Opioid-induced hyperalgesia: where are we now?

Diagnosing and managing prescription opioid use disorder in patients prescribed opioids for chronic pain in Australian general practice settings: a qualitative study using the theory of Planned Behaviour

BACKGROUND

Chronic pain is a debilitating and common health issue. General Practitioners (GPs) often prescribe opioids to treat chronic pain, despite limited evidence of benefit and increasing evidence of harms, including prescription Opioid Use Disorder (pOUD). Australian GPs are worried about the harms of long-term opioids, but few are involved in the treatment of pOUD. There is little research on GPs' experiences diagnosing and managing pOUD in their chronic pain patients.

METHODS

This qualitative research used semi-structured interviews and a case study to investigate GPs' experiences through the lens of the Theory of Planned Behaviour (TPB). TPB describes three factors, an individual's perceived beliefs/attitudes, perceived social norms and perceived behavioural controls. Participants were interviewed via an online video conferencing platform. Interviews were transcribed verbatim and thematically analysed.

RESULTS

Twenty-four GPs took part. Participants were aware of the complex presentations for chronic pain patients and concerned about long-term opioid use. Their approach was holistic, but they had limited understanding of pOUD diagnosis and suggested that pOUD had only one treatment: Opioid Agonist Treatment (OAT). Participants felt uncomfortable prescribing opioids and were fearful of difficult, conflictual conversations with patients about the possibility of pOUD. This led to avoidance and negative attitudes towards diagnosing pOUD. There were few positive social norms, few colleagues diagnosed or managed pOUD. Participants reported that their colleagues only offered positive support as this would allow them to avoid managing pOUD themselves, while patients and other staff were often unsupportive. Negative behavioural controls were common with low levels of knowledge, skill, professional supports, inadequate time and remuneration described by many participants. They felt OAT was not core general practice and required specialist management. This dichotomous approach was reflected in their views that the health system only supported treatment for chronic pain or pOUD, not both conditions.

CONCLUSIONS

Negative beliefs, negative social norms and negative behavioural controls decreased individual behavioural intention for this group of GPs. Diagnosing and managing pOUD in chronic pain patients prescribed opioids was perceived as difficult and unsupported. Interventions to change behaviour must address negative perceptions in order to lead to more positive intentions to engage in the management of pOUD.

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

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

Safety, Tolerability, and Dose-Limiting Toxicity of Lacosamide in Patients With Painful Chronic Pancreatitis: Protocol for a Phase 1 Clinical Trial to Determine Safety and Identify Side Effects

BACKGROUND

Chronic abdominal pain is the hallmark symptom of chronic pancreatitis (CP), with 50% to 80% of patients seeking medical attention for pain control. Although several management options are available, outcomes are often disappointing, and opioids remain a mainstay of therapy. Opioid-induced hyperalgesia is a phenomenon resulting in dose escalation, which may occur partly because of the effects of opioids on voltage-gated sodium channels associated with pain. Preclinical observations demonstrate that the combination of an opioid and the antiseizure drug lacosamide diminishes opioid-induced hyperalgesia and improves pain control.

OBJECTIVE

In this phase 1 trial, we aim to determine the safety, tolerability, and dose-limiting toxicity of adding lacosamide to opioids for the treatment of painful CP and assess the feasibility of performance of a pilot study of adding lacosamide to opioid therapy in patients with CP. As an exploratory aim, we will assess the efficacy of adding lacosamide to opioid therapy in patients with painful CP.

METHODS

Using the Bayesian optimal interval design, we will conduct a dose-escalation trial of adding lacosamide to opioid therapy in patients with painful CP enrolled in cohorts of size 3. The initial dose will be 50 mg taken orally twice a day, followed by incremental increases to a maximum dose of 400 mg/day, with lacosamide administered for 7 days at each dose level. Adverse events will be documented according to Common Terminology Criteria for Adverse Events (version 5.0).

RESULTS

As of December 2023, we have currently enrolled 6 participants. The minimum number of participants to be enrolled is 12 with a maximum of 24. We expect to publish the results by March 2025.

CONCLUSIONS

This trial will test the feasibility of the study design and provide reassurance regarding the tolerability and safety of opioids in treating painful CP. It is anticipated that lacosamide will prove to be safe and well tolerated, supporting a subsequent phase 2 trial assessing the efficacy of lacosamide+opioid therapy in patients with painful CP, and that lacosamide combined with opiates will lower the opioid dose necessary for pain relief and improve the safety profile of opioid use in treating painful CP.

TRIAL REGISTRATION

Clinicaltrials.gov NCT05603702; https://clinicaltrials.gov/study/NCT05603702.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/50513.

Omission of perioperative morphine reduces postoperative pain in proctological interventions: a single-center analysis

There is an increase in outpatient procedures and this trend will continue in the future. For hemorrhoidectomy, it is the standard of treatment in many health care systems. Perioperative management including adequate pain control is of paramount importance to ensure successful ambulatory surgery. This study investigates the role and effect of morphine compared to short-acting opiates applied before, during, or after proctological interventions and with focus on hemorrhoidectomy. A retrospective analysis of a prospective database was conducted comparing two populations. The control cohort received morphine (Yes-Mô) intra- and postoperatively, while the intervention group did not receive morphine (No-Mô) between January 2018 and January 2020. Both cohorts were balanced by propensity score matching. The outcomes were postoperative pain measured by numeric ratings scale (NRS) one hour postoperatively, pain 24 h postoperatively, success rate of outpatient management, and complication rate including postoperative nausea and vomiting as well as urinary retention. The intervention population comprised 54 patients and the control group contained 79 patients. One hour after surgery, patients in No-Mô reported lower NRS (1.44 ± 1.41) compared to Yes-Mô (2.48 ± 2.30) (p = 0.029). However, there was no difference in NRS 24 h postoperatively (No-Mô: 1.61 ± 1.41 vs Yes-Mô: 1.63 ± 1.72; p = 0.738). 100% of No-Mô was managed as outpatients while only 50% of Yes-Mô was dismissed on the day of the operation (p = < 0.001). There was no difference in postoperative complications (including postoperative nausea and vomiting (PONV) and urinary retention) between the two groups (PONV No-Mô 7.4% vs Yes-Mô 5.6%, p = 1.0 and urinary retention No-Mô 3.7% vs Yes-Mô 7.4%, p = 0.679). No-Mô received an oral morphine equivalent of 227.25 ± 140.35 mg intraoperatively and 11.02 ± 18.02 mg postoperatively. Yes-Mô received 263.17 ± 153.60 mg intraoperatively and 15.97 ± 14.17 mg postoperatively. The difference in received morphine equivalent between the groups was not significant after matching for the intraoperative (p = 0.212) and postoperative (p = 0.119) received equivalent. Omission of perioperative morphine is a viable but yet not understood method for reducing postoperative pain. Omission of morphine leads to a lower use of total morphine equivalent to attain satisfactory analgesia. The reduction of the overall opiate load and using opiates with a very short half-life potentially leads to a reduction of side effects like sedation. This in turn promotes discharge of the patient on the day of surgery. Omission of morphine is safe and does not increase postoperative complications.

Short-chain fatty acid, butyrate prevents morphine-and paclitaxel-induced nociceptive hypersensitivity

Nociceptive hypersensitivity is a significant side effect with the chronic administration of opioids as well as chemotherapeutics. Both opioid-induced hypersensitivity (OIH) and chemotherapy-induced hypersensitivity (CIH) are characterized by an increased sensitivity to painful stimuli which can significantly reduce the quality of life for individuals on either drug(s). Here we demonstrate the nociceptive hypersensitivity associated with repeated administration of morphine (opioid) and paclitaxel (chemotherapeutic) treatment can be reversed by oral supplementation with the short-chain fatty acid (SCFA) sodium butyrate (NaBut). In two separate mouse behavioral models for nociceptive hypersensitivity, we found that thermal hyperalgesia (for OIH) and cold allodynia (for CIH) were prevented by treatment with oral butyrate (p.o, b.i.d). Electrophysiological recordings of small diameter dorsal root ganglia (DRG) neurons from morphine and paclitaxel treated mice showed an increase in neuronal hyperexcitability in both drug models which was likewise prevented by oral butyrate treatment. Using colonic conditioned media obtained from excised colon segments we found that gut mediators of morphine treated mice can induce hyperexcitability in naïve DRG neurons, but such enhanced excitability is not present when animals are co-treated with NaBut suggesting gut derived mediators modulate neuronal hyperexcitability. In-vitro NaBut treatment did not prevent morphine-induced excitability, suggesting an indirect role of butyrate in modulating neuronal hypersensitivity. These data taken together suggest that gut derived mediators affect opioid and chemotherapeutic-induced neuronal hypersensitivity that is prevented by the SCFA butyrate.

Pancreatic QST Differentiates Chronic Pancreatitis Patients into Distinct Pain Phenotypes Independent of Psychiatric Comorbidities

BACKGROUND & AIMS

Quantitative sensory testing (QST) has been previously used to study pain in chronic pancreatitis (CP) but included methods that are not suitable for clinical purposes. The aims of this study were to determine if pancreatic QST (P-QST) can differentiate patients into distinct pain phenotypes and to determine the association of these with their clinical pain and psychiatric comorbidities.

METHODS

A multicenter cross-sectional study was conducted where patients completed validated questionnaires assessing quality of life (QoL), depression and anxiety scores as well as clinical pain symptoms followed by P-QST which included a cold pressor test, repetitive pinprick stimuli and pressure stimulation of the upper abdominal (T10) and control dermatomes. P-QST categorized patients into pain phenotypes based on a previously established nomogram. QoL, clinical pain and psychiatric assessment scores were compared across these groups.

RESULTS

A total of 179 patients were enrolled with a mean age of 54.1±13.6 years among whom 59% were males and 42% had an alcoholic etiology. P-QST showed no hyperalgesia in 91 (51%), segmental hyperalgesia in 50 (28%) and widespread hyperalgesia in 38 (21%) patients. Patients with widespread hyperalgesia had significantly higher pain intensity scores (P = .03) and rates of constant pain (P = .002) as well as decreased QoL (P < .001) and physical functioning (P =.03) in comparison with the other two pain phenotypes. In contrast, psychiatric comorbidities were similar across all groups.

CONCLUSIONS

P-QST may serve as a novel unbiased pain assessment tool in CP as it categorizes patients into distinct pain phenotypes independent of their psychiatric comorbidities.

Pre-Visit Education on Pain Management Options Prior to the First Clinic Visit Improves Chronic Pain Patient Satisfaction with Proposed Treatment Plans

OBJECTIVE

This study sought to evaluate if actively informing new chronic pain patients about treatment options and setting realistic expectations for care, through the use of a pre-visit informational handout prior to the first clinic visit, improved patient satisfaction with subsequently proposed treatment plans.

METHODS

The study was divided into two 3-month periods. During the first 3 months, with our current pain clinic practices in place, new patients (n = 147) were given surveys to establish a baseline of patient satisfaction with treatment plans proposed on their first visit. During the second 3 months, a different group of new patients (n = 156) was given a detailed informational handout which described our clinic's multimodal approach to pain management and therapeutic expectations prior to their visit with a provider. Patient satisfaction with subsequently proposed treatment plans was then assessed and compared with the baseline group.

RESULTS

The average patient satisfaction score for the group of patients given the informational handout was 4.21 (on a 5-point Likert scale), compared to an average score of 3.25 for the baseline group (P < .0001, unpaired t-test). 77.6% of patients given the informational handout said their proposed treatment plan met their expectations compared to 46.3% of patients in the baseline group (χ2= 31.61, two-tailed P < .0001).

CONCLUSIONS

Patient satisfaction with proposed chronic pain treatment plans was improved when clinic approaches to pain were explicitly outlined and therapeutic expectations were clearly established in the form of an informational handout at the outset of the first visit.

European clinical practice recommendations on opioids for chronic noncancer pain - Part 2: Special situations

BACKGROUND

Opioid use for chronic non-cancer pain (CNCP) is under debate. In the absence of pan-European guidance on this issue, a position paper was commissioned by the European Pain Federation (EFIC).

METHODS

The clinical practice recommendations were developed by eight scientific societies and one patient self-help organization under the coordination of EFIC. A systematic literature search in MEDLINE (up until January 2020) was performed. Two categories of guidance are given: Evidence-based recommendations (supported by evidence from systematic reviews of randomized controlled trials or of observational studies) and Good Clinical Practice (GCP) statements (supported either by indirect evidence or by case-series, case-control studies and clinical experience). The GRADE system was applied to move from evidence to recommendations. The recommendations and GCP statements were developed by a multiprofessional task force (including nursing, service users, physicians, physiotherapy and psychology) and formal multistep procedures to reach a set of consensus recommendations. The clinical practice recommendations were reviewed by five external reviewers from North America and Europe and were also posted for public comment.

RESULTS

The European Clinical Practice Recommendations give guidance for combination with other medications, the management of frequent (e.g. nausea, constipation) and rare (e.g. hyperalgesia) side effects, for special clinical populations (e.g. children and adolescents, pregnancy) and for special situations (e.g. liver cirrhosis).

CONCLUSION

If a trial with opioids for chronic noncancer pain is conducted, detailed knowledge and experience are needed to adapt the opioid treatment to a special patient group and/or clinical situation and to manage side effects effectively.

SIGNIFICANCE

If a trial with opioids for chronic noncancer pain is conducted, detailed knowledge and experience are needed to adapt the opioid treatment to a special patient group and/or clinical situation and to manage side effects effectively. A collaboration of medical specialties and of all health care professionals is needed for some special populations and clinical situations.

Divergent profiles of fentanyl withdrawal and associated pain in mice and rats

Opioid abuse has devastating effects on patients, their families, and society. Withdrawal symptoms are severely unpleasant, prolonged, and frequently hinder recovery or lead to relapse. The sharp increase in abuse and overdoses arising from the illicit use of potent and rapidly-acting synthetic opioids, such as fentanyl, highlights the urgency of understanding the withdrawal mechanisms related to these drugs. Progress is impeded by inconsistent reports on opioid withdrawal in different preclinical models. Here, using rats and mice of both sexes, we quantified withdrawal behaviors during spontaneous and naloxone-precipitated withdrawal, following two weeks of intermittent fentanyl exposure. We found that both mice and rats lost weight during exposure and showed increased signs of distress during spontaneous and naloxone precipitated withdrawal. However, these species differed in their expression of withdrawal associated pain, a key contributor to relapse in humans. Spontaneous or ongoing pain was preferentially expressed in rats in both withdrawal conditions, while no change was observed in mice. In contrast, withdrawal associated thermal hyperalgesia was found only in mice. These data suggest that rats and mice diverge in how they experience withdrawal and which aspects of the human condition they most accurately model. These differences highlight each species' strengths as model systems and can inform experimental design in studies of opioid withdrawal.

Optimizing the management of chronic pain in sickle cell disease

Chronic pain in sickle cell disease (SCD) refers to pain present on most days lasting over six months. It can start during childhood and the prevalence increases with age. By adulthood, over 55% of patients experience pain on over 50% of days; 29% reporting pain on 95% of days. The true prevalence of chronic pain in SCD is likely underappreciated as it is mostly managed at home. Patients with chronic pain and SCD frequently seek acute care for exacerbation of underlying chronic pain difficult to distinguish from their usual acute vaso-occlusive crises. When treating chronic pain in SCD, the challenge is distinguishing between non-SCD related etiologies versus chronic pain resulting from SCD pathophysiological processes. This distinction is important to delineate as it will drive appropriate management strategies. Chronic pain in SCD has profound consequences for the patient; is often associated with comorbid psychiatric illnesses (depression and anxiety), not dissimilar from other chronic pain syndromes. They may also experience challenges with sleep hygiene, various somatic symptoms, and chronic fatigue that impair quality of life. How best to treat chronic pain in SCD is not definitively established. Both acute and chronic pain in SCD is typically treated with opioids. Emerging data suggests that chronic opioid therapy (COT) is a suboptimal treatment strategy for chronic pain. This review will discuss the complexity of managing chronic pain in SCD; pain that may be dependent or independent of the underlying SCD diagnosis. We will also describe alternative treatment approaches to high-dose COT.

Epidural analgesia for acute ischemic pain after intra-arterial zolpidem injection in opioid-addicted patient-A case report

A patient taking opioid maintenance therapy unintentionally injected dissolved zolpidem pills into the femoral artery and suffered acute limb ischemia. High amounts of opioids with supplemental therapies were inefficient for intractable ischemic pain, suggesting the presence of opioid-induced hyperalgesia (OIH). Epidural analgesia efficiently relieved pain and symptoms of OIH.

Pearls for opioid use in seriously ill patients

Opioids are often the foundation of pain management in seriously ill patients. Unfortunately, even experienced providers carry with them information that they consider "fact", when this information is not based on scientific evidence, but on "myth". Several topics were elicited based on common beliefs and misconceptions in clinical practice. These were identified via a survey of pharmacist pain and palliative care providers. Pearls from these topics were chosen that were based on evidence and would have the greatest bearing on clinical practice. The pearls address topics such as not using opioids as first-line analgesics for all types of pain, opioid-induced hyperalgesia, opioid risk management in cancer patients, use of buprenorphine in hospice and palliative care settings and use of naloxone in seriously ill patients. The pearls are supported by clinical evidence extracted from several references. They are intended to make readers give thought to opioid therapy which is strictly evidence-based, and not historical or anecdote-based. Practical recommendations are provided to give readers a starting point to base clinical decisions going forward. Readers may discover that "facts" they once learned about opioid use in seriously ill patients are actually "myths" that are a figment of the past.

Systemic Morphine Produces Dose-dependent Nociceptor-mediated Biphasic Changes in Nociceptive Threshold and Neuroplasticity

We investigated the dose dependence of the role of nociceptors in opioid-induced side-effects, hyperalgesia and pain chronification, in the rat. Systemic morphine produced a dose-dependent biphasic change in mechanical nociceptive threshold. At lower doses (0.003-0.03 mg/kg, s.c.) morphine induced mechanical hyperalgesia, while higher doses (1-10 mg/kg, s.c.) induced analgesia. Intrathecal (i.t.) oligodeoxynucleotide (ODN) antisense to mu-opioid receptor (MOR) mRNA, attenuated both hyperalgesia and analgesia. 5 days after systemic morphine (0.03-10 mg/kg s.c.), mechanical hyperalgesia produced by intradermal (i.d.) prostaglandin E₂ (PGE₂) was prolonged, indicating hyperalgesic priming at the peripheral terminal of the nociceptor. The hyperalgesia induced by i.t. PGE₂ (400 ng/10 µl), in groups that received 0.03 (that induced hyperalgesia) or 3 mg/kg (that induced analgesia) morphine, was also prolonged, indicating priming at the central terminal of the nociceptor. The prolongation of the hyperalgesia induced by i.d. or i.t. PGE₂, in rats previously treated with either a hyperalgesic (0.03 mg/kg, s.c.) or analgesic (3 mg/kg, s.c.) dose, was reversed by i.d. or i.t. injection of the protein translation inhibitor cordycepin (1 µg), indicative of Type I priming at both terminals. Although pretreatment with MOR antisense had no effect on priming induced by 0.03 mg/kg morphine, it completely prevented priming by 3 mg/kg morphine, in both terminals. Thus, the induction of hyperalgesia, but not priming, by low-dose morphine, is MOR-dependent. In contrast, induction of both hyperalgesia and priming by high-dose morphine is MOR-dependent. The receptor at which low-dose morphine acts to produce priming remains to be established.

Physiological Response to Opioids

The clinical setting in which women's health physicians practice, whether as generalist, obstetricians and gynecologists, or subspecialists, dictates our frequent clinical interaction with "pain." Opioid-containing medications are frequently prescribed within our specialty as a means of immediate pain relief. Opioid-containing medication causes a deep physiological alteration of several systems resulting in potential harm to acute and chronic opioid users. This article includes a thorough system-based review of opioid-containing medications on physiological systems. Women's health providers should have an in-depth understanding of such reverberations on patients' wellbeing to maintain the safest level of care. A solid grasp of physiological repercussions of opioid use would encourage physicians to seek alternative treatment options. Such practice is essential in curbing the opioid epidemic our patients are facing.

Linking opioid-induced hyperalgesia and withdrawal-associated injury site pain: a case report

Introduction and objectives:

Understanding the details of one individual's experience with pain, opioid use and withdrawal may generate insights into possible relationships between opioid-induced hyperalgesia and withdrawal-associated injury site pain (WISP).

Methods:

This case study was extracted from a mixed methods study that characterized WISP. In 2014, the individual was recruited from a primary care clinic that prescribes opioid agonist therapy. In an interview, she completed a 35-item survey and elaborated on her own experience. Follow-up contact was made in June of 2017.

Results:

This 34-year-old white woman had several twisting injuries of her right knee between ages 13 and 15. The pain resolved each time in a few days, and she was pain free for 15 years. Around age 30, she initiated illicit oxycodone recreationally (not for pain) and developed an opioid use disorder. On detoxification, she experienced severe knee pain for 6 weeks that resolved postdetoxification but returned after subsequent oxycodone use and withdrawal episodes along with generalized skin sensitivity. This experience of WISP became a barrier to opioid cessation. Although nonsteroidal anti-inflammatories and gabapentin relieved WISP and methadone therapy assisted her opioid use disorder, an eventual change to sublingual buprenorphine/naloxone provided superior control of both.

Conclusion:

This case report illustrates that both opioid use and withdrawal can reactivate injury site pain, which can increase with dose escalation and repeated withdrawal events. The timing, trajectory, and neuropathic features of WISP reported here are consistent with those previously reported for the development of opioid-induced hyperalgesia, possibly linking these phenomena.

Opioid medication use in patients with gastrointestinal diagnoses vs unexplained gastrointestinal symptoms in the US Veterans Health Administration

BACKGROUND

While opioid prescriptions have increased alarmingly in the United States (US), their use for unexplained chronic gastrointestinal (GI) pain (eg, irritable bowel syndrome) carries an especially high risk for adverse effects and questionable benefit.

AIM

To compare opioid use among US veterans with structural GI diagnoses (SGID) and those with unexplained GI symptoms or functional GI diagnoses (FGID), a group for whom opioids have no accepted role.

METHODS

Veterans Health Administration (VHA) administrative data from fiscal year 2012 were used to identify veterans with diagnostic codes recorded for SGID and FGID. This cohort study examined VHA pharmacy data to compare groups receiving ≥ 1 opioid prescription during the year and number of prescriptions filled. Bivariate and multiple logistic regression analyses adjusted for potential confounding factors (demographics, medical diagnoses, social factors) and identified potential mediators (service use, psychiatric comorbidity) of opioid use in these groups.

RESULTS

A greater proportion of veterans with FGID received an opioid prescription during fiscal year 2012 (36.0% of 272 431) compared to only 28.9% of 1 223 744 in the SGID group (Relative Risk [RR] = 1.25). In multivariate logistic regression, personality disorders and drug abuse (OR 1.23 for each group), recent homelessness (OR 1.22), psychotropic medication fills (OR 1.55) and emergency department encounters (OR 1.21) were independently associated with opioid prescription use.

CONCLUSIONS

Despite the potential for adverse consequences, opioids more often are prescribed for veterans with chronic, unexplained GI symptoms compared to those with structural diagnoses. Psychiatric comorbidities and frequent healthcare encounters mediate some of the opioid use risk.

Withdrawal-associated injury site pain (WISP): a descriptive case series of an opioid cessation phenomenon

Supplemental Digital Content is Available in the Text.

This descriptive case series among adults documents that pain can return temporarily at healed, previously pain-free injury sites during acute opioid withdrawal.

Withdrawal pain can be a barrier to opioid cessation. Yet, little is known about old injury site pain in this context. We conducted an exploratory mixed-methods descriptive case series using a web-based survey and in-person interviews with adults recruited from pain and addiction treatment and research settings. We included individuals who self-reported a past significant injury that was healed and pain-free before the initiation of opioids, which then became temporarily painful upon opioid cessation—a phenomenon we have named withdrawal-associated injury site pain (WISP). Screening identified WISP in 47 people, of whom 34 (72%) completed the descriptive survey, including 21 who completed qualitative interviews. Recalled pain severity scores for WISP were typically high (median: 8/10; interquartile range [IQR]: 2), emotionally and physically aversive, and took approximately 2 weeks to resolve (median: 14; IQR: 24 days). Withdrawal-associated injury site pain intensity was typically slightly less than participants' original injury pain (median: 10/10; IQR: 3), and more painful than other generalized withdrawal symptoms which also lasted approximately 2 weeks (median: 13; IQR: 25 days). Fifteen surveyed participants (44%) reported returning to opioid use because of WISP in the past. Participants developed theories about the etiology of WISP, including that the pain is the brain's way of communicating a desire for opioids. This research represents the first known documentation that previously healed, and pain-free injury sites can temporarily become painful again during opioid withdrawal, an experience which may be a barrier to opioid cessation, and a contributor to opioid reinitiation.

Abhängigkeitspotenzial und andere Risiken von Opioidanalgetika im Alter

Zusammenfassung. Zielsetzung: Übersicht über Suchtpotenzial und andere Risiken von Opioidanalgetika im höheren Lebensalter. Methodik: Narrativ review. Literaturrecherche in PubMed (Suchbegriffe: opioid analgesics UND abuse; opioid analgesics UND dependence; opioid analgesics UND addiction; opioid analgesics UND adverse effects; jeweils UND elderly) sowie aktuellen einschlägigen Standardwerken; Auswahl nach altersmedizinischer Relevanz und Aktualität. Ergebnisse: Die Verordnung von Opioidanalgetika (OA) hat in den letzten 25 Jahren massiv zugenommen, die weitaus meisten Verordnungen entfallen auf alte Menschen und Menschen mit chronischen Nicht-Tumorschmerzen (CNTS). Die diagnostischen Kriterien für die Opiatabhängigkeit in ICD-10 und DSM-5 sind für die OA-Behandlung von CNTS ungeeignet. Bei langfristiger OA-Behandlung bei CNTS kann eine spezifische Form von Abhängigkeit entstehen, die nicht mit der illegalen Opiat-(Heroin-)Sucht gleichzusetzen ist. Vorbestehende Suchterkrankungen und andere psychische Störungen sind die wesentlichsten Risikofaktoren. Weitere Nebenwirkungen sind zu beachten. Schmerztherapie bei Suchtkranken stellt eine besondere Herausforderung dar. Schlussfolgerungen: Die Anwendung von OA bei CNTS verlangt eine sorgfältige Indikationsstellung. Die besondere Form der Abhängigkeit von OA ist nicht ausreichend erforscht und wird zu wenig beachtet.

Monocyte chemoattractant protein-1 contributes to morphine tolerance in rats with cancer-induced bone pain

Cancer-induced bone pain can severely compromise the life quality of patients, while tolerance limits the use of opioids in the treatment of cancer pain. Monocyte chemoattractant protein-1 (MCP-1) is known to contribute to neuropathic pain. However, the role of spinal MCP-1 in the development of morphine tolerance in patients with cancer-induced bone pain remains unclear. The aim of the present study was to investigate the role of spinal MCP-1 in morphine tolerance in bone cancer pain rats (MTBP rats). Bone cancer pain was induced by intramedullary injection of Walker 256 cells into the tibia of the rats, while morphine tolerance was induced by continuous intrathecal injection of morphine over a period of 9 days. In addition, anti-MCP-1 antibodies were intrathecally injected to rats in various groups in order to investigate the association of MCP-1 with mechanical and heat hyperalgesia using the paw withdrawal threshold (PWT) and thermal withdrawal latency (TWL) tests, respectively. Furthermore, MCP-1 and CCR2 expression levels were measured using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis, and CCR2 expression levels were measured using RT-qPCR. The results indicated that MCP-1 and CCR2 expression levels were significantly increased in the spinal cord of MTBP rats. Intrathecal administration of anti-MCP-1 neutralizing antibodies was observed to attenuate the mechanical and thermal allodynia in MTBP rats. Therefore, the upregulation of spinal MCP-1 and CCR2 expression levels may contribute to the development of mechanical allodynia in MTBP rats. In conclusion, MCP-1/CCR2 signaling may serve a crucial role in morphine tolerance development in rats suffering from cancer-induced bone pain.

Anti-nerve growth factor antibody attenuates chronic morphine treatment-induced tolerance in the rat

Background

Nerve growth factor (NGF) is known to induce inflammation and pain; however its role in opioid-induced tolerance has not been studied. This study investigated the effects of an anti-NGF neutralizing antibody on the development of tolerance following chronic morphine treatment in naïve rats.

Methods

Four groups of rats were used in this study; one treated with saline alone, one with 10 mg/kg of morphine, one with 10 μg of anti-NGF and the other with 10 mg/kg of morphine + 10 μg of anti-NGF, twice per day for 5 days. The route of treatment was subcutaneous (S.C.) for morphine and saline, and intraperitoneal (i.p.) for anti-NGF. Response to a noxious thermal stimulus during the course of drug treatment was assessed (Hargreaves’ test). Further, the change in the NGF levels in the lumbar spinal cord was measured by ELISA.

Results

Our results showed that repeated administration of morphine produced an apparent tolerance which was significantly attenuated by co-administration of anti-NGF (P < 0.001). Additionally, the area under the curve (AUC) of the analgesic effect produced by the combination of morphine and anti-NGF was significantly (P < 0.001) greater than for saline controls and chronic morphine treated rats. Moreover, the level of NGF in the spinal cord of chronic morphine treated rats was significantly higher (P < 0.05) than in both the saline control group and the group receiving simultaneous administration of anti-NGF with morphine. These results indicate that anti-NGF has the potential to attenuate morphine-induced tolerance behavior by attenuating the effects of NGF at the spinal level.

Conclusion

Taken together, our study strongly suggests that the NGF signaling system is a potential novel target for treating opioid-induced tolerance.