analgesics upon an outpatient visit for pain. Nearly a quarter (23.5%) of the cohort received an opioid refill prescription during follow-up. The likelihood of a refill generally increased with initial duration for most pain diagnoses. About 1 to 3 fewer patients would receive a refill within 3 months for every 100 patients initially prescribed 3 vs. 7 days of opioids for most pain diagnoses. The lowest likelihood of refill was for a 1-day supply for all pain diagnoses, except for severe musculoskeletal pain (9 days' supply) and headache (3-4 days' supply).

CONCLUSIONS

Long-term prescription opioid use increased modestly with initial opioid prescription duration for most but not all pain diagnoses examined.

Isolectin B4 (IB4)-conjugated streptavidin for the selective knockdown of proteins in IB4-positive (+) nociceptors

In vivo analysis of protein function in nociceptor subpopulations using antisense oligonucleotides and short interfering RNAs is limited by their non-selective cellular uptake. To address the need for selective transfection methods, we covalently linked isolectin B4 (IB4) to streptavidin and analyzed whether it could be used to study protein function in IB4(+)-nociceptors. Rats treated intrathecally with IB4-conjugated streptavidin complexed with biotinylated antisense oligonucleotides for protein kinase C epsilon (PKCε) mRNA were found to have: a) less PKCε in dorsal root ganglia (DRG), b) reduced PKCε expression in IB4(+) but not IB4(-) DRG neurons, and c) fewer transcripts of the PKCε gene in the DRG. This knockdown in PKCε expression in IB4(+) DRG neurons is sufficient to reverse hyperalgesic priming, a rodent model of chronic pain that is dependent on PKCε in IB4(+)-nociceptors. These results establish that IB4-streptavidin can be used to study protein function in a defined subpopulation of nociceptive C-fiber afferents.

Developing mathematical models to compare and analyse the pharmacokinetics of morphine and fentanyl

Background and Aims

The two-compartment model is generally used in pharmacokinetics to illustrate the distribution and excretion of drugs. In this study, we evaluated the distribution patterns of morphine and fentanyl by using a two-compartment model.

Methods

Using numeric analysis techniques, non-linear ordinary differential equations were used to mathematically analyse drug distribution, transition, and concentration in the body compartments. Math Works, Inc., MATLAB, version 2023a, a programming tool, was used to characterise the impact of initial concentration and rate constants on the kinetics of the drug. For a definite therapeutic concentration of morphine and fentanyl in blood, pharmacokinetic characteristics were plotted.

Results

The study results showed the time taken by morphine and fentanyl to reach a target concentration in the blood that is sufficient to generate the preferred therapeutic effects. The mathematical models comparing morphine and fentanyl pharmacokinetics showed that fentanyl reached the target therapeutic concentration 125 minutes earlier than morphine and was metabolised and removed from the body more rapidly (44 minutes earlier than morphine).

Conclusion

These comparative mathematical models on morphine and fentanyl enable the determination of drug dosages and understanding of drug efficacy that facilitates optimising dosing regimens. The right choice between them can be made based on the time to reach the target therapeutic concentration in the blood, elimination time, severity of pain, and patient characteristics.

Resistant and refractory migraine: clinical presentation, pathophysiology, and management

Migraine is a leading cause of disability worldwide. A minority of individuals with migraine develop resistant or refractory conditions characterised by ≥ 8 monthly days of debilitating headaches and inadequate response, intolerance, or contraindication to ≥3 or all preventive drug classes, respectively. Resistant and refractory migraine are emerging clinical definitions stemming from better knowledge of the pathophysiology of migraine and from the advent of migraine-specific preventive treatments. Resistant migraine mostly results from drug failures, while refractory migraine has complex and still unknown mechanisms that impair the efficacy of preventive treatments. Individuals with resistant migraine can be treated with migraine-specific preventive drugs. The management of refractory migraine is challenging and often unsuccessful, being based on combinations of different drugs and non-pharmacological treatment. Future research should aim to identify individuals at risk of developing treatment failures, prevent the condition, investigate the mechanisms of refractoriness to treatments, and find effective treatment strategies.

A Review of Drug Abuse, Misuse, and Related Laboratory Challenges

Various definitions can be considered for drugs and substance abuse. According to the National Institute on Abuse, the use of an over-the-counter drug in a different way than that prescribed to experience or arouse emotion is a simple form of drug abuse. The World Health Organization (WHO) also defines drug abuse as the persistent or sporadic use of drugs that are incompatible or unrelated to acceptable medical practice. With the increasing non-therapeutic use of prescription drugs, serious related consequences have also increased. Therefore, there is a need to know more precisely about the types of substances and drug abuse, which is the most important part of diagnosis and recognizing the tests that cause false positive and negative results. The purpose of this review article is to collect and summarize the most important and more common types of drugs of abuse and review the drugs that cause false results in screening tests. In addition, the most common detection methods of the drug will be reviewed and the advantages and drawbacks of each method will be discussed. In this article, we aimed to point out all the facts about the emerging problems in drug abuse, the methods of screening, and the possible false results in addition to troubleshooting strategies.

Traumatic Brain Injury and Opioids: Twin Plagues of the Twenty-First Century

Traumatic brain injury (TBI) and opioid use disorder (OUD) comprise twin plagues causing considerable morbidity and mortality worldwide. As interactions between TBI and OUD are to our knowledge uncharted, we review the possible mechanisms by which TBI may stimulate the development of OUD and discuss the interaction or crosstalk between these two processes. Central nervous system damage due to TBI appears to drive adverse effects of subsequent OUD and opioid use/misuse affecting several molecular pathways. Pain, a neurological consequence of TBI, is a risk factor that increases the likelihood of opioid use/misuse after TBI. Other comorbidities including depression, anxiety, posttraumatic stress disorder, and sleep disturbances are also associated with deleterious outcomes. We examine the hypothesis that a TBI "first hit" induces a neuroinflammatory process involving microglial priming, which, on a second hit related to opioid exposure, exacerbates neuroinflammation, modifies synaptic plasticity, and spreads tau aggregates to promote neurodegeneration. As TBI also impairs myelin repair by oligodendrocytes, it may reduce or degrade white matter integrity in the reward circuit resulting in behavioral changes. Along with approaches focused on specific patient symptoms, understanding the CNS effects following TBI offers a promise of improved management for individuals with OUD.

Isolectin B4 (IB4)-conjugated streptavidin for the selective knockdown of proteins in IB4-positive (+) nociceptors

In vivo analysis of protein function in nociceptor subpopulations using antisense oligonucleotides and short interfering RNAs is limited by their non-selective cellular uptake. To address the need for selective transfection methods, we covalently linked isolectin B4 (IB4) to streptavidin and analyzed whether it could be used to study protein function in IB4(+)-nociceptors. Rats treated intrathecally with IB4-conjugated streptavidin complexed with biotinylated antisense oligonucleotides for protein kinase C epsilon (PKCε) mRNA were found to have: (a) less PKCε in dorsal root ganglia (DRG), (b) reduced PKCε expression in IB4(+) but not IB4(-) DRG neurons, and (c) fewer transcripts of the PKCε gene in the DRG. This knockdown in PKCε expression in IB4(+) DRG neurons is sufficient to reverse hyperalgesic priming, a rodent model of chronic pain that is dependent on PKCε in IB4(+)-nociceptors. These results establish that IB4-streptavidin can be used to study protein function in a defined subpopulation of nociceptive C-fiber afferents.

L-cysteine ethyl ester prevents and reverses acquired physical dependence on morphine in male Sprague Dawley rats

The molecular mechanisms underlying the acquisition of addiction/dependence on morphine may result from the ability of the opioid to diminish the transport of L-cysteine into neurons via inhibition of excitatory amino acid transporter 3 (EAA3). The objective of this study was to determine whether the co-administration of the cell-penetrant L-thiol ester, L-cysteine ethyl ester (L-CYSee), would reduce physical dependence on morphine in male Sprague Dawley rats. Injection of the opioid-receptor antagonist, naloxone HCl (NLX; 1.5 mg/kg, IP), elicited pronounced withdrawal phenomena in rats which received a subcutaneous depot of morphine (150 mg/kg) for 36 h and were receiving a continuous infusion of saline (20 μL/h, IV) via osmotic minipumps for the same 36 h period. The withdrawal phenomena included wet-dog shakes, jumping, rearing, fore-paw licking, 360° circling, writhing, apneas, cardiovascular (pressor and tachycardia) responses, hypothermia, and body weight loss. NLX elicited substantially reduced withdrawal syndrome in rats that received an infusion of L-CYSee (20.8 μmol/kg/h, IV) for 36 h. NLX precipitated a marked withdrawal syndrome in rats that had received subcutaneous depots of morphine (150 mg/kg) for 48 h) and a co-infusion of vehicle. However, the NLX-precipitated withdrawal signs were markedly reduced in morphine (150 mg/kg for 48 h)-treated rats that began receiving an infusion of L-CYSee (20.8 μmol/kg/h, IV) at 36 h. In similar studies to those described previously, neither L-cysteine nor L-serine ethyl ester (both at 20.8 μmol/kg/h, IV) mimicked the effects of L-CYSee. This study demonstrates that 1) L-CYSee attenuates the development of physical dependence on morphine in male rats and 2) prior administration of L-CYSee reverses morphine dependence, most likely by intracellular actions within the brain. The lack of the effect of L-serine ethyl ester (oxygen atom instead of sulfur atom) strongly implicates thiol biochemistry in the efficacy of L-CYSee. Accordingly, L-CYSee and analogs may be a novel class of therapeutics that ameliorate the development of physical dependence on opioids in humans.

Oxycodone, Morphine, and Fentanyl in Patients With Chronic Pain: Proposal of Dose-Specific Concentration Ranges

BACKGROUND

Interpreting opioid concentrations is challenging because of the lack of reference ranges. Therefore, the authors aimed to propose dose-specific concentration ranges in serum for oxycodone, morphine, and fentanyl in patients with chronic pain, based on concentration measurements from a large number of patients and supported by theoretical pharmacokinetic calculations and previously published concentrations.

METHODS

The opioid concentrations in patients undergoing therapeutic drug monitoring (TDM) for various indications (TDM group) and patients with cancer (cancer group) were investigated. Patients were divided based on the daily opioid doses, and the 10th and 90th percentiles of the concentrations in each dose interval were evaluated. In addition, the expected average serum concentrations were calculated for each dose interval based on published pharmacokinetic data, and a targeted literature search for previously reported dose-specific concentrations was performed.

RESULTS

The opioid concentrations in 1054 patient samples were included: 1004 in the TDM group and 50 in the cancer group. In total, 607 oxycodone, 246 morphine, and 248 fentanyl samples were evaluated. The authors proposed dose-specific concentration ranges based mainly on 10th-90th percentiles of the concentrations measured in patient samples, whereas the calculated average concentrations and previously published concentrations were used to adjust the ranges. In general, results from calculations and concentrations retrieved from previous literature were within the 10th-90th percentiles of concentrations from patient samples. However, the lowest calculated average concentrations of fentanyl and morphine were below the 10th percentiles of patient samples in all dose groups.

CONCLUSIONS

The proposed dose-specific ranges may be useful for interpreting steady-state opioid serum concentrations in clinical and forensic settings.

Modification and Delivery of Enkephalins for Pain Modulation

Chronic pain negatively affects patient's quality of life and poses a significant economic burden. First line pharmaceutical treatment of chronic pain, including NSAIDs or antidepressants, is often inefficient to reduce pain, or produces intolerable adverse effects. In such cases, opioids are frequently prescribed for their potent analgesia, but chronic opioid use is also frequently associated with debilitating side effects that may offset analgesic benefits. Nonetheless, opioids continue to be widely utilized due to the lack of effective alternative analgesics. Since their discovery in 1975, a class of endogenous opioids called enkephalins (ENKs) have been investigated for their ability to relieve pain with significantly reduced adverse effects compared to conventional opioids. Their low metabolic stability and inability to cross biological membranes, however, make ENKs ineffective analgesics. Over past decades, much effort has been invested to overcome these limitations and develop ENK-based pain therapies. This review summarizes and describes chemical modifications and ENK delivery technologies utilizing ENK conjugates, nanoparticles and ENK gene delivery approaches and discusses valid lessons, challenges, and future directions of this evolving field.

A cholinergic circuit that relieves pain despite opioid tolerance

Chronic pain is a tremendous burden for afflicted individuals and society. Although opioids effectively relieve pain, significant adverse outcomes limit their utility and efficacy. To investigate alternate pain control mechanisms, we explored cholinergic signaling in the ventrolateral periaqueductal gray (vlPAG), a critical nexus for descending pain modulation. Biosensor assays revealed that pain states decreased acetylcholine release in vlPAG. Activation of cholinergic projections from the pedunculopontine tegmentum to vlPAG relieved pain, even in opioid-tolerant conditions, through ⍺7 nicotinic acetylcholine receptors (nAChRs). Activating ⍺7 nAChRs with agonists or stimulating endogenous acetylcholine inhibited vlPAG neuronal activity through Ca2+ and peroxisome proliferator-activated receptor α (PPAR⍺)-dependent signaling. In vivo 2-photon imaging revealed that chronic pain induces aberrant excitability of vlPAG neuronal ensembles and that ⍺7 nAChR-mediated inhibition of these cells relieves pain, even after opioid tolerance. Finally, pain relief through these cholinergic mechanisms was not associated with tolerance, reward, or withdrawal symptoms, highlighting its potential clinical relevance.

A qualitative study of chronic pain and opioid use: The impact of restrictive prescribing

OBJECTIVES

To explore the continuum of pain and addiction for patients with chronic pain (CP) who used opioids during a time of restrictive opioid prescribing in West Virginia.

DESIGN

This qualitative descriptive study used a content analysis of semistructured interviews. Themes were identified through a reflective, iterative coding process. Consolidated criteria for reporting qualitative research guidelines were followed.

SETTING

West Virginia.

PARTICIPANTS

Twenty people who used opioids to treat a CP condition, 10 pharmacists, 10 primary care providers, and 10 specialists.

INTERVENTION

Semistructured interviews.

MAIN OUTCOME MEASURE

To better understand the impact of restrictive prescribing measures on people who used opioids for CP.

RESULTS

Patients initiated opioids for acute, painful conditions and described how long-term use led to physical dependence and, for some, opioid use disorder. Restrictive opioid prescribing laws led to care interruptions and decreased access and availability of prescribed opioid pain medication, driving some patients to seek illicit drugs. Economic considerations influenced drug use as the price of purchasing prescription opioids on the street went up, making heroin a cheaper alternative. Patients who transitioned to buprenorphine/naloxone as a treatment for pain or opioid use disorder viewed it as a positive change and a "life saver."

CONCLUSIONS

Opioid use for CP is complex and multifaceted. The continuum of pain and opioid use disorder can begin with a prescription for acute pain and continue for the treatment of CP. Patients described how continued opioid use was not to "get high" but for pain control to improve their quality of life, continue to work, and be productive. For those who experience physical dependence on opioids, access to treatment is vital to recovery and pain management.

KEY MESSAGE

Without individualized managed care, people confronted with a sudden interruption in prescription opioids may turn to illicit drugs to mitigate symptoms of opioid withdrawal and physical dependence.

Poppy Seeds Signal Limitations of Urine Drug Testing Protocols

Appropriate care for patients with chronic pain is complex, requiring a thoughtful and holistic approach to pharmacologic intervention, as well as appropriate monitoring when opioids are employed as part of a multimodal regimen. The urine drug test has become an expected standard when longterm opioids are prescribed, but it should be remembered that this test is not intended to be punitive. It is ordered to promote patient safety (Dowell et al., 2022). Recent literature and events surrounding the effect of poppy seeds on urine drug test results have drawn attention to the risks of misinterpreting this test (Bloch, 2023; Lewis et al., 2021; Reisfield et al., 2023; Temple, 2023). Misinterpretation of urine drug tests creates a potential for unfounded accusations from health care workers toward patients, thus, undermining therapeutic relationships and intensifying stigma. Such circumstances may also preclude chances to offer patients needed interventions. Therefore, a valuable opportunity exists for nurses to mitigate untoward consequences by developing a robust understanding of urine drug testing, destigmatizing chronic pain and opioid use, advocating for patients, and enacting change at both an individual and a systems-level.

An ethogram analysis of cutaneous thermal pain sensitivity and oxycodone reward-related behaviors in rats

Inter-relationships between pain sensitivity, drug reward, and drug misuse are of considerable interest given that many analgesics exhibit misuse potential. Here we studied rats as they underwent a series of pain- and reward-related tests: cutaneous thermal reflex pain, induction and extinction of conditioned place preference to oxycodone (0.56 mg/kg), and finally the impact of neuropathic pain on reflex pain and reinstatement of conditioned place preference. Oxycodone induced a significant conditioned place preference that extinguished throughout repeated testing. Correlations identified of particular interest included an association between reflex pain and oxycodone-induced behavioral sensitization, and between rates of behavioral sensitization and extinction of conditioned place preference. Multidimensional scaling analysis followed by k-clustering identified three clusters: (1) reflex pain, rate of behavioral sensitization and rate of extinction of conditioned place preference (2) basal locomotion, locomotor habituation, acute oxycodone-stimulated locomotion and rate of change in reflex pain during repeated testing, and (3) magnitude of conditioned place preference. Nerve constriction injury markedly enhanced reflex pain but did not reinstate conditioned place preference. These results suggest that high rates of behavioral sensitization predicts faster rates of extinction of oxycodone seeking/reward, and suggest that cutaneous thermal reflex pain may be predictive of both.

Chronic inflammatory pain promotes place preference for fentanyl in male rats but does not change fentanyl self-administration in male and female rats

The current opioid epidemic is a national health crisis marked by skyrocketing reports of opioid misuse and overdose deaths. Despite the risks involved, prescription opioid analgesics are the most powerful and effective medications for treating pain. There is a clear need to investigate the risk of opioid misuse liability in male and female adults experiencing chronic pain. In the present study, we tested the hypothesis that chronic inflammatory pain would increase fentanyl intake, motivation to acquire fentanyl, and drug seeking in the absence of fentanyl in rats. Fentanyl intake, motivation for fentanyl, and drug seeking were tested under limited and extended access conditions using intravenous fentanyl self-administration. Fos activity in ventral tegmental area (VTA) dopamine neurons following intravenous fentanyl challenge (35 μg/kg) was examined using immunohistochemistry. Finally, we tested whether low-dose fentanyl supports development of conditioned place preference under an inflammatory pain state in rats. Contrary to our hypothesis, fentanyl self-administration and VTA Fos activity were unaffected by inflammatory pain status. During acquisition, males exhibited increased fentanyl intake compared to females. Animals given extended access to fentanyl escalated fentanyl intake over time, while animals given limited access did not. Males given extended access to fentanyl demonstrated a greater increase in fentanyl intake over time compared to females. During the dose-response test, females given limited access to fentanyl demonstrated increased motivation to acquire fentanyl compared to males. Both sexes displayed significant increases in responding for fentanyl as unit fentanyl doses were lowered. Following fentanyl challenge, females exhibited higher numbers of Fos-positive non-dopaminergic VTA neurons compared to males. Using conditioned place preference, we found that chronic inflammatory pain promotes fentanyl preference in males, but not females. These findings suggest that established fentanyl self-administration is resistant to change by inflammatory pain manipulation in both sexes, but chronic inflammatory pain increases the rewarding properties of low-dose fentanyl in males.

Peripheralization Strategies Applied to Morphinans and Implications for Improved Treatment of Pain

Opioids are considered the most effective analgesics for the treatment of moderate to severe acute and chronic pain. However, the inadequate benefit/risk ratio of currently available opioids, together with the current 'opioid crisis', warrant consideration on new opioid analgesic discovery strategies. Targeting peripheral opioid receptors as effective means of treating pain and avoiding the centrally mediated side effects represents a research area of substantial and continuous attention. Among clinically used analgesics, opioids from the class of morphinans (i.e., morphine and structurally related analogues) are of utmost clinical importance as analgesic drugs activating the mu-opioid receptor. In this review, we focus on peripheralization strategies applied to N-methylmorphinans to limit their ability to cross the blood-brain barrier, thus minimizing central exposure and the associated undesired side effects. Chemical modifications to the morphinan scaffold to increase hydrophilicity of known and new opioids, and nanocarrier-based approaches to selectively deliver opioids, such as morphine, to the peripheral tissue are discussed. The preclinical and clinical research activities have allowed for the characterization of a variety of compounds that show low central nervous system penetration, and therefore an improved side effect profile, yet maintaining the desired opioid-related antinociceptive activity. Such peripheral opioid analgesics may represent alternatives to presently available drugs for an efficient and safer pain therapy.

Everybody Hurts: Intersecting and Colliding Epidemics and the Need for Integrated Behavioral Treatment of Chronic Pain and Substance Use

Chronic pain and substance use disorders are both common, debilitating, and often persist over the longer term. On their own, each represents a significant health problem, with estimates indicating a substantial proportion of the adult population has chronic pain or a substance use disorder (SUD), and their co-occurrence is increasing. Chronic pain and SUD are also both often invisible, stigmatized disorders and persons with both regularly have difficulty accessing evidence-based treatments, particularly those that offer coordinated and integrated treatment for both conditions. But there is hope. Research is unraveling the mechanisms of chronic pain and substance use, as well as their co-occurrence, integrated behavioral treatment options based on acceptance- and mindfulness-based approaches are increasingly being developed and tested, government agencies are devoting more funds and resources to increase research on chronic pain and SUD, and there have been growing efforts in training, dissemination, and implementation of evidence-based treatments. At the very heart of the matter, though, is to recognize that everybody hurts sometimes, and treatments must empower people to life effectively with these experiences of being human.

A Need for Further Education on Buprenorphine in Pain Medicine

With the ongoing opioid epidemic in the United States there has been a strong transition towards utilizing multi-modal analgesia, interventional procedures, and non-opioid medications when managing acute and chronic pain. There has also been an increased interest in utilizing buprenorphine. Buprenorphine is a novel long-acting analgesic with partial mu-opioid agonist activity that can be utilized for analgesia as well as opioid use disorder. Buprenorphine also has a unique set of side effects as well pharmacodynamic and pharmacokinetic properties that require special attention, especially if these patients require future surgical interventions. Given the increased interest in this medication we believe that there needs to be increased education and awareness regarding this medication amongst physicians, specifically pain management physicians and trainees.

Molecular and Epigenetic Aspects of Opioid Receptors in Drug Addiction and Pain Management in Sport

Opioids are substances derived from opium (natural opioids). In its raw state, opium is a gummy latex extracted from Papaver somniferum. The use of opioids and their negative health consequences among people who use drugs have been studied. Today, opioids are still the most commonly used and effective analgesic treatments for severe pain, but their use and abuse causes detrimental side effects for health, including addiction, thus impacting the user's quality of life and causing overdose. The mesocorticolimbic dopaminergic circuitry represents the brain circuit mediating both natural rewards and the rewarding aspects of nearly all drugs of abuse, including opioids. Hence, understanding how opioids affect the function of dopaminergic circuitry may be useful for better knowledge of the process and to develop effective therapeutic strategies in addiction. The aim of this review was to summarize the main features of opioids and opioid receptors and focus on the molecular and upcoming epigenetic mechanisms leading to opioid addiction. Since synthetic opioids can be effective for pain management, their ability to induce addiction in athletes, with the risk of incurring doping, is also discussed.

Myofascial Temporomandibular Disorders at a Turning Point: Pragmatic or Evidence-Based Management?

Unvalidated theories have been proposed for the etiopathogenesis of masticatory myofascial temporomandibular disorders (mTMD). Modalities such as cone-beam computed tomography/computed tomography and MRI contributes little to the diagnosis of mTMD. Diagnosing mTMD is based on the recognition of "familiar pain" presentation in the masticatory myofascial tissue. This assessment tool contributes little our understanding of the underlying disease process. Thus, management of mTMD is empirical and arbitrary. Exploring emerging technologies to identify biomarkers and objectively assess myofascial tissue physiology in disease and health may be key in moving the diagnosis of mTMD from the pragmatic paradigm to an evidence-based paradigm.

Opioid Agents and Cardiac Arrhythmia: A Literature Review

Opioids are compounds that cause similar effects to morphine by binding to its receptors. Opioids can be synthetic, semi-synthetic, or natural and can easily bind to the receptors of opioids in order to depict their effects, which may vary depending upon the exposure of the drug and its dose. However, several side effects of opioids can also be observed, with the most crucial being their impact on the heart's electrical activity. This review majorly focuses on opioids' impact on the prolongation of the QT curve and their arrhythmogenic susceptibility. Articles published up to the year 2022 in various databases were identified and searched with the use of keywords. Search terms included "cardiac arrhythmias," "QT interval," "opioids," "opioid dependence," and "torsade de pointes (TdP)". These terms highlight the impact of each opioid agent on the activity of the heart on an electrocardiogram. The results of the available data depict that opioids, such as methadone, pose higher risks, even when taken in smaller amounts, and have the capability for QT interval prolongation and TdP development. A variety of opioids, i.e., oxycodone and tramadol, are considered as intermediary risk drugs and can build long QT intervals and TdP in large doses. Several other opioids are considered low-risk drugs, including buprenorphine and morphine, which lead to no production of TdP and QT interval prolongation in daily routine doses. Evidence indicates a high risk of sinus bradycardia, atrial fibrillation, cardiac block, and supra-ventricular arrhythmias in opium consumers. This literature review will play a key role in determining the association between the use of opioids and cardiac arrhythmias. It will further highlight the practical implications of opioids for the management of cardiac issues based on their dose, frequency, and intensity. Moreover, it will also depict the adverse effects of opioids along with their dose-specific relationship. Opioids display disparate cardiac arrhythmogenicity, and methadone contains a greater ability to induce long QT intervals and hazardous arrhythmias at conventional doses. In order to reduce arrhythmogenic risk, opioids taken in large amounts should be monitored with a regular electrocardiogram in high-risk consumers, i.e., patients on opioid maintenance.

Targeting the chemokine ligand 2-chemokine receptor 2 axis provides the possibility of immunotherapy in chronic pain

Chronic pain affects patients' physical and psychological health and quality of life, entailing a tremendous public health challenge. Currently, drugs for chronic pain are usually associated with a large number of side effects and poor efficacy. Chemokines in the neuroimmune interface combine with their receptors to regulate inflammation or mediate neuroinflammation in the peripheral and central nervous system. Targeting chemokines and their receptor-mediated neuroinflammation is an effective means to treat chronic pain. In recent years, growing evidence has shown that the expression of chemokine ligand 2 (CCL2) and its main chemokine receptor 2 (CCR2) is involved in its occurrence, development and maintenance of chronic pain. This paper summarises the relationship between the chemokine system, CCL2/CCR2 axis, and chronic pain, and the CCL2/CCR2 axis changes under different chronic pain conditions. Targeting chemokine CCL2 and its chemokine receptor CCR2 through siRNA, blocking antibodies, or small molecule antagonists may provide new therapeutic possibilities for managing chronic pain.

A small molecule ligand for the novel pain target, GPR171, produces minimal reward in mice

ProSAAS is one of the most abundant proteins in the brain and is processed into several smaller peptides. One of which, BigLEN, is an endogenous ligand for the G protein-coupled receptor, GPR171. Recent work in rodent models has shown that a small-molecule ligand for GPR171, MS15203, increases morphine antinociception and is effective in lessening chronic pain. While these studies provide evidence for GPR171 as a possible pain target, its abuse liability has not yet been assessed and was evaluated in the current study. We first mapped the distribution of GPR171 and ProSAAS throughout the reward circuit of the brain using immunohistochemistry and showed that GPR171 and ProSAAS are localized in the hippocampus, basolateral amygdala, nucleus accumbens, prefrontal cortex. In the major dopaminergic structure, the ventral tegmental area (VTA), GPR171 appeared to be primarily localized in dopamine neurons while ProSAAS is outside of dopamine neurons. Next, MS15203 was administered to mice with or without morphine, and VTA slices were stained for the immediate early gene c-Fos as a marker of neuronal activation. Quantification of c-Fos-positive cells revealed no statistical difference between MS15203 and saline, suggesting that MS15203 does not increase VTA activation and dopamine release. The results of a conditioned place preference experiment showed that treatment with MS15203 produced no place preference indicating a lack of reward-related behavior. Taken together this data provides evidence that the novel pain therapeutic, MS15203, has minimal reward liability. Therefore, GPR171 deserves further exploration as a pain target. SIGNIFICANCE STATEMENT: MS15203, a drug that activates the receptor GPR171, was previously shown to increase morphine analgesia. The authors use in vivo and histological techniques to show that it fails to activate the rodent reward circuitry, providing support for the continued exploration of MS15203 as a novel pain drug, and GPR171 a novel pain target.

Piloting Smart Home Sensors to Detect Overnight Respiratory and Withdrawal Symptoms in Adults Prescribed Opioids

BACKGROUND

Novel strategies are needed to curb the opioid overdose epidemic. Smart home sensors have been successfully deployed as digital biomarkers to monitor health conditions, yet they have not been used to assess symptoms important to opioid use and overdose risks.

AIM

This study piloted smart home sensors and investigated their ability to accurately detect clinically pertinent symptoms indicative of opioid withdrawal or respiratory depression in adults prescribed methadone.

METHODS

Participants (n = 4; 3 completed) were adults with opioid use disorder exhibiting moderate levels of pain intensity, withdrawal symptoms, and sleep disturbance. Participants were invited to two 8-hour nighttime sleep opportunities to be recorded in a sleep research laboratory, using observed polysomnography and ambient smart home sensors attached to lab bedroom walls. Measures of feasibility included completeness of data captured. Accuracy was determined by comparing polysomnographic data of sleep/wake and respiratory status assessments with time and event sensor data.

RESULTS

Smart home sensors captured overnight data on 48 out of 64 hours (75% completeness). Sensors detected sleep/wake patterns in alignment with observed sleep episodes captured by polysomnography 89.4% of the time. Apnea events (n = 118) were only detected with smart home sensors in two episodes where oxygen desaturations were less severe (>80%).

CONCLUSIONS

Smart home technology could serve as a less invasive substitute for biologic monitoring for adults with pain, sleep disturbances, and opioid withdrawal symptoms. Supplemental sensors should be added to detect apnea events. Such innovations could provide a step forward in assessing overnight symptoms important to populations taking opioids.

Intrathecal liproxstatin-1 delivery inhibits ferroptosis and attenuates mechanical and thermal hypersensitivities in rats with complete Freund’s adjuvant-induced inflammatory pain

Previous studies have confirmed the relationship between iron-dependent ferroptosis and a peripheral nerve injury-induced neuropathic pain model. However, the role of ferroptosis in inflammatory pain remains inconclusive. Therefore, we aimed to explore whether ferroptosis in the spinal cord and dorsal root ganglion contributes to complete Freund’s adjuvant (CFA)-induced painful behaviors in rats. Our results revealed that various biochemical and morphological changes were associated with ferroptosis in the spinal cord and dorsal root ganglion tissues of CFA rats. These changes included iron overload, enhanced lipid peroxidation, disorders of anti-acyl-coenzyme A synthetase long-chain family member 4 and glutathione peroxidase 4 levels, and abnormal morphological changes in mitochondria. Intrathecal treatment of liproxstatin-1 (a ferroptosis inhibitor) reversed these ferroptosis-related changes and alleviated mechanical and thermal hypersensitivities in CFA rats. Our study demonstrated the occurrence of ferroptosis in the spinal cord and dorsal root ganglion tissues in a rodent model of inflammatory pain and indicated that intrathecal administration of ferroptosis inhibitors, such as liproxstatin-1, is a potential therapeutic strategy for treating inflammatory pain.

A Pilot Study Comparing Algorithmic Adaptive Conventional Stimulation with High-Dose Stimulation in Chronic Pain Patients

INTRODUCTION

Spinal cord stimulation is an effective method of treatment for chronic pain. We previously showed that programming using accelerometry was advantageous for paresthesia-based stimulation. However, programming can be labor intensive.

OBJECTIVE

Here we focus on standardized programming for both accelerometer-based paresthesia-induced programming (termed "shuffle") and high-dose (HD) subthreshold programming with stimulation delivered over the T9-10 interspace.

METHODS

In this prospective cross-over study, patients received 4 weeks of shuffle programming and 4 weeks of HD programming in a randomized order. In both intervals, contacts overlying T9-10 were programmed. Pain scales with measurements of activity and sleep were collected at the end of each study arm and compared with preoperative baseline scores.

RESULTS

Twelve patients were enrolled, with 10 patients completing this study. Compared with baseline, during the HD study period, significant improvements were seen in worst pain of week (P = 0.03) and current pain (P = 0.04) as rated on Numeric Rating Scale scores and walking on the Activity Test (P = 0.012). No difference was seen from baseline compared with shuffle stimulation or in shuffle stimulation compared with HD stimulation.

CONCLUSION

In this pilot study, we demonstrated that HD stimulation at T9-10 is superior to algorithmic programming of paresthesia-based stimulation. These results compared with our previous work with shuffle suggest that paresthesia-based stimulation may necessitate stimulation of additional contact locations and additional programming to optimize. This algorithmic programming of paresthesia-based stimulation continues to warrant exploration.

Demographic and Clinical Correlates of Treatment Completion among Older Adults with Heroin and Prescription Opioid Use Disorders

In this study using 2015-2018 Treatment Episode Data Set-Discharge (TEDS-D) cases age 55+ for heroin (N = 101,524) or prescription opioids (PO; N = 25,510) as the primary substance, we examined treatment completion rates and correlates. We fit separate logistic regression models for heroin and PO cases with treatment completion status (completed vs. discontinued due to dropout/termination/other reasons) for each treatment setting (detoxification, residential rehabilitation, and outpatient) as the dependent variable. Results show that detoxification cases had the highest completion rates and outpatient cases had the lowest (14.8% for heroin and 24.0% for PO cases). A consistently significant correlate of treatment completion was legal system referral for heroin cases and having a bachelor's degree for PO cases. Medication-assisted therapy was associated with higher odds of completing residential treatment for both types of opioids but lower odds of completing detoxification and outpatient treatment. Treatment duration >30 days tended to have higher odds of completion. PO cases age 65+ had higher odds of completing residential treatment than cases age 55-64. Racial/ethnic minorities tended to have lower odds of outpatient treatment completion. Study findings underscore the importance of helping older adults complete treatment, especially those who are racial/ethnic minorities and receiving outpatient treatment.

Variations in mitragynine content in the naturally growing Kratom (Mitragyna speciosa) population of Thailand

We analyzed the content of mitragynine (MG) found in kratom leaves (Mitragyna speciosa) and the influence of different environmental conditions (air and soil variables) on the yield in various regions of Thailand. The content of MG in kratom leaves ranged from 7.5 - 26.6 mg g^-1 of dry leaf weight. Canonical correspondence analysis showed that the most significant environmental variables affecting the MG content among the various regions were light intensity, relative humidity, soil volumetric water content (VW), soil pH, and calcium. This study is a first step towards providing information about environmental conditions suitable to maximize the quality and quantity of bioactive alkaloids in kratom. Future studies should focus on leaf collection and the post-harvest processes in order to assure the desired alkaloidal content in finished products, when produced under suitable environmental conditions identified in this study.

Endogenous opioid systems alterations in pain and opioid use disorder

Decades of research advances have established a central role for endogenous opioid systems in regulating reward processing, mood, motivation, learning and memory, gastrointestinal function, and pain relief. Endogenous opioid systems are present ubiquitously throughout the central and peripheral nervous system. They are composed of four families, namely the μ (MOPR), κ (KOPR), δ (DOPR), and nociceptin/orphanin FQ (NOPR) opioid receptors systems. These receptors signal through the action of their endogenous opioid peptides β-endorphins, dynorphins, enkephalins, and nociceptins, respectfully, to maintain homeostasis under normal physiological states. Due to their prominent role in pain regulation, exogenous opioids-primarily targeting the MOPR, have been historically used in medicine as analgesics, but their ability to produce euphoric effects also present high risks for abuse. The ability of pain and opioid use to perturb endogenous opioid system function, particularly within the central nervous system, may increase the likelihood of developing opioid use disorder (OUD). Today, the opioid crisis represents a major social, economic, and public health concern. In this review, we summarize the current state of the literature on the function, expression, pharmacology, and regulation of endogenous opioid systems in pain. Additionally, we discuss the adaptations in the endogenous opioid systems upon use of exogenous opioids which contribute to the development of OUD. Finally, we describe the intricate relationship between pain, endogenous opioid systems, and the proclivity for opioid misuse, as well as potential advances in generating safer and more efficient pain therapies.

Oxycodone-Naloxone Combination Hinders Opioid Consumption in Osteoarthritic Chronic Low Back Pain: A Retrospective Study with Two Years of Follow-Up

Chronic low back pain (CLBP) due to osteoarthritis represents a therapeutic challenge worldwide. Opioids are extensively used to treat such pain, but the development of tolerance, i.e., less susceptibility to the effects of the opioid, which can result in a need for higher doses to achieve the same analgesic effect, may limit their use. Animal models suggest that ultra-low doses of opioid antagonists combined with opioid agonists can decrease or block the development of opioid tolerance. In this retrospective study, we tested this hypothesis in humans. In 2019, 53 patients suffering from CLBP were treated with either Oxycodone and Naloxone Prolonged Release (27 patients, OXN patients) or Oxycodone Controlled Release (26 patients, OXY patients). The follow-up period lasted 2 years, during which 10 patients discontinued the treatment, 5 out of each group. The remaining 43 patients reached and maintained the targeted pain relief, but at 18 and 24 months, the OXY patients showed a significantly higher oxycodone consumption than OXN patients to reach the same level of pain relief. No cases of respiratory depression or opioid abuse were reported. There were no significant differences in the incidence of adverse effects between the two treatments, except for constipation, more common in OXY patients. From our results, we can affirm that a long-term opioid treatment with oxycodone-naloxone combination, when compared with oxycodone only, may significantly hinder the development of opioid tolerance. We were also able to confirm, in our cohort, the well known positive effect of naloxone in terms of opioid-induced bowel dysfunction incidence reduction.

A bioresorbable peripheral nerve stimulator for electronic pain block

Local electrical stimulation of peripheral nerves can block the propagation of action potentials, as an attractive alternative to pharmacological agents for the treatment of acute pain. Traditional hardware for such purposes, however, involves interfaces that can damage nerve tissue and, when used for temporary pain relief, that impose costs and risks due to requirements for surgical extraction after a period of need. Here, we introduce a bioresorbable nerve stimulator that enables electrical nerve block and associated pain mitigation without these drawbacks. This platform combines a collection of bioresorbable materials in architectures that support stable blocking with minimal adverse mechanical, electrical, or biochemical effects. Optimized designs ensure that the device disappears harmlessly in the body after a desired period of use. Studies in live animal models illustrate capabilities for complete nerve block and other key features of the technology. In certain clinically relevant scenarios, such approaches may reduce or eliminate the need for use of highly addictive drugs such as opioids.

Mechanism of opioid addiction and its intervention therapy: Focusing on the reward circuitry and mu-opioid receptor

Opioid abuse and addiction have become a global pandemic, posing tremendous health and social burdens. The rewarding effects and the occurrence of withdrawal symptoms are the two mainstays of opioid addiction. Mu-opioid receptors (MORs), a member of opioid receptors, play important roles in opioid addiction, mediating both the rewarding effects of opioids and opioid withdrawal syndrome (OWS). The underlying mechanism of MOR-mediated opioid rewarding effects and withdrawal syndrome is of vital importance to understand the nature of opioid addiction and also provides theoretical basis for targeting MORs to treat drug addiction. In this review, we first briefly introduce the basic concepts of MORs, including their structure, distribution in the nervous system, endogenous ligands, and functional characteristics. We focused on the brain circuitry and molecular mechanism of MORs-mediated opioid reward and withdrawal. The neuroanatomical and functional elements of the neural circuitry of the reward system underlying opioid addiction were thoroughly discussed, and the roles of MOR within the reward circuitry were also elaborated. Furthermore, we interrogated the roles of MORs in OWS, along with the structural basis and molecular adaptions of MORs-mediated withdrawal syndrome. Finally, current treatment strategies for opioid addiction targeting MORs were also presented.

An analgesic peptide H-20 attenuates chronic pain via the PD-1 pathway with few adverse effects

The lack of effective and safe analgesics for chronic pain management has been a health problem associated with people's livelihoods for many years. Analgesic peptides have recently shown significant therapeutic potential, as they are devoid of opioid-related adverse effects. Programmed cell death protein 1 (PD-1) is widely expressed in neurons. Activation of PD-1 by PD-L1 modulates neuronal excitability and evokes significant analgesic effects, making it a promising target for pain treatment. However, the research and development of small molecule analgesic peptides targeting PD-1 have not been reported. Here, we screened the peptide H-20 using high-throughput screening. The in vitro data demonstrated that H-20 binds to PD-1 with micromolar affinity, evokes Src homology 2 domain-containing tyrosine phosphatase 1 (SHP-1) phosphorylation, and diminishes nociceptive signals in dorsal root ganglion (DRG) neurons. Preemptive treatment with H-20 effectively attenuates perceived pain in naïve WT mice. Spinal H-20 administration displayed effective and longer-lasting analgesia in multiple preclinical pain models with a reduction in or absence of tolerance, abuse liability, constipation, itch, and motor coordination impairment. In summary, our findings reveal that H-20 is a promising candidate drug that ameliorates chronic pain in the clinic.