The dark side of opioids in pain management: basic science explains clinical observation

Assessing Risk Factors and Comorbidities in the Treatment of Chronic Pain: A Narrative Review

PURPOSE OF REVIEW

Chronic pain affects a significant portion of the population globally, making it a leading cause of disability. Understanding the multifaceted nature of chronic pain, its various types, and the intricate relationship it shares with risk factors, comorbidities, and mental health issues like depression and anxiety is critical for comprehensive patient care. Factors such as socioeconomic status (SES), age, gender, and obesity collectively add layers of complexity to chronic pain experiences and pose management challenges.

RECENT FINDINGS

Low SES presents barriers to effective pain care, while gender differences and the prevalence of chronic pain in aging adults emphasize the need for tailored approaches. The association between chronic pain and physical comorbidities like cardiovascular disease, chronic obstructive pulmonary disease (COPD), and diabetes mellitus reveals shared risk factors and further highlights the importance of integrated treatment strategies. Chronic pain and mental health are intricately linked through biochemical mechanisms, profoundly affecting overall quality of life. This review explores pharmacologic treatment for chronic pain, particularly opioid analgesia, with attention to the risk of substance misuse and the ongoing opioid epidemic. We discuss the potential role of medical cannabis as an alternative treatment with a nuanced perspective on its impact on opioid use. Addressing the totality and complexity of pain states is crucial to individualizing chronic pain management. With different types of pain having different underlying mechanisms, considerations should be made when approaching their treatment. Moreover, the synergistic relationship that pain states can have with other comorbidities further complicates chronic pain conditions.

Safety and efficacy of ketorolac continuous infusion for multimodal analgesia of vaso-occlusive crisis in patients with sickle cell disease

Pain is an hallmark of sickle-cell-related acute clinical manifestations as part of acute vaso-occlusive crisis (VOC). In SCD pain has different origins such as vascular or neuropathic pain, which requires multimodal analgesia. This is based on the administration of drugs with different pharmacological mechanisms of action, maximizing analgesia and minimizing their adverse events and the risk of drug-addition in patients experiencing acute-recurrent pain events as in SCD. Ketorolac is a potent non-narcotic analgesic, being relatively safe and effective during pain-management in children and adults. Up to now, there is a lack of safety information on continuous infusion ketorolac as used to control acute pain in patients with SCD, and the benefits/risks ratio needs to be investigated. Here, we report for the first time the safety profile of ketorolac in the special population of patients with SCD. We confirmed that ketorolac in combination with tramadol, an opioid like molecule, is effective in pain control of adult patients with SCD experiencing acute severe VOCs defined by pain visual analog scale. Our study shows that short term (72 h) continuous infusion of ketorolac plus tramadol is not associated with adverse events such as liver or kidney acute disfunction or abnormalities in coagulation parameters during patients' hospitalization and within 30 days after patients discharge. This is extremely important for patients with SCD, who should have access to multimodal therapy to control recurrent acute pain crisis in order to limit central sensitization a fearsome issue of undertreated recurrent acute pain and of chronic pain.

Can gabapentinoids decrease perioperative opioid requirements in orthopaedic trauma patients? A single-centre retrospective analysis

INTRODUCTION

Perioperative pain control in patients with orthopaedic trauma/extremity fractures has gained a lot of attraction from the scientific community in the last two decades. In addition to multimodal analgesia, the use of non-opioid drugs like gabapentinoids for pain relief is gradually finding its place in several orthopaedic subspecialties like spinal surgery, arthroplasty, and arthroscopic procedures. We envisage investigating the effectiveness of gabapentin in perioperative pain control in patients with extremity fractures undergoing surgical fixation.

METHODOLOGY

This was a retrospective comparative study conducted between January 2020 and January 2022. Patients with isolated fractures of the extremity involving long bones who were treated at our trauma centre, during the study period were divided into two groups based on the analgesics they received. Patients who received gabapentin and paracetamol were placed in group GP and those who received only paracetamol were assigned group NGP. Gabapentin was given in a single dose of 300 mg 4 h before surgery. Postoperatively, they were given 300 mg 12 hourly for 2 days. All patients in our trauma centre are usually managed with parenteral paracetamol administration pre and postoperatively. VAS score was calculated postoperatively at 2, 6, 12, 24 and 48 h. Patients requiring additional analgesics for pain relief were administered intravenous tramadol or a buprenorphine patch was applied. Patients in both groups were compared in terms of pain control, the additional requirement of opioid analgesics, and any adverse event related to medications.

RESULTS

One hundred and nineteen patients were enrolled in the study. Out of 65 patients in the NGP group (non-gabapentin group), 74% of patients received additional opioid analgesics apart from paracetamol. Out of the 54 patients in the GP group (gabapentin group), only 41% required additional opioid analgesia for pain control. There was a significant difference in opioid consumption between the two groups (p < 0.01). VAS scores were not significantly different between the two groups at 2, 4, 6, 12, 24 and 48 h. Gender and fracture morphology did not affect opioid intake in the GP group. However, in the non-gabapentin group, there was a significant difference in opioid requirement in patients with intraarticular fractures (p < 0.01).

CONCLUSION

Analgesic requirements vary from patient to patient depending on the injury's severity and surgery duration. However, there are no strict guidelines for pain relief in limb trauma surgeries which often leads to overuse and opioid-related complications or underuse and chronic pain. Gabapentinoids can supplement the analgesic effect of paracetamol in trauma patients during the perioperative period, decreasing the need for opioids.

Direct inhibition of microglial activation by a μ receptor selective agonist alleviates inflammatory-induced pain hypersensitivity

Opioids are widely used in the treatment of moderate and severe pain. Nociceptive stimulation has been reported to potentially promote microglial activation and neuroinflammation, which also causes chronic pain sensitization. The aim of this study was to demonstrate whether the novel μ receptor agonist MEL-0614 could inhibit activated microglia directly and the associated signaling pathway. Mice were administered lipopolysaccharide and formalin to induce allodynia. Von Frey test was used to detect the anti-allodynia effect of MEL-0614 before and after LPS and formalin injection. In the spinal cord, the levels of proinflammatory cytokines and microglial activation were determined after MEL-0614 administration. BV2 and primary microglia were cultured to further explore the effect of MEL-0614 on LPS-induced microglial activation and key signaling pathways involved. MEL-0614 partially prevented and reversed allodynia induced by LPS and formalin in vivo, which was not inhibited by the μ receptor antagonist CTAP. Minocycline was effective in reversing the established allodynia. MEL-0614 also downregulated the activation of microglia and related proinflammatory cytokines in the spinal cord. Additionally, in BV2 and primary microglia, MEL-0614 inhibited the LPS-induced upregulation of proinflammatory factors, which was unaffected by CTAP. The NLR family pyrin domain containing 3 (NLRP3) related signaling pathway may be involved in the interaction between MEL-0614 and microglia. The opioid agonist MEL-0614 inhibited the activation of microglia and the subsequent upregulation of proinflammatory factors both in vivo and in vitro. Notably, this effect is partially mediated by the μ receptor.

The heavy-tailed valence hypothesis: the human capacity for vast variation in pleasure/pain and how to test it

Introduction

Wellbeing policy analysis is often criticized for requiring a cardinal interpretation of measurement scales, such as ranking happiness on an integer scale from 0-10. The commonly-used scales also implicitly constrain the human capacity for experience, typically that our most intense experiences can only be at most ten times more intense than our mildest experiences. This paper presents the alternative "heavy-tailed valence" (HTV) hypothesis: the notion that the accessible human capacity for emotional experiences of pleasure and pain spans a minimum of two orders of magnitude.

Methods

We specify five testable predictions of the HTV hypothesis. A pilot survey of adults aged 21-64 (n = 97) then tested two predictions, asking respondents to comment on the most painful and most pleasurable experiences they can recall, alongside the second most painful and pleasurable experiences.

Results

The results find tentative support for the hypothesis. For instance, over half of respondents said their most intense experiences were at least twice as intense as the second most intense, implying a wide capacity overall. Simulations further demonstrate that survey responses are more consistent with underlying heavy-tailed distributions of experience than a "constrained valence" psychology.

Discussion

A synthesis of these results with prior findings suggests a "kinked" scale, such that a wide range of felt experience is compressed in reports at the high end of intensity scales, even if reports at lower intensities behave more cardinally. We present a discussion of three stylized facts that support HTV and six against, lessons for a future survey, practical guidelines for existing analyses, and implications for current policy. We argue for a dramatic increase in societal ambition. Even in high average income countries, the HTV hypothesis suggests we remain far further below our wellbeing potential than a surface reading of the data might suggest.

Microglial inflammation modulates opioid analgesic tolerance

As we all know, opioids are the drugs of choice for treating severe pain. However, very often, opioid use leads to tolerance, dependence, and hyperalgesia. Therefore, understanding the mechanisms underlying opioid tolerance and designing strategies for increasing the efficacy of opioids in chronic pain are important areas of research. Microglia are brain macrophages that remove debris and dead cells from the brain and participate in immune defense of the central nervous system during an insult or injury. However, recent studies indicate that microglial activation and generation of proinflammatory molecules (e.g., cytokines, nitric oxide, eicosanoids, etc.) in the brain may contribute to opioid tolerance and other side effects of opioid use. In this review, we will summarize the evidence and possible mechanisms by which proinflammatory molecules produced by activated microglia may antagonize the analgesic effect induced by opioids, and thus, lead to opioid tolerance. We will also delineate specific examples of studies that suggest therapeutic targets to counteract the development of tolerance clinically using suppressors of microglial inflammation.

Opioid-Free Versus Opioid-Based Anesthesia on Postoperative Pain After Thoracoscopic Surgery: The Use of Intravenous and Epidural Esketamine

BACKGROUND

The effectiveness and safety of opioid-free anesthesia (OFA) regimens in distinct types of surgeries remain controversial. In this study, we investigated whether OFA could reduce the occurrence of chronic postoperative pain in patients receiving video-assisted thoracoscopic surgery (VATS).

METHODS

We conducted a 2-center, randomized, controlled trial from September 2021 to January 2022. A total of 162 lung tumor patients scheduled to undergo VATS were randomly divided into an opioid-based anesthesia (OA) group and an OFA group. The OA group received general anesthesia combined with thoracic epidural block using morphine, while the OFA group received general anesthesia combined with thoracic epidural block using esketamine. Patient-controlled epidural analgesia (PCEA) was used after surgery (ropivacaine and morphine for the OA group versus ropivacaine and esketamine for the OFA group). The primary end point was chronic pain rates at 3 months after VATS, which were analyzed using a logistic regression model. The secondary end points were chronic pain rates at 6 months, acute pain rates at 24 hours and 48 hours postoperatively, postoperative side effects, and perioperative variables.

RESULTS

The final analysis included 159 patients. Acute postoperative pain at 24 hours occurred in 0 of the 79 (0%) patients in the OA group and 10 of the 80 (17.5%) patients in the OFA group (odds ratio, 52.14; 95% confidence interval [CI], 6.47-420.10; P < .001). Acute postoperative pain at 48 hours occurred in 3 of the 79 (3.8%) patients in the OA group and 2 of the 80 (2.5%) patients in the OFA group (odds ratio, 2.07; 95% CI, 0.99-4.32; P = .053). In this study, none of the patients had moderate or severe pain in either group at 3 and 6 months postsurgically. Mild chronic postoperative pain at 3 months occurred in 27 of the 79 (34.2%) patients in the OA group and 14 of the 80 (17.5%) patients in the OFA group (odds ratio, 3.52; 95% CI, 1.49-8.31; P = .004). At 6 months, mild chronic pain still occurred in 23 of the 79 (29.1%) patients in the OA group and 9 of the 80 (11.3%) patients in the OFA group (odds ratio, 5.55; 95% CI, 2.01-15.33; P = .001). In addition, the OFA group included fewer patients with side effects, including nausea, vomiting, and pruritus, within 48 hours after surgery.

CONCLUSIONS

Replacement of opioids by esketamine, intraoperatively as intravenous injection and epidural infusion and postoperatively as epidural infusion, reduces the incidence of mild chronic postoperative pain and side effects in patients after VATS.

The mechanisms and management of persistent postsurgical pain

An estimated 10%-50% of patients undergoing a surgical intervention will develop persistent postsurgical pain (PPP) lasting more than 3 months despite adequate acute pain management and the availability of minimally invasive procedures. The link between early and late pain outcomes for surgical procedures remains unclear-some patients improve while others develop persistent pain. The elective nature of a surgical procedure offers a unique opportunity for prophylactic or early intervention to prevent the development of PPP and improve our understanding of its associated risk factors, such as pre-operative anxiety and the duration of severe acute postoperative pain. Current perioperative pain management strategies often include opioids, but long-term consumption can lead to tolerance, addiction, opioid-induced hyperalgesia, and death. Pre-clinical models provide the opportunity to dissect mechanisms underpinning the transition from acute to chronic, or persistent, postsurgical pain. This review highlights putative mechanisms of PPP, including sensitisation of peripheral sensory neurons, neuroplasticity in the central nervous system and nociceptive signalling along the neuro-immune axis.

Pharmacological treatments for low back pain in adults: an overview of Cochrane Reviews

BACKGROUND

Pharmacological interventions are the most used treatment for low back pain (LBP). Use of evidence from systematic reviews of the effects of pharmacological interventions for LBP published in the Cochrane Library, is limited by lack of a comprehensive overview.

OBJECTIVES

To summarise the evidence from Cochrane Reviews of the efficacy, effectiveness, and safety of systemic pharmacological interventions for adults with non-specific LBP.

METHODS

The Cochrane Database of Systematic Reviews was searched from inception to 3 June 2021, to identify reviews of randomised controlled trials (RCTs) that investigated systemic pharmacological interventions for adults with non-specific LBP. Two authors independently assessed eligibility, extracted data, and assessed the quality of the reviews and certainty of the evidence using the AMSTAR 2 and GRADE tools. The review focused on placebo comparisons and the main outcomes were pain intensity, function, and safety.

MAIN RESULTS

Seven Cochrane Reviews that included 103 studies (22,238 participants) were included. There is high confidence in the findings of five reviews, moderate confidence in one, and low confidence in the findings of another. The reviews reported data on six medicines or medicine classes: paracetamol, non-steroidal anti-inflammatory drugs (NSAIDs), muscle relaxants, benzodiazepines, opioids, and antidepressants. Three reviews included participants with acute or sub-acute LBP and five reviews included participants with chronic LBP. Acute LBP Paracetamol There was high-certainty evidence for no evidence of difference between paracetamol and placebo for reducing pain intensity (MD 0.49 on a 0 to 100 scale (higher scores indicate worse pain), 95% CI -1.99 to 2.97), reducing disability (MD 0.05 on a 0 to 24 scale (higher scores indicate worse disability), 95% CI -0.50 to 0.60), and increasing the risk of adverse events (RR 1.07, 95% CI 0.86 to 1.33). NSAIDs There was moderate-certainty evidence for a small between-group difference favouring NSAIDs compared to placebo at reducing pain intensity (MD -7.29 on a 0 to 100 scale (higher scores indicate worse pain), 95% CI -10.98 to -3.61), high-certainty evidence for a small between-group difference for reducing disability (MD -2.02 on a 0-24 scale (higher scores indicate worse disability), 95% CI -2.89 to -1.15), and very low-certainty evidence for no evidence of an increased risk of adverse events (RR 0.86, 95% CI 0. 63 to 1.18). Muscle relaxants and benzodiazepines There was moderate-certainty evidence for a small between-group difference favouring muscle relaxants compared to placebo for a higher chance of pain relief (RR 0.58, 95% CI 0.45 to 0.76), and higher chance of improving physical function (RR 0.55, 95% CI 0.40 to 0.77), and increased risk of adverse events (RR 1.50, 95% CI 1. 14 to 1.98). Opioids None of the included Cochrane Reviews aimed to identify evidence for acute LBP. Antidepressants No evidence was identified by the included reviews for acute LBP. Chronic LBP Paracetamol No evidence was identified by the included reviews for chronic LBP. NSAIDs There was low-certainty evidence for a small between-group difference favouring NSAIDs compared to placebo for reducing pain intensity (MD -6.97 on a 0 to 100 scale (higher scores indicate worse pain), 95% CI -10.74 to -3.19), reducing disability (MD -0.85 on a 0-24 scale (higher scores indicate worse disability), 95% CI -1.30 to -0.40), and no evidence of an increased risk of adverse events (RR 1.04, 95% CI -0.92 to 1.17), all at intermediate-term follow-up (> 3 months and ≤ 12 months postintervention). Muscle relaxants and benzodiazepines There was low-certainty evidence for a small between-group difference favouring benzodiazepines compared to placebo for a higher chance of pain relief (RR 0.71, 95% CI 0.54 to 0.93), and low-certainty evidence for no evidence of difference between muscle relaxants and placebo in the risk of adverse events (RR 1.02, 95% CI 0.67 to 1.57). Opioids There was high-certainty evidence for a small between-group difference favouring tapentadol compared to placebo at reducing pain intensity (MD -8.00 on a 0 to 100 scale (higher scores indicate worse pain), 95% CI -1.22 to -0.38), moderate-certainty evidence for a small between-group difference favouring strong opioids for reducing pain intensity (SMD -0.43, 95% CI -0.52 to -0.33), low-certainty evidence for a medium between-group difference favouring tramadol for reducing pain intensity (SMD -0.55, 95% CI -0.66 to -0.44) and very low-certainty evidence for a small between-group difference favouring buprenorphine for reducing pain intensity (SMD -0.41, 95% CI -0.57 to -0.26). There was moderate-certainty evidence for a small between-group difference favouring strong opioids compared to placebo for reducing disability (SMD -0.26, 95% CI -0.37 to -0.15), moderate-certainty evidence for a small between-group difference favouring tramadol for reducing disability (SMD -0.18, 95% CI -0.29 to -0.07), and low-certainty evidence for a small between-group difference favouring buprenorphine for reducing disability (SMD -0.14, 95% CI -0.53 to -0.25). There was low-certainty evidence for a small between-group difference for an increased risk of adverse events for opioids (all types) compared to placebo; nausea (RD 0.10, 95% CI 0.07 to 0.14), headaches (RD 0.03, 95% CI 0.01 to 0.05), constipation (RD 0.07, 95% CI 0.04 to 0.11), and dizziness (RD 0.08, 95% CI 0.05 to 0.11). Antidepressants There was low-certainty evidence for no evidence of difference for antidepressants (all types) compared to placebo for reducing pain intensity (SMD -0.04, 95% CI -0.25 to 0.17) and reducing disability (SMD -0.06, 95% CI -0.40 to 0.29).

AUTHORS' CONCLUSIONS

We found no high- or moderate-certainty evidence that any investigated pharmacological intervention provided a large or medium effect on pain intensity for acute or chronic LBP compared to placebo. For acute LBP, we found moderate-certainty evidence that NSAIDs and muscle relaxants may provide a small effect on pain, and high-certainty evidence for no evidence of difference between paracetamol and placebo. For safety, we found very low- and high-certainty evidence for no evidence of difference with NSAIDs and paracetamol compared to placebo for the risk of adverse events, and moderate-certainty evidence that muscle relaxants may increase the risk of adverse events. For chronic LBP, we found low-certainty evidence that NSAIDs and very low- to high-certainty evidence that opioids may provide a small effect on pain. For safety, we found low-certainty evidence for no evidence of difference between NSAIDs and placebo for the risk of adverse events, and low-certainty evidence that opioids may increase the risk of adverse events.

Modeling spontaneous opioid withdrawal in male and female outbred mice using traditional endpoints and hyperalgesia

Opioid withdrawal significantly impacts drug dependence cycles as hyperalgesia associated with withdrawal is often a reason for continued drug use. Animal models of addiction are important tools for studying how drug dependence and withdrawal impact not only normal neurocircuitry but also the effectiveness of potential treatments for dependence and withdrawal. We conducted a study of the time course of spontaneous morphine withdrawal in outbred male and female mice that can be used to examine sex differences in male and female mice using both traditional somatic endpoints and mechanical hyperalgesia as an endpoint of withdrawal. Male and female national institute of health (NIH) Swiss mice were made dependent upon morphine using an escalating dosing schedule. Injections were stopped after 5 days. Withdrawal behavior was assessed at time intervals up to 106 h after the final injection. Numbers of forepaw tremors, wet-dog shakes, jumps and other behaviors were scored to create a global score. Paw pressure readings were then also taken to track changes in sensitivity to a painful stimulus over time. Male and female mice had approximately similar withdrawal severity peaking at 24 h after the final injection as measured by composite global scores. Females did exhibit an earlier and greater frequency of tremors than males. Although males and females showed similar hyperalgesia during withdrawal, females recovered faster. Spontaneous opioid withdrawal peaking at 24 h was demonstrated in male and female NIH Swiss mice. We also successfully demonstrated that hyperalgesia is an endpoint that varies over the course of withdrawal.

Peripheral Regional Anesthesia Using Local Anesthetics: Old Wine in New Bottles?

During the past decade, numerous efforts were undertaken aiming at prolonging the analgesic effect of regional anesthesia. With the development of extended-release formulations and enhanced selectivity for nociceptive sensory neurons, a very promising contribution to the development of pain medications has been achieved. At present, liposomal bupivacaine is the most popular, non-opioid, controlled drug delivery system, but its duration of action, which is still controversially discussed, and its expensiveness have decreased initial enthusiasm. Continuous techniques can be seen as an elegant alternative for providing a prolonged duration of analgesia, but for logistic or anatomical reasons, they are not always the best choice. Therefore, focus has been directed towards the perineural and/or intravenous addition of old and established substances. As for perineural application, most of these so-called 'adjuvants' are used outside their indication, and their pharmacological efficacy is often not or only poorly understood. This review aims to summarize the recent developments for prolonging the duration of regional anesthesia. It will also discuss the potential harmful interactions and side effects of frequently used analgesic mixtures.

A multicenter study to evaluate pain characteristics in osteogenesis imperfecta

The objective was to describe pain characteristics and treatments used in individuals with varying severity of osteogenesis imperfecta (OI) and investigate pain-associated variables. This work was derived from a multicenter, longitudinal, observational, natural history study of OI conducted at 12 clinical sites of the NIH Rare Diseases Clinical Research Network's Brittle Bone Disorders Consortium. Children and adults with a clinical, biochemical, or molecular diagnosis of OI were enrolled in the study. We did a cross-sectional analysis of chronic pain prevalence, characteristics, and treatments used for pain relief and longitudinal analysis to find the predictors of chronic pain. We included 861 individuals with OI, in 41.8% chronic pain was present, with similar frequency across OI types. Back pain was the most frequent location. Nonsteroidal anti-inflammatory drugs followed by bisphosphonates were the most common treatment used. Participants with chronic pain missed more days from school or work/year and performed worse in all mobility metrics than participants without chronic pain. The variables more significantly associated with chronic pain were age, sex, positive history of rodding surgery, scoliosis, other medical problems, assistive devices, lower standardized height, and higher body mass index. The predictors of chronic pain for all OI types were age, use of a wheelchair, and the number of fractures/year. Chronic pain is prevalent in OI across all OI types, affects mobility, and interferes with participation. Multiple covariates were associated with chronic pain.

A scoping review of outpatient interventions to support the reduction of prescription opioid medication for chronic non cancer pain

BACKGROUND

Prescription opioid use is a global health issue. Previous systematic reviews have not identified that any specific intervention supports prescription opioid reduction effectively. In keeping with the nature of a scoping review, this review details an overview of the existing literature on this topic, with quality of evidence being discussed rather than formally analysed.

AIM

This review aimed to examine and describe outpatient interventions that support the reduction of prescription opioid medication for chronic non cancer pain.

ELIGIBILITY CRITERIA

Abstracts were reviewed against the inclusion criteria of outpatient clinical interventions, for the purpose of prescription opioid dose reduction, offered to adults with CNCP.

SOURCES OF EVIDENCE

Following a structured review approach an electronic database search, of Medline, Embase, Cochrane, Cinahl, and Proquest and grey literature was undertaken. Search results were screened by title for relevance.

CHARTING METHODS

Two reviewers adhering to the PRISMA-ScR checklist charted and assessed studies for quality using Critical Appraisal Skills Programme checklist assessment tools. Extracted data were collated and synthesised for presentation as a tabular and narrative review.

RESULTS

From the initial search of 5089 papers, 19 underwent full-text review and quality appraisal. A variety of interventions were described to support reduction in prescription opioid use, however only one study of at least fair quality was able to demonstrate a demonstrated a statistically significant benefit in reducing measured opioid dose compared with a control group. Interventions were implemented in both specialist pain services and in primary care with multidisciplinary and interdisciplinary clinician care. Barriers and facilitators were observed in both settings.

CONCLUSION AND IMPLICATIONS FOR CLINICAL PRACTICE

Further rigorous research needs to be conducted to conclusively answer the question of what outpatient interventions support opioid reduction in chronic non cancer pain. This scoping review is the first step of inquiry in the development of a nursing intervention to support reduction of prescription opioids.

Early Initiation of Sub-Anesthetic Ketamine Infusion in Adults with Vaso-Occlusive Crises Is Associated with Greater Reduction in Sickle Cell Pain Intensity: A Single Center's Experience

OBJECTIVES

Recurrent, severely painful episodes, known as vaso-occlusive crises (VOCs) are the hallmark of sickle cell disease (SCD) and the primary reason for hospitalization. Opioids have been the gold standard for VOC treatment without significant improvement pain outcomes. To aid analgesia and combat opioid related adverse effects (ORAEs), some SCD clinicians have trialed infusions of sub-anesthetic ketamine along with opioids to treat VOCs. In this retrospective analysis, we compared adult SCD patients who received early vs late adjunctive sub-anesthetic ketamine infusions for VOCs.

METHODS

We identified adult SCD patients (age 18-50 years) who presented to Duke University with a VOC and received sub-anesthetic ketamine infusions from July 2015 to June 2019. We assessed both daily opioid consumption (measured as oral morphine milligram equivalents (MME)) and self-reported 0-10 numeric pain ratings (NPR) at 1, 2, and 3 days after infusion initiation, as well as 1 day after discontinuation.

RESULTS

A total of 56 patients were identified with a median age of 30 years. Compared to late administration, early infusion of sub-anesthetic ketamine was associated with a 24.5% (P = .0003) and 25.9% (P = .0006) reduction, respectively, in median NPR at 1 day and 2 days after infusion initiation but did not persist at 3 days following initiation of the infusion. A statistically significant reduction in MME was not observed.

CONCLUSIONS

In a nonrandomized study of sickle cell patients with VOCs, early sub-anesthetic ketamine infusion led to greater reduction in subjective pain intensity than late initiation of the infusion. Randomized studies should further explore whether early vs late ketamine infusion improves management of acute SCD pain.

The Effect of State-Level Prescription Opioid Legislation on Patient Outcomes After Lumbar Tubular Microdecompression

BACKGROUND

In the United States, a statewide legislation titled the Strengthen Opioid Misuse Prevention (STOP) Act was enacted in 2017 to limit prescription opioid use and reduce dependence. The impact of state legislation curbing opioid prescription on outcomes after spine surgery is unknown.

STUDY DESIGN

Case series.

METHODS

Data from consecutive patients undergoing lumbar tubular microdecompression for symptomatic lumbar spine stenosis from June 2016 to June 2019 were retrospectively analyzed. Cases between June 2016 and December 2017 represent the group before the STOP act (pre-STOP), while cases between January 2018 and June 2019 represent the group after legislation enactment (post-STOP). Preoperative and postoperative patient functional scores including the EuroQol-Five Dimensions Index, Oswestry Disability Index (ODI), and the visual analog scale (VAS) for back and leg pain were compared between both groups. The meaningful clinically important difference (MCID) was calculated for each score and was compared between both groups as well.

RESULTS

A total of 147 patients met inclusion criteria, with 86 in the pre-STOP group and 61 in the post-STOP group. Analysis of postoperative scores demonstrated statistically lower VAS leg pain score averages in the post-STOP group (P < 0.05). Higher trends in achieving MCID among the post-STOP group were observed; however, the differences between both groups were not statistically significant (P > 0.05 for all). Additionally, there were no statistical differences in rates of unplanned pain-related clinic visits and emergency department (ED) visits, as well as no differences in the number of pain-related calls within 90 days after surgery between both groups.

CONCLUSION

The enactment of state legislation to curb the prescribing of opioids for postoperative pain did not negatively affect the rate of achieving clinically meaningful outcomes among patients undergoing lumbar tubular microdecompression for spinal stenosis. Additionally, decreasing the amount of opioids prescribed for postoperative pain does not increase the number of unplanned clinic or ED visits due to pain within 90 days after surgery.

LEVEL OF EVIDENCE: 4

Yokukansan Inhibits the Development of Morphine Tolerance by Regulating Presynaptic Proteins in DRG Neurons

Opioids, such as morphine, are used in clinical settings for the management of acute and chronic pain. However, long-term use of morphine leads to antinociceptive tolerance and hypersensitivity. The cellular and molecular mechanisms of morphine tolerance seem to be quite complex, with suggestions including internalization of the μ-opioid receptor (MOR), neuroinflammation with activation of microglia and astrocytes, and changes in synaptic function in the central nervous system. Yokukansan (YKS), a traditional Kampo medicine consisting of seven herbs, has been used to treat emotional instability, neurosis, and insomnia. Interestingly, recent studies have begun to reveal the inhibitory effect of YKS on the development of morphine tolerance. In the present study, we determined the effect of YKS on morphine tolerance formation and its mechanisms in a rat model, focusing on the synapses between primary sensory neurons and spinal dorsal horn secondary neurons. We found that morphine tolerance formation was significantly inhibited by YKS (0.3 or 1.0 g/kg/day) preadministration for 7 days. Repeated administration of morphine (10 mg/kg/day) increased the expression of presynaptic proteins, including synaptotagmin I, in the spinal cord, which was suppressed by YKS. Furthermore, these changes in presynaptic protein expression were more pronounced at isolectin B4 (IB4)-positive excitatory synapses around the lamina II of the dorsal horn. These results suggest that YKS suppresses the development of morphine tolerance by inhibiting the enhancement of presynaptic function of dorsal root ganglia neurons projecting to spinal dorsal horn neurons caused by continuous morphine administration.

Chronic Cancer Pain: Opioids within Tumor Microenvironment Affect Neuroinflammation, Tumor and Pain Evolution

Simple Summary

Pain is a worrisome symptom that 60–80% of patients with cancer experience chronically. In the last twenty years, immunological and pain research have shown that cancer pain is attributable to the neuroinflammatory response driven by the cellular and soluble components of the tumor microenvironment, with features similar to that induced in many other painful chronic non-cancer diseases. Neuroinflammation leads to central sensitization and neuroplastic remodeling of the central nervous system with alteration of pain sensitivity (hyperalgesia), responsiveness (behavior), and drive (centralization). Engagement of opioid receptors by both endogenous and exogenous opioids, namely, the cornerstone of pain therapy morphine, results in modulation of pain intensity and quality, in addition to cancer growth and progression. The effects of opioids on the evolution of pain, (relief or immune-mediated hyperalgesia) and cancer (promotion or inhibition), are dual and ambiguous. This ambiguity currently represents a major limitation of long-term opioid therapy, and encourages novel immunotherapeutic strategies.

Abstract

Pain can be a devastating experience for cancer patients, resulting in decreased quality of life. In the last two decades, immunological and pain research have demonstrated that pain persistence is primarily caused by neuroinflammation leading to central sensitization with brain neuroplastic alterations and changes in pain responsiveness (hyperalgesia, and pain behavior). Cancer pain is markedly affected by the tumor microenvironment (TME), a complex ecosystem consisting of different cell types (cancer cells, endothelial and stromal cells, leukocytes, fibroblasts and neurons) that release soluble mediators triggering neuroinflammation. The TME cellular components express opioid receptors (i.e., MOR) that upon engagement by endogenous or exogenous opioids such as morphine, initiate signaling events leading to neuroinflammation. MOR engagement does not only affect pain features and quality, but also influences directly and/or indirectly tumor growth and metastasis. The opioid effects on chronic cancer pain are also clinically characterized by altered opioid responsiveness (tolerance and hyperalgesia), a hallmark of the problematic long-term treatment of non-cancer pain. The significant progress made in understanding the immune-mediated development of chronic pain suggests its exploitation for novel alternative immunotherapeutic approaches.

Digital Analgesic Comprising a Second-Generation Digital Health System: Increasing Effectiveness by Optimizing the Dosing and Minimizing Side Effects

Opioids remain an essential part of the treatment of chronic pain. However, their use and increasing rates of misuse are associated with high morbidity and mortality. The development of tolerance to opioids and analgesics further complicates dosing and the need to reduce side effects. First-generation digital systems were developed to improve analgesics but are not always capable of making clinically relevant associations and do not necessarily lead to better clinical efficacy. A lack of improved clinical outcomes makes these systems less applicable for adoption by clinicians and patients. There is a need to enhance the therapeutic regimens of opioids. In the present paper, we present the use of a digital analgesic that consists of an analgesic administered under the control of a second-generation artificial intelligence system. Second-generation systems focus on improved patient outcomes measured based on clinical response and reduced side effects in a single subject. The algorithm regulates the administration of analgesics in a personalized manner. The digital analgesic provides advantages for both users and providers. The system enables dose optimization, improving effectiveness, and minimizing side effects while increasing adherence to beneficial therapeutic regimens. The algorithm improves the clinicians’ experience and assists them in managing chronic pain. The system reduces the financial burden on healthcare providers by lowering opioid-related morbidity and provides a market disruptor for pharma companies.

Current Strategies for the Management of Painful Diabetic Neuropathy

The development of painful diabetic neuropathy (PDN) is a common complication of chronic diabetes that can be associated with significant disability and healthcare costs. Prompt symptom identification and aggressive glycemic control is essential in controlling the development of neuropathic complications; however, adequate pain relief remains challenging and there are considerable unmet needs in this patient population. Although guidelines have been established regarding the pharmacological management of PDN, pain control is inadequate or refractory in a high proportion of patients. Pharmacotherapy with anticonvulsants (pregabalin, gabapentin) and antidepressants (duloxetine) are common first-line agents. The use of oral opioids is associated with considerable morbidity and mortality and can also lead to opioid-induced hyperalgesia. Their use is therefore discouraged. There is an emerging role for neuromodulation treatment modalities including intrathecal drug delivery, spinal cord stimulation, and dorsal root ganglion stimulation. Furthermore, consideration of holistic alternative therapies such as yoga and acupuncture may augment a multidisciplinary treatment approach. This aim of this review is to focus on the current management strategies for the treatment of PDN, with a discussion of treatment rationale and practical considerations for their implementation.

The complications of opioid use during and post-intensive care admission: A narrative review

Opioids are a commonly administered analgesic medication in the intensive care unit, primarily to facilitate invasive mechanical ventilation. Consensus guidelines advocate for an opioid-first strategy for the management of acute pain in ventilated patients. As a result, these patients are potentially exposed to high opioid doses for prolonged periods, increasing the risk of adverse effects. Adverse effects relevant to these critically ill patients include delirium, intensive care unit-acquired infections, acute opioid tolerance, iatrogenic withdrawal syndrome, opioid-induced hyperalgesia, persistent opioid use, and chronic post-intensive care unit pain. Consequently, there is a challenge of optimising analgesia while minimising these adverse effects. This narrative review will discuss the characteristics of opioid use in the intensive care unit, outline the potential short-term and long-term adverse effects of opioid therapy in critically ill patients, and outline a multifaceted strategy for opioid minimisation.

Does aerobic exercise effect pain sensitisation in individuals with musculoskeletal pain? A systematic review

Background

Pain sensitisation plays a major role in musculoskeletal pain. However, effective treatments are limited, and although there is growing evidence that exercise may improve pain sensitisation, the amount and type of exercise remains unclear. This systematic review examines the evidence for an effect of aerobic exercise on pain sensitisation in musculoskeletal conditions.

Methods

Systematic searches of six electronic databases were conducted. Studies were included if they examined the relationship between aerobic physical activity and pain sensitisation in individuals with chronic musculoskeletal pain, but excluding specific patient subgroups such as fibromyalgia. Risk of bias was assessed using Cochrane methods and a qualitative analysis was conducted.

Results

Eleven studies (seven repeated measures studies and four clinical trials) of 590 participants were included. Eight studies had low to moderate risk of bias. All 11 studies found that aerobic exercise increased pressure pain thresholds or decreased pain ratings in those with musculoskeletal pain [median (minimum, maximum) improvement in pain sensitisation: 10.6% (2.2%, 24.1%)]. In these studies, the aerobic exercise involved walking or cycling, performed at a submaximal intensity but with incremental increases, for a 4-60 min duration. Improvement in pain sensitisation occurred after one session in the observational studies and after 2-12 weeks in the clinical trials.

Conclusions

These findings provide evidence that aerobic exercise reduces pain sensitisation in individuals with musculoskeletal pain. Further work is needed to determine whether this translates to improved patient outcomes, including reduced disability and greater quality of life.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05047-9.

Combined opioid free and loco-regional anaesthesia enhances the quality of recovery in sleeve gastrectomy done under ERAS protocol: a randomized controlled trial

Background

It is debatable whether opioid-free anaesthesia (OFA) is better suited than multimodal analgesia (MMA) to achieve the goals of enhanced recovery after surgery (ERAS) in patients undergoing laparoscopic sleeve gastrectomy.

Methods

In all patients, anaesthesia was conducted with an i.v. induction with propofol (2 mg. kg-1), myorelaxation with cisatracurium (0.15 mg.kg-1), in addition to an ultrasound-guided bilateral oblique subcostal transverse abdominis plane block. In addition, patients in the OFA group (n = 51) received i.v. dexmedetomidine 0.1 μg.kg-1 and ketamine (0.5 mg. kg-1) at induction, then dexmedetomidine 0.5 μg. kg-1.h-1, ketamine 0.5 mg.kg-1.h-1, and lidocaine 1 mg. kg-1.h-1 for maintenance, while patients in the MMA group (n = 52) had only i.v. fentanyl (1 μg. kg-1) at induction. The primary outcome was the quality of recovery assessed by QoR-40, at the 6th and the 24th postoperative hour. Secondary outcomes were postoperative opioid consumption, time to ambulate, time to tolerate oral fluid, and time to readiness for discharge.

Results

At the 6th hour, the QoR-40 was higher in the OFA than in the MMA group (respective median [IQR] values: 180 [173–195] vs. 185 [173–191], p < 0.0001), but no longer difference was found at the 24th hour (median values = 191 in both groups). OFA also significantly reduced postoperative pain and morphine consumption (20 mg [1–21] vs. 10 mg [1–11], p = 0.005), as well as time to oral fluid tolerance (238 [151–346] vs. 175 min [98–275], p = 0.022), and readiness for discharge (505 [439–626] vs. 444 min [356–529], p = 0.001), but did not influence time to ambulate.

Conclusion

While regional anaesthesia achieved most of the intraoperative analgesia, avoiding intraoperative opioids with the help of this OFA protocol was able to improve several sensible parameters of postoperative functional recovery, thus improving our knowledge on the OFA effects.

Clinical trial number

Registration number NCT04285255.

Pain Reduction in Rheumatoid Arthritis Patients Who Use Opioids: A Post Hoc Analysis of Phase 3 Trials of Baricitinib

Objective

Pain reduction with baricitinib was assessed in patients with rheumatoid arthritis (RA) who either used opioids or did not use opioids during three randomized, double‐blind phase 3 trials.

Methods

Analysis populations were as follows: i) baricitinib 4 mg once daily versus placebo groups integrated from RA‐BEAM (NCT01710358) for patients with inadequate response (IR) to methotrexate, RA‐BUILD (NCT01721057) with IR to conventional disease‐modifying antirheumatic drugs, and RA‐BEACON (NCT01721044) with IR to at least one tumor necrosis factor inhibitors; ii) baricitinib 2 mg versus placebo from RA‐BUILD and RA‐BEACON; and iii) adalimumab 40 mg every other week versus placebo from RA‐BEAM. Pain was measured by the Patient Assessment of Pain Visual Analog Scale. Analysis of covariance modeling assessed differences in pain reduction between treatments at each time point through Week 24, with an interaction term to test heterogeneous treatment effects across opioid users and nonusers.

Results

Baricitinib 4 mg had greater pain reduction versus placebo in opioid users and nonusers (P < 0.05) at all time points starting from Week 1; the pain reduction was similar between opioid users and nonusers. Baricitinib 2 mg had greater pain reduction versus placebo in opioid users and nonusers starting at Week 4. A significant difference in pain reduction was not observed for adalimumab versus placebo in the opioid users but was observed in nonusers at all time points.

Conclusion

Pain reduction was observed and was similar between opioid users and nonusers with baricitinib 2 mg and 4 mg but not adalimumab in this post hoc analysis.

Association between clusters of back and joint pain with opioid use in middle-aged community-based women: a prospective cohort study

Background

To determine the relationship between clusters of back pain and joint pain and prescription opioid dispensing.

Methods

Of 11,221 middle-aged participants from the Australian Longitudinal Study of Women’s Health, clusters of back pain and joint pain from 2001 to 2013 were identified using group-based trajectory modelling. Prescription opioid dispensing from 2003 to 2015 was identified by linking the cohort to Pharmaceutical Benefit Scheme dispensing data. Multinomial logistic regression was used to examine the association between back pain and joint pain clusters and dispensing of prescription opioids. The proportion of opioids dispensed in the population attributable to back and join pain was calculated.

Results

Over 12 years, 68.5 and 72.0% women reported frequent or persistent back pain and joint pain, respectively. There were three clusters (‘none or infrequent’, ‘frequent’ and ‘persistent’) for both back pain and joint pain. Those in the persistent back pain cluster had a 6.33 (95%CI 4.38-9.16) times increased risk of having > 50 opioid prescriptions and those in persistent joint pain cluster had a 6.19 (95%CI 4.18-9.16) times increased risk of having > 50 opioid prescriptions. Frequent and persistent back and joint pain clusters together explained 41.7% (95%CI 34.9-47.8%) of prescription opioid dispensing. Women in the frequent and persistent back pain and joint pain clusters were less educated and reported more depression and physical inactivity.

Conclusion

Back pain and joint pain are major contributors to opioid prescription dispensing in community-based middle-aged women. Additional approaches to reduce opioid use, targeted at those with frequent and persistent back pain and joint pain, will be important in order to reduce the use of opioids and their consequent harm in this population.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04741-4.

Unconditioned and learned morphine tolerance influence hippocampal-dependent short-term memory and the subjacent expression of GABA-A receptor alpha subunits

BACKGROUND

ɣ-aminobutyric acid (GABA) facilitator valproic acid may be able to curb memory disruption induced by morphine exposure.

OBJECTIVE

The effects of the GABA facilitator valproic acid on the behavioral tolerance induced by morphine were investigated. Then hippocampal-dependent tasks named spatial-working and short-term memory procedures using the Y-maze apparatus were examined in morphine tolerant rats. Finally, the changes in the expression of hippocampal GABA-A receptors underlying morphine tolerance were also examined.

METHODS

Rats were treated with daily morphine injections, with or without distinct contextual pairing. To examine the effect of valproic acid on morphine tolerance expression, valproic acid was pretreated an hour before morphine. Spatial-working and short-term memory procedures using the Y-maze apparatus were examined in morphine tolerant rats. Afterwards the changes in the expression of hippocampal GABAα receptors using the quantitative real-time PCR and western blot techniques to detect GABArα subunits mRNAs and protein level were studied.

RESULTS

Our results showed that both learned and non-associative morphine tolerance influence short-term memory and the subjacent expression of GABArα mRNAs and protein level. Despite its attenuating effects on the development and expression of both learned and non-associative morphine tolerance, only associative morphine tolerance-induced memory dysfunction was ameliorated by valproic acid pretreatment. We also found that the expression of GABArα1, α2, α5 subunits mRNAs and GABAα protein level were affected heavier in associative morphine tolerant rats.

CONCLUSION

Our data supports the hypothesis that unconditioned and learned morphine tolerance influences short-term memory and the expression of GABArα 1, α2, α5 mRNAs and GABArα protein level differently, and adds to our understanding of the behavioral and molecular aspects of the learned tolerance to morphine effects.

No Evidence of Altered Reactivity to Experimentally Induced Pain Among Regular Cannabis Users

OBJECTIVES

Recent years have seen an increase in the adoption of cannabinoid medicines, which have demonstrated effectiveness for the treatment of chronic pain. However, the extent to which frequent cannabis use (CU) influences sensitivity to acute pain has not been systematically examined. Such a determination is clinically relevant in light of hypersensitivity to pain associated with prolonged use of other analgesics such as opioids, and reports of increased pain sensitivity to experimentally induced pain during acute cannabis intoxication. This study explored differences in measures of pain intensity and tolerance. The authors hypothesized that individuals who report frequent CU would demonstrate greater experimental pain sensitivity.

MATERIALS AND METHODS

Frequent cannabis users (≥3× per week; n=40) and nonusers (n=40) were compared on pain sensitivity, pain tolerance, and pain intensity in response to a cold-pressor task. Group differences were examined.

RESULTS

Frequent CU was not associated with hyperalgesia as cannabis users and nonusers did not exhibit differences on measures of pain tolerance (t (78)=-0.05; P=0.96), sensitivity (t (78)=-0.83; P=0.41), or intensity (t (78)=0.36; P=0.72).

DISCUSSION

Frequent cannabis users did not demonstrate hyperalgesia. This finding should help to inform evaluations of the relative harms and benefits of cannabis analgesic therapies.

Treatment use and satisfaction in Australian women with endometriosis: A mixed-methods study

AIMS

This study aimed to document the frequency of conventional and complementary treatments used by Australian women with endometriosis and the perceived efficacy of these treatments; and to qualitatively explore women's treatment satisfaction.

METHODS

Using a mixed-methods design, 532 women with self-reported endometriosis were recruited from the community.

METHOD

Participants were asked about their medication, complementary and self-care treatment use, as well as perceived efficacy on a 0 (not effective) - 10 (extremely effective) numeric rating scale (NRS), and open-ended qualitative survey items about treatment satisfaction.

RESULTS

97% of women used medication for pain relief (mean perceived efficacy = 5.05) and 89% used complementary/ self-care strategies (mean perceived efficacy = 3.70), with medication rated as significantly more effective (p <.001). Content analysis of the qualitative data identified that 36% of women were dissatisfied with treatment, 34% were somewhat satisfied, and 24% were satisfied. We identified qualitative themes relating to: 1) Barriers to treatment, which included lack of access, stigma, and disappointment with medical professionals who were perceived as uncaring, unhelpful and in some cases, psychologically damaging; 2) The need for holistic, interdisciplinary care; and 3) Patient knowledge, advocacy and resilience in endometriosis management.

CONCLUSIONS

Our findings reveal important limitations in the current Australian healthcare model, including the need for patient-centred interdisciplinary care that treats the biopsychosocial needs of people with endometriosis; and widespread pain education, spanning medical training to community awareness. This article is protected by copyright. All rights reserved.

Association of sociodemographic factors with the prescription pattern of opioids for dental patients: A systematic review protocol

INTRODUCTION

Oral health practitioners are responsible for a significant share of opioid prescriptions that seem to be influenced by many aspects, including sociodemographic factors. However, there is no consensus on the factors associated with opioid prescription in Dentistry.

OBJECTIVE

To identify whether patients' sociodemographic factors are associated with the prescription pattern of opioids in Dentistry.

MATERIALS AND METHODS

This systematic review will include observational studies (cross-sectional, case-control, and cohort). Electronic searches will be conducted in MEDLINE (PubMed), EMBASE, Scopus, Web of science, LILACS, SciELO, and Google Scholar. Grey literature will also be consulted. Two independent reviewers will screen all retrieved articles for eligibility, extract data, and assess the methodological quality of the included studies. The results will be presented as a narrative synthesis and, where possible, a meta-analysis will be conducted. Certainty of the evidence will be assessed with the Grading of Recommendations, Assessment, Development, and Evaluation approach.

SYSTEMATIC REVIEW REGISTRATION NUMBER

PROSPERO CRD42020211226.

Co-Players in Chronic Pain: Neuroinflammation and the Tryptophan-Kynurenine Metabolic Pathway

Chronic pain is an unpleasant sensory and emotional experience that persists or recurs more than three months and may extend beyond the expected time of healing. Recently, nociplastic pain has been introduced as a descriptor of the mechanism of pain, which is due to the disturbance of neural processing without actual or potential tissue damage, appearing to replace a concept of psychogenic pain. An interdisciplinary task force of the International Association for the Study of Pain (IASP) compiled a systematic classification of clinical conditions associated with chronic pain, which was published in 2018 and will officially come into effect in 2022 in the 11th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-11) by the World Health Organization. ICD-11 offers the option for recording the presence of psychological or social factors in chronic pain; however, cognitive, emotional, and social dimensions in the pathogenesis of chronic pain are missing. Earlier pain disorder was defined as a condition with chronic pain associated with psychological factors, but it was replaced with somatic symptom disorder with predominant pain in the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) in 2013. Recently clinical nosology is trending toward highlighting neurological pathology of chronic pain, discounting psychological or social factors in the pathogenesis of pain. This review article discusses components of the pain pathway, the component-based mechanisms of pain, central and peripheral sensitization, roles of chronic inflammation, and the involvement of tryptophan-kynurenine pathway metabolites, exploring the participation of psychosocial and behavioral factors in central sensitization of diseases progressing into the development of chronic pain, comorbid diseases that commonly present a symptom of chronic pain, and psychiatric disorders that manifest chronic pain without obvious actual or potential tissue damage.

Prescription Opioids Higher Among Knee Arthroplasty Recipients Randomized to Inpatient Rehabilitation

Objective

To determine whether the purchase of prescription opioids was lower among people randomized to inpatient rehabilitation (IR) compared with those discharged directly home following total knee arthroplasty (TKA).

Method

A secondary analysis of a previous clinical trial in which participants were randomized 3 to 5 days after ‐surgery to 10 days of IR and a home program or to a home program alone. The primary outcome for this secondary analysis was the purchase of opioid‐based pain relief up to 10‐weeks after surgery, which was captured via patient diaries. Between‐group differences were analyzed using a χ² test and relative risk (RR) (95% confidence interval [CI]). We report this outcome alongside the main outcomes observed at 10 weeks for the original study (6‐minute walk test, index joint pain, and function) for context.

Results

At 10 weeks, 158 participants were available for follow‐up; 120 (76%) provided diaries, with 113 providing generic or brand names for the pain relief purchased. In the IR group, 60% (33/55) reported the purchase of opioid‐based medications after discharge compared with 34% (20/58) in the home group (χ² = 7.4; P = 0.007); thus, the risk of purchasing opioids for those in the IR group was almost double (RR, 1.7 [95% CI, 1.1‐2.6]). No significant or meaningful between‐group differences in index joint pain, function, or mobility were observed.

Conclusion

Contrary to what was hypothesized, IR is a strong driver of opioid purchase after discharge from the hospital following TKA.

Monoaminergic and Opioidergic Modulation of Brainstem Circuits: New Insights Into the Clinical Challenges of Pain Treatment?

The treatment of neuropathic pain remains a clinical challenge. Analgesic drugs and antidepressants are frequently ineffective, and opioids may induce side effects, including hyperalgesia. Recent results on brainstem pain modulatory circuits may explain those clinical challenges. The dual action of noradrenergic (NA) modulation was demonstrated in animal models of neuropathic pain. Besides the well-established antinociception due to spinal effects, the NA system may induce pronociception by directly acting on brainstem pain modulatory circuits, namely, at the locus coeruleus (LC) and medullary dorsal reticular nucleus (DRt). The serotoninergic system also has a dual action depending on the targeted spinal receptor, with an exacerbated activity of the excitatory 5-hydroxytryptamine 3 (5-HT3) receptors in neuropathic pain models. Opioids are involved in the modulation of descending modulatory circuits. During neuropathic pain, the opioidergic modulation of brainstem pain control areas is altered, with the release of enhanced local opioids along with reduced expression and desensitization of μ-opioid receptors (MOR). In the DRt, the installation of neuropathic pain increases the levels of enkephalins (ENKs) and induces desensitization of MOR, which may enhance descending facilitation (DF) from the DRt and impact the efficacy of exogenous opioids. On the whole, the data discussed in this review indicate the high plasticity of brainstem pain control circuits involving monoaminergic and opioidergic control. The data from studies of these neurochemical systems in neuropathic models indicate the importance of designing drugs that target multiple neurochemical systems, namely, maximizing the antinociceptive effects of antidepressants that inhibit the reuptake of serotonin and noradrenaline and preventing desensitization and tolerance of MOR at the brainstem.

A118G polymorphism of OPRM1 gene caused different morphine consumption in female patients after total knee replacement

BACKGROUND

We intended to clarify the effect of gender and A118G polymorphism of Opioid Receptor μ1 (OPRM1) on the required morphine for patients to maintain Visual Analogue Scale ≦ 3 for post-operative pain control after total knee replacement (TKR).

METHODS

With approval from Institutional Review Board (IRB) and obtainment of informed consents, 111 patients undergoing primary TKR were enrolled without violating the exclusion criteria, including previous history of allergy to morphine, alcohol or substance abuse, use of psychotropic medications, morbid obesity of body mass index (BMI) > 40 kg/m², chronic pain with evidence of central sensitization, and uncooperative use of patient controlled analgesia (PCA) device. The amount of PCA-delivered morphine for pain control and the 'demand' (the count of button pushing for requiring pain medication from PCA) were recorded at 3, 6, 12, 24, 36, 48 and 72 h after the operation. One-way ANOVA with post-hoc test by Scheffe's method was adopted for statistical analysis of each variant (AA, AG, GG). The side-effects (nausea, vomiting and sedation) from morphine were recorded. P < 0.05 was considered to be statistically significant.

RESULTS

With sequencing by ABI PRISM 310 Genetic Analyser, we disclosed that the allele frequency was 75.5% for the A allele (female: 77.5%, male: 69.6%) and 24.5% for the G allele (female: 22.5%, male: 30.4%). The frequency of genotype occurrence was 61.3% for AA, 24.3% for AG and 14.4% for GG. Female patients of homozygous G118G of OPRMI required more morphine from PCA device for post-operative pain control than patients of AA and AG genotypes. No significant difference in morphine consumption for post-operative pain control was disclosed among three genotypes for male patients.

CONCLUSIONS

The impact caused by G118G polymorphism of OPRM1 on requirement of morphine consumption for post-operative pain control is potentially gender-linked.

Current Status of Neuraxial and Paravertebral Blocks for Adult Cardiac Surgery

Cardiac surgeries are known to produce moderate to severe pain. Pain management has traditionally been based on intravenous opioids. Poorly controlled pain can result in increased incidence of respiratory complications such as atelectasis and pneumonia leading to prolonged intubation and intensive care unit length of stay and subsequent prolonged hospital stay. Adequate perioperative analgesia improves hemodynamics and immunologic responses, which would result in better outcomes after cardiac surgery. Opioid sparing "Enhanced Recovery After Surgery" protocols are increasingly being incorporated into cardiac surgeries. This will reduce opioid requirements and opioid-related side effects and facilitate fast-tracking of patients. Regional analgesia can be provided by neuraxial blocks, fascial plane blocks, peripheral nerve blocks, or simply by the infiltration of the wound with local anesthetics for cardiac surgery. Neuraxial analgesia is provided through epidural, spinal, and paravertebral routes. Though they are being replaced by peripheral fascial plane blocks, epidural and spinal analgesia are still being used in some centers. In this article, neuraxial forms of analgesia are focused. We sought to review epidural analgesia and its impact in suppressing hemodynamic stress response, reducing pulmonary complications, and development of chronic pain. The relationship between intraoperative heparinization and potential neuraxial hematoma is discussed. Other neuraxial options such as spinal and paravertebral analgesia and their usefulness, benefits, and limitations are also reviewed.

Spinal A3 adenosine receptor activation acutely restores morphine antinociception in opioid tolerant male rats

Opioids are potent analgesics, but their pain-relieving effects diminish with repeated use. The reduction in analgesic potency is a hallmark of opioid analgesic tolerance, which hampers opioid pain therapy. In the central nervous system, opioid analgesia is critically modulated by adenosine, a purine nucleoside implicated in the beneficial and detrimental actions of opioid medications. Here, we focus on the A₃ adenosine receptor (A₃ AR) in opioid analgesic tolerance. Intrathecal administration of the A₃ AR agonist MRS5698 with daily systemic morphine in male rats attenuated the reduction in morphine antinociception over 7 days. In rats with established morphine tolerance, intrathecal MRS5698 partially restored the antinociceptive effects of morphine. However, when MRS5698 was discontinued, these animals displayed a reduced antinociceptive response to morphine. Our results suggest that MRS5698 acutely and transiently potentiates morphine antinociception in tolerant rats. By contrast, in morphine-naïve rats MRS5698 treatment did not impact thermal nociceptive threshold or affect antinociceptive response to a single injection of morphine. Furthermore, we found that morphine-induced adenosine release in cerebrospinal fluid was blunted in tolerant animals, but total spinal A₃ AR expression was not affected. Collectively, our findings indicate that spinal A₃ AR activation acutely potentiates morphine antinociception in the opioid tolerant state.

Training endogenous pain modulation: a preliminary investigation of neural adaptation following repeated exposure to clinically-relevant pain

Analgesic treatments that aim to eliminate pain display marginal success in relieving chronic pain and may increase pain vulnerability. Repeated exposure to pain may result in increased pain modulation via engagement of anti-nociceptive brain regions. It was hypothesized that repeated exposure to delayed onset muscle soreness (DOMS) would result in increased pain modulatory capacity (PMC) via functional neural adaptation. 23 healthy participants completed Baseline and Follow Up resting-state fMRI and quantitative sensory testing (QST) visits 40 days apart. Participants were randomized to two groups: A Repeated DOMS Group (RD Group) that received four, weekly DOMS inductions and a Control Group that received one baseline induction. Daily pain ratings were collected for seven days post-induction, as were quantitative sensory testing (QST) metrics at baseline and Follow Up. Regional functional connectivity (FC) was estimated among areas involved in pain modulation. Seed and network FC was estimated among areas involved in pain modulation and sensory processing. Changes in FC were compared between groups. The RD Group displayed significant reductions in post-DOMS pain ratings and significant changes in thermal QST measures. RD Group participants displayed greater adaptation in nucleus accumbens-medial prefrontal cortex (NAc-mPFC) FC and in sensorimotor network (SMN) connectivity with the dorsomedial, ventromedial, and rostromedial prefrontal cortices. Changes in SMN-PFC connectivity correlated with reductions in post-DOMS affective distress. Results suggest that repeated exposure to clinically-relevant pain results in adaptations among brain regions involved in pain modulation. Repeated exposure to clinically-relevant pain may serve as a mechanism to increase PMC via inhibition of emotional valuation of painful stimuli.

Regular dosing compared with as-needed dosing of opioids for management of chronic cancer pain: systematic review and meta-analysis

Opioids are the recommended form of analgesia for patients with persistent cancer pain, and regular dosing "by the clock" is advocated in many international guidelines on cancer pain management. The development of sustained-release opioid preparations has made regular dosing easier for patients. However, patients report that the intensity and impact of their cancer pain varies considerably day to day, and many try to find a trade-off between acceptable pain control and impact of cognitive (and other) adverse effects on daily activities. In acute care settings, (eg, postoperative) as-needed dosing and other opioid-sparing approaches have resulted in better patient outcomes compared with regular dosing. The aim of this study was to determine whether regular dosing of opioids was superior to as-needed dosing for persistent cancer pain. We systematically searched for randomised controlled trials that directly compared pain outcomes from regular dosing of opioids with as-needed dosing in adult cancer patients. We identified 4347 records, 25 randomised controlled trials meet the inclusion criteria, 9 were included in the review, and 7 of these included in meta-analysis. We found no clear evidence demonstrating superiority of regular dosing of opioids compared with as-needed dosing in persistent cancer pain, and regular dosing was associated with significantly higher total opioid doses. There was, however, a paucity of trials directly answering this question, and low-quality evidence limits the conclusions that can be drawn. It is clear that further high-quality clinical trials are needed to answer this question and to guide clinical practice.

Mechanisms, diagnosis, prevention and management of perioperative opioid-induced hyperalgesia

Opioid-induced hyperalgesia (OIH) occurs when opioids paradoxically enhance the pain they are prescribed to ameliorate. To address a lack of perioperative awareness, we present an educational review of clinically relevant aspects of the disorder. Although the mechanisms of OIH are thought to primarily involve medullary descending pathways, it is likely multifactorial with several relevant therapeutic targets. We provide a suggested clinical definition and directions for clinical differentiation of OIH from other diagnoses, as this may be confusing but is germane to appropriate management. Finally, we discuss prevention including patient education and analgesic management choices. As prevention may serve as the best treatment, patient risk factors, opioid mitigation, and both pharmacologic and non-pharmacologic strategies are discussed.

Modeling SARS-CoV-2 infection in individuals with opioid use disorder with brain organoids

The COVID-19 pandemic has aggravated a preexisting epidemic: the opioid crisis. Much literature has shown that the circumstances imposed by COVID-19, such as social distancing regulations, medical and financial instability, and increased mental health issues, have been detrimental to those with opioid use disorder (OUD). In addition, unexpected neurological sequelae in COVID-19 patients suggest that COVID-19 compromises neuroimmunity, induces hypoxia, and causes respiratory depression, provoking similar effects as those caused by opioid exposure. Combined conditions of COVID-19 and OUD could lead to exacerbated complications. With limited human in vivo options to study these complications, we suggest that iPSC-derived brain organoid models may serve as a useful platform to investigate the physiological connection between COVID-19 and OUD. This mini-review highlights the advances of brain organoids in other neuropsychiatric and infectious diseases and suggests their potential utility for investigating OUD and COVID-19, respectively.

Chronic cancer and non-cancer pain and opioid-induced hyperalgesia share common mechanisms: neuroinflammation and central sensitization

Neuroinflammation, a peculiar form of inflammation that occurs in response to noxious stimuli in peripheral and central nervous system (CNS), consists in altered vascular permeability followed by leukocyte recruitment and activation in the inflamed tissue, release of inflammatory mediators including cytokines and chemokines, and finally in the activation of microglia and astrocytes in the spinal cord and CNS. This phenomenon mediates and even worsen the inflammatory pain in many painful states and is responsible for central sensitization leading to pain chronicity. We describe the major neuroinflammatory mechanisms shared by cancer and non-cancer pain. Particular attention is given to two different chronic inflammatory painful diseases such as the complex regional pain syndrome and the rheumatoid arthritis as prototypes of neuroinflammatory diseases (gliopathies). In addition, we describe the complexity of tumor microenvironment, their main cellular components (tumor cells, tumor infiltrating leukocytes and sensory neurons) and their reciprocal interactions that characterize different forms and intensity of cancer pain. We also hypothesize that one type of cancer pain, the breakthrough pain, can be attributable to receptor-mediated interaction of opioids with tumor cells and intratumoral leukocytes. Surprisingly, long-term opioid treatment shares the same neuroinflammatory potential responsible for the chronicity of both cancer and non-cancer pain; thus, resulting in paradoxical worsening rather than relieving pain. This paradox has upset the world of pain therapy, with neuroinflammation now being a main target of emerging therapies.

Targeting Adenosine Receptors: A Potential Pharmacological Avenue for Acute and Chronic Pain

Adenosine is a purine nucleoside, responsible for the regulation of multiple physiological and pathological cellular and tissue functions by activation of four G protein-coupled receptors (GPCR), namely A₁, A_2A, A_2B, and A₃ adenosine receptors (ARs). In recent years, extensive progress has been made to elucidate the role of adenosine in pain regulation. Most of the antinociceptive effects of adenosine are dependent upon A₁AR activation located at peripheral, spinal, and supraspinal sites. The role of A_2AAR and A_2BAR is more controversial since their activation has both pro- and anti-nociceptive effects. A₃AR agonists are emerging as promising candidates for neuropathic pain. Although their therapeutic potential has been demonstrated in diverse preclinical studies, no AR ligands have so far reached the market. To date, novel pharmacological approaches such as adenosine regulating agents and allosteric modulators have been proposed to improve efficacy and limit side effects enhancing the effect of endogenous adenosine. This review aims to provide an overview of the therapeutic potential of ligands interacting with ARs and the adenosinergic system for the treatment of acute and chronic pain.

Sex differences in neuro(auto)immunity and chronic sciatic nerve pain

Chronic pain occurs with greater frequency in women, with a parallel sexually dimorphic trend reported in sufferers of many autoimmune diseases. There is a need to continue examining neuro-immune-endocrine crosstalk in the context of sexual dimorphisms in chronic pain. Several phenomena in particular need to be further explored. In patients, autoantibodies to neural antigens have been associated with sensory pathway hyper-excitability, and the role of self-antigens released by damaged nerves remains to be defined. In addition, specific immune cells release pro-nociceptive cytokines that directly influence neural firing, while T lymphocytes activated by specific antigens secrete factors that either support nerve repair or exacerbate the damage. Modulating specific immune cell populations could therefore be a means to promote nerve recovery, with sex-specific outcomes. Understanding biological sex differences that maintain, or fail to maintain, neuroimmune homeostasis may inform the selection of sex-specific treatment regimens, improving chronic pain management by rebalancing neuroimmune feedback. Given the significance of interactions between nerves and immune cells in the generation and maintenance of neuropathic pain, this review focuses on sex differences and possible links with persistent autoimmune activity using sciatica as an example.

Withdrawal-associated injury site pain prevalence and correlates among opioid-using people who inject drugs in Vancouver, Canada

BACKGROUND

Pain can return temporarily to old injury sites during opioid withdrawal. The prevalence and impact of opioid withdrawal-associated injury site pain (WISP) in various groups is unknown.

METHODS

Using data from observational cohorts, we estimated the prevalence and correlates of WISP among opioid-using people who inject drugs (PWID). Between June and December 2015, data on WISP and opioid use behaviours were elicited from participants in three ongoing prospective cohort studies in Vancouver, Canada, who were aged 18 years and older and who self-reported at least daily injection of heroin or non-medical presciption opioids.

RESULTS

Among 631 individuals, 276 (43.7 %) had a healed injury (usually pain-free), among whom 112 (40.6 %) experienced WISP, representing 17.7 % of opioid-using PWID interviewed. In a multivariable logistic regression model, WISP was positively associated with having a high school diploma or above (Adjusted Odds Ratio [AOR] = 2.23, 95 % Confidence Interval [CI]: 1.31-3.84), any heroin use in the last six months (AOR = 2.00, 95 % CI: 1.14-3.57), feeling daily pain that required medication (AOR = 2.06, CI: 1.18-3.63), and negatively associated with older age at first drug use (AOR = 0.96, 95 % CI: 0.93-0.99). Among 112 individuals with WISP, 79 (70.5 %) said that having this pain affected their opioid use behaviour, of whom 57 (72.2 %) used more opioids, 19 (24.1 %) avoided opioid withdrawal, while 3 (3.8 %) no longer used opioids to avoid WISP.

CONCLUSIONS

WISP is prevalent among PWID with a previous injury, and may alter opioid use patterns. Improved care strategies for WISP are warrented.