Opioid-Induced Hyperalgesia: A Diagnostic Dilemma

Effects of Multimodal Analgesia on Recovery From Percutaneous Spinal Cord Stimulator Implantation

OBJECTIVE

We aimed to determine the relationship between number and type of analgesic modalities utilized and postoperative pain after percutaneous spinal cord stimulator implantation. Secondary measures include opioid requirements, discharge times, and effects of specific modalities.

MATERIALS AND METHODS

This single-center retrospective cohort at Brooke Army Medical Center from April 2008 through July 2017 reviewed 70 patients undergoing stimulator implantation by a pain specialist. Data included: home opioid regimen; preoperative/postoperative medications and pain; intraoperative medications; and discharge times. Analysis utilized a Wilcoxon nonparametric mode, and chi-square testing for specific modalities. We compared outcomes based on the number of modalities administered and whether patients received specific medications.

RESULTS

Patients averaged receiving 3.8 modalities (standard deviation 1.4). Patients receiving ≥5 modalities had increased pain from preoperative to postoperative scores by two points, while those who received ≤4 had no increase (p < 0.01). Patients receiving ketamine had a median three point increase in pain scores from their baseline vs no change for others (p < 0.05). Patients receiving four modalities had shorter phase one recovery times vs ≤ 2 (median 66 vs 91.5 min; p = 0.01). Patients receiving ≥4 modalities had shorter times vs ≤3 (median 74 vs 88.5 min; p < 0.01). Patients receiving NSAIDs had shorter times than others (median 78 vs 87 min; p < 0.05).

CONCLUSIONS

Ketamine administration and use of ≥5 analgesic modalities were associated with more postoperative pain for unclear reasons. Patients receiving NSAIDs or ≥4 analgesic modalities had shorter recovery times. These data may lead to further work that could optimize ambulatory practices for stimulator implantation. More work is warranted on this subject.

Opioid-induced Hyperalgesia in Patients With Chronic Pain: A Systematic Review of Published Cases

INTRODUCTION

Opioid-induced hyperalgesia (OIH) remains an issue in patients with chronic pain. Multiple cases of OIH in patients with chronic pain exposed to opioids have been reported worldwide. The objective of this systematic review was to summarize the evidence of OIH from clinical reports.

METHODS

We searched the PubMed, Cochrane, EMBASE, and LILACS databases for case reports and case series of OIH published up to December 2020, with the aim to summarize the evidence for OIH in patients with chronic pain from clinical reports and to discuss issues relevant to the clinical diagnosis and management of OIH.

RESULTS

We retrieved and reviewed 41 articles describing 72 cases. Clinical features of OIH were observed in patients of both sexes, all ages, and with various types of pain treated with different classes of opioids. OIH was reported at all doses, but most published studies reported a pattern of OIH following treatment with very high daily doses of opioids (median oral morphine equivalent dose of 850 mg). OIH was diagnosed clinically in all cases. Three different strategies for OIH management were described: opioid rotation, opioid cessation, and the use of adjuvant pharmacotherapies. All had statistically similar success rates for OIH treatment: 72%, 57%, and 79%, respectively. The decrease in pain was achieved rapidly (mean: 8 d; range: 1 to 28 d). Adjuvant therapies resulted in the largest decrease in dose. Ketamine and dexmedetomidine were the most widely used adjuvant drugs.

CONCLUSION

The key finding is that clinical symptoms of OIH can be resolved when this condition is diagnosed and managed.

Alleviating Terminal Pediatric Cancer Pain

Terminal cancer pain remains one of the most distressing aspects of pediatric oncology practice. Opioids are the cornerstone of cancer pain management at end-of-life and fortunately, most pain at end-of-life can be managed successfully. This article presents a practical step-by-step approach to alleviating pediatric terminal cancer pain, which can be delivered across settings.

Effect of preoperative long-term opioid therapy on patient outcomes after total knee arthroplasty: an analysis of multicentre population-based administrative data

Background

Up to 40% of patients are receiving opioids at the time of total knee arthroplasty (TKA) in the United States despite evidence suggesting opioids are ineffective for pain associated with arthritis and have substantial risks. Our primary objective was to determine whether preoperative opioid users had worse knee pain and physical function outcomes 12 months after TKA than patients who were opioid-naive preoperatively; our secondary objective was to determine the prevalence of opioid use before and after TKA in Alberta, Canada.

Methods

In this retrospective analysis of population-based data, we identified adult patients who underwent TKA between 2013 and 2015 in Alberta. We used multivariable linear regression to examine the association between preoperative opioid use and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain and physical function scores 12 months after TKA, adjusting for potentially confounding variables.

Results

Of the 1907 patients, 592 (31.0%) had at least 1 opioid dispensed before TKA, and 124 (6.5%) were classified as long-term opioid users. Long-term opioid users had worse adjusted WOMAC pain and physical function scores 12 months after TKA than patients who were opioid-naive preoperatively (pain score β = 7.7, 95% confidence interval [CI] 4.0 to 11.6; physical function score β = 7.8, 95% CI 4.0 to 11.6; p < 0.001 for both). The majority (89 ([71.8%]) of patients who were long-term opioid users preoperatively were dispensed opioids 180–360 days after TKA, compared to 158 (12.0%) patients who were opioid-naive preoperatively.

Conclusion

A substantial number of patients were dispensed opioids before and after TKA, and patients who received opioids preoperatively had worse adjusted pain and functional outcome scores 12 months after TKA than patients who were opioid-naive preoperatively. These results suggest that patients prescribed opioids preoperatively should be counselled judiciously regarding expected outcomes after TKA.

A prospective randomized controlled study of auricular point acupressure to manage chronic low back pain in older adults: study protocol

BACKGROUND

Chronic low back pain (cLBP) is a major health problem and the most common pain condition among those aged 60 years or older in the US. Despite the development of pharmacological and nonpharmacological interventions, cLBP outcomes have not improved and disability rates continue to rise. This study aims to test auricular point acupressure (APA) as a non-invasive, nonpharmacological self-management strategy to manage cLBP and to address current shortcomings of cLBP treatment.

METHODS/DESIGN

For this prospective randomized controlled study, participants will be randomly assigned to three groups: (1) APA group (active points related to cLBP), (2) Comparison group-1 (non-active points, unrelated to cLBP), and (3) Comparison group-2 (enhanced educational control, an educational booklet on cLBP will be given and the treatment used by participants for their cLBP will be recorded). The ecological momentary assessment smartphone app will be used to collect real-time cLBP outcomes and adherence to APA practice. Treatment and nonspecific psychological placebo effects will be measured via questionnaires for all participants. This proposed trial will evaluate the APA sustained effects for cLBP at 12-month follow-up. Monthly telephone follow-up will be used to collect study outcomes. Blood will be collected during study visits at baseline, post APA treatment, and follow-up study visits at 1, 3, 6, 9 and 12 months post completion of treatment for a total of seven assessments. Appointments will start between 9 and 11 am to control for circadian variation in cytokine levels.

DISCUSSION

This study is expected to provide vital information on the efficacy, sustainability, and underlying mechanism of APA on cLBP necessary for APA to gain acceptance from both healthcare providers and patients, which would provide a strong impetus for including APA as part of cLBP management in clinical and home settings.

TRIAL REGISTRATION

ClinicalTrials.gov, ID: NCT03589703. Registered on 22 May 2018.

Low- versus high-dose intraoperative opioids: A systematic review with meta-analyses and trial sequential analyses

BACKGROUND

Opioid-induced hyperalgesia is a state of nociceptive sensitisation secondary to opioid administration. The objective of this meta-analysis was to test the hypothesis that high-dose intraoperative opioids contribute to increased post-operative pain and hyperalgesia when compared with a low-dose regimen in patients under general anaesthesia.

METHODS

We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement guidelines and rated the certainty of evidence with the Grading of Recommendations, Assessment, Development and Evaluation system. Only trials investigating pain outcomes and comparing two different dosages of the same intraoperative opioid in patients under general anaesthesia were included. The primary outcome was pain score (analogue scale, 0-10) at 24 post-operative hours. Secondary outcomes included pain score and cumulative intravenous morphine equivalents (mg) consumed at 2 post-operative hours, together with mechanical pain threshold (g·mm^-2 ).

RESULTS

Twenty-seven randomised controlled trials, including 1630 patients, were identified. Pain score at rest at 24 post-operative hours was increased in the high-dose group (mean difference [95% CI]: -0.2 [-0.4, -0.1]; trial sequential analysis-adjusted CI: -0.4, -0.02; low certainty of evidence). Similarly, at 2 post-operative hours, both pain score (mean difference [95% CI]: -0.4 [-0.6, -0.2]; low certainty of evidence) and cumulative intravenous morphine equivalents consumed (mean difference [95% CI]: -1.6 mg [-2.6, -0.7]; low certainty of evidence) were significantly higher in the high-dose group. Finally, the threshold for mechanical pain was significantly lower in the high-dose group (mean difference to pressure [95% CI]: 3.8 g·mm^-2 [1.8, 5.8]; low certainty of evidence).

CONCLUSIONS

There is low certainty of evidence that high-dose intraoperative opioid administration increases pain scores in the post-operative period, when compared with a low-dose regimen.

Opioid and Benzodiazepine Iatrogenic Withdrawal Syndrome in Patients in the Intensive Care Unit

Iatrogenic withdrawal syndrome is an increasingly recognized issue among adult patients in the intensive care unit. The prolonged use of opioids and benzodiazepines during the intensive care unit stay and preexisting disorders associated with their use put patients at risk of developing iatrogenic withdrawal syndrome. Although research to date is scant regarding iatrogenic withdrawal syndrome in adult patients in the intensive care unit, it is important to recognize and adequately manage iatrogenic withdrawal syndrome in order to prevent possible negative outcomes during and after a patient's intensive care unit stay. This article discusses in depth 8 studies of iatrogenic withdrawal syndrome among adult patients in the intensive care unit. It also addresses important aspects of opioid and benzodiazepine iatrogenic withdrawal syndrome, including prevalence, risk factors, and assessment and considers its prevention and management.

In Vitro Nociceptor Neuroplasticity Associated with In Vivo Opioid-Induced Hyperalgesia

Opioid-induced hyperalgesia (OIH) is a serious adverse event produced by opioid analgesics. Lack of an in vitro model has hindered study of its underlying mechanisms. Recent evidence has implicated a role of nociceptors in OIH. To investigate the cellular and molecular mechanisms of OIH in nociceptors, in vitro, subcutaneous administration of an analgesic dose of fentanyl (30 μg/kg, s.c.) was performed in vivo in male rats. Two days later, when fentanyl was administered intradermally (1 μg, i.d.), in the vicinity of peripheral nociceptor terminals, it produced mechanical hyperalgesia (OIH). Additionally, 2 d after systemic fentanyl, rats had also developed hyperalgesic priming (opioid-primed rats), long-lasting nociceptor neuroplasticity manifested as prolongation of prostaglandin E₂ (PGE₂) hyperalgesia. OIH was reversed, in vivo, by intrathecal administration of cordycepin, a protein translation inhibitor that reverses priming. When fentanyl (0.5 nm) was applied to dorsal root ganglion (DRG) neurons, cultured from opioid-primed rats, it induced a μ-opioid receptor (MOR)-dependent increase in [Ca²⁺]_i in 26% of small-diameter neurons and significantly sensitized (decreased action potential rheobase) weakly IB4⁺ and IB4^- neurons. This sensitizing effect of fentanyl was reversed in weakly IB4⁺ DRG neurons cultured from opioid-primed rats after in vivo treatment with cordycepin, to reverse of OIH. Thus, in vivo administration of fentanyl induces nociceptor neuroplasticity, which persists in culture, providing evidence for the role of nociceptor MOR-mediated calcium signaling and peripheral protein translation, in the weakly IB4-binding population of nociceptors, in OIH.SIGNIFICANCE STATEMENT Clinically used μ-opioid receptor agonists such as fentanyl can produce hyperalgesia and hyperalgesic priming. We report on an in vitro model of nociceptor neuroplasticity mediating this opioid-induced hyperalgesia (OIH) and priming induced by fentanyl. Using this model, we have found qualitative and quantitative differences between cultured nociceptors from opioid-naive and opioid-primed animals, and provide evidence for the important role of nociceptor μ-opioid receptor-mediated calcium signaling and peripheral protein translation in the weakly IB4-binding population of nociceptors in OIH. These findings provide information useful for the design of therapeutic strategies to alleviate OIH, a serious adverse event of opioid analgesics.

Preliminary Effectiveness of Auricular Point Acupressure on Chemotherapy-Induced Neuropathy: Part 1 Self-Reported Outcomes

PURPOSE

To reduce chemotherapy-induced neuropathy (CIN)-a significant challenge among cancer patients following chemotherapy-we explored the effects of auricular point acupressure (APA), which involves needleless, acupuncture-like stimulation on specific ear points.

DESIGN/METHOD

This pilot study examined the effects of a 4-week APA intervention in the management of CIN. Descriptive analysis was used to examine the changes in study outcomes.

RESULTS

Fifteen participants were enrolled. Two participants dropped out because they developed new medical conditions. Thirteen participants completed the study (87% retention rate). Study participants had more severe symptoms in their lower extremities (i.e., toes, feet, soles) than in their upper extremities (i.e., fingers, wrists, elbows). After the 4-week APA intervention, the mean percentage change scores ranged from 38% (tingling) to 49% (numbness); compared to pre-intervention, the therapeutic effects of APA were sustained at the 1-month follow-up. Function in both upper and lower extremities improved after the APA intervention (≥28%) and continued to improve at the 1-month follow-up (≥36%).

CONCLUSIONS

Preliminary results from this small sample provide initial evidence of the effectiveness of APA on CIN. Future studies should confirm these results using a larger sample, a comparative sham control, and an examination of the underlying physiological mechanisms of the anti-CIN effects of APA.

CLINICAL IMPLICATIONS

APA may provide an inexpensive and effective complementary approach for the self-management of CIN. Once the seeds have been taped to the patient's ear by the provider, patients are empowered to self-manage their CIN in their own environment.

Managing severe pain and abuse potential: the potential impact of a new abuse-deterrent formulation oxycodone/naltrexone extended-release product

Proper management of severe pain represents one of the most challenging clinical dilemmas. Two equally important goals must be attained: the humanitarian/medical goal to relieve suffering and the societal/legal goal to not contribute to the drug abuse problem. This is an age-old problem, and the prevailing emphasis placed on one or the other goal has resulted in pendulum swings that have resulted in either undertreatment of pain or the current epidemic of misuse and abuse. In an effort to provide efficacious strong pain relievers (opioids) that are more difficult to abuse by the most dangerous routes of administration, pharmaceutical companies are developing products in which the opioid is manufactured in a formulation that is designed to be tamper resistant. Such a product is known as an abuse-deterrent formulation (ADF). ADF opioid products are designed to deter or resist abuse by making it difficult to tamper with the product and extracting the opioid for inhalation or injection. To date, less than a dozen opioid formulations have been approved by the US Food and Drug Administration to carry specific ADF labeling, but this number will likely increase in the coming years. Most of these products are extended-release formulations.

Genetic deletion of microglial Panx1 attenuates morphine withdrawal, but not analgesic tolerance or hyperalgesia in mice

Opioids are among the most powerful analgesics for managing pain, yet their repeated use can lead to the development of severe adverse effects. In a recent study, we identified the microglial pannexin-1 channel (Panx1) as a critical substrate for opioid withdrawal. Here, we investigated whether microglial Panx1 contributes to opioid-induced hyperalgesia (OIH) and opioid analgesic tolerance using mice with a tamoxifen-inducible deletion of microglial Panx1. We determined that escalating doses of morphine resulted in thermal pain hypersensitivity in both Panx1-expressing and microglial Panx1-deficient mice. In microglial Panx1-deficient mice, we also found that acute morphine antinociception remained intact, and repeated morphine treatment at a constant dose resulted in a progressive decline in morphine antinociception and a reduction in morphine potency. This reduction in morphine antinociceptive potency was indistinguishable from that observed in Panx1-expressing mice. Notably, morphine tolerant animals displayed increased spinal microglial reactivity, but no change of microglial Panx1 expression. Collectively, our findings indicate microglial Panx1 differentially contributes to opioid withdrawal, but not the development of opioid-induced hyperalgesia or tolerance.

Opioid-Induced Hyperalgesia: Clinical Implications for Advanced Practice Nurses in Oncology

Opioid-induced hyperalgesia (OIH) is a key factor in the clinical management of patients experiencing pain. However, limited knowledge exists regarding the specific mechanisms involved in OIH and its treatment. A thorough assessment is usually required, and clinical diagnosis is mainly determined by exclusion in medical practice. Patients who are taking opioids should receive ongoing, comprehensive assessment by a clinician. Early identification of OIH will lead to improved patient outcomes.
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Opioid-induced hyperalgesia: Cellular and molecular mechanisms

Opioids produce strong analgesia but their use is limited by a paradoxical hypersensitivity named opioid-induced hyperalgesia (OIH) that may be associated to analgesic tolerance. In the last decades, a significant number of preclinical studies have investigated the factors that modulate OIH development as well as the cellular and molecular mechanisms underlying OIH. Several factors have been shown to influence OIH including the genetic background and sex differences of experimental animals as well as the opioid regimen. Mu opioid receptor (MOR) variants and interactions of MOR with different proteins were shown important. Furthermore, at the cellular level, both neurons and glia play a major role in OIH development. Several neuronal processes contribute to OIH, like activation of neuroexcitatory mechanisms, long-term potentiation (LTP) and descending pain facilitation. Increased nociception is also mediated by neuroinflammation induced by the activation of microglia and astrocytes. Neurons and glial cells exert synergistic effects, which contribute to OIH. The molecular actors identified include the Toll-like receptor 4 and the anti-opioid systems as well as some other excitatory molecules, receptors, channels, chemokines, pro-inflammatory cytokines or lipids. This review summarizes the intracellular and intercellular pathways involved in OIH and highlights some mechanisms that may be challenged to limit OIH in the future.

Opioid-induced redistribution of 6TM and 7TM μ opioid receptors: A hypothesized mechanistic facilitator model of opioid-induced hyperalgesia

Opioids are still the most popular form of pain treatment, but many unavoidable side effects make opioids a big challenge in effective pain management. Opioid-induced hyperalgesia (OIH), a paradoxical phenomenon, portrays an increased sensitivity to harmful stimuli caused by opioid exposure. Changes in the neural modulation are considered a major contributor to the development of OIH. Activation of opioid receptors (ORs) and corresponding downstream molecules are the vital composition of functional performance of opioids. Increasing interests were proposed of the interaction between ORs and other neural transmitter systems such as glutamatergic, GABAergic and adrenergic ones to the genesis of OIH. G protein coupled μ-opioid receptor (MOR) was studied comprehensively on its role in the development of OIH. In addition to the relationship between MOR and other neurotransmitter receptors, a new intracellular MOR that has six transmembrane (6TM) domains was identified, and found to perform a pro-nociceptive task in contrast to the counterpart 7TM isoform. A mechanistic model of OIH in which both 6TM and 7TM MORs undergoing membrane redistribution upon opioid exposure is proposed which eventually facilitates the neurons more sensitive to nociceptive stimulation than that of the preceding opioid exposure.