Personalized medicine and opioid analgesic prescribing for chronic pain: opportunities and challenges

Medical Marijuana for Pain Management in Hospice Care as a Complementary Approach to Scheduled Opioids: A Single Arm Study

Background: Opioid therapy is critical for pain relief for most hospice patients but may be limited by adverse side effects. Combining medical cannabis with opioids may help mitigate adverse effects while maintaining effective pain relief. Aim: This single-arm study investigated the impact of combined medical cannabis/opioid therapy on pain relief, opioid dose, appetite, respiratory function, well-being, nausea, and adverse events in hospice inpatients. Design: Adult hospice inpatients using scheduled oral, parenteral, or transdermal opioids for pain were administered standardized oral medical cannabis, 40 mg CBD/1.5 mg THC or 80 mg CBD/3 mg THC. Descriptive statistics detailed demographic and clinical baseline characteristics, the Mann-Whitney test compared outcomes, and the longitudinal mixed effects regression model analyzed longitudinal effects of combined therapy. Setting/Participants: Sixty-six inpatients at The Connecticut Hospital, Inc. were assessed over 996 treatment days; average age was 68.2 ± 12.9 years, 90.9% were white. Cancer was the most common diagnosis. Results: The medical cannabis/opioid combination showed a significant longitudinal reduction in pain intensity (P = .0029) and a non-significant trend toward lower opioid doses. Well-being, appetite, nausea, and respiratory function showed non-statistically significant changes. Three patients (4.5%) experienced minor, reversible adverse events potentially related to medical cannabis. No serious or life-threatening adverse events were seen. Conclusion: Combination medical cannabis/opioid therapy showed statistically significant pain relief and may have the potential for reducing opioid dose and mitigating opioid toxicity, offering a safe pain management alternative to opioids alone for patients in end-of-life care settings, and warrants further investigation in larger controlled trials.

Chronic wound-related pain, wound healing and the therapeutic potential of cannabinoids and endocannabinoid system modulation

Chronic wounds represent a significant burden on the individual, and the healthcare system. Individuals with chronic wounds report pain to be the most challenging aspect of living with a chronic wound, with current therapeutic options deemed insufficient. The cutaneous endocannabinoid system is an important regulator of skin homeostasis, with evidence of system dysregulation in several cutaneous disorders. Herein, we describe the cutaneous endocannabinoid system, chronic wound-related pain, and comorbidities, and review preclinical and clinical evidence investigating endocannabinoid system modulation for wound-related pain and wound healing. Based on the current literature, there is some evidence to suggest efficacy of endocannabinoid system modulation for promotion of wound healing, attenuation of cutaneous disorder-related inflammation, and for the management of chronic wound-related pain. However, there is 1) a paucity of preclinical studies using validated models, specific for the study of chronic wound-related pain and 2) a lack of randomised control trials and strong clinical evidence relating to endocannabinoid system modulation for wound-related pain. In conclusion, while there is some limited evidence of benefit of endocannabinoid system modulation in wound healing and wound-related pain management, further research is required to better realise the potential of targeting the endocannabinoid system for these therapeutic applications.

The role of chronic pain and pain anxiety in delay discounting of pain and monetary losses

Pain may alter intertemporal decisions by modifying the value of pain-related outcomes. For example, a person with chronic back pain may be faced with two choices: undergo surgery that could provide long-term relief but would involve additional short-term pain and discomfort during recovery; or continue living with the chronic pain and avoid the surgery, thus leading to overall deteriorated health. Such choices are well captured by delay discounting, which is defined as the decline in the subjective value of an outcome as the delay of its receipt increases. We investigated general pain anxiety and delay discounting of monetary losses and pain in 255 individuals with and without chronic pain. We found that people with chronic pain tend to discount the value of pain outcomes more than those without chronic pain, suggesting that chronic pain may contribute to impulsivity in decision-making related to pain. Moreover, the effect of chronic pain on delay discounting was mediated through general pain anxiety. This result, however, should be taken with caution, because the effect sizes were small, and the path model was underpowered. In conclusion, people with chronic pain might be more likely to prioritize avoiding immediate discomfort and may undervalue the potential long-term benefits of actions that could alleviate their pain in the future.

Fibromyalgia - etiology, diagnosis and treatment including perioperative management in patients with fibromyalgia

Fibromyalgia (FM) is considered a multifactorial disorder/syndrome with not fully understood etiology. Chronic generalized pain is the main symptom. A broad spectrum of factors is proposed to explain the etiology. Its multifactorial nature is inherently associated with challenges in diagnosis and therapy. Various evidence of etiology has been evaluated with the aim of establishing a novel therapeutic approach. The main issue in the diagnosis and management is to focus on the evaluation of strict diagnostic criteria to minimize under- and overdiagnosis. Fibromyalgia is a challenge for perioperative management because of the increased risk of possible complications and poorer outcomes, including postoperative pain chronification. The authors have proposed an up-to-date evaluation of perioperative management considering the current guidelines. Multimodal analgesia combined with tailored perioperative care is the most appropriate assessment. Interdisciplinary research with special interest in pain management, including perioperative medicine, seems to be the main theme for the future.

The power of integrating data: advancing pain research using meta-analysis

Publications related to pain research have increased significantly in recent years. The abundance of new evidence creates challenges staying up to date with the latest information. A comprehensive understanding of the literature is important for both clinicians and investigators involved in pain research. One commonly used method to combine and analyse data in health care research is meta-analysis. The primary aim of a meta-analysis is to quantitatively synthesise the results of multiple studies focused on the same research question. Meta-analysis is a powerful tool that can be used to advance pain research. However, there are inherent challenges when combining data from multiple sources. There are also numerous models and statistical considerations when undertaking a meta-analysis. This review aims to discuss the planning and preparation for completing a meta-analysis, review commonly used meta-analysis models, and evaluate the clinical implications of meta-analysis in pain research.

Development and testing of data infrastructure in the American College of Emergency Physicians' Clinical Emergency Data Registry for opioid-related research

Objective

Prior research has identified gaps in the capacity of electronic health records (EHRs) to capture the intricacies of opioid-related conditions. We sought to enhance the opioid data infrastructure within the American College of Emergency Physicians' Clinical Emergency Data Registry (CEDR), the largest national emergency medicine registry, through data mapping, validity testing, and feasibility assessment.

Methods

We compared the CEDR data dictionary to opioid common data elements identified through prior environmental scans of publicly available data systems and dictionaries used in national informatics and quality measurement of policy initiatives. Validity and feasibility assessments of CEDR opioid-related data were conducted through the following steps: (1) electronic extraction of CEDR data meeting criteria for an opioid-related emergency care visit, (2) manual chart review assessing the quality of the extracted data, (3) completion of feasibility scorecards, and (4) qualitative interviews with physician reviewers and informatics personnel.

Results

We identified several data gaps in the CEDR data dictionary when compared with prior environmental scans including urine drug testing, opioid medication, and social history data elements. Validity testing demonstrated correct or partially correct data for >90% of most extracted CEDR data elements. Factors affecting validity included lack of standardization, data incorrectness, and poor delimitation between emergency department (ED) versus hospital care. Feasibility testing highlighted low-to-moderate feasibility of date and social history data elements, significant EHR platform variation, and inconsistency in the extraction of common national data standards (eg, Logical Observation Identifiers Names and Codes, International Classification of Diseases, Tenth Revision codes).

Conclusions

We found that high-priority data elements needed for opioid-related research and clinical quality measurement, such as demographics, medications, and diagnoses, are both valid and can be feasibly captured in a national clinical quality registry. Future work should focus on implementing structured data collection tools, such as standardized documentation templates and adhering to data standards within the EHR that would better characterize ED-specific care for opioid use disorder and related research.

Aiding the prescriber: developing a machine learning approach to personalized risk modeling for chronic opioid therapy amongst US Army soldiers

The opioid epidemic is a major policy concern. The widespread availability of opioids, which is fueled by physician prescribing patterns, medication diversion, and the interaction with potential illicit opioid use, has been implicated as proximal cause for subsequent opioid dependence and mortality. Risk indicators related to chronic opioid therapy (COT) at the point of care may influence physicians' prescribing decisions, potentially reducing rates of dependency and abuse. In this paper, we investigate the performance of machine learning algorithms for predicting the risk of COT. Using data on over 12 million observations of active duty US Army soldiers, we apply machine learning models to predict the risk of COT in the initial months of prescription. We use the area under the curve (AUC) as an overall measure of model performance, and we focus on the positive predictive value (PPV), which reflects the models' ability to accurately target military members for intervention. Of the many models tested, AUC ranges between 0.83 and 0.87. When we focus on the top 1% of members at highest risk, we observe a PPV value of 8.4% and 20.3% for months 1 and 3, respectively. We further investigate the performance of sparse models that can be implemented in sparse data environments. We find that when the goal is to identify patients at the highest risk of chronic use, these sparse linear models achieve a performance similar to models trained on hundreds of variables. Our predictive models exhibit high accuracy and can alert prescribers to the risk of COT for the highest risk patients. Optimized sparse models identify a parsimonious set of factors to predict COT: initial supply of opioids, the supply of opioids in the month being studied, and the number of prescriptions for psychotropic medications. Future research should investigate the possible effects of these tools on prescriber behavior (e.g., the benefit of clinician nudging at the point of care in outpatient settings).

The Symmetry of Lower Back Pain as a Potential Screening Factor for Serious Pathology: A Survey Study

Background: Pain maps provide reliable information on pain location in various conditions. This study explored the feasibility of pain maps as a screening tools for serious underlying conditions. The pain symmetry was evaluated as the possible distinguishing feature. Methods: A Web-based survey on the correlation of pain-related disability and pain pattern was developed. Respondents with lower back pain were asked to mark the exact location of their pain over the pain chart. The symmetry index was calculated and used to divide subjects into two groups that were then compared in terms of the prevalence of red flags for serious pathologies, as well as the pain-related disability measured with COMI and ODI instruments. Results: Of the 4213 respondents who completed the survey, 1018 were included in the study. The pain related disability was greater in respondents with asymmetrical pain patterns, as shown with all instruments. The distribution of red flags was also dependent on pain symmetry. The history of weight loss (6.70 vs. 1.76 p < 0.001) and fever (4.91 vs. 2.14 p < 0.001) were more prevalent with symmetrical pain patterns, and the history of trauma was more frequent with asymmetrical pain (21.41 vs. 10.71 p < 0.001). Conclusions: It was shown that the symmetry of pain is correlated to the prevalence of red flags and pain-related disability.

Genetic Factors Associated With Pain Severity, Daily Opioid Dose Requirement, and Pain Response Among Advanced Cancer Patients Receiving Supportive Care

BACKGROUND

Current understanding of genetic factors associated with pain severity, and improvement of pain with opioids in advanced cancer patients (AC) is inadequate for delivery of personalized pain therapy (PPT). Therefore, the aim of this study was to determine the genetic factors associated with pain severity, daily opioid dose, and pain response in AC patients receiving supportive care.

METHODS

In this prospective study, AC patients were eligible if they had cancer pain ≥4/10 on Edmonton Symptom Assessment Scale (ESAS) - Pain Item and needed opioid rotation for pain control by specialist at the outpatient supportive care center. Association of genetic factors with pain phenotype was assessed using logistic regression models and SKATO (Gene-block) analysis.

RESULTS

About 174/178 (98%) patient samples were analyzed. After adjustment for demographic and clinical variables, pain severity was negatively associated with intron variant alleles in OPRM1 rs9322446, P = 0.02; rs2270459, P = 0.038; rs62052210, P = 0.038. Opioid daily dose was positively associated NFKBIA rs2233419, P = 0.008; rs2233417, P = 0.007; rs3138054, P = 0.008; rs1050851, P = 0.015; ORPM1 rs9479759, P = 0.046; rs2003185, P = 0.047; rs636433, P = 0.044; COMT (rs9306234, P = 0.014; rs165728, P = 0.014; rs2020917, P = 0.036; rs165728, P = 0.034); ARRB2 (rs1045280, P = 0.045); and pain response to opioids was negatively associated OPRM1 rs1319339, P = 0.024; rs34427887, P = 0.048; and COMT rs4646316, P = 0.03; rs35478083, P = 0.028, respectively. SKATO analysis showed association between pain severity and CXCL8 (P = 0.0056), and STAT6 (P = 0.0297) genes respectively, and pain response with IL-6 (P = 0.00499).

CONCLUSIONS

This study identified that SNPs of OPRM1, COMT, NFKBIA, CXCL8, IL-6, STAT6, and ARRB2 genes were associated with pain severity, opioid daily dose, and pain response in AC receiving supportive care. Additional studies are needed to validate our findings for PPT.

Effects of Wearable Transcutaneous Electrical Nerve Stimulation on Fibromyalgia: A Randomized Controlled Trial

Purpose

Fibromyalgia is a chronic condition characterized by widespread pain and interference with daily activities. The aim of this study is to assess the benefit of transcutaneous electrical nerve stimulation (TENS) for persons diagnosed with fibromyalgia.

Patients and Methods

Adults meeting diagnostic criteria for fibromyalgia were randomized in a double-blind trial to receive either an active (n=62) or sham (n=57) wearable TENS device for 3-months. Subjects were classified as having lower or higher pain sensitivity by Quantitative Sensory Testing (QST). Patient Global Impression of Change (PGIC, primary outcome) and secondary efficacy measures including Fibromyalgia Impact Questionnaire (FIQR), Brief Pain Inventory (BPI) and painDETECT questionnaire (PDQ) were assessed at baseline, 6-weeks and 3-months. Treatment effects were determined by a mixed model for repeated measures (MMRM) analysis of the intention-to-treat (ITT) population (N=119). A pre-specified subgroup analysis of pain sensitivity was conducted using an interaction term in the model.

Results

No differences were found between active and sham treatment on PGIC scores at 3-months (0.34, 95% CI [−0.37, 1.04], p=0.351) in the ITT population. However, in subjects with higher pain sensitivity (n=60), PGIC was significantly greater for active treatment compared to sham (1.19, 95% CI [0.24, 2.13], p=0.014). FIQR total score (−7.47, 95% CI [−12.46, −2.48], p=0.003), FIQR pain item (−0.62, 95% CI [−1.17, −0.06], p=0.029), BPI Interference (−0.70, 95% CI [−1.30, −0.11], p=0.021) and PDQ (−1.69, 95% CI [−3.20, −0.18], p=0.028) exhibited significant improvements for active treatment compared to sham in the ITT population. Analgesics use was stable and comparable in both groups.

Conclusion

This study demonstrated modest treatment effects of reduced disease impact, pain and functional impairment from wearable TENS in individuals with fibromyalgia. Subjects with higher pain sensitivity exhibited larger treatment effects than those with lower pain sensitivity. Wearable TENS may be a safe treatment option for people with fibromyalgia.

Clinicaltrials.gov Registration

NCT03714425.

Postoperative duration of opioid use and acute healthcare services use in cancer patients hospitalized for thoracic surgery

BACKGROUND

Postoperative pain control is an important cancer care component. However, opioid consumption has resulted in a surge of adverse events, with thoracic surgery patients having the highest rate of persistent use. The effect of opioid duration post-discharge and the risk of increased acute healthcare use in this population remains unclear.

METHODS

A prospective cohort of non-metastatic cancer patients was assembled from an academic health center in Montreal (Canada). Clinical data linked to administrative claims from the universal healthcare program was used to determine the association between time-varying opioid patterns and emergency department (ED) visits/re-admissions/death 3 months following thoracic surgery.

RESULTS

Of the 610 patients, 77% had at least one opioid dispensed post-discharge. Compared to non-opioid users, <15 days of use was associated with a 42% decreased risk of acute healthcare events, adjusted HR 0.58, 95% CI (0.40-0.85); longer durations were not associated with an increased risk. Compared to short-term use (<15 days), use of >30 days was associated with a 72% increased risk of the outcome, aHR: 1.72, 95% CI (1.01-2.93).

CONCLUSION

There was a variation in the risk of acute healthcare use associated with postsurgical opioid use. Findings from this study may be used to inform postoperative prescribing practices.

Treatment of Neck Pain with Opioids in the Primary Care Setting: Trends and Geographic Variation

OBJECTIVE

Neck pain is a leading cause of years lived with disability and is often managed with opioid medications in primary care settings, though this is contraindicated by national guidelines. The aim of this study was to determine the prevalence of opioid prescription for neck pain at a primary care visit and to analyze the geographic variation and trends in opioid prescriptions between 2011 and 2017.

METHODS

Using a prescription drug claims database, we identified 591,961 adult patients who presented for neck pain in primary care settings between 2011 and 2017. Patients who had outpatient specialty visits within 1 year before presentation, a concomitant diagnosis of a non-musculoskeletal cause of neck pain, or preexisting chronic opioid use were excluded.

RESULTS

The mean age of the patients was 45 ± 12 years, and 64% were female. Fifteen percent of patients were prescribed opioids within 30 days of their encounter. Eleven percent of patients were prescribed moderate- to high-dose opioids (>20 morphine milligram equivalents). From 2011-2017, the proportion of both overall opioid prescriptions and moderate- to high-dose prescriptions given to first time presenters to an outpatient clinic for neck pain was highest in Mississippi (20%) and lowest in New Mexico (6%) (P < 0.001). In 2017, the proportion of both overall opioid prescriptions and moderate- to high-dose prescriptions was highest in the Midwest (10.4%) and lowest in the Northeast (4.9%). The proportion of patients with filled opioid prescriptions declined between 2011 (19%) and 2017 (13%) (P < 0.001), and the proportion of patients with moderate- to high-dose prescriptions declined from 2011 (13%) to 2017 (8%) (P < 0.001). first-time presenters of neck pain to an outpatient clinic.

CONCLUSIONS

Opioid medication use for neck pain in the primary care setting is significant. Although opioid prescriptions are declining, there remains a need for further standardization in prescription practices.

Diet and companionship modulate pain via a serotonergic mechanism

Treatment of severe chronic and acute pain in sickle cell disease (SCD) remains challenging due to the interdependence of pain and psychosocial modulation. We examined whether modulation of the descending pain pathway through an enriched diet and companionship could alleviate pain in transgenic sickle mice. Mechanical and thermal hyperalgesia were reduced significantly with enriched diet and/or companionship. Upon withdrawal of both conditions, analgesic effects observed prior to withdrawal were diminished. Serotonin (5-hydroxytryptamine, 5-HT) was found to be increased in the spinal cords of mice provided both treatments. Additionally, 5-HT production improved at the rostral ventromedial medulla and 5-HT accumulated at the dorsal horn of the spinal cord of sickle mice, suggesting the involvement of the descending pain pathway in the analgesic response. Modulation of 5-HT and its effect on hyperalgesia was also investigated through pharmaceutical approaches. Duloxetine, a serotonin-norepinephrine reuptake inhibitor, showed a similar anti-nociceptive effect as the combination of diet and companionship. Depletion of 5-HT through p-chlorophenylalanine attenuated the anti-hyperalgesic effect of enriched diet and companionship. More significantly, improved diet and companionship enhanced the efficacy of a sub-optimal dose of morphine for analgesia in sickle mice. These findings offer the potential to reduce opioid use without pharmacological interventions to develop effective pain management strategies.

Greater Conditioned Pain Modulation Is Associated With Enhanced Morphine Analgesia in Healthy Individuals and Patients With Chronic Low Back Pain

OBJECTIVES

Conditioned pain modulation (CPM) protocols index magnitude of descending pain inhibition. This study evaluated whether the degree of CPM, controlling for CPM expectancy confounds, was associated with analgesic and subjective responses to morphine and whether chronic pain status or sex moderated these effects.

MATERIALS AND METHODS

Participants included 92 individuals with chronic low back pain and 99 healthy controls, none using daily opioid analgesics. In a cross-over design, participants attended 2 identical laboratory sessions during which they received either intravenous morphine (0.08 mg/kg) or saline placebo before undergoing evoked pain assessment. In each session, participants engaged in ischemic forearm and heat pain tasks, and a CPM protocol combining ischemic pain (conditioning stimulus) and heat pain (test stimulus). Placebo-controlled morphine outcomes were derived as differences in pain and subjective effects across drug conditions.

RESULTS

In hierarchical regressions controlling for CPM expectancies, greater placebo-condition CPM was associated with less subjective morphine unpleasantness (P=0.001) and greater morphine analgesia (P's<0.05) on both the ischemic pain task (Visual Analog Scale Pain Intensity and Unpleasantness) and heat pain task (Visual Analog Scale Pain Intensity, McGill Pain Questionnaire-Sensory, and Present Pain Intensity subscales). There was no moderation by sex or chronic low back pain status, except for the ischemic Present Pain Intensity outcome for which a significant 2-way interaction (P<0.05) was noted, with men showing a stronger positive relationship between CPM and morphine analgesia than women.

DISCUSSION

Results suggest that CPM might predict analgesic and subjective responses to opioid administration. Further evaluation of CPM as an element of precision pain medicine algorithms may be warranted.

Opioid and neuroHIV Comorbidity - Current and Future Perspectives

With the current national opioid crisis, it is critical to examine the mechanisms underlying pathophysiologic interactions between human immunodeficiency virus (HIV) and opioids in the central nervous system (CNS). Recent advances in experimental models, methodology, and our understanding of disease processes at the molecular and cellular levels reveal opioid-HIV interactions with increasing clarity. However, despite the substantial new insight, the unique impact of opioids on the severity, progression, and prognosis of neuroHIV and HIV-associated neurocognitive disorders (HAND) are not fully understood. In this review, we explore, in detail, what is currently known about mechanisms underlying opioid interactions with HIV, with emphasis on individual HIV-1-expressed gene products at the molecular, cellular and systems levels. Furthermore, we review preclinical and clinical studies with a focus on key considerations when addressing questions of whether opioid-HIV interactive pathogenesis results in unique structural or functional deficits not seen with either disease alone. These considerations include, understanding the combined consequences of HIV-1 genetic variants, host variants, and μ-opioid receptor (MOR) and HIV chemokine co-receptor interactions on the comorbidity. Lastly, we present topics that need to be considered in the future to better understand the unique contributions of opioids to the pathophysiology of neuroHIV. Graphical Abstract Blood-brain barrier and the neurovascular unit. With HIV and opiate co-exposure (represented below the dotted line), there is breakdown of tight junction proteins and increased leakage of paracellular compounds into the brain. Despite this, opiate exposure selectively increases the expression of some efflux transporters, thereby restricting brain penetration of specific drugs.

Leftover opioids following adult surgical procedures: a systematic review and meta-analysis

BACKGROUND

US opioid prescribing and use escalated over the last two decades, with parallel increases in opioid misuse, opioid-related deaths, and concerns about diversion. Postoperatively prescribed opioids contribute to these problems. Policy makers have addressed this issue by limiting postoperative opioid prescribing. However, until recently, little data existed to guide prescribers on opioid needs postoperatively. This meta-analysis quantitatively integrated the growing literature regarding extent of opioids leftover after surgery and identified factors associated with leftover opioid proportions.

METHODS

We conducted a meta-analysis of observational studies quantifying postoperative opioid consumption in North American adults, and evaluated effect size moderators using robust variance estimation meta-regression. Medline, EMBASE, Cumulative Index of Nursing and Allied Health Literature, and Cochrane Database of Systematic Reviews were searched for relevant articles published January 1, 2000 to November 10, 2018. The Methodological Index for Non-Randomized Studies (MINORS) tool assessed risk of study bias. The proportion effect size quantified the primary outcome: proportion of prescribed postoperative opioids leftover at the time of follow-up. Primary meta-regression analyses tested surgical type, amount of opioids prescribed, and study publication year as possible moderators. Secondary meta-regression models included surgical invasiveness, age, race, gender, postoperative day of data collection, and preoperative opioid use.

RESULTS

We screened 911 citations and included 44 studies (13,068 patients). The mean weighted effect size for proportion of postoperative opioid prescriptions leftover was 61% (95% CI, 56-67%). Meta-regression models revealed type of surgical procedure and level of invasiveness had a statistically significant effect on proportion of opioids leftover. Proportion of opioids leftover was greater for "other soft tissue" surgeries than abdominal/pelvic surgeries, but did not differ significantly between orthopedic and abdominal/pelvic surgeries. Minimally invasive compared to open surgeries resulted in a greater proportion of opioids leftover. Limitations include predominance of studies from academic settings, inconsistent reporting of confounders, and a possible publication bias toward studies reporting smaller leftover opioid proportions.

CONCLUSIONS AND IMPLICATIONS OF KEY FINDINGS

A significant proportion of opioids are leftover postoperatively. Surgery type and level of invasiveness affect postoperative opioid consumption. Integration of such factors into prescribing guidelines may help minimize opioid overprescribing while adequately meeting analgesic needs.

Scheduled versus as-needed postpartum analgesia and oxycodone utilization

Background: An optimal approach for providing sufficient postpartum analgesia while minimizing the risk of opioid misuse or diversion has yet to be elucidated. Moreover, there is scant literature on the efficacy of around-the-clock (ATC) scheduled dosing of opioid analgesia compared to pro re nata (PRN; as-needed) dosing for postpartum pain management. Here we evaluate a quality improvement intervention that aimed to proactively provide pain relief with a multimodal analgesic regimen that includes oxycodone at scheduled time intervals. This new protocol stands in stark contrast to many contemporary postpartum pain management regimens in which oral opioid medications are reserved for treating breakthrough pain.Objective: Our aim was to determine how inpatient oxycodone use is affected by as-needed compared to ATC scheduled dosing of acetaminophen, ibuprofen, and low-dose oxycodone, with the option to decline any of these medications. We also sought to determine the effect of each modality on patient satisfaction with pain control.Methods: Retrospective cohort study of singleton deliveries at ≥37 weeks of gestation at a tertiary hospital from 2013 to 2016. In month 21 of the 48-month study period, a new institutional protocol for postpartum pain management was implemented which consisted of scheduled dosing of a multimodal analgesic regimen. Prior to this, patients received pain relief only as needed, by reporting elevated pain scores to nursing staff. Patients were excluded for the following: NSAID or opioid allergies, protocol deviations, transition month deliveries, history of drug abuse, positive urine toxicology, delivery with general anesthesia, prolonged hospitalization, postpartum hemorrhage, hypertensive disorders of pregnancy, incomplete records. Outcomes evaluated were the percentage of patients receiving oxycodone and mean oxycodone use per inpatient day (milligrams). Segmented regression analysis of interrupted time series was performed to estimate linear time trends of oxycodone consumption pre- and post-protocol implementation. Results of the Hospital Consumer Assessment of Healthcare Providers and Systems (HCAHPS) standardized survey were also compared before and after implementation.Results: A total of 19,192 deliveries were included. After adjusting for confounders, a significant downward trend in the percentage of patients receiving oxycodone was noted among both cesarean (0.004% decrease per month; p < .006) and vaginal deliveries (0.005% decrease per month; p < .0001) before implementation of the scheduled pain management protocol. Among cesarean deliveries, there was no shift at the time of implementation, and no change in the slope of the trend after implementation. Among vaginal deliveries, there was an upward shift at implementation (+7.4%, p < .0001) but no change in the slope of the trend after implementation. Regardless of mode of delivery, no trend in monthly mean oxycodone consumption per day existed before or after implementation of the new protocol, and there was no shift at the time of implementation. Scheduled multimodal analgesia was associated with an improvement in HCAHPS scores for patient reported pain control after cesarean section (63 versus 71% reporting "Always" well controlled; p < .001) but had no effect after vaginal delivery.Conclusion: After cesarean delivery, scheduled multimodal analgesia that includes ATC dosing of acetaminophen, ibuprofen, and low-dose oxycodone, with the option to decline any of these medications, does not increase the percentage of women who receive oxycodone or mean oxycodone consumption per inpatient day compared to as-needed analgesia. After vaginal delivery, scheduled multimodal analgesia is associated with an increase in the percentage of women who receive oxycodone but no change in mean oxycodone consumption per inpatient day.

Opioid free onco-anesthesia: Is it time to convict opioids? A systematic review of literature

The epidemic of opioid crisis started getting recognised as a public health emergency in view of increasing opioid-related deaths occurring due to undetected respiratory depression. Prescribing opioids at discharge has become an independent risk factor for chronic opioid use, following which, prescription practices have undergone a radical change. A call to action has been voiced recently to end the opioid epidemic although with the pain practitioners still struggling to make opioids readily available. American Society of Anesthesiologist (ASA) has called for reducing patient exposure to opioids in the surgical setting. Opioid sparing strategies have emerged embracing loco-regional techniques and non-opioid based multimodal pain management whereas opioid free anesthesia is the combination of various opioid sparing strategies culminating in complete elimination of opioid usage. The movement away from opioid usage perioperatively is a massive but necessary shift in anesthesia which has rationalised perioperative opioid usage. Ideal way moving forward would be to adapt selective low opioid effective dosing which is both procedure and patient specific while reserving it as rescue analgesia, postoperatively. Many unknowns persist in the domain of immunologic effects of opioids, as complex interplay of factors gets associated during real time surgery towards outcome. At present it would be too premature to conclude upon opioid-induced immunosuppression from the existing evidence. Till evidence is established, there are no recommendations to change current clinical practice. At the same time, consideration for multimodal opioid sparing strategies should be initiated in each patient undergoing surgery.

Opioid receptors: drivers to addiction?

Drug addiction is a worldwide societal problem and public health burden, and results from recreational drug use that develops into a complex brain disorder. The opioid system, one of the first discovered neuropeptide systems in the history of neuroscience, is central to addiction. Recently, opioid receptors have been propelled back on stage by the rising opioid epidemics, revolutions in G protein-coupled receptor research and fascinating developments in basic neuroscience. This Review discusses rapidly advancing research into the role of opioid receptors in addiction, and addresses the key questions of whether we can kill pain without addiction using mu-opioid-receptor-targeting opiates, how mu- and kappa-opioid receptors operate within the neurocircuitry of addiction and whether we can bridge human and animal opioid research in the field of drug abuse.

Neuroimaging-based pain biomarkers: definitions, clinical and research applications, and evaluation frameworks to achieve personalized pain medicine

One of the key ambitions of neuroimaging-based pain biomarker research is to augment patient and clinician reporting of clinically relevant phenomena with neural measures for prediction, prognosis, and detection of pain. Despite years of productive research on the neuroimaging of pain, such applications have seen little advancement. However, recent developments in identifying brain-based biomarkers of pain through advances in technology and multivariate pattern analysis provide some optimism. Here, we (1) define and review the different types of potential neuroimaging-based biomarkers, their clinical and research applications, and their limitations and (2) describe frameworks for evaluation of pain biomarkers used in other fields (eg, genetics, cancer, cardiovascular disease, immune system disorders, and rare diseases) to achieve broad clinical and research utility and minimize the risks of misapplication of this emerging technology. To conclude, we discuss future directions for neuroimaging-based biomarker research to achieve the goal of personalized pain medicine.

The association between endogenous opioid function and morphine responsiveness: a moderating role for endocannabinoids

We sought to replicate previous findings that low endogenous opioid (EO) function predicts greater morphine analgesia and extended these findings by examining whether circulating endocannabinoids and related lipids moderate EO-related predictive effects. Individuals with chronic low-back pain (n = 46) provided blood samples for endocannabinoid analyses, then underwent separate identical laboratory sessions under 3 drug conditions: saline placebo, intravenous (i.v.) naloxone (opioid antagonist; 12-mg total), and i.v. morphine (0.09-mg/kg total). During each session, participants rated low-back pain intensity, evoked heat pain intensity, and nonpain subjective effects 4 times in sequence after incremental drug dosing. Mean morphine effects (morphine-placebo difference) and opioid blockade effects (naloxone-placebo difference; to index EO function) for each primary outcome (low-back pain intensity, evoked heat pain intensity, and nonpain subjective effects) were derived by averaging across the 4 incremental doses. The association between EO function and morphine-induced back pain relief was significantly moderated by endocannabinoids [2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (AEA)]. Lower EO function predicted greater morphine analgesia only for those with relatively lower endocannabinoids. Endocannabinoids also significantly moderated EO effects on morphine-related changes in visual analog scale-evoked pain intensity (2-AG), drug liking (AEA and 2-AG), and desire to take again (AEA and 2-AG). In the absence of significant interactions, lower EO function predicted significantly greater morphine analgesia (as in past work) and euphoria. Results indicate that EO effects on analgesic and subjective responses to opioid medications are greatest when endocannabinoid levels are low. These findings may help guide development of mechanism-based predictors for personalized pain medicine algorithms.

Opioid-Induced Hyperalgesia Is Associated with Dysregulation of Circadian Rhythm and Adaptive Immune Pathways in the Mouse Trigeminal Ganglia and Nucleus Accumbens

The benefits of opioid-based treatments to mitigate chronic pain can be hindered by the side effects of opioid-induced hyperalgesia (OIH) that can lead to higher consumption and risk of addiction. The present study advances the understanding of the molecular mechanisms associated with OIH by comparing mice presenting OIH symptoms in response to chronic morphine exposure (OIH treatment) relative to control mice (CON treatment). Using RNA-Seq profiles, gene networks were inferred in the trigeminal ganglia (TG), a central nervous system region associated with pain signaling, and in the nucleus accumbens (NAc), a region associated with reward dependency. The biological process of nucleic acid processing was over-represented among the 122 genes that exhibited a region-dependent treatment effect. Within the 187 genes that exhibited a region-independent treatment effect, circadian rhythm processes were enriched among the genes over-expressed in OIH relative to CON mice. This enrichment was supported by the differential expression of the period circadian clock 2 and 3 genes (Per2 and Per3). Transcriptional regulators in the PAR bZip family that are influenced by the circadian clock and that modulate neurotransmission associated with pain and drug addiction were also over-expressed in OIH relative to CON mice. Also notable was the under-expression in OIH relative to CON mice of the Toll-like receptor, nuclear factor-kappa beta, and interferon gamma genes and enrichment of the adaptive immune processes. The results from the present study offer insights to advance the effective use of opioids for pain management while minimizing hyperalgesia.

Circulating miRNA Signature as a Potential Biomarker for the Prediction of Analgesic Efficacy of Hydromorphone

No practical biomarkers currently exist for the prediction of the analgesic efficacy of opioids. Previously, we reported circulating miRNA signatures differentially regulated by µ-opioid receptor (MOR) agonists in healthy subjects. We hypothesized that these miRNAs could be potential pharmacodynamic biomarkers to estimate MOR stimulation, and predict the efficacy of opioids; i.e., patients with low MOR stimulation may be more vulnerable to strengthening of the MOR signal upon hydromorphone treatment. To test this hypothesis, plasma samples were obtained from 25 patients with cancer pain prior to the initiation of hydromorphone treatment and the circulating miRNA levels were evaluated, focusing on four miRNAs (i.e., hsa-miR-423-3p, hsa-let-7a-5p, hsa-miR-26a-5p, and hsa-let-7f-5p) and four miRNAs (i.e., hsa-miR-144-3p, hsa-miR-451a, hsa-miR-215, and hsa-miR-363-3p) that were most clearly up and downregulated by hydromorphone and oxycodone. The patients were classified into two classes with putative high and low MOR signal, estimated based on the plasma miRNA signature. A significant correlation was observed between the analgesic efficacy and the putative MOR signal level, and patients with low MOR signal achieved better pain control (i.e., ΔVAS < 0) through hydromorphone. These results suggested that plasma miRNA signatures could serve as clinical biomarkers for the prediction of the analgesic efficacy of hydromorphone.

Effect of chronic opioid therapy on pain and survival in a humanized mouse model of sickle cell disease

Chronic morphine treatment leads to decreased survival in control mice, but not in sickle mice. Chronic morphine treatment leads to hyperalgesia in sickle mice, but does not lead to analgesic tolerance.

Chronic neuropathic pain reduces opioid receptor availability with associated anhedonia in rat

Supplemental Digital Content is Available in the Text.

Chronic pain reduces opioid receptor expression in the rat striatum, where the correlation between receptor expression and anhedonia may represent a molecular substrate for comorbid depression.

The opioid system plays a critical role in both the experience and management of pain. Although acute activation of the opioid system can lead to pain relief, the effects of chronic pain on the opioid system remain opaque. Cross-sectional positron emission tomography (PET) studies show reduced availability of brain opioid receptors in patients with chronic pain but are unable to (1) determine whether these changes are due to the chronic pain itself or due to preexisting or medication-induced differences in the endogenous opioid system, and (2) identify the neurobiological substrate of reduced opioid receptor availability. We investigated these possibilities using a well-controlled longitudinal study design in rat. Using [¹⁸F]-FDPN-PET in either sham rats (n = 17) or spared nerve injury rats (n = 17), we confirmed reduced opioid receptor availability in the insula, caudate–putamen, and motor cortex of nerve injured rats 3 months after surgery, indicating that painful neuropathy altered the endogenous opioid system. Immunohistochemistry showed reduced expression of the mu-opioid receptor, MOR1, in the caudate–putamen and insula. Neither the opioid peptide enkephalin nor the neuronal marker NeuN differed between groups. In nerve-injured animals, sucrose preference, a measure of anhedonia/depression-like behavior, positively correlated with PET opioid receptor availability and MOR1-immunoreactivity in the caudate–putamen. These findings provide new evidence that the altered supraspinal opioid receptor availability observed in human patients with chronic pain may be a direct result of chronic pain. Moreover, reduced opioid receptor availability seems to reflect decreased receptor expression, which may contribute to pain-induced depression.

Self-reported cumulative medical opioid exposure and subjective responses on first use of opioids predict analgesic and subjective responses to placebo-controlled opioid administration

BACKGROUND AND OBJECTIVES

To expand the evidence base needed to enable personalized pain medicine, we evaluated whether self-reported cumulative exposure to medical opioids and subjective responses on first opioid use predicted responses to placebo-controlled opioid administration.

METHODS

In study 1, a survey assessing cumulative medical opioid exposure and subjective responses on first opioid use was created (History of Opioid Medical Exposure (HOME)) and psychometric features documented in a general sample of 307 working adults. In study 2, 49 patients with chronic low back pain completed the HOME and subsequently rated back pain intensity and subjective opioid effects four times after receiving saline placebo or intravenous morphine (four incremental doses) in two separate double-blinded laboratory sessions. Placebo-controlled morphine effects were derived for all outcomes.

RESULTS

Two HOME subscales were supported: cumulative opioid exposure and euphoric response, both demonstrating high test-retest reliability (Intraclass Correlation Coefficients > 0.93) and adequate internal consistency (Revelle's Omega Total = 0.73-0.77). In study 2, higher cumulative opioid exposure scores were associated with significantly greater morphine-related reductions in back pain intensity (p=0.02), but not with subjective drug effects. Higher euphoric response subscale scores were associated with significantly lower overall perceived morphine effect (p=0.003), less sedation (p=0.04), greater euphoria (p=0.03) and greater desire to take morphine again (p=0.02).

DISCUSSION

Self-reports of past exposure and responses to medical opioid analgesics may have utility for predicting subsequent analgesic responses and subjective effects. Further research is needed to establish the potential clinical and research utility of the HOME.

TRIAL REGISTRATION NUMBER

NCT02469077.

Medication Exposure Patterns in Primary Care Patients Prescribed Pharmacogenetically Actionable Opioids

Current approaches to assessing medication exposure fail to capture the complexity of the phenomenon and the context in which it occurs. This study's purpose was to develop a typology of subgroups of patients who share common patterns of medication exposure. To create the typology, we used an exemplar sample of 30 patients in a large public healthcare system who had been prescribed the pharmacogenetically actionable opioids codeine or tramadol. Data related to medication exposure were drawn from large data repositories. Using a person-oriented qualitative approach, eight subgroups of patients who shared common patterns of medication exposure were identified. The subgroups had one of five opioid prescription patterns (i.e., singular, episodic, switching, sustained, multiplex), and one of three types of primary foci of medical care (i.e., pain, comorbidities, both). The findings reveal medication exposure patterns that are dynamic, multidimensional, and complex, and the typology offers an innovative approach to assessing medication exposure.

Clinical application of pharmacogenetics in pain management

There is growing experience translating genomic data into clinical practice, as seen with the Implementing GeNomics In pracTicE (IGNITE) network. A primary example is the influence of CYP2D6 genotype on the beneficial and adverse effects of some opioids. Clinical recommendations exist to guide drug therapy based on CYP2D6 genotype for codeine, tramadol, oxycodone and hydrocodone, although the level of supporting evidence differs by drug. Limited evidence also supports the use of genetic data to guide other medications in chronic pain therapy, including tricyclic antidepressants and celecoxib. Pragmatic clinical trial data are needed in this area to better understand the impact of diverse populations, therapeutic interventions and clinical care environments on genotype-guided drug therapy for chronic pain.

Prediction of opioid dose in cancer pain patients using genetic profiling: not yet an option with support vector machine learning

OBJECTIVE

Use of opioids for pain management has increased over the past decade; however, inadequate analgesic response is common. Genetic variability may be related to opioid efficacy, but due to the many possible combinations and variables, statistical computations may be difficult. This study investigated whether data processing with support vector machine learning could predict required opioid dose in cancer pain patients, using genetic profiling. Eighteen single nucleotide polymorphisms (SNPs) within the µ and δ opioid receptor genes and the catechol-O-methyltransferase gene were selected for analysis.

RESULTS

Data from 1237 cancer pain patients were included in the analysis. Support vector machine learning did not find any associations between the assessed SNPs and opioid dose in cancer pain patients, and hence, did not provide additional information regarding prediction of required opioid dose using genetic profiling.

Risk factors for addiction among patients receiving prescribed opioids: a systematic review protocol

BACKGROUND

Opioid addiction prevention has become an urgent public health priority, with several countries declaring a state of emergency due to rising death tolls from opioid abuse. Reducing the risk of developing addiction among opioid-naïve patients exposed to prescribed opioids during the process of medical care may be an important primary prevention strategy. Our objective is to synthesize the available evidence about factors associated with the development of addiction among patients first exposed to prescribed opioids, with a focus on opioid-naïve patients.

METHODS

We will perform a systematic search of MEDLINE, Embase, Cochrane Central Register of Controlled Trials, and other databases in collaboration with a health information specialist using a comprehensive search strategy. We will also supplement our search with a scan of the grey literature to identify relevant ongoing and unpublished studies. We will include studies reporting on risk factors for opioid addiction in patients prescribed opioid analgesic therapy through a prescription from a licensed medical professional, with a focus on opioid-naïve patients. We will exclude studies focusing on patients who are first exposed to illicit opioids, those who use prescription opioids for cancer pain, and/or who are palliative. Two reviewers will independently review titles, abstracts, and full texts for inclusion and exclusion criteria. They will then extract data from included full texts using standardized piloted data extraction forms and assess study quality through risk of bias assessment. We will synthesize the effect sizes of risk factors derived from clinically homogenous studies with similar designs and the remaining ones qualitatively.

DISCUSSION

Understanding risk factors for opioid addiction among patients who require analgesia has the potential to inform clinical care and opioid prescribing guidelines aiming to reduce opioid addiction. We will also use this information as a starting point for developing interventions for primary prevention.

Do Resting Plasma β-Endorphin Levels Predict Responses to Opioid Analgesics?

OBJECTIVES

Clinically feasible predictors of opioid analgesic responses for use in precision pain medicine protocols are needed. This study evaluated whether resting plasma β-endorphin (BE) levels predicted responses to an opioid analgesic, and whether chronic pain status or sex moderated these effects.

METHODS

Participants included 73 individuals with chronic low back pain (CLBP) and 88 pain-free controls, all using no daily opioid analgesics. Participants attended 2 identical laboratory sessions during which they received either intravenous morphine (0.08 mg/kg) or saline placebo, with blood samples obtained before drug administration to assay resting plasma BE levels. Once peak drug activity was achieved in each session, participants engaged in an ischemic forearm pain task (ISC) and a heat pain task. Morphine analgesic effects were derived reflecting the difference in pain outcomes between placebo and morphine conditions.

RESULTS

In hierarchical regressions, significant Type (CLBP vs. control)×BE interactions (Ps<0.05) were noted for morphine effects on ISC tolerance, ISC intratask pain ratings, and thermal VAS unpleasantness ratings. These interactions derived primarily from associations between higher BE levels and smaller morphine effects restricted to the CLBP subgroup. All other BE-related effects, including sex interactions, for predicting morphine analgesia failed to reach statistical significance.

DISCUSSION

BE was a predictor of morphine analgesia for only 3 out of 9 outcomes examined, with these effects moderated by chronic pain status but not sex. On the whole, results do not suggest that resting plasma BE levels are likely to be a clinically useful predictor of opioid analgesic responses.

Identification of Circulating miRNAs Differentially Regulated by Opioid Treatment

Emerging evidence demonstrates functional contributions of microRNAs (miRNAs) to μ-opioid receptor (MOR) signaling, but the information so far has been mostly limited to their intracellular regulatory mechanisms. The present study aimed to investigate changes in plasma miRNA profiles elicited by opioid treatment in blood samples collected from clinical studies. Healthy male subjects were orally administered with hydromorphone or oxycodone and blood samples were collected at a specified time after the drug treatment. A total of 179 plasma miRNAs were measured using multiplex qRT-PCR. Nine and seventeen miRNAs were commonly upregulated (let-7a-5p, miR-423-3p, miR-199a-3p, miR-146a-5p, miR-23b-3p, miR-24-3p, miR-221-3p, miR-223-3p, and miR-146b-5p) and downregulated (miR-144-3p, miR-215, miR-363-3p, etc.), respectively, following opioid treatment. The MOR signaling-associated miRNAs, namely let-7 family miRNAs (i.e., let-7d-5p, let-7f-5p, let-7c, let-7e-5p), miR-103a-3p, miR-339-3p, miR-146a-5p, miR-23b-3p, miR-23a-3p, and miR-181a-5p, were differentially expressed following drug treatment. These differentially expressed miRNAs are circulating biomarker candidates that can be used to evaluate MOR stimulation and serve as novel clinical diagnostic tools for improving clinical outcomes.

Patient-Reported Outcomes and Opioid Use in Outpatients With Chronic Pain

The Weill Cornell Medical College Pain Registry database contains patient characteristics, treatments, and outcomes for a prospective cohort of 1,159 chronic pain patients who were seen at the Weill Cornell Medical College Pain Medicine outpatient clinic from July 8, 2011 to December 10, 2014. Patients aged 45 to 64 years comprised 43% followed by age ≥ 65 years at 37%. Fifty-eight percent were female. Average pain intensity (Brief Pain Inventory) was reported as mild by 22.3% of patients, moderate by 34.7%, and severe by 43.0%. For each pain intensity category, patient's report of average percent pain relief and health state (EuroQOL 5 Dimensions) was inversely related to average pain intensity category, whereas measures of pain interference, number of worst pain locations, and physical and psychological distress were directly related to pain intensity category. Seventy-seven percent of patients received an opioid at 1 or more clinic encounters. Median daily opioid dose in morphine equivalents was 55 with a range from 2 to 1,145 morphine equivalents. Regression analysis revealed that being male was associated with greater likelihood of an opioid ordered and higher average dosage than being female. The registry can identify patient characteristics and treatments that provide new insights into chronic pain management.

PERSPECTIVE

This article describes results of analyses of patient-reported outcomes and patient-related electronic health record data collected under standard of care from a prospective cohort of chronic pain outpatients at a New York City pain management clinic. The registry provides an opportunity to learn how to improve individualized chronic pain management.

Analgesic properties of aqueous leaf extract of Haematostaphis barteri: involvement of ATP-sensitive potassium channels, adrenergic, opioidergic, muscarinic, adenosinergic and serotoninergic pathways

BACKGROUND

Pain is the most common cause of patients seeking medical advice as a result of its association with different pathologies. This study evaluated the antinociceptive property of Haematostaphis barteri as well as the possible mechanism(s) associated with its antinociceptive property.

METHODS

Mice were administered H. barteri (30-300 mg kg-1; p.o.), followed by intraplantar injection of 10 μL of 5% formalin into the hind paws. The pain score was determined for 1 h in the formalin test. The possible nociceptive pathways involved in the antinociceptive action of H. barteri were determined by pre-treating mice with theophylline (5 mg kg-1, a non-selective adenosine receptor antagonist), naloxone (2 mg kg-1, a non-selective opioid receptor antagonist), glibenclamide (8 mg kg-1; an ATP-sensitive K+ channel inhibitor), and atropine (3 mg kg-1; non-selective muscarinic antagonist).

RESULTS

H. barteri (30-300 mg kg-1) significantly and dose dependently precluded both first and second phases of nociception. Pre-treatment with naloxone had no effect on the analgesic activities of H. barteri in the first phase. Again, pre-treatment with atropine and glibenclamide did not significantly reverse the neurogenic antinociception of the extract in phase 1. However, theophylline reversed the analgesic effect of the extract in the first phase. In phase 2, theophylline had no effect on the analgesic activities of the extract. Naloxone, atropine, and glibenclamide significantly blocked the antinociception of H. barteri in the inflammatory phase of the formalin test.

CONCLUSIONS

H. barteri possesses antinociceptive property mediated via the opioidergic, adrenergic, muscarinic, ATP-sensitive K+ channels, and adenosinergic nociceptive pathways.

Objective methods for the assessment of the spinal and supraspinal effects of opioids

BACKGROUND AND PURPOSE

Opioids are potent analgesics. Opioids exert effects after interaction with opioid receptors. Opioid receptors are present in the peripheral- and central nervous system (CNS), but the analgesic effects are primarily mediated via receptors in the CNS. Objective methods for assessment of opioid effects may increase knowledge on the CNS processes responsible for analgesia. The aim of this review was to provide an overview of the most common objective methods for assessment of the spinal and supraspinal effects of opioids and discuss their advantages and limitations.

METHOD

The literature search was conducted in Pub Med (http://www.ncbi.nlm.nih.gov/pubmed) from November 2014 to June 2016, using free-text terms: "opioid", "morphine" and "oxycodone" combined with the terms "pupillometry," "magnetic resonance spectroscopy," "fMRI," "BOLD," "PET," "pharmaco-EEG", "electroencephalogram", "EEG," "evoked potentials," and "nociceptive reflex". Only original articles published in English were included.

RESULTS

For assessment of opioid effects at the supraspinal level, the following methods are evaluated: pupillometry, proton magnetic resonance spectroscopy, functional resonance magnetic imaging (fMRI), positron emission tomography (PET), spontaneous electroencephalogram (EEG) and evoked potentials (EPs). Pupillometry is a non-invasive tool used in research as well as in the clinical setting. Proton magnetic resonance spectroscopy has been used for the last decades and it is a non-invasive technique for measurement of in vivo brain metabolite concentrations. fMRI has been a widely used non-invasive method to estimate brain activity, where typically from the blood oxygen level-dependent (BOLD) signal. PET is a nuclear imaging technique based on tracing radio labeled molecules injected into the blood, where receptor distribution, density and activity in the brain can be visualized. Spontaneous EEG is typically quantified in frequency bands, power spectrum and spectral edge frequency. EPs are brain responses (assessed by EEG) to a predefined number of short phasic stimuli. EPs are quantified by their peak latencies and amplitudes, power spectrum, scalp topographies and brain source localization. For assessment of opioid effects at the spinal level, the following methods are evaluated: the nociceptive withdrawal reflex (NWR) and spinal EPs. The nociceptive withdrawal reflex can be recorded from all limbs, but it is standard to record the electromyography signal at the biceps femoris muscle after stimulation of the ipsilateral sural nerve; EPs can be recorded from the spinal cord and are typically recorded after stimulation of the median nerve at the wrist.

CONCLUSION AND IMPLICATIONS

The presented methods can all be used as objective methods for assessing the centrally mediated effects of opioids. Advantages and limitations should be considered before implementation in drug development, future experimental studies as well as in clinical settings. In conclusion, pupillometry is a sensitive measurement of opioid receptor activation in the CNS and from a practical and economical perspective it may be used as a biomarker for opioid effects in the CNS. However, if more detailed information is needed on opioid effects at different levels of the CNS, then EEG, fMRI, PET and NWR have the potential to be used. Finally, it is conceivable that information from different methods should be considered together for complementary information.

Digital Pain Drawings: Assessing Touch-Screen Technology and 3D Body Schemas

OBJECTIVES

To assess the consistency and level of agreement between pain drawings collected on (1) paper and a personal computer tablet; and (2) between a 2-dimensional (2D) line drawing and 3-dimensional (3D) body schema.

MATERIALS AND METHODS

Pain-free participants (N=24) recreated a premarked "pain" area from a 2D line drawing displayed on paper onto paper or tablet, and individuals with chronic neck pain (N=29) expressed their current pain on paper and tablet. A heterogeneous group (N=26) was recruited from cross-disciplinary pain clinic and expressed their pain on a 2D line drawing and a 3D body schema, as displayed on a tablet, and then completed an user-experience questionnaire.

RESULTS

Pain drawings showed moderate to high level of consistency and a high level of agreement for paper and tablet and between 2D line drawing and 3D body schema. A fixed bias (-1.0042, P<0.001) revealed that pain areas were drawn slightly smaller on paper than on tablet, and larger on the 2D than the 3D body schema (-0.6371, P=0.003), as recorded on a tablet. Over one-third of individuals with chronic pain preferred and/or believed that the 3D body schema enabled a more accurate record; 12 believed they were equal, and 3 preferred the 2D line drawing.

DISCUSSION

Pain drawings recorded with touch-screen technology provide equal reliability to paper but the size of the drawing slightly differs between the platforms. Although, 2D line drawings and 3D body schemas were similar in terms of consistency and reliability, it remains to be confirmed whether 3D body schemas increase the accuracy and precision of pain drawings.

Take-home naloxone treatment for opioid emergencies: a comparison of routes of administration and associated delivery systems

INTRODUCTION

Naloxone reversal of opioid-induced respiratory depression outside of medical facilities has become more prevalent because of the escalating opioid epidemic in the USA. Take-home naloxone for treatment of opioid emergencies is now being recommended by numerous federal, state, and professional organizations. Areas covered: The scope of the opioid overdose epidemic is reviewed along with practical, clinical, regulatory, and usability considerations for take-home naloxone routes of administration currently available and associated delivery systems. Specific opioid-related factors are discussed in detail with emphasis placed on life-threatening respiratory depression and naloxone antagonism. A clinical overview, including pharmacokinetic and FDA approval information for each take-home naloxone product is discussed in detail as well as the impact of take-home naloxone in the community. Finally, given these products are to be used in a panic-stricken, life-threatening opioid emergency, an analysis of available usability data is provided with proposed directions for further study. Expert opinion: Based on the available clinical evidence, auto-injectable naloxone should be the preferred administration route for take-home naloxone treatment until additional safety, efficacy, and comparative outcomes data are available for unconventional routes of administration that unequivocally provide equal or superior results.

Prediction of postoperative opioid analgesia using clinical-experimental parameters and electroencephalography

BACKGROUND

Opioids are often used for pain treatment, but the response is often insufficient and dependent on e.g. the pain condition, genetic factors and drug class. Thus, there is an urgent need to identify biomarkers to enable selection of the appropriate drug for the individual patient, a concept known as personalized medicine. Quantitative sensory testing (QST) and clinical parameters can provide some guidance for response, but better and more objective biomarkers are urgently warranted. Electroencephalography (EEG) may be suitable since it assesses the central nervous system where opioids mediate their effects.

METHODS

Clinical parameters, QST and EEG (during rest and tonic pain) was recorded from patients the day prior to total hip replacement surgery. Postoperative pain treatment was performed using oxycodone and piritramide as patient-controlled analgesia. Patients were stratified into responders and non-responders based on pain ratings 24 h post-surgery. Parameters were analysed using conventional group-wise statistical methods. Furthermore, EEG was analysed by machine learning to predict individual response.

RESULTS

Eighty-one patients were included, of which 51 responded to postoperative opioid treatment (30 non-responders). Conventional statistics showed that more severe pre-existing chronic pain was prevalent among non-responders to opioid treatment (p = 0.04). Preoperative EEG analysis was able to predict responders with an accuracy of 65% (p = 0.009), but only during tonic pain.

CONCLUSIONS

Chronic pain grade before surgery is associated with the outcome of postoperative pain treatment. Furthermore, EEG shows potential as an objective biomarker and might be used to predict postoperative opioid analgesia.

SIGNIFICANCE

The current clinical study demonstrates the viability of EEG as a biomarker and with results consistent with previous experimental results. The combined method of machine learning and electroencephalography offers promising results for future developments of personalized pain treatment.

Placebo Response is Driven by UCS Revaluation: Evidence, Neurophysiological Consequences and a Quantitative Model

Despite growing scientific interest in the placebo effect and increasing understanding of neurobiological mechanisms, theoretical modeling of the placebo response remains poorly developed. The most extensively accepted theories are expectation and conditioning, involving both conscious and unconscious information processing. However, it is not completely understood how these mechanisms can shape the placebo response. We focus here on neural processes which can account for key properties of the response to substance intake. It is shown that placebo response can be conceptualized as a reaction of a distributed neural system within the central nervous system. Such a reaction represents an integrated component of the response to open substance administration (or to substance intake) and is updated through “unconditioned stimulus (UCS) revaluation learning”. The analysis leads to a theorem, which proves the existence of two distinct quantities coded within the brain, these are the expected or prediction outcome and the reactive response. We show that the reactive response is updated automatically by implicit revaluation learning, while the expected outcome can also be modulated through conscious information processing. Conceptualizing the response to substance intake in terms of UCS revaluation learning leads to the theoretical formulation of a potential neuropharmacological treatment for increasing unlimitedly the effectiveness of a given drug.