Pharmacological Treatment Of Chronic Pain Research Articles

How to treat chronic pain in rheumatic and musculoskeletal diseases (RMDs) – A pharmacological review

IntroductionChronic pain is a common symptom of rheumatic diseases that impacts patients’ quality of life. While non-pharmacological approaches are often recommended as first-line treatments, pharmacological interventions are important for pain management. However, the effectiveness and safety of different pharmacological treatments for chronic pain in rheumatic diseases are unclear. MethodsThis review critically synthesizes the current evidence base to guide clinicians in selecting appropriate pharmacological treatments for their patients, considering the expected benefits and potential risks and side effects. ResultsFor osteoarthritis, nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen, opioids, and antidepressants are commonly used, with NSAIDs being the most recommended. In addition, topical agents, such as topical NSAIDs, are recommended for localized pain relief. For fibromyalgia, amitriptyline, serotonin and noradrenaline reuptake inhibitors (SNRIs), and gabapentinoids are commonly used, with SNRIs being the most recommended. For back pain, nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen, opioids are used only for acute of flare-up pain, whereas neuropathic pain drugs are only used for chronic radicular pain. For inflammatory rheumatic diseases, disease-modifying antirheumatic drugs (DMARDs) and biological agents are recommended to slow disease progression and manage symptoms. ConclusionWhile DMARDs and biological agents are recommended for inflammatory rheumatic diseases, pharmacological treatments for other rheumatic diseases only alleviate symptoms and do not provide a cure for the underlying condition. The use of pharmacological treatments should be based on the expected benefits and evaluation of side effects, with non-pharmacological modalities also being considered, especially for fibromyalgia.

The Pharmacological Treatment of Chronic Pain: From Guidelines to Daily Clinical Practice.

In agreement with the International Association for the Study of Pain, chronic pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage. To date, there are several types of pain: nociceptive, neuropathic, and nociplastic. In the present narrative review, we evaluated the characteristics of the drugs used for each type of pain, according to guidelines, and their effects in people with comorbidity to reduce the development of severe adverse events.

Exploring patient preference heterogeneity for pharmacological treatments for chronic pain: A latent class analysis.

BackgroundSeveral pharmaceutical treatments for chronic pain caused by osteoarthritis (OA) and chronic low back pain (CLBP) are available or currently under development, each associated with different adverse events (AEs) and efficacy profiles. It is therefore important to understand what trade‐offs patients are willing to make when choosing between treatments.MethodsA discrete‐choice experiment (DCE) was conducted with 437 adults with chronic pain caused by OA and/or CLBP. Respondents were presented with a series of scenarios and asked to choose between pairs of hypothetical treatments, each defined by six attributes: level of symptom control; risks of heart attack, rapidly progressive osteoarthritis and dependency; frequency and mode of administration and cost. Attributes were based on known profiles of oral nonsteroidal anti‐inflammatory drugs, opioids and injected nerve growth factor inhibitors, the last of which were under clinical development at the time of the study. Data were analysed using a latent class (LC) model to explore preference heterogeneity.ResultsOverall, respondents considered improving symptom control and reducing risk of physical dependency to be the most important attributes. The LC analysis identified four participant classes: an ‘efficacy‐focused’ class (33.7%), a ‘cost‐averse’ class (29.4%), a ‘physical‐dependence–averse’ class (19.6%) and a ‘needle‐averse’ class (17.3%). Subgroup membership was incompletely predicted by participant age and their responses to comprehension questions.ConclusionsPreference heterogeneity across respondents indicates a need for a personalized approach to offering treatment options. Symptom improvement, cost, physical dependence and route of administration might be important to different patients.SignificanceMultiple treatment options that differ substantially in terms of efficacy and adverse events are available for the management of chronic pain. With a growing emphasis on a patient‐centred care model that incorporates patients’ priorities and values into treatment decisions, there is a need to understand how individuals with chronic musculoskeletal pain balance the benefits and risks of treatment and how treatment priorities vary among individuals. This study was designed to identify patient preferences for different characteristics of treatments for the management of chronic pain and to investigate how preferences differ among respondents.

Chronic pain and mental health problems among Syrian refugees: associations, predictors and use of medication over time: a prospective cohort study

ObjectivesThis study aims to examine associations, predictors and pharmacological treatment of chronic pain and mental health problems among Syrian refugees in a longitudinal perspective.DesignProspective cohort study.SettingWe collected survey data among...

Adenosine Metabotropic Receptors in Chronic Pain Management.

The pharmacological treatment of chronic pain is still unsatisfactory. The cellular and molecular mechanisms at the basis of pain chronification are still poorly understood. The commercially available drugs for treating chronic pain, including neuropathic pain, are effective in few patients and own several side effects that often limit the compliance of the patients. In addition, the opioids, which are the most potent analgesics, often fail in chronic pain conditions, especially in neuropathic pain syndromes. Moreover, it is well known that opiates can lead to addiction, tolerance and hyperalgesia. Therefore, new targets for treating neuropathic pain are needed. Purines, including ATP, ADP and adenosine and their receptors are deeply involved in the pathophysiology of neuropathic pain, particularly in the immune-mediated reactions that are responsible for the induction of the tactile allodynia, that represents the main symptom of neuropathic pain. The first response to the insult is mediated by the production of ATP and the activation of P2X receptors (Jacobson et al., 2020). In particular, the P2X4 receptors on microglia have been identified to be essential for the involvement of microglia cells in the pain pathophysiology (Trang et al., 2012). Beside the P2X, the P2Y receptors tend to boost the immune cells in response to nucleotides, with their ligands acting as immediate danger signals (Cekic and Linden, 2016). The subsequent stimulation of the metabotropic P1 adenosine receptors (ARs), of which are known four subtypes (A1, A2A, A2B, and A3), is overall associated with the reduction of both immunoinflammatory response and pain (Vincenzi et al., 2020). In the present opinion paper we will focus on the role of the P1 adenosine receptors in the pathophysiology of chronic neuropathic pain. The involvement of P2X and P2Y receptors in chronic pain has been discussed elsewhere (Jacobson et al., 2020).

Resting-state brain functional connectivity in patients with chronic pain who responded to subanesthetic-dose ketamine

Ketamine has been used to treat chronic pain; however, it is still unknown as to what types of chronic pain is ketamine effective against. To identify the effect of administration of subanesthetic-dose ketamine in patients with chronic pain and to clarify the mechanism of the effect, we retrospectively investigated brain functional connectivity using resting-state functional magnetic resonance imaging (rs-fMRI). Patients were divided into responders (Group R: ≥50% improvement on Numerical Rating Scale) and non-responders (Group NR). We compared the differences in terms of brain functional connectivity by seed-to-voxel correlation analysis. Two-sample t-test revealed significant lower connectivity between the medial prefrontal cortex (mPFC) and precuneus in Group R. We also found a significant negative correlation between the improvement rate and functional connectivity strength between the mPFC and precuneus. These findings suggest that subanesthetic-dose ketamine is effective in patients with chronic pain whose brain functional connectivity between the mPFC and precuneus is low. We believe that the current study explored for the first time the correlation between brain functional connectivity and the effect of subanesthetic-dose ketamine for chronic pain and indicated the possibility of use of the predictive marker in pharmacological treatment of chronic pain.

Fibromyalgia as a Biopsychosocial Model for the Intersections of Physical and Emotional Pain

The evaluation and treatment of pain and chronic pain conditions has been a dynamic and perpetually evolving area of focus as we strive towards a more standardized and comprehensive approach informed by ongoing research. The recent emergence of disorders focused on the recognition of the pain experience outside of a definitive physical lesion, specifically Fibromyalgia, has continued to challenge previously held beliefs about pain and our approach to its treatment. This article reviews the history of pain management through review of past and present guidelines and the unintended consequences of the interpretation of these guidelines. The biologic cause and function of pain, types of pain, and the neurologic basis of pain are presented with illustrative figures. Fibromyalgia as a syndrome, its evolving diagnostic criteria according to the American College of Rheumatology, and the insight this disorder gives us into the pharmacologic treatment of chronic pain are discussed. Psychosocial considerations are also presented as they do play a significant role in both diagnosis and treatment of this order. Overall the purpose of this article is to better inform treatment plans, recommendations, provider communication, and expectations for pain relief through the understanding that not all pain is the same and thus should not be treated as such. This review contains 6 figures, and 30 references. Key Words: Dorsal Horn Neurons, Sensory/Discriminatory Pathways, Emotional/Motivation Pathways, Serotonin, Norepinephrine, Opioids, Endorphins, Peripheral Sensitization, Central Segmental Sensitization, Central Suprasegmental Sensitization, Fibromyalgia

Managing Chronic Pain in Cancer Survivors Prescribed Long-Term Opioid Therapy: A National Survey of Ambulatory Palliative Care Providers

ContextChronic pain, or pain lasting more than three months, is common among cancer survivors, who are often prescribed long-term opioid therapy (LTOT). ObjectiveOur objective was to explore palliative care providers' experiences with managing chronic pain in cancer survivors prescribed LTOT, specifically in ambulatory palliative care settings, and their strategies for overcoming challenges. MethodsWe recruited providers through leading national palliative care organizations who manage chronic pain in cancer survivors. Asked to consider only cancer survivors with chronic pain when responding, participants completed an online survey that included questions about use of opioid risk mitigation tools, confidence in addressing opioid misuse behaviors and discussing/recommending management approaches, and access to addiction treatment. ResultsOf 157 participants, most were physicians (83%) or nurse practitioners (15%). Most reported using opioid risk mitigation tools such as urine drug testing (71%), opioid treatment agreements (85%), and practitioner database monitoring programs (94%). Participants were confident (7–8/10) managing the most commonly encountered opioid misuse behaviors (missing appointments, marijuana use, and using more opioids than prescribed) and in their ability to recommend nonpharmacologic and nonopioid pharmacologic treatments for chronic pain (10/10). They were least confident prescribing naloxone or managing addiction (5/10); only 27% reported having training or systems in place to address addiction. Only 13% had a waiver to prescribe buprenorphine. ConclusionPalliative care providers are comfortable with many aspects of managing chronic pain in cancer survivors on LTOT, although challenges persist, including the lack of systems-based approaches and training in addiction treatment.

Prevalence, characteristics and treatment of chronic pain in elderly patients hospitalized in internal medicine wards

BackgroundChronic pain is a frequent characteristic of elderly people and represents an actual and still poorly debated topic. ObjectiveWe investigated pain prevalence and intensity, and its pharmacological therapy in elderly patients hospitalized in 101 internal medicine wards. MethodsTaking advantage of the “REgistro POliterapie Società Italiana Medicina Interna” (REPOSI), we collected 2535 patients of whom almost a quarter was older than 85 years old. Among them, 582 patients were affected by pain (either chronic or acute) and 296 were diagnosed with chronic pain. ResultsPatients with pain showed worse cognitive status, higher depression and comorbidities, and a longer duration of hospital stay compared to those without pain (all p < .0366). Patients with chronic pain revealed lower level of independency in their daily life, worse cognitive status and higher level of depression compared to acute pain patients (all p < .0156). Moreover, most of them were not treated for pain at admission (73.4%) and half of them was not treated with any analgesic drug at discharge (50.5%). This difference affected also the reported levels of pain intensity. Patients who received analgesics at both admission and discharge remained stable (p = .172). Conversely, those not treated at admission who received an analgesic treatment during the hospital stay decreased their perceived pain (p < .0001). ConclusionsOur results show the need to focus more attention on the pharmacological treatment of chronic pain, especially in hospitalized elderly patients, in order to support them and facilitate their daily life after hospital discharge.

Reporting of cross-over clinical trials of analgesic treatments for chronic pain: Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks systematic review and recommendations.

Cross-over trials are typically more efficient than parallel group trials in that the sample size required to yield a desired power is substantially smaller. It is important, however, to consider some issues specific to cross-over trials when designing and reporting them, and when evaluating the published results of such trials. This systematic review evaluated the quality of reporting and its evolution over time in articles of cross-over clinical trials of pharmacologic treatments for chronic pain published between 1993 and 2013. Seventy-six (61%) articles reported a within-subject primary analysis, or if no primary analysis was identified, reported at least 1 within-subject analysis, which is required to achieve the gain in power associated with the cross-over design. For 39 (31%) articles, it was unclear whether analyses conducted were within-subject or between-group. Only 36 (29%) articles reported a method to accommodate missing data (eg, last observation carried forward, n = 29), and of those, just 14 included subjects in the analysis who provided data from only 1 period. Of the articles that identified a within-subject primary analysis, 21 (51%) provided sufficient information for the results to be included in a meta-analysis (ie, estimates of the within-subject treatment effect and variability). These results and others presented in this article demonstrate deficiencies in reporting of cross-over trials for analgesic treatments. Clearer reporting in future trials could improve readers' ability to critically evaluate the results, use these data in meta-analyses, and plan future trials. Recommendations for proper reporting of cross-over trials that apply to any condition are provided.

Novel Three-Day, Community-Based, Nonpharmacological Group Intervention for Chronic Musculoskeletal Pain (COPERS): A Randomised Clinical Trial.

BackgroundChronic musculoskeletal pain is the leading cause of disability worldwide. The effectiveness of pharmacological treatments for chronic pain is often limited, and there is growing concern about the adverse effects of these treatments, including opioid dependence. Nonpharmacological approaches to chronic pain may be an attractive alternative or adjunctive treatment. We describe the effectiveness of a novel, theoretically based group pain management support intervention for chronic musculoskeletal pain.Methods and FindingsWe conducted a multi-centre, pragmatic, randomised, controlled effectiveness and cost-effectiveness (cost–utility) trial across 27 general practices and community musculoskeletal services in the UK. We recruited 703 adults with musculoskeletal pain of at least 3 mo duration between August 1, 2011, and July 31, 2012, and randomised participants 1.33:1 to intervention (403) or control (300). Intervention participants were offered a participative group intervention (COPERS) delivered over three alternate days with a follow-up session at 2 wk. The intervention introduced cognitive behavioural approaches and was designed to promote self-efficacy to manage chronic pain. Controls received usual care and a relaxation CD. The primary outcome was pain-related disability at 12 mo (Chronic Pain Grade [CPG] disability subscale); secondary outcomes included the CPG disability subscale at 6 mo and the following measured at 6 and 12 mo: anxiety and depression (Hospital Anxiety and Depression Scale [HADS]), pain acceptance (Chronic Pain Acceptance Questionnaire), social integration (Health Education Impact Questionnaire social integration and support subscale), pain-related self-efficacy (Pain Self-Efficacy Questionnaire), pain intensity (CPG pain intensity subscale), the census global health question (2011 census for England and Wales), health utility (EQ-5D-3L), and health care resource use. Analyses followed the intention-to-treat principle, accounted for clustering by course in the intervention arm, and used multiple imputation for missing or incomplete primary outcome data.The mean age of participants was 59.9 y, with 81% white, 67% female, 23% employed, 85% with pain for at least 3 y, and 23% on strong opioids. Symptoms of depression and anxiety were common (baseline mean HADS scores 7.4 [standard deviation 4.1] and 9.2 [4.6], respectively). Overall, 282 (70%) intervention participants met the predefined intervention adherence criterion. Primary outcome data were obtained from 88% of participants. There was no significant difference between groups in pain-related disability at 6 or 12 mo (12 mo: difference −1.0, intervention versus control, 95% CI −4.9 to 3.0), pain intensity, or the census global health question. Anxiety, depression, pain-related self-efficacy, pain acceptance, and social integration were better in the intervention group at 6 mo; at 12 mo, these differences remained statistically significant only for depression (−0.7, 95% CI −1.2 to −0.2) and social integration (0.8, 95% CI 0.4 to 1.2). Intervention participants received more analgesics than the controls across the 12 mo. The total cost of the course per person was £145 (US$214). The cost–utility analysis showed there to be a small benefit in terms of quality-adjusted life years (QALYs) (0.0325, 95% CI −0.0074 to 0.0724), and on the cost side the intervention was a little more expensive than usual care (i.e., £188 [US$277], 95% CI −£125 [−US$184] to £501 [US$738]), resulting in an incremental cost-effectiveness ratio of £5,786 (US$8,521) per QALY. Limitations include the fact that the intervention was relatively brief and did not include any physical activity components.ConclusionsWhile the COPERS intervention was brief, safe, and inexpensive, with a low attrition rate, it was not effective for reducing pain-related disability over 12 mo (primary outcome). For secondary outcomes, we found sustained benefits on depression and social integration at 6 and 12 mo, but there was no effect on anxiety, pain-related self-efficacy, pain acceptance, pain intensity, or the census global health question at 12 mo. There was some evidence that the intervention may be cost-effective based on a modest difference in QALYs between groups.Trial registrationISRCTN Registry 24426731

Nonpharmacological Treatment Approach to Pain

Chronic pain has various forms such as inflammatory pain, visceral pain, headache, disk-related pain, neuropathic pain, cancer pain. Although the biological basis of chronic pain is related to vulnerability, it continues with behavioral and psychological components. In the context of multimodal interventions, interventions other than systemic pharmacologic treatments for chronic pain are also present. Besides interventional approaches; there are several noninvasive options including cognitive behavioral therapy, biofeedback, relaxation therapy, physical therapy, thermal applications, spinal cord stimulation and transcutaneous electrical stimulation. The neuroscientific approach to pain can only be achieved by combining physical and mental components of the pain with neuroscience

Subanesthetic ketamine infusions for the treatment of children and adolescents with chronic pain: a longitudinal study.

BackgroundChronic pain is common in children and adolescents and is often associated with severe functional disability and mood disorders. The pharmacological treatment of chronic pain in children and adolescents can be challenging, ineffective, and is mostly based on expert opinions and consensus. Ketamine, an N-methyl-D-aspartate receptor antagonist, has been used as an adjuvant for treatment of adult chronic pain and has been shown, in some instances, to improve pain and decrease opioid-requirement. We examined the effects of subanesthetic ketamine infusions on pain intensity and opioid use in children and adolescents with chronic pain syndromes treated in an outpatient setting.MethodsLongitudinal cohort study of consecutive pediatric patients treated with subanesthetic ketamine infusions in a tertiary outpatient center. Outcome measurements included self-reported pain scores (numeric rating scale) and morphine-equivalent intake.ResultsOver a 15-month period, 63 children and adolescents (median age 15, interquartile range 12–17 years) with chronic pain received 277 ketamine infusions. Intravenous administration of subanesthetic doses of ketamine to children and adolescents on an outpatient basis was safe and not associated with psychotropic effects or hemodynamic perturbations. Overall, ketamine significantly reduced pain intensity (p <0.001) and yielded greater pain reduction in patients with complex regional pain syndrome (CRPS) than in patients with other chronic pain syndromes (p = 0.029). Ketamine-associated reductions in pain scores were the largest in postural orthostatic tachycardia syndrome (POTS) and trauma patients and the smallest in patients with chronic headache (p = 0.007). In 37 % of infusions, patients had a greater than 20 % reduction in pain score. Conversely, ketamine infusions did not change overall morphine-equivalent intake (p = 0.3).ConclusionsThese data suggest that subanesthetic ketamine infusion is feasible in an outpatient setting and may benefit children and adolescents with chronic pain. Further, patients with CRPS, POTS, and a history of trauma-related chronic pain are more likely to benefit from this therapeutic modality.

Retrospective Evaluation on the Analgesic Activities of 2 Compounded Topical Creams and Voltaren Gel in Chronic Noncancer Pain.

Pharmacologic treatment of chronic pain is challenging. Oral therapy may require multiple medications; each has side effects, dose limitations, and limited efficacy. Compounded topical formulations have evolved as potential treatment options. The objective of this study was to evaluate the efficacy of 2 compounded topical creams, "Cream I" and "Cream II," in patients with chronic extremity, joint, musculoskeletal, neuropathic, or other chronic topical pain conditions and compare their efficacy with Voltaren gel. The primary efficacy outcome was the change in visual numeric pain intensity score from pretreatment to posttreatment. The Cream I contained Flurbiprofen (20%), Tramadol (5%), Clonidine (0.2%), Cyclobenzaprine (4%), and Bupivacaine (3%). The Cream II contained Flurbiprofen (20%), Baclofen (2%), Clonidine (0.2%), Gabapentin (10%), and Lidocaine (5%). The Voltaren gel contained 1% diclofenac sodium. A total of 2177 patients were evaluated, 826 males and 1351 females. During their medical treatment, 1141 patients received Cream I, 527 patients received Cream II, and 509 patients received Voltaren gel. After treatment, the pain intensity score decreased by 3.11 ± 1.65 (37%) with Cream I (from 8.44 ± 1.19 to 5.33 ± 2.0, P < 0.001), by 2.93 ± 1.58 (35%) with Cream II (from 8.42 ± 1.27 to 5.50 ± 1.96, P < 0.001), and by 1.49 ± 0.73 (19%) with Voltaren gel (from 7.93 ± 0.81 to 6.44 ± 1.14, P < 0.001). Cream I and Cream II did not differ significantly in efficacy, and both were significantly more effective than Voltaren gel (P < 0.001). It is concluded that Voltaren gel had less efficacy than the compounded creams, which were effective and provided pain relief in the majority of the patients studied.

β-arrestin-2-biased agonism of delta opioid receptors sensitizes transient receptor potential vanilloid type 1 (TRPV1) in primary sensory neurons.

Despite advances in understanding the signaling mechanisms involved in the development and maintenance of chronic pain, the pharmacologic treatment of chronic pain has seen little advancement. Agonists at the mu opioid receptor (MOPr) continue to be vital in the treatment of many forms of chronic pain, but side-effects limit their clinical utility and range from relatively mild, such as constipation, to major, such as addiction and dependence. Additionally, chronic activation of MOPr results in pain hypersensitivity known as opioid-induced hyperalgesia (OIH), and we have shown recently that recruitment of β-arrestin2 to MOPr, away from transient potential vanilloid eceptor type 1 (TRPV1) in primary sensory neurons contributes to this phenomenon. The delta opioid receptor (DOPr) has become a promising target for the treatment of chronic pain, but little is known about the effects of chronic activation of DOPr on nociceptor sensitivity and OIH. Here we report that chronic activation of DOPr by the DOPr-selective agonist, SNC80, results in the sensitization of TRPV1 and behavioral signs of OIH via β-arrestin2 recruitment to DOPr and away from TRPV1. Conversely, chronic treatment with ARM390, a DOPr-selective agonist that does not recruit β-arrestin2, neither sensitized TRPV1 nor produced OIH. Interestingly, the effect of SNC80 to sensitize TRPV1 is species-dependent, as rats developed OIH but mice did not. Taken together, the reported data identify a novel side-effect of chronic administration of β-arrestin2-biased DOPr agonists and highlight the importance of potential species-specific effects of DOPr agonists.

α9-nicotinic acetylcholine receptors contribute to the maintenance of chronic mechanical hyperalgesia, but not thermal or mechanical allodynia.

BackgroundThe current pharmacological treatments for chronic pain are limited. The first analgesic drug approved for clinical use in decades that has a novel molecular target is the synthetic version of a naturally occurring conotoxin. Several conotoxins that target ion channels have progressed to clinical trials for the relief of pain. Vc1.1 and RgIA are analgesic α-conotoxins that target α9-subunit-containing nicotinic acetylcholine receptors (α9-nAChR) as well as GABAB receptor mechanisms. However, the evidence for the involvement of α9-nAChRs in pain is controversial. In the present study, the role of the α9-nAChR in pain was assessed using a battery of behavioural pain tests and pain models in α9-nAChR knockout (KO) mice.Resultsα9-nAChR KO mice showed normal responses to acute noxious thermal and mechanical stimuli, and developed normal chronic cold and mechanical allodynia in inflammatory and nerve injury pain models. However, KO animals developed mechanical hyperalgesia to a lesser extent than their wild type (WT) counterparts in both inflammatory and neuropathic pain models. Chronic neuropathic pain is sustained in WT mice for at least 21 days post injury, while KO mice show significant recovery by 14 days post injury. KO sham mice were also resistant to the repeated-measures effect of the noxious pain test that caused a gradual onset of mild mechanical hyperalgesia in WT sham animals.ConclusionsThe α9-nAChR is not involved in acute pain perception or chronic thermal or mechanical allodynia or thermal hyperalgesia but does contribute to the intensity and duration of chronic mechanical hyperalgesia, suggesting that pain-relieving actions of antagonists that target this site may be restricted to high threshold mechanosensation. The α9-nAChR appears to be a valid target for pharmacological compounds that alleviate long-term mechanical hyperalgesia and may be of use as a prophylactic drug to prevent the development of some symptoms of chronic pain.

Comprehensive management of chronic pain in haemophilia

Chronic pain, most often due to haemophilic arthropathy, is a pervasive problem in persons with haemophilia (PWH) that adversely impacts function and quality of life. PWH with inhibitors and older PWH may be especially vulnerable to progressive arthropathy and resulting chronic pain. The development of chronic pain from acute pain involves a complex interplay of biological and psychosocial factors that may all contribute to the perpetuation of chronic pain and the outcome of therapy. In the absence of evidence-based guidelines, an individualized, multimodal approach to chronic pain management is proposed, as it is in individuals without haemophilia who have chronic pain. Pharmacological treatment is central to the management of chronic pain and must be modified based on pain intensity, ongoing response to therapy and the risk for adverse events. Non-pharmacological interventions, including physiotherapy, complementary treatments and surgical (e.g. orthopaedic) or other invasive procedures, may be integral to chronic pain management in this population. Ongoing psychosocial assessment is critical to identify those factors that may be contributing to the perpetuation of chronic pain or acting as barriers to effective management. Additional study is needed to identify optimal pharmacological treatments for chronic pain in PWH based on the unique pathophysiology of haemophilic arthropathy and on risk profile. Systematic determination of the particular psychosocial factors impacting the experience and management of chronic pain in PWH would likewise add value to the treatment of this pervasive problem.

Pharmacogenetics of analgesic drugs.

Summary points• Individual variability in pain perception and differences in the efficacy of analgesic drugs are complex phenomena and are partly genetically predetermined.• Analgesics act in various ways on the peripheral and central pain pathways and are regarded as one of the most valuable but equally dangerous groups of medications.• While pharmacokinetic properties of drugs, metabolism in particular, have been scrutinised by genotype–phenotype correlation studies, the clinical significance of inherited variants in genes governing pharmacodynamics of analgesics remains largely unexplored (apart from the µ-opioid receptor).• Lack of replication of the findings from one study to another makes meaningful personalised analgesic regime still a distant future.• This narrative review will focus on findings related to pharmacogenetics of commonly used analgesic medications and highlight authors’ views on future clinical implications of pharmacogenetics in the context of pharmacological treatment of chronic pain.

Using fMRI to evaluate the effects of milnacipran on central pain processing in patients with fibromyalgia

BackgroundIn recent years, the prescription of serotonin-noradrenalin reuptake inhibitors (SNRIs) for treatment of fibromyalgia (FM) has increased with reports of their efficacy. The SNRI milnacipran is approved by the U.S. Food and Drug Administration (FDA) for treatment of FM, yet, the mechanisms by which milnacipran reduces FM symptoms are unknown. A large number of neuroimaging studies have demonstrated altered brain function in patients with FM but the effect of milnacipran on central pain processing has not been investigated. The primary objective of this study was to assess the effect of milnacipran on sensitivity to pressure-evoked pain in FM. Secondary objectives were to assess the effect of milnacipran on cerebral processing of pressure-evoked pain using fMRI and the tolerability and safety of milnacipran 200mg/day in FM. Methods92 patients were randomized to either 13-weeks milnacipran treatment (200mg/day) or placebo in this double-blind, placebo-controlled multicenter clinical trial. Psychophysical measures and functional MRI (fMRI) assessments were performed before and after treatment using a computer-controlled pressure-pain stimulator. Here, we present the results of several a priori defined statistical analyses. ResultsMilnacipran-treated patients displayed a trend toward lower pressure-pain sensitivity after treatment, compared to placebo, and the difference was greater at higher pain intensities. A single group fMRI analysis of milnacipran-treated patients indicated increased pain-evoked brain activity in the caudatus nucleus, anterior insula and amygdala after treatment, compared to before treatment; regions implicated in pain inhibitory processes. A 2×2 repeated measures fMRI analysis, comparing milnacipran and placebo, before and after treatment, showed that milnacipran-treated patients had greater pain-evoked activity in the precuneus/posterior cingulate cortex after treatment; a region previously implicated in intrinsic brain function and FM pathology. This finding was only significant when uncorrected for multiple comparisons. The safety analysis revealed that patients from both treatment groups had treatment-emergent adverse events where nausea was the most common complaint, reported by 43.5% of placebo patients and 71.7% of milnacipran-treated patients. Patients on milnacipran were more likely to discontinue treatment because of side effects. ConclusionsOur results provide preliminary indications of increased pain inhibitory responses in milnacipran-treated FM patients, compared to placebo. The psychophysical assessments did not reach statistical significance but reveal a trend toward higher pressure-pain tolerance after treatment with milnacipran, compared to placebo, especially for higher pain intensities. Our fMRI analyses point toward increased activation of the precuneus/posterior cingulum in patients treated with milnacipran, however results were not corrected for multiple comparisons. The precuneus/posterior cingulum is a key region of the default mode network and has previously been associated with abnormal function in FM. Future studies may further explore activity within the default mode network as a potential biomarker for abnormal central pain processing. ImplicationsThe present study provides novel insights for future studies where functional neuroimaging may be used to elucidate the central mechanisms of common pharmacological treatments for chronic pain. Furthermore, our results point toward a potential mechanism for pain normalization in response to milnacipran, involving regions of the default mode network although this finding needs to be replicated in future studies.

Acupuncture as an adjunctive therapy to pharmacological treatment in patients with chronic pain due to osteoarthritis of the knee: A 3-armed, randomized, placebo-controlled trial

The efficacy of acupuncture as an adjunctive therapy to pharmacological treatment of chronic pain due to knee osteoarthritis was studied with a 3-armed, single-blind, randomized, sham-controlled trial; it compared acupuncture combined with pharmacological treatment, sham acupuncture including pharmacological treatment, and pharmacological treatment alone. A total of 120 patients with knee osteoarthritis were randomly allocated to 3 groups: group I was treated with acupuncture and etoricoxib, group II with sham acupuncture and etoricoxib, and group III with etoricoxib. The primary efficacy variable was the Western Ontario and McMaster Universities (WOMAC) index and its subscales at the end of treatment at week 8. Secondary efficacy variables included the WOMAC index at the end of weeks 4 and 12, a visual analogue scale (VAS) at the end of weeks 4, 8, and 12, and the Short Form 36 version 2 (SF-36v2) health survey at the end of week 8. An algometer was used to determine changes in a predetermined unique fixed trigger point for every patient at the end of weeks 4, 8, and 12. Group I exhibited statistically significant improvements in primary and secondary outcome measures, except for Short Form mental component, compared with the other treatment groups. We conclude that acupuncture with etoricoxib is more effective than sham acupuncture with etoricoxib, or etoricoxib alone for the treatment of knee osteoarthritis.