Opioid-induced analgesia among persons with opioid use disorder receiving methadone or buprenorphine: A systematic review of experimental pain studies

Pain in people seeking and receiving opioid agonist treatment: A systematic review and meta-analysis of prevalence and correlates

BACKGROUND AND AIMS

People with opioid use disorder (OUD) commonly experience pain including chronic pain. Despite the high prevalence, few studies have systematically examined the prevalence and correlates of pain among people seeking or receiving opioid agonist treatment (OAT) for OUD. This review aimed to determine the prevalence of pain in this population globally, and estimate the association between chronic pain and other demographic and clinical characteristics.

METHODS

Electronic searches were conducted in three databases (Medline, Embase and PsycINFO) from the inception until October 2022. Eligible studies reported prevalence rates of current and/or chronic pain. Meta-analyses examining the main prevalence estimates were conducted by Stata SE 18.0, and comorbid clinical conditions were analysed by Review Manager 5.4.

RESULTS

Fifty-six studies (n participants = 35 267) from sixty-seven publications were included. Prevalence estimates of current and chronic pain were reported in 27 (48.2%) and 40 studies (71.4%), respectively. Most studies were conducted in North America (71.4%, n = 40) and used cross-sectional designs (64.3%, n = 36). Meta-analyses revealed a pooled prevalence of 60.0% (95% confidence interval [CI]: 52.0-68.0) for current pain and 44.0% [95% CI: 40.0-49.0] for chronic pain. Chronic pain was positively associated with older age (mean deviation of mean age: 2.39 years, 95% CI: 1.40-3.37; I2 = 43%), unemployment (odds ratio [OR] = 0.57, 95% CI: 0.42-0.76; I2 = 78%), more severe mental health symptoms (e.g. more severe depression (standardised mean difference [SMD] of mean scores: 0.45, 95% CI: 0.20-0.70; I2 = 48%) and anxiety symptoms (SMD: 0.52, 95% CI: 0.17-0.88; I2 = 67%), and hepatitis C (OR = 1.41, 95% CI: 1.03-1.94; I2 = 0%). No association was observed between chronic pain and the onset and type of OAT, geographic location, study design, survey year, participant age or use of specific pain assessment tools.

CONCLUSIONS

There appears to be a high prevalence of pain among people seeking or receiving opioid agonist treatment for opioid use disorder compared with the general population, with positive associations for older age, unemployment, hepatitis C and the severity of some mental health symptoms.

Brief report: The influence of childhood trauma on the effects of delta-9-tetrahydrocannabinol in persons with opioid use disorder

BACKGROUND AND OBJECTIVES

Childhood trauma (CT) increases addiction vulnerability. We examined CT's impact on delta-9-tetrahydrocannabinol (THC) effects.

METHODS

This is a post-hoc analysis of a randomized, placebo-controlled, crossover trial investigating the effects of oral THC (10, 20 mg) among 25 persons receiving methadone for opioid use disorder (OUD).

RESULTS

Greater CT was associated with lower aversive effects from higher THC doses (20 mg) (p = .006).

DISCUSSION AND CONCLUSIONS

CT may reduce the subjective aversive effects of THC, potentially leading to greater cannabis use in individuals with OUD.

SCIENTIFIC SIGNIFICANCE

These findings offer insights into THC's risks versus benefits in OUD subgroups and emphasize assessing CT in OUD treatment and research.

The Dose-Response Relationship between Opioid Agonist Therapy and Alterations in Pain Pathways in Patients with Opioid Use Disorders: A Cross-Sectional Study

INTRODUCTION

The administration of opioids can be followed by enduring neuroplastic changes in the peripheral and central nervous systems. This remodeling can lead to opioid-induced hyperalgesia, causing an increased sensitivity to painful stimuli. The description of opioid-induced changes in the somatosensory system has seldom been described in the setting of opioid agonist therapy in the treatment of opioid use disorders, and the few existing reports provide no guidance with respect to the effect of varied doses or substances.

OBJECTIVE

The aim of the present study was to assess alterations of pain pathways among patients receiving opioid agonist therapy and to elucidate the dose-response relationship.

METHODS

This study was planned as cross-sectional in an outpatient clinic in Graz, Austria. Patients receiving opioid agonist therapy for opioid use disorders (including methadone, levomethadone, buprenorphine, and extended-release morphine) were asked to fill out a questionnaire, including the central sensitization inventory. A battery of somatosensory system assessments was then performed.

RESULTS

A total of 120 patients participated (85 men/35 women). The mean oral morphine milligram equivalent (MME) was 694 ± 249 mg/day. Our study found significant alterations in pain perception, conditioned pain modulation, and wind-up. We demonstrated a moderate dose-response relationship between high-dose opioids and markers of central sensitization.

CONCLUSION

The present trial demonstrates the clear effects of opioid agonist therapy on the somatosensory system. Both central sensitization and descending pain modulation are negatively affected by high doses of opioids and our data elucidate a moderate dose-response relationship for these phenomena.

Assessing pain in persons with opioid use disorder: Approaches, techniques and special considerations

Pain and opioid use disorder (OUD) are inextricably linked, as the former can be a risk factor for the development of the latter, and over a third of persons with OUD suffer concomitant chronic pain. Assessing pain among people with OUD is challenging, because ongoing opioid use brings changes in pain responses and most pain assessment tools have not been validated for this population. In this narrative review, we discuss the fundamentals of pain assessment for populations with OUD. First, we describe the biological, psychological and social aspects of the pain experience among people with OUD, as well as how opioid-related phenomena may contribute to the pain experience in this population. We then review methods to assess pain, including (1) traditional self-reported methods, such visual analogue scales and structured questionnaires; (2) behavioural observations and physiological indicators; (3) and laboratory-based approaches, such as quantitative sensory testing. These methods are considered from a perspective that encompasses both pain and OUD. Finally, we discuss strategies for improving pain assessment in persons with OUD and implications for future research, including educational strategies for multidisciplinary teams. We highlight the substantial gaps that persist in this literature, particularly regarding the applicability of current pain assessment methods to persons with OUD, as well as the generalizability of the existing results from adjacent populations on chronic opioid therapy but without OUD. As research linking pain and OUD evolves, considering the needs of diverse populations with complex psychosocial backgrounds, clinicians will be better equipped to reduce these gaps.

Delta-9-tetrahydrocannabinol modulates pain sensitivity among persons receiving opioid agonist therapy for opioid use disorder: A within-subject, randomized, placebo-controlled laboratory study

The opioid and cannabinoid receptor systems are inextricably linked-overlapping at the anatomical, functional and behavioural levels. Preclinical studies have reported that cannabinoid and opioid agonists produce synergistic antinociceptive effects. Still, there are no experimental data on the effects of cannabinoid agonists among humans who receive opioid agonist therapies for opioid use disorder (OUD). We conducted an experimental study to investigate the acute effects of the delta-9-tetrahydrocannabinol (THC) among persons receiving methadone therapy for OUD. Using a within-subject, crossover, human laboratory design, 25 persons on methadone therapy for OUD (24% women) were randomly assigned to receive single oral doses of THC (10 or 20 mg, administered as dronabinol) or placebo, during three separate 5-h test sessions. Measures of experimental and self-reported pain sensitivity, abuse potential, cognitive performance and physiological effects were collected. Mixed-effects models examined the main effects of THC dose and interactions between THC (10 and 20 mg) and methadone doses (low-dose methadone defined as <90 mg/day; high dose defined as >90 mg/day). Results demonstrated that, for self-reported rather than experimental pain sensitivity measures, 10 mg THC provided greater relief than 20 mg THC, with no substantial evidence of abuse potential, and inconsistent dose-dependent cognitive adverse effects. There was no indication of any interaction between THC and methadone doses. Collectively, these results provide valuable insights for future studies aiming to evaluate the risk-benefit profile of cannabinoids to relieve pain among individuals receiving opioid agonist therapy for OUD, a timely endeavour amidst the opioid crisis.

Developing non-opioid therapeutics to alleviate pain among persons with opioid use disorder: a review of the human evidence

The opioid crisis remains a major public health concern, causing significant morbidity and mortality worldwide. Pain is frequently observed among individuals with opioid use disorder (OUD), and the current opioid agonist therapies (OAT) have limited efficacy in addressing the pain needs of this population. We reviewed the most promising non-opioid analgesic therapies for opioid-dependent individuals synthesising data from randomised controlled trials in the Medline database from December 2022 to March 2023. Ketamine, gabapentin, serotoninergic antidepressants, and GABAergic drugs were found to be the most extensively studied non-opioid analgesics with positive results. Additionally, we explored the potential of cannabinoids, glial activation inhibitors, psychedelics, cholecystokinin antagonists, alpha-2 adrenergic agonists, and cholinergic drugs. Methodological improvements are required to advance the development of novel analgesic strategies and establish their safety profile for opioid-dependent populations. We highlight the need for greater integration of experimental pain methods and abuse liability assessments, more granular assessments of prior opioid exposure, greater uniformity of pain types within study samples, and a particular focus on individuals with OUD receiving OAT. Finally, future research should investigate pharmacokinetic interactions between OAT and various non-opioid analgesics and perform reverse translation basic experiments, particularly with methadone and buprenorphine, which remain the standard OUD treatment.

Acute Pain Management in Traumatically Injured Patients With Outpatient Buprenorphine Therapy

INTRODUCTION

Acute pain management is challenging in trauma patients undergoing outpatient buprenorphine therapy at the time of injury due to the high binding affinity of this partial agonist. The purpose of this study was to evaluate acute pain management in admitted trauma patients with discontinued versus continued outpatient buprenorphine therapy.

MATERIALS AND METHODS

This retrospective study included adult trauma patients admitted to a level-1 trauma center between January 2017 and August 2020 who were receiving buprenorphine prior to admission. Groups were defined as buprenorphine discontinued (BD) or continued (BC) during hospitalization. The primary outcome compared median daily morphine milligram equivalents between groups. Secondary outcomes utilized patient-reported numeric rating scale (NRS) scores to compare incidences of no pain (NRS 0), mild (NRS 1-3), moderate (NRS 4-6), and severe (NRS 7-10) pain.

RESULTS

A total of 57 patients were included (BD 37 [64.9%] and BC 20 [35.1%]). The median (interquartile range) outpatient daily buprenorphine dose was similar between groups (8 [8-16] mg versus 16 [8-16], P = 0.25). Median daily morphine milligram equivalents was significantly higher during admission in the BD group (103.7 [80.7-166] versus 67 [30.8-97.4], P = 0.002). Incidence of no pain (7.1% versus 5.7%, P = 0.283), mild (5.5% versus 4.3%, P = 0.295), moderate (20.2%, 19.8%, P = 0.855), or severe (67.2% versus 70.2%, P = 0.185) pain was similar between BD and BC groups, respectively.

CONCLUSIONS

Continuation of outpatient buprenorphine therapy in acute trauma patients is associated with decreased daily opioid requirements and similar analgesic efficacy compared to patients with BD. Based on our findings, trauma patients receiving outpatient buprenorphine and not requiring ventilator support may benefit from buprenorphine continuation within 48 h of initial presentation.

Long-Term Exposure to Morphine Induces Cross-Tolerance to Acute Antinociceptive Effect of Remifentanil on Somatic and Visceral Stimuli in Rats

Purpose

Remifentanil is one of the most commonly used opioids intraoperatively. Previous reports indicate that long-term use of opioids may lead to cross-tolerance to remifentanil, which poses a challenge in the control of acute pain intraoperatively. However, there is limited information regarding cross-tolerance to remifentanil, especially in visceral pain. Therefore, this study aimed to examine cross-tolerance to remifentanil in somatic and visceral tolerance using morphine-tolerant rats.

Methods

Six male Sprague-Dawley rats were allocated to the morphine and saline groups each. Tolerance to the antinociceptive effect of morphine was induced in rats in the morphine group. Remifentanil was continuously infused intravenously at 10 mcg/kg/min for 120 min to assess cross-tolerance from morphine to remifentanil. The antinociceptive effects on somatic and visceral nociceptive stimuli were measured using the tail-flick (TF) and colorectal distension (CD) tests, respectively. The antinociceptive efficacy was evaluated by converting the response threshold to the percentage maximal possible effect (%MPE).

Results

Remifentanil increased the %MPE in the morphine and saline groups in both the tests; however, the increase in %MPE was attenuated significantly in the morphine group compared with that in the saline group at 60, 90, and 120 min (all P < 0.01) in the TF test and at 90 and 120 min in the CD test (all P <0.05).

Conclusion

Our results indicate that morphine-tolerant rats exhibit cross-tolerance to remifentanil's acute antinociceptive effects on somatic and visceral stimuli. Cross-tolerance to remifentanil should be considered in the perioperative management of patients using morphine.

Perioperative and Periprocedural anesthetic management of opioid tolerant patients and patients with active and medically treated opioid use disorder

PURPOSE OF REVIEW

The increasing prevalence of opioid tolerant individuals, in combination with the expanding scope and utilization of nonoperating room anesthesia (NORA) necessitates ongoing investigation into best clinical practice for managing surgical/procedural pain in this population. The purpose of this article is to review recent guidelines, identify specific challenges, and offer considerations for managing pain in patients who are opioid tolerant secondary to opioid use disorder (OUD), with or without medications for the treatment of OUD.

RECENT FINDINGS

A comprehensive preoperative evaluation in conjunction with a multidisciplinary, multimodal pain approach is optimal. NORA adds unique situational and environmental challenges for optimizing acute on chronic pain control in tolerant individuals while maintaining safety. Direct and partial/mixed mu-agonists should typically be continued throughout the perioperative period, while mu-antagonists (naltrexone) should be held 72 h. Postprocedural discharge instructions and follow-up must be carefully arranged and ensured.

SUMMARY

Clinical recommendations continue to evolve as new consensus guidelines are published, although institution-specific guidelines are most often followed. This review focuses on most recent best practices, within NORA and operating room settings, for managing opioid tolerant patients, patients with OUD and those on medications for the treatment of OUD.