A pooled analysis evaluating the efficacy and tolerability of tapentadol extended release for chronic, painful diabetic peripheral neuropathy

Comprehensive Analysis of Strong Opioid Side Effects in Palliative Care Using the SIDER Database

Background/Objectives: There exist multiple opioid-based treatments in palliative care, each with distinct side effect profiles. When adverse events occur, switching opioids can help maintain effective pain management. However, owing to limited clinical evidence, no comprehensive guidelines exist for opioid switching. This study employed the Side Effect Resource (SIDER) database, which aggregates adverse event data from clinical trials and package inserts, to analyze the side effects of five commonly used "strong opioids" in palliative care in Japan, namely morphine, fentanyl, oxycodone, hydromorphone, and tapentadol. Methods: Data on the names and incidence of adverse events for each opioid were extracted from SIDER 4.1, developed by the Max Delbrück Center for Molecular Medicine. Cluster analysis and principal component analysis were performed to interpret the data. Results: The key side effects of opioids were nausea, vomiting, constipation, and drowsiness. Fentanyl was more frequently associated with nausea and vomiting but less frequently with constipation and drowsiness. Tapentadol caused nausea relatively more frequently and constipation less frequently. Oxycodone was prominently linked to drowsiness, whereas morphine was frequently associated with constipation and drowsiness. Hydromorphone was associated with higher rates of constipation and vomiting but lower incidences of nausea and drowsiness. Conclusions: All side effects characterizing the opioids were related to μ-opioid receptor stimulation, although the present study findings highlight differences in the frequency of specific side effects among the opioids. These results provide objective insights that can guide opioid switching in response to adverse effects.

Sex-Gender Differences Are Completely Neglected in Treatments for Neuropathic Pain

As sex-gender differences have been described in the responses of patients to certain medications, we hypothesized that the responses to medications recommended for neuropathic pain may differ between men and women. We conducted a literature review to identify articles reporting potential sex-gender differences in the efficacy and safety of these medications. Only a limited number of studies investigated potential sex-gender differences. Our results show that women seem to achieve higher blood concentrations than men during treatment with amitriptyline, nortriptyline, duloxetine, venlafaxine, and pregabalin. Compared to men, higher rates of women develop side effects during treatment with gabapentin, lidocaine, and tramadol. Globally, the sex-gender differences would suggest initially administering smaller doses of these medications to women with neuropathic pain compared to those administered to men. However, most of these differences have been revealed by studies focused on the treatment of other diseases (e.g., depression). Studies focused on neuropathic pain have overlooked potential sex-gender differences in patient responses to medications. Despite the fact that up to 60% of patients with neuropathic pain fail to achieve an adequate response to medications, the potential role of sex-gender differences in the efficacy and safety of pharmacotherapy has not adequately been investigated. Targeted studies should be implemented to facilitate personalized treatments for neuropathic pain.

Update on Treating Painful Diabetic Peripheral Neuropathy: A Review of Current US Guidelines with a Focus on the Most Recently Approved Management Options

Painful diabetic peripheral neuropathy (DPN) is a highly prevalent and disabling complication of diabetes that is often misdiagnosed and undertreated. The management of painful DPN involves treating its underlying cause via lifestyle modifications and intensive glucose control, targeting its pathogenesis, and providing symptomatic pain relief, thereby improving patient function and health-related quality of life. Four pharmacologic options are currently approved by the US Food and Drug Administration (FDA) to treat painful DPN. These include three oral medications (duloxetine, pregabalin, and tapentadol extended release) and one topical agent (capsaicin 8% topical system). More recently, the FDA approved several spinal cord stimulation (SCS) devices to treat refractory painful DPN. Although not FDA-approved specifically to treat painful DPN, tricyclic antidepressants, serotonin/norepinephrine reuptake inhibitors, gabapentinoids, and sodium channel blockers are common first-line oral options in clinical practice. Other strategies may be used as part of individualized comprehensive pain management plans. This article provides an overview of the most recent US guidelines for managing painful DPN, with a focus on the two most recently approved treatment options (SCS and capsaicin 8% topical system), as well as evidence for using FDA-approved and guideline-supported drugs and devices. Also discussed are unmet needs for this patient population, and evidence for potential future treatments for painful DPN, including drugs with novel mechanisms of action, electrical stimulation devices, and nutraceuticals.

[Diabetic neuropathy and diabetic foot syndrome (update 2023)]

These are the guidelines for diagnosis and treatment of diabetic neuropathy and diabetic foot.The position statement summarizes characteristic clinical symptoms and techniques for diagnostic assessment of diabetic neuropathy, including the complex situation of the diabetic foot syndrome. Recommendations for the therapeutic management of diabetic neuropathy, especially for the control of pain in sensorimotor neuropathy, are provided. The needs to prevent and treat diabetic foot syndrome are summarized.

Prevention and Management Strategies for Diabetic Neuropathy

Diabetic neuropathy (DN) is a common complication of diabetes that is becoming an increasing concern as the prevalence of diabetes rapidly rises. There are several types of DN, but the most prevalent and studied type is distal symmetrical polyneuropathy, which is the focus of this review and is simply referred to as DN. It can lead to a wide range of sensorimotor and psychosocial symptoms and is a major risk factor for diabetic foot ulceration and Charcot neuropathic osteoarthropathy, which are associated with high rates of lower limb amputation and mortality. The prevention and management of DN are thus critical, and clinical guidelines recommend several strategies for these based on the best available evidence. This article aims to provide a narrative review of DN prevention and management strategies by discussing these guidelines and the evidence that supports them. First, the epidemiology and diverse clinical manifestations of DN are summarized. Then, prevention strategies such as glycemic control, lifestyle modifications and footcare are discussed, as well as the importance of early diagnosis. Finally, neuropathic pain management strategies and promising novel therapies under investigation such as neuromodulation devices and nutraceuticals are reviewed.

An Insight into Potential Pharmacotherapeutic Agents for Painful Diabetic Neuropathy

Diabetes is the 4th most common disease affecting the world's population. It is accompanied by many complications that deteriorate the quality of life. Painful diabetic neuropathy (PDN) is one of the debilitating consequences of diabetes that effects one-third of diabetic patients. Unfortunately, there is no internationally recommended drug that directly hinders the pathological mechanisms that result in painful diabetic neuropathy. Clinical studies have shown that anticonvulsant and antidepressant therapies have proven fruitful in management of pain associated with PDN. Currently, the FDA approved medications for painful diabetic neuropathies include duloxetine, pregabalin, tapentadol extended release, and capsaicin (for foot PDN only). The FDA has also approved the use of spinal cord stimulation system for the treatment of diabetic neuropathy pain. The drugs recommended by other regulatory bodies include gabapentin, amitriptyline, dextromethorphan, tramadol, venlafaxine, sodium valproate, and 5 % lidocaine patch. These drugs are only partially effective and have adverse effects associated with their use. Treating painful symptoms in diabetic patient can be frustrating not only for the patients but also for health care workers, so additional clinical trials for novel and conventional treatments are required to devise more effective treatment for PDN with minimal side effects. This review gives an insight on the pathways involved in the pathogenesis of PDN and the potential pharmacotherapeutic agents. This will be followed by an overview on the FDA-approved drugs for PDN and commercially available topical analgesic and their effects on painful diabetic neuropathies.

Pharmacotherapy of Painful Diabetic Neuropathy: A Clinical Update

The rising prevalence of diabetes mellitus (DM) leads on to an increase in chronic diabetic complications. Diabetic peripheral neuropathies (DPNs) are common chronic complications of diabetes. Distal symmetric polyneuropathy is the most prevalent form. Most patients with DPN will remain pain-free; however, painful DPN (PDPN) occurs in 6-34% of all DM patients and is associated with reduced health-related-quality-of-life and substantial economic burden. Symptomatic treatment of PDPN and diabetic autonomic neuropathy is the key treatment goals. Using certain patient related characteristics, subjects with PDPN can be stratified and assigned targeted therapies to produce better pain outcomes. The aim of this review is to discuss the various pathogenetic mechanisms of DPN with special reference to the mechanisms leading to PDPN and the various pharmacological and non-pharmacological therapies available for its management. Recommended pharmacological therapies include anticonvulsants, antidepressants, opioid analgesics, and topical medications.

Comparison of opioid prescribing upon hospital discharge in patients receiving tapentadol versus oxycodone following orthopaedic surgery

Background The changing of opioids during the transition of care from hospital to home may be associated with harm. Objective To compare patients receiving tapentadol IR versus oxycodone IR following orthopaedic surgery during hospitalisation with regard to the changing of opioids at hospital discharge. Setting A major metropolitan tertiary referral hospital in Australia. Methods This is a retrospective cohort study. Participants included adult orthopaedic surgery patients receiving postoperative tapentadol IR or oxycodone IR during hospitalisation between 1 January 2018 and 30 June 2019. Main outcome measure The proportion of patients for whom the opioid prescribed was changed at hospital discharge. Results The study cohort included 199 patients. Of these, 100 patients received oxycodone and 99 patients received tapentadol post-operatively during hospitalisation. The mean age was 66 years (SD, 12 years) and 111 (56%) were female. The most common surgeries were total knee arthroplasty (91, 46%), total hip arthroplasty (63, 32%) and shoulder surgery (26, 13%). Patients in the tapentadol group were more likely to be changed to a different opioid upon hospital discharge than the oxycodone group (57% versus 9%, difference 48% [95% CI 36-59%, p < 0.01). After adjusting for confounders, post-operative tapentadol use was more likely to be associated with opioid changing upon discharge (OR 16.5, 95% CI 6.7 to 40.8, p < 0.01). Conclusions The post-operative use of tapentadol IR during hospitalisation was associated with an increased likelihood of opioid changing at hospital discharge. This practice could have patient safety implications.

Tapentadol and Sleepwalking: A Case Report

OBJECTIVE

This is a case report of a patient with sleepwalking likely caused by tapentadol ER secondary to higher than the recommended dose for the treatment of pain.

METHODS

This report presents the relevant patient history, laboratory data and literature review on possible causes of this patient's sleepwalking.

RESULTS

A 39-year-old female reported sleepwalking as the dose of tapentadol increased above the recommended maximum provided in the package insert. The mechanism of action of tapentadol involving norepinephrine reuptake inhibition affecting the central nervous system, higher dosage and drug interactions with other home medications likely contributed to her sleepwalking.

CONCLUSION

This case highlights the importance of adhering to the recommended dosage of a medication and if it is clinically warranted to exceed the maximum recommended dose, the importance of diligent monitoring for any adverse effects.

Novel treatment modalities for painful diabetic neuropathy

BACKGROUND AND AIMS

Painful diabetic neuropathy significantly affects the quality of life in people with diabetic peripheral neuropathy (DPN). Existing pharmacological agents have limited efficacy and development of tolerance is a limitation.

METHODS

The present review focuses on novel pharmacological (systemic and topical) and non-pharmacological modalities for the alleviation of pain in people with DPN. We identified English language articles concerning studies with novel agents (animal or human) targeting symptomatic relief of painful diabetic neuropathy.

RESULTS

Though the pathophysiology of pain in DPN is complex, a better understanding of pain pathways (peripheral and central) have helped to identify potential targets for therapeutic success. Studies of pharmacological agents acting on various aspects of pain pathways including μ-opioid receptor agonist- norepinephrine reuptake inhibitor (MONRI), cannabinoid receptor, dual serotonin-nor-adrenergic (SNRI)-and triple dopamine reuptake inhibitor (SNDRI), purinergic receptors and sodium channel v1.7 blockers have undergone trials in humans and shown to improve pain symptoms and quality of life in people with DPN. A few other investigational agents targeting acetylcholine receptor, vanilloid channel, chemokine signaling, micro-RNA or mesenchymal stem cell based therapies (animal studies) have demonstrated promise in alleviation of pain. Topical agents like high-dose lidocaine, capsaicin, clonidine, amitriptyline and ketamine may benefit refractory neuropathic pain.

CONCLUSIONS

Novel MONRI, SNRI and cannabinoid receptor agonists have shown some promise for neuropathic pain relief in human trials, but await regulatory approvals. However, most of the novel pharmacological agents (systemic or topical) require appropriately powered placebo-controlled studies for clinical usage in painful diabetic neuropathy.

Management of Neuropathic Pain in Polyneuropathy

PURPOSE OF REVIEW

Many polyneuropathies cause significant neuropathic pain, resulting in substantial morbidity and reduced quality of life. Appropriate management is crucial for maintaining quality of life for patients with painful polyneuropathies. The US Food and Drug Administration (FDA) has only approved one new drug for painful diabetic neuropathy in the past decade, a topical capsaicin patch that was initially approved for the treatment of postherpetic neuralgia in 2009. Gabapentinoids and serotonin norepinephrine reuptake inhibitors (SNRIs) continue to have an advantage in safety profiles and efficacy. Other antiepileptic medications remain second-line agents because of fewer studies documenting efficacy.

RECENT FINDINGS

This article reviews recent literature on complementary and pharmacologic therapies for the management of painful polyneuropathies. Exercise has emerged as an important therapeutic tool and may also improve the underlying polyneuropathy in the setting of obesity, metabolic syndrome, and diabetes.

SUMMARY

The approach to management of painful polyneuropathies is multifactorial, using both pharmacologic and nonpharmacologic measures to improve pain severity and patient quality of life.

Guideline "diagnosis and non interventional therapy of neuropathic pain" of the German Society of Neurology (deutsche Gesellschaft für Neurologie)

2019 the DGN (Deutsche Gesellschaft für Neurology) published a new guideline on the diagnosis and non-interventional therapy of neuropathic pain of any etiology excluding trigeminal neuralgia and CRPS (complex regional pain syndrome). Neuropathic pain occurs after lesion or damage of the somatosensory system. Besides clinical examination several diagnostic procedures are recommended to assess the function of nociceptive A-delta and C-Fibers (skin biopsy, quantitative sensory testing, Laser-evoked potentials, Pain-evoked potentials, corneal confocal microscopy, axon reflex testing). First line treatment in neuropathic pain is pregabalin, gabapentin, duloxetine and amitriptyline. Second choice drugs are topical capsaicin and lidocaine, which can also be considered as primary treatment in focal neuropathic pain. Opioids are considered as third choice treatment. Botulinum toxin can be considered as a third choice drug for focal limited pain in specialized centers only. Carbamazepine and oxcarbazepine cannot be generally  recommended, but might be helpful in single cases. In Germany, cannabinoids can be prescribed, but only after approval of reimbursement. However, the use is not recommended, and can only be considered as off-label therapy within a multimodal therapy concept.

Challenges of neuropathic pain: focus on diabetic neuropathy

Neuropathic pain is a frequent condition caused by a lesion or disease of the central or peripheral somatosensory nervous system. A frequent cause of peripheral neuropathic pain is diabetic neuropathy. Its complex pathophysiology is not yet fully elucidated, which contributes to underassessment and undertreatment. A mechanism-based treatment of painful diabetic neuropathy is challenging but phenotype-based stratification might be a way to develop individualized therapeutic concepts. Our goal is to review current knowledge of the pathophysiology of peripheral neuropathic pain, particularly painful diabetic neuropathy. We discuss state-of-the-art clinical assessment, validity of diagnostic and screening tools, and recommendations for the management of diabetic neuropathic pain including approaches towards personalized pain management. We also propose a research agenda for translational research including patient stratification for clinical trials and improved preclinical models in relation to current knowledge of underlying mechanisms.

Tapentadol for neuropathic pain: a review of clinical studies

Neuropathic pain (NP) is an enormous burden for patients, caregivers and society. NP is a pain state that may develop after injury of the peripheral or central nervous system because of a wide range of diseases and traumas. A NP symptom component can be found also in several types of chronic pain. Many NP patients are substantially disabled for years. Due to its chronicity, severity and unpredictability, NP is difficult to treat. Tapentadol is a central-acting oral analgesic with combined opioid and noradrenergic properties, which make it potentially suitable for a wide range of pain conditions, particularly whenever a NP component is present or cannot be excluded. In randomized controlled trials, tapentadol has proved to be effective in relieving NP in diabetic peripheral neuropathy and in chronic low back pain. In observational studies, tapentadol reduced NP in chemotherapy-induced peripheral neuropathies, blood and solid cancers, and the NP component in neck pain and Parkinson's disease. This narrative review aims to provide clinicians with a broad overview of tapentadol effects on NP.

Spinal α2 -adrenoceptors and neuropathic pain modulation; therapeutic target

Neuropathic pain can arise from disease or damage to the nervous system. The most common symptoms of neuropathic pain include spontaneous pain, allodynia, and hyperalgesia. There is still limited knowledge about the factors that initiate and maintain neuropathic pain. However, ample evidence has proved the antinociceptive role of spinal α-adrenoceptors following nerve injury. It is well-documented that noradrenergic descending pathways from supraspinal loci exert an inhibitory influence on the spinal cord nociceptive neurons, mostly through the activation of spinal α₂ -adrenoceptors. This, in turn, suppresses transmission of pain input and the hyperexcitability of spinal dorsal horn neurons. There is considerable evidence demonstrating that spinal application of α₂ -adrenoceptor agonists leads to analgesic effects in animal models of neuropathic pain. Today, despite the recent rapid development of neuroscience and drug discovery, effective drugs with clear basic mechanisms have remained a mystery. Here, we give an overview of the cellular mechanisms through which brainstem adrenergic descending inhibitory processing can alter spinal pain transmission to the higher centres, and how these pathways change in neuropathic pain conditions focusing on the role of spinal α₂ -adrenoceptors in the spinal dorsal horn. We then suggest that α₂ -adrenoceptor agonist may be useful to treat neuropathic pain. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

An update on the diagnosis and treatment of diabetic somatic and autonomic neuropathy

Diabetic peripheral neuropathy (DPN) is the most common chronic complication of diabetes. It poses a significant challenge for clinicians as it is often diagnosed late when patients present with advanced consequences such as foot ulceration. Autonomic neuropathy (AN) is also a frequent and under-diagnosed complication unless it is overtly symptomatic. Both somatic and autonomic neuropathy are associated with increased mortality. Multiple clinical trials have failed because of limited efficacy in advanced disease, inadequate trial duration, lack of effective surrogate end-points and a lack of deterioration in the placebo arm in clinical trials of DPN. Multifactorial risk factor reduction, targeting glycaemia, blood pressure and lipids can reduce the progression of DPN and AN. Treatment of painful DPN reduces painful symptoms by about 50% at best, but there is limited efficacy with any single agent. This reflects the complex aetiology of painful DPN and argues for improved clinical phenotyping with the use of targeted therapy, taking into account co-morbid conditions such as anxiety, depression and sleep disturbance.

Diagnosing and managing diabetic somatic and autonomic neuropathy

The diagnosis and management of diabetic neuropathy can be a major challenge. Late diagnosis contributes to significant morbidity in the form of painful diabetic neuropathy, foot ulceration, amputation, and increased mortality. Both hyperglycaemia and cardiovascular risk factors are implicated in the development of somatic and autonomic neuropathy and an improvement in these risk factors can reduce their rate of development and progression. There are currently no US Food and Drug Administration (FDA)-approved disease-modifying treatments for either somatic or autonomic neuropathy, as a consequence of multiple failed phase III clinical trials. While this may be partly attributed to premature translation, there are major shortcomings in trial design and outcome measures. There are a limited number of partially effective FDA-approved treatments for the symptomatic relief of painful diabetic neuropathy and autonomic neuropathy.

Tapentadol Prolonged Release: A Review in Pain Management

Tapentadol prolonged release (tapentadol PR) [Palexia® SR in EU] is a long-acting tablet formulation of the strong central analgesic tapentadol, which acts as both a μ-opioid receptor (MOR) agonist and a noradrenaline reuptake inhibitor. Tapentadol PR is approved for chronic pain in various countries, with its EU indication (severe chronic pain manageable only with opioid analgesics) being the focus here. Well-designed trials and clinical practice data support tapentadol PR use in this setting. Short term, tapentadol PR was an effective and generally well tolerated analgesic for moderate to severe pain of varying aetiologies, including neuropathic pain. It provided analgesia at least as good as that of conventional strong opioids and appeared more favourable in terms of gastrointestinal tolerability, likely due to less potent MOR binding. Severe back pain with a neuropathic component responded well to moderate-dose tapentadol PR in some patients, while for others, an increase to the maximum recommended tapentadol PR dosage provided analgesia at least as good as that of moderate-dose tapentadol PR plus pregabalin and appeared to have some CNS tolerability benefits. Data also support the use of tapentadol PR in opioid rotation, including when conventional opioids are intolerable. Longer-term data in musculoskeletal pain conditions indicate continued benefit over up to 2 years' treatment with tapentadol PR with no evidence of tolerance. Thus, tapentadol PR is a useful option for the management of severe chronic pain.

Does 'Strong Analgesic' Equal 'Strong Opioid'? Tapentadol and the Concept of 'µ-Load'

INTRODUCTION

The distinct properties of the centrally-acting analgesic tapentadol derive from the combined contributions of an opioid component and a nonopioid component. However, the opioid component's relative contribution to analgesic and adverse effects has not previously been elucidated. Tapentadol's analgesic effect derives from the combined contribution of an opioid mechanism and a nonopioid mechanism, the extent of which can vary for different pains. Likewise, the interaction can vary for various adverse effects. Hence, the contribution of each mechanism to adverse effects can be different from the contribution to analgesia. We here estimate the percent contribution of each component of the mechanism of action to analgesia and to adverse effects.

AREAS COVERED

Several approaches to in vitro and in vivo data to estimate the contribution of tapentadol's opioid component to analgesia and to the two important opioid adverse effects, respiratory depression and constipation. The results are then compared with clinical data.

EXPERT OPINION

Traditional opioids, such as morphine, oxycodone, and others, produce their analgesic effects primarily through a single mechanism-the activation of µ-opioid receptors (MOR). Therefore, the contribution of the opioid component to adverse effects is 100%. In contrast, the newer strong analgesic tapentadol produces its analgesic effect via two separate and complementary analgesic mechanisms, only one of which is µ-opioid. We applied standard drug-receptor theory and novel techniques to in vitro and in vivo data to estimate by several different ways the μ-load of tapentadol (the % contribution of the opioid component to the adverse effect magnitude relative to a pure/classical µ-opioid at equianalgesia) in respiratory depression and constipation, and we compared the results to clinical evidence. The estimate is remarkably consistent over the various approaches and indicates that the μ-load of tapentadol is ≤ 40% (relative to pure MOR agonists, which have, by definition, a µ-load of 100%).

FUNDING

Grünenthal GmbH.

Opioid and noradrenergic contributions of tapentadol to the inhibition of locus coeruleus neurons in the streptozotocin rat model of polyneuropathic pain

Tapentadol is an analgesic that acts as an agonist of µ opioid receptors (MOR) and that inhibits noradrenaline reuptake. Data from healthy rats show that tapentadol inhibits neuronal activity in the locus coeruleus (LC), a nucleus regulated by both the noradrenergic and opioid systems. Thus, we set out to investigate the effect of tapentadol on LC activity in streptozotocin (STZ)-induced diabetic rats, a model of diabetic polyneuropathy, by analyzing single-unit extracellular recordings of LC neurons. Four weeks after inducing diabetes, tapentadol dose-response curves were obtained from animals pre-treated with RX821002 or naloxone (alpha2-adrenoceptors and opioid receptors antagonists, respectively). In STZ rats, the spontaneous activity of LC neurons (0.9 ± 0.1 Hz) was lower than in naïve animals (1.5 ± 0.1 Hz), and tapentadol's inhibitory effect was also weaker. Alpha2-adrenoceptors blockade by RX821002 (100 μg/kg i.v.) in STZ animals significantly increased the spontaneous activity (from 0.8 ± 0.1 to 1.4 ± 0.2 Hz) and it dampened the inhibition of LC neurons produced by tapentadol. However, opioid receptors blockade following naloxone pre-treatment (5 mg/kg i.v.) did not alter the spontaneous firing rate (0.9 ± 0.2 vs 0.9 ± 0.2 Hz) or the inhibitory effect of tapentadol on LC neurons in STZ animals. Thus, diabetic polyneuropathy appears to exert neuroplastic changes in LC neurotransmission, enhancing the sensitivity of alpha2-adrenoceptors and dampening opioid receptors expression. Tapentadol's activity seems to be predominantly mediated through its noradrenergic effects rather than its influence on opioid receptors in the STZ model of diabetic polyneuropathy.

Nature's first "atypical opioids": Kratom and mitragynines

WHAT IS KNOWN AND OBJECTIVE

Advances in pain research have led to an understanding that many pains are driven by more than one underlying (patho)physiologic cause (ie, they are "multimechanistic") and that better pain relief is obtained with fewer adverse effects when an analgesic is correspondingly multimechanistic. At least two of the more-modern analgesics combine opioid and non-opioid mechanisms, and have become known as "atypical opioids." Less well known is that just as Nature evolved opioids, it also evolved atypical opioids, presaging modern drug discovery efforts.

COMMENT

Traditional (typical) opioids are extracts or analogs of substances derived from the poppy plant. They produce their analgesic and adverse effects primarily through a single, opioid mechanism (albeit with individual differences). Two most recent analgesics were developed to have both an opioid mechanism and, a second, non-opioid mechanism of action (inhibition of monoamine neurotransmitter reuptake). Little known is that Nature had already evolved a plant source of compounds with the same properties.

WHAT IS NEW AND CONCLUSION

As debate about the use and abuse potential of kratom swirls, conflicting, often contradicting, opinions are expressed. A review of the basic pharmacology of kratom reveals the explanation for the bifurcation in viewpoints: kratom has both opioid and non-opioid properties. Fascinatingly, just as the poppy plant (Papaver) evolved the typical opioids, Mitragyna evolved the mitragynines-Nature's "atypical opioids."

Assessment and manifestation of central sensitisation across different chronic pain conditions

Different neuroplastic processes can occur along the nociceptive pathways and may be important in the transition from acute to chronic pain and for diagnosis and development of optimal management strategies. The neuroplastic processes may result in gain (sensitisation) or loss (desensitisation) of function in relation to the incoming nociceptive signals. Such processes play important roles in chronic pain, and although the clinical manifestations differ across condition processes, they share some common mechanistic features. The fundamental understanding and quantitative assessment of particularly some of the central sensitisation mechanisms can be translated from preclinical studies into the clinic. The clinical perspectives are implementation of such novel information into diagnostics, mechanistic phenotyping, prevention, personalised treatment, and drug development. The aims of this paper are to introduce and discuss (1) some common fundamental central pain mechanisms, (2) how they may translate into the clinical signs and symptoms across different chronic pain conditions, (3) how to evaluate gain and loss of function using quantitative pain assessment tools, and (4) the implications for optimising prevention and management of pain. The chronic pain conditions selected for the paper are neuropathic pain in general, musculoskeletal pain (chronic low back pain and osteoarthritic pain in particular), and visceral pain (irritable bowel syndrome in particular). The translational mechanisms addressed are local and widespread sensitisation, central summation, and descending pain modulation.

Significance

Central sensitisation is an important manifestation involved in many different chronic pain conditions. Central sensitisation can be different to assess and evaluate as the manifestations vary from pain condition to pain condition. Understanding central sensitisation may promote better profiling and diagnosis of pain patients and development of new regimes for mechanism based therapy. Some of the mechanisms underlying central sensitisation can be translated from animals to humans providing new options in development of therapies and profiling drugs under development.

Tapentadol Prolonged Release Reduces the Severe Chronic Ischaemic Pain and Improves the Quality of Life in Patients with Type 2 Diabetes

This study has been performed in diabetic type 2 patients with pain due to peripheral artery disease (PAD) in order to evaluate the efficacy and tolerability of tapentadol prolonged release (PR). Methods. 25 patients with type 2 diabetes (13 F and 12 M) were admitted in the study. The evaluation of the analgesic efficacy of tapentadol PR was based on both the assessment of the intensity of the pain (NRS scale from 0 to 10) and the nature of the pain (DN4 questionnaire) and on assessment of the patient's quality of life and state of health (SF-12 Health Survey). Study duration was 3 months: a baseline visit and follow-up included visits after 1 week, 1 month, 2 months, and 3 months. Results. At the beginning of the study, the mean intensity of the pain was 7.88 ± 1.17 on the NRS scale and at visit 2 it reduced in a statistically significant way; at the end of the treatment with tapentadol PR, the mean intensity was 2.84 points on the NRS scale. Conclusion. In type 2 diabetic patients with chronic severe pain due to PAD, tapentadol PR reduced pain intensity, improving the quality of life.

The switch from buprenorphine to tapentadol: is it worth?

Opioid analgesia continues to be the primary pharmacologic intervention for managing acute pain and malignant pain in both hospitalized and ambulatory patients. The increasing use of opioids in chronic nonmalignant pain is more problematic. Opioid treatment is complicated with the risks raised by adverse effects, especially cognitive disturbance, respiratory depression but also the risk of tolerance, opioid abuse and drug-disease interactions. Despite the growing number of available opioids within the last years, adequate trials of opioid rotation are lacking and most of the information is anecdotal. This article reviews the clinical evidence surrounding the switch from transdermal buprenorphine to tapentadol in malignant and non-malignant pain. Tapentadol acts on both the μ-opioid receptors (MOR) and on the neuronal reuptake of noradrenaline with a limited usefulness in acute pain management while buprenorphine is a mixed agonist-antagonist, and both present some advantages over other opioids. Both drugs show particular pharmacodynamic and pharmacokinetic properties which reduce the risks of development of tolerance, opioid abuse, diversion and determine fewer hormone changes than the "classical opioids" making these opioids more attractive than other opioids in long term opioid treatment. However, in the absence of powered clinical trials, the evidence to support the method used for transdermal buprenorphine rotation to tapentadol is weak.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Tapentadol Prolonged Release for Chronic Pain: A Review of Clinical Trials and 5 Years of Routine Clinical Practice Data

Tapentadol prolonged release (PR) for the treatment of moderate to severe chronic pain combines 2 modes of action. These are μ-opioid receptor agonism and noradrenaline reuptake inhibition in a single molecule that allow higher analgesic potency through modulation of different pharmacological targets within the pain transmitting systems. At the same time, this can also serve as a clue for modulation of different pain-generating mechanisms according to nociceptive, neuropathic, or mixed pain conditions. Tapentadol PR has now been on the market for 5 years, with over 4.6 million people treated worldwide. A panel of pain specialists convened in Germany to review the clinical program and to discuss the role of tapentadol PR in the management of chronic pain. The clinical study program demonstrated effective and generally well-tolerated treatment for up to 2 years in a broad range of chronic pain conditions, including those with neuropathic pain components. This was confirmed in routine clinical practice observations. Head-to-head studies with World Health Organization (WHO) III opioids such as oxycodone controlled release and oxycodone/naloxone PR showed at least comparable pain relief in the treatment of moderate-to-severe musculoskeletal pain. Rotation from poorly tolerated WHO III opioids to tapentadol PR provided effective pain relief and better symptom control for musculoskeletal pain compared to previous medication. Functionality, health status and quality of life also improved under tapentadol PR treatment. The gastrointestinal tolerability profile was more favorable compared to other tested WHO III opioids. Tapentadol PR has a good safety profile and no evidence of acquired tolerance from the long-term data so far collected. Overall, tapentadol PR represents an effective and generally well-tolerated alternative to "classical" opioidergic drugs.

Treatment with α-Lipoic Acid over 16 Weeks in Type 2 Diabetic Patients with Symptomatic Polyneuropathy Who Responded to Initial 4-Week High-Dose Loading

Effective treatment of diabetic sensorimotor polyneuropathy remains a challenge. To assess the efficacy and safety of α-lipoic acid (ALA) over 20 weeks, we conducted a multicenter randomized withdrawal open-label study, in which 45 patients with type 2 diabetes and symptomatic polyneuropathy were initially treated with ALA (600 mg tid) for 4 weeks (phase 1). Subsequently, responders were randomized to receive ALA (600 mg qd; n = 16) or to ALA withdrawal (n = 17) for 16 weeks (phase 2). During phase 1, the Total Symptom Score (TSS) decreased from 8.9 ± 1.8 points to 3.46 ± 2.0 points. During phase 2, TSS improved from 3.7 ± 1.9 points to 2.5 ± 2.5 points in the ALA treated group (p < 0.05) and remained unchanged in the ALA withdrawal group. The use of analgesic rescue medication was higher in the ALA withdrawal group than ALA treated group (p < 0.05). In conclusion, in type 2 diabetic patients with symptomatic polyneuropathy who responded to initial 4-week high-dose (600 mg tid) administration of ALA, subsequent treatment with ALA (600 mg qd) over 16 weeks improved neuropathic symptoms, whereas ALA withdrawal was associated with a higher use of rescue analgesic drugs. This trial is registered with ClinicalTrials.gov Identifier: NCT02439879.