(–)-(1R,2R)-3-(3-Dimethylamino-1-ethyl-2-methyl-propyl)-phenol Hydrochloride (Tapentadol HCl): a Novel μ-Opioid Receptor Agonist/Norepinephrine Reuptake Inhibitor with Broad-Spectrum Analgesic Properties

Novel insights on the management of pain: highlights from the ‘Science of Relief’ meeting

The ‘Science of Relief’ event, held in Milan on 10–11 May 2019, was aimed at promoting dialog between different stakeholders among scientific associations, pharma industry, healthcare services and related institutions. The goal was to renew interest and attention on the management of pain, sharing new solutions in order to bring the patients and their quality of life to the center of attention. An international group of scientists and clinicians presented and discussed new and known evidence in the field of chronic pain, from physiopathology and diagnosis to the choice of appropriate and timely pharmacological treatments. This paper reports the highlights of those presentations.

The anaesthetist, opioid analgesic drugs, and serotonin toxicity: a mechanistic and clinical review

Most cases of serotonin toxicity are provoked by therapeutic doses of a combination of two or more serotonergic drugs, defined as drugs affecting the serotonin neurotransmitter system. Common serotonergic drugs include many antidepressants, antipsychotics, and opioid analgesics, particularly fentanyl, tramadol, meperidine (pethidine), and methadone, but rarely morphine and other related phenanthrenes. Symptoms of serotonin toxicity are attributable to an effect on monoaminergic transmission caused by an increased synaptic concentration of serotonin. The serotonin transporter (SERT) maintains low serotonin concentrations and is important for the reuptake of the neurotransmitter into the presynaptic nerve terminals. Some opioids inhibit the reuptake of serotonin by inhibiting SERT, thus increasing the plasma and synaptic cleft serotonin concentrations that activate the serotonin receptors. Opioids that are good inhibitors of SERT (tramadol, dextromethorphan, methadone, and meperidine) are most frequently associated with serotonin toxicity. Tramadol also has a direct serotonin-releasing action. Fentanyl produces an efflux of serotonin, and binds to 5-hydroxytryptamine (5-HT)_1A and 5-HT_2A receptors, whilst methadone, meperidine, and more weakly tapentadol, bind to 5-HT_2A but not 5-HT_1A receptors. The perioperative period is a time where opioids and other serotonergic drugs are frequently administered in rapid succession, sometimes to patients with other serotonergic drugs in their system. This makes the perioperative period a relatively risky time for serotonin toxicity to occur. The intraoperative recognition of serotonin toxicity is challenging as it can mimic other serious syndromes, such as malignant hyperthermia, sepsis, thyroid storm, and neuroleptic malignant syndrome. Anaesthetists must maintain a heightened awareness of its possible occurrence and a readiness to engage in early treatment to avoid poor outcomes.

Comprehensive molecular pharmacology screening reveals potential new receptor interactions for clinically relevant opioids

Most clinically used opioids are thought to induce analgesia through activation of the mu opioid receptor (MOR). However, disparities have been observed between the efficacy of opioids in activating the MOR in vitro and in inducing analgesia in vivo. In addition, some clinically used opioids do not produce cross-tolerance with each other, and desensitization produced in vitro does not match tolerance produced in vivo. These disparities suggest that some opioids could be acting through other targets in vivo, but this has not been comprehensively tested. We thus screened 9 clinically relevant opioids (buprenorphine, hydrocodone, hydromorphone, morphine, O-desmethyl-tramadol, oxycodone, oxymorphone, tapentadol, tramadol) against 9 pain-related receptor targets (MOR, delta opioid receptor [DOR], kappa opioid receptor [KOR], nociceptin receptor [NOP], cannabinoid receptor type 1 [CB1], sigma-1 receptor [σ1R], and the monoamine transporters [NET/SERT/DAT]) expressed in cells using radioligand binding and functional activity assays. We found several novel interactions, including monoamine transporter activation by buprenorphine and σ1R binding by hydrocodone and tapentadol. Tail flick anti-nociception experiments with CD-1 mice demonstrated that the monoamine transporter inhibitor duloxetine selectively promoted buprenorphine anti-nociception while producing no effects by itself or in combination with the most MOR-selective drug oxymorphone, providing evidence that these novel interactions could be relevant in vivo. Our findings provide a comprehensive picture of the receptor interaction profiles of clinically relevant opioids, which has not previously been performed. Our findings also suggest novel receptor interactions for future investigation that could explain some of the disparities observed between opioid performance in vitro and in vivo.

Outcomes Associated with Treatment of Chronic Pain with Tapentadol Compared with Morphine and Oxycodone: A UK Primary Care Observational Study

Introduction

This study compared adverse outcomes and resource use for patients with a diagnosis of pain treated with tapentadol prolonged-release (PR) versus those treated with morphine controlled-release (CR) and oxycodone CR.

Methods

Data were sourced from the Clinical Practice Research Datalink (CPRD), a database derived from UK primary care. Patients prescribed tapentadol PR between May 2011 and December 2016 were selected and matched to two groups of controls treated with either morphine CR or oxycodone CR on gender, age, pain duration, pain site, pain aetiology, Charlson index and prior analgesia. Times to first adverse event (constipation or nausea/vomiting) were compared within a Cox proportional hazards model. Rates of primary care contacts, accident and emergency contacts and, for a subset of patients linked to Hospital Episode Statistics (HES), inpatient admissions and outpatient contacts were compared using incidence rate ratios (IRRs) derived from Poisson regression.

Results

A total of 1907 patients prescribed tapentadol PR were identified and 1791 (93.9%) had a pain diagnosis. Of these 1246 (65.3%) were matched to morphine controls and 829 (43.4%) to oxycodone controls. Compared to controls, gastrointestinal adverse events with tapentadol PR treatment were reduced; aHR = 0.532 (0.402–0.703; p < 0.001) versus morphine CR and 0.517 (0.363–0.735; p < 0.001) versus oxycodone CR. Compared with morphine CR, primary care contacts [IRR = 0.831 (0.802–0.861)], accident and emergency attendance [0.739 (0.572–0.951)], outpatient contacts [0.917 (0.851–0.989)] and inpatients contacts [0.789 (0.664–0.938)] were reduced. For oxycodone, the respective figures were 0.735 (0.703–0.768), 0.971 (0.699–1.352), 0.877 (0.799–0.962) and 0.748 (0.601–0.932).

Conclusion

Tapentadol PR was associated with significantly fewer adverse gastrointestinal events than morphine CR and oxycodone CR in patients with a diagnosis of pain. There was also significantly reduced primary and secondary care resource use. As with all observational studies, potential bias due to residual confounding and confounding by indication should be considered.

Funding

Grünenthal Ltd.

Electronic supplementary material

The online version of this article (10.1007/s12325-019-00932-7) contains supplementary material, which is available to authorized users.

Opioid Use and Potency Are Associated With Clinical Features, Quality of Life, and Use of Resources in Patients With Gastroparesis

BACKGROUND & AIMS

Many patients with gastroparesis are prescribed opioids for pain control, but indications for opioid prescriptions and the relationship of opioid use to gastroparesis manifestations are undefined. We characterized associations of use of potent vs weaker opioids and presentations of diabetic and idiopathic gastroparesis.

METHODS

We collected data on symptoms, gastric emptying, quality of life, and health care resource use from 583 patients with gastroparesis (>10% 4-h scintigraphic retention) from the National Institute of Diabetes and Digestive and Kidney Diseases Gastroparesis Consortium, from January 2007 through November 2016. Patients completed medical questionnaires that included questions about opioid use. The opioid(s) were categorized for potency relative to oral morphine. Symptom severities were quantified by Patient Assessment of Upper Gastrointestinal Disorders Symptoms questionnaires. Subgroup analyses compared patients on potent vs weaker opioids and opioid effects in diabetic vs idiopathic etiologies.

RESULTS

Forty-one percent of patients were taking opioids; 82% of these took potent agents (morphine, hydrocodone, oxycodone, methadone, hydromorphone, buprenorphine, or fentanyl). Abdominal pain was the reason for prescription for 61% of patients taking opioids. Mean scores for gastroparesis, nausea/vomiting, bloating/distention, abdominal pain, and constipation scores were higher in opioid users (P ≤ .05). Opioid use was associated with greater levels of gastric retention, worse quality of life, increased hospitalization, and increased use of antiemetic and pain modulator medications compared with nonusers (P ≤ .03). Use of potent opioids was associated with worse gastroparesis, nausea/vomiting, upper abdominal pain, and quality-of-life scores, and more hospitalizations compared with weaker opioids (tapentadol, tramadol, codeine, or propoxyphene) (P ≤ .05). Opioid use was associated with larger increases in gastric retention in patients with idiopathic vs diabetic gastroparesis (P = .008).

CONCLUSIONS

Opioid use is prevalent among patients with diabetic or idiopathic gastroparesis, and is associated with worse symptoms, delays in gastric emptying, and lower quality of life, as well as greater use of resources. Potent opioids are associated with larger effects than weaker agents. These findings form a basis for studies to characterize adverse outcomes of opioid use in patients with gastroparesis and to help identify those who might benefit from interventions to prevent opioid overuse.

Pharmacokinetics, safety, and efficacy of tapentadol oral solution for treating moderate to severe pain in pediatric patients

Background: This trial is part of the global pediatric clinical development program investigating the administration of the strong analgesic tapentadol in children and adolescents. Patients and methods: The single site, open-label phase 2 trial evaluated the pharmacokinetic profile of tapentadol and its major metabolite, tapentadol-O-glucuronide, as well as safety and tolerability and efficacy of a single dose of tapentadol oral solution (1 mg/kg) in patients (2 to <18 years) undergoing dental, ear, nose, or throat surgery. Blood sampling and pain intensity measurements were conducted using age-appropriate schedules and rating scales, respectively. Adverse events were monitored throughout the trial. Results: Sixty-six patients were treated. They were stratified by age: Group 1 (12 to <18 years), n=21; Group 2 (6 to <12 years), n=28; and Groups 3 (3 to <6 years) and 4 (2 to <3 years), n=17. Serum tapentadol concentrations observed in these pediatric patients were within the range observed in adults after administration of a single tapentadol immediate-release dose (50-100 mg), whereas those of the metabolite tapentadol-O-glucuronide were within the same range or lower than in adults who received comparable single doses of tapentadol. Pain intensity improved over time across all age groups. The most common treatment-emergent adverse events were nausea (24.2%), vomiting (16.7%), dizziness (9.1%), and headache (6.1%). Conclusion: A single dose of tapentadol oral solution (1 mg/kg) administered to pediatric patients (2 to <18 years) resulted in serum tapentadol concentrations within the targeted range shown to be safe and efficacious in adults. Tapentadol demonstrated good tolerability and safety; within the limitations of the trial design, improvements in postsurgical pain intensity were observed across the age groups. Tapentadol may provide a new treatment option in the management of moderate to severe pediatric pain.

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.

Inhibitory effect of valproate sodium on pain behavior in diabetic mice involves suppression of spinal histone deacetylase 1 and inflammatory mediators

Anti-epileptic medications are included in the international guidelines for managing neuropathic pain. Valproate sodium (VPS) was recently described as "the forgotten analgesic" and has been reported to relief pain in various models of neuropathic pain. Some studies reported anti-inflammatory and histone deacetylase 1 (HDA1) inhibitory properties for sodium valproate. The aim of the current study was to investigate the modulatory effect of VPS on pain behavior and inflammatory reactions in alloxan-induced diabetic neuropathy focusing on HDA1 inhibition and glia reactivity. 28 Male Swiss albino mice were allocated into four groups, (1) vehicle group, (2) alloxan-diabetic group, (3 & 4) alloxan+VPS (25 or 50 mg/kg) groups. VPS was given daily for 5 weeks by oral gavage. Pain behavior demonstrated increased allodynia (von-Frey filaments) and hyperalgesia (hot-plate test) in alloxan-diabetic mice that was reduced significantly by at least one of VPS doses. Sciatic nerves in diabetic mice showed increased histopathology score, increased silver staining for the nerves-indicating myelopathy- and a decrease in immunostaining for nerve growth factor. Spinal cord of diabetic mice showed greater histopathologic score, increased CD11b and glia fibrillary acidic protein (GFAP) immunostaining than vehicle treated mice. Molecular investigations highlighted greater content of spinal histone deacetylases, tumor necrosis factor-α (TNF-α) and interlukin-1β (IL1β) that were favorably modified by VPS. Overall, the current data confirmed that the pain killing and anti-inflammatory activity of VPS is at least partly mediated through inhibition of spinal HDA1 and glia reactivity. These findings support the view of inviting antiepileptics for treating neuropathies.

Opioid-induced constipation: a narrative review of therapeutic options in clinical management

Pain therapy often entails gastrointestinal adverse events. While opioids are effective drugs for pain relief, the incidence of opioid-induced constipation (OIC) varies greatly from 15% to as high as 81%. This can lead to a significant impairment in quality of life, often resulting in discontinuation of opioid therapy. In this regard, a good doctor-patient relationship is especially pivotal when initiating opioid therapy. In addition to a detailed history of bowel habits, patient education regarding the possible gastrointestinal side effects of the drugs is crucial. In addition, the bowel function must be regularly evaluated for the entire duration of treatment with opioids. Furthermore, if the patient has preexisting constipation that is well under control, continuation of that treatment is important. In the absence of such history, general recommendations should include sufficient fluid intake, physical activity, and regular intake of dietary fiber. In patients of OIC with ongoing opioid therapy, the necessity of opioid use should be critically reevaluated in terms of an with acceptable quality of life, particularly in cases of non-cancer pain. If opioids must be continued, lowering the dose may help, as well as changing the type of opioid. If these measures do not suffice, the next step for persistent OIC is the administration of laxatives. If these are ineffective as well, treatment with peripherally active μ-opioid receptor antagonists should be considered. Enemas and irrigation are emergency measures, often used as a last resort.

A combination pharmacotherapy of tapentadol and pregabalin to tackle centrally driven osteoarthritis pain

BACKGROUND

Many Osteoarthritis (OA) patients report with clinical features to their pain that cannot be explained by purely peripheral mechanisms. Yet, the analgesic agents available that tackle centrally driven chronic pain often provide only partial pain relief, or have dose-limiting side effects. We explored a combination therapy of the centrally acting analgesic agents tapentadol and pregabalin, to investigate if they could be used in combination to provide superior analgesia.

METHODS

Using electrophysiological single-unit recordings taken from spinal wide dynamic range neurons, Diffuse Noxious Inhibitory Controls (DNIC) were assessed as a marker of potential changes in descending controls in a monoiodoacetate (MIA) model of OA. We investigated if a subcutaneous injection of tapentadol or pregabalin, both alone and in combination, inhibited neuronal responses and restored the expression of DNIC, quantified as a reduction in neuronal firing in the presence of a conditioning noxious stimulus.

RESULTS

Tapentadol restored DNIC-induced neuronal inhibition in MIA animals, while pregabalin inhibited pre-conditioned mechanically evoked neuronal responses but did not restore DNIC. Given in combination, tapentadol and pregabalin restored DNIC expression and also inhibited spinal neuronal responses.

CONCLUSIONS

We propose that there is both central sensitization and an imbalance in inhibitory and facilitatory descending controls in MIA animals. The combination therapy of tapentadol and pregabalin restored descending noradrenergic inhibitory tone and also inhibited nociceptive transmission at the level of the spinal cord.

SIGNIFICANCE

This study shows that pregabalin and tapentadol target different mechanisms of centrally driven chronic pain associated with osteoarthritis, and that when administered together can restore descending inhibitory tone whilst also tackling spinal neuronal hyperexcitability and may therefore provide superior analgesia.

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.

Tapentadol: an analgesic that differs from classic opioids due to its noradrenergic mechanism of action

Chronic pain treatment represents one of the most complex clinical challenges and even though opioids exhibit particular efficacy on nociceptive pain, their use must be controlled to avoid the risk of adverse reactions. A useful approach, aimed at maintaining analgesia and mitigating side effects, is represented by the use of a new class of analgesics endowed of µ-opioid (MOR) receptor agonism and noradrenaline reuptake inhibition (NRI) mechanisms. Tapentadol is the progenitor of this new class of drugs called MOP-NRI. A literature review has been conducted to gain information about the efficacy and the tolerability profile of tapentadol shifting from MOR agonism (acute pain) to NRI activity (chronic pain). The tolerability and therapeutic safety of tapentadol in neuropathic pain models, as well as in clinical settings, has been analyzed showing a good gastrointestinal tolerability profile, a moderate effect on hormone levels (in healthy volunteers and in patients) and on cognitive performance, a lack of significant alteration of the electrocardiogram recording and no changes of the QT/QTc interval, a minimal effect on serotonin reuptake in vivo with a low risk of serotonin syndrome, a longer time for the onset of analgesic tolerance and a less occurrence of abuse liability compared to formulations containing other comparator compounds. Tapentadol represents a great innovation in chronic pain therapy with a unique analgesic profile different form classical opioids, therefore, thanks to its synergistic MOR-NRI action, it may be a good option for the treatment of chronic, neuropathic and mixed pain.

Cebranopadol: A Novel First-in-Class Potent Analgesic Acting via NOP and Opioid Receptors

Cebranopadol is a novel first-in-class analgesic with highly potent agonistic activity at nociceptin/orphanin FQ peptide (NOP) and opioid receptors. It is highly potent and efficacious across a broad range of preclinical pain models. Its side effect profile is better compared to typical opioids. Mechanistic studies have shown that cebranopadol's activity at NOP receptors contributes to its anti-hyperalgesic effects while ameliorating some of its opioid-type side effects, including respiratory depression and abuse potential. Phase II of clinical development has been completed, demonstrating efficacy and good tolerability in acute and chronic pain conditions.This article focusses on reviewing data on the preclinical in vitro and in vivo pharmacology, safety, and tolerability, as well as clinical trials with cebranopadol.

Multiple effectiveness aspects of tapentadol for moderate-severe cancer-pain treatment: an observational prospective study

Background

Previous studies have shown the efficacy of tapentadol (TP) for chronic cancer pain. We evaluated multiple effectiveness aspects of TP prolonged release on moderate–severe cancer-related pain, neuropathic pain (NeP), patient satisfaction, and quality of life.

Methods

An observational prospective study was conducted on 80 cancer patients. Opioid-naïve patients received a starting dose of prolonged-release TP 50 mg twice daily, and opioid-experienced patients were switched to TP, not to exceed 500 mg/day. Treatment response was evaluated at 3, 6, 30–40, and 60–70 days through response rate, numeric rating-scale scoring, survival analysis (time to event for response), pain-intensity difference, TP escalation-index percentage, and effects on NeP. The drug-sparing effect on concomitant therapies was evaluated.

Results

Seventy of 80 patients (88%) were responders to treatment (95% CI 78%–94%). Compared to T₀, pain-intensity reductions were statistically significant for all intervals (P<0.01), with better results at T₃/T₄. NeP was significantly reduced at T₄ (P<0.01). The probability of response was low at the initial stages and increased during the study. Pain-intensity differences decreased during the study, though without significance. Two patients (2.5%) left the study for TP-induced side effects. A significant improvement in quality of life was observed after 30–40 days (P<0.01). The majority of patients were “satisfied”, “very satisfied”, or “extremely satisfied” (T₃–T₄).

Conclusion

TP was effective in terms of drug-sparing effect, response rate, TP escalation-index percentage, and NeP management. By comparing data from the survival analysis with the response rate and time to response (numeric rating scale from T₀ to T₄), we found that although TP induced a quick response, a longer period of therapy and higher doses were needed to improve the positive result.

An investigation into the noradrenergic and serotonergic contributions of diffuse noxious inhibitory controls in a monoiodoacetate model of osteoarthritis

Osteoarthritis (OA) is a debilitating conditioning with pain as the major clinical symptom. Understanding the mechanisms that drive OA-associated chronic pain is crucial for developing the most effective analgesics. Although the degradation of the joint is the initial trigger for the development of chronic pain, the discordance between radiographic joint damage and the reported pain experience in patients, coupled with clinical features that cannot be explained by purely peripheral mechanisms, suggest there are often other factors at play. Therefore, this study considers the central contributions of chronic pain, using a monoiodoacetate (MIA) model of OA. Particularly, this study explores the functionality of descending controls over the course of the model by assessing diffuse noxious inhibitory controls (DNIC). Early-phase MIA animals have a functional DNIC system, whereas DNIC are abolished in late-phase MIA animals, indicating a dysregulation in descending modulation over the course of the model. In early-phase animals, blocking the actions of spinal α₂-adrenergic receptors completely abolishes DNIC, whereas blocking the actions of spinal 5-HT₇ receptors only partially decreases the magnitude of DNIC. However, activating the spinal α₂-adrenergic or 5-HT₇ receptors in late-phase MIA animals restored DNIC-induced neuronal inhibition. This study confirms that descending noradrenergic signaling is crucial for DNIC expression. Furthermore, we suggest a compensatory increase in descending serotonergic inhibition acting at 5-HT₇ receptors as the model progresses such that receptor activation is sufficient to override the imbalance in descending controls and mediate neuronal inhibition. NEW & NOTEWORTHY This study showed that there are both noradrenergic and serotonergic components contributing to the expression of diffuse noxious inhibitory controls (DNIC). Furthermore, although a tonic descending noradrenergic tone is always crucial for the expression of DNIC, variations in descending serotonergic signaling over the course of the model mean this component plays a more vital role in states of sensitization.

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.

[Opioid switch and change of route of administration in cancer patients treated by morphine]

This paper reviewed the 2002 guidelines established by the National Federation of Cancer Centres. A group of experts nominated by the 3 French Societies involved in the treatment of cancer pain (AFSOS, SFAP, SFETD), established new guidelines ratios for morphine switching and/or changing of route of administration, in patients for whom either pain was not adequatly managed or adverse effects were unbearable. After a rapid reminder of the pharmacokinetics and metabolism properties of morphine, experts explained why the theory of opioid rotation (oxycodone, hydromorphone, fentanyl, methadone, tapentadol) using fixed equianalgesic ratios is not any more appropriate for a secure clinical practice. In the light of recent publications enhancing our knowledge on the efficacy of new drug switching ratios and for changing the route of administration of morphine, the group of experts recommended to use reconsidered switching ratios favoring security upon efficacy, to minimize overdosing and adverse effects. Consequently, after the new conversion ratio (using slow release opioids) was applied, a second titration should be done by means of normal release rescue formulations for breakthrough pain episodes. A smartphone App. OpioConvert^® will be available for rapid and secure dose conversions.

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.

Effects of tapentadol on pain, motor symptoms and cognitive functions in Parkinson's disease

Background

Pain is a common and undertreated non-motor symptom in patients with Parkinson's disease (PD). Opioids have been seldom used in PD because they could worsen cognitive and motor functions.

Objective

We aimed to assess efficacy and tolerability of tapentadol in PD patients.

Methods

We retrospectively reviewed 21 PD patients treated with tapentadol extended release (ER) for chronic pain. Patients were evaluated before treatment and at 3 and 6 months during treatment for pain intensity (current, 24-hour average, and minimum and worst) with a 0-10 Numerical Rating Scale and the painDETECT questionnaire; for motor symptom severity with the Unified PD Rating Scale part III and the Hoehn and Yahr scale; for cognitive functions with Mini-Mental Status Examination, Corsi's Block-Tapping test, Digit Span test, Digit-Symbol Substitution test, FAS test, Rey's Auditory Verbal Learning test, Trail-Making test A and B and the 9-Hole Peg test; for anxiety and depression with the Hospital Anxiety and Depression Scale; and for the quality of life with the Short Form-12. Data were analyzed by 1-way analysis of variance and paired t-test, and by Friedman's and Wilcoxon's tests. Statistical significance was taken in all cases as P<0.05.

Results

Pain intensity decreased over the course of treatment. No differences were found in PD symptom severity and dopaminergic drug dosages between pretreatment and treatment evaluations. No decrement in cognitive neuropsychological performances was found and an improvement was observed in Digit Span test, Digit-Symbol Substitution test, and FAS test. The levels of anxiety, depression, and quality of life improved. Overall, tapentadol ER was well tolerated and most patients reported no or mild and short-lived gastroenterological and neurological side effects.

Conclusion

These results indicate the potential efficacy and tolerability of medium-high doses of tapentadol ER for the treatment of pain in PD.

Efficacy of tapentadol for first-line opioid-resistant neuropathic pain in Japan

Background

Cancer-related neuropathic pain is sometimes unresponsive to multidrug treatment. Novel drugs are required to treat such severe pain without necessitating the use of adjuvant analgesics. Tapentadol is a new drug that has a dual mechanism as both an opioid agonist and noradrenalin reuptake inhibitor. The study objective was to investigate the effectiveness of oral tapentadol for relieving cancer-related neuropathic pain.

Methods

A retrospective, single-center, open, non-randomized study was conducted at the Nagoya City University Hospital. The study included 38 Japanese patients with advanced cancer who received opioids, such as tramadol, oral oxycodone and transdermal fentanyl, with or without adjuvant analgesics. Eastern Cooperative Oncology Group performance status, Numerical Rating Scale, primary tumor type, primary opioid and tapentadol doses, adjuvant analgesic prescriptions, outcomes and adverse events of opioid switching were assessed for 7 days.

Results

Eighteen (47.3%) out of 38 patients were enrolled in this study. The average performance status was 2.13 ± 0.94 (mean ± standard deviation). After switching to oral tapentadol, the pain score decreased from 3.78 to 2.78. The patients who had clinically improved effective pain scores had a higher percentage of prior opioid use for more than 2 months. After switching to tapentadol, adverse events were usually mild, with a grade of 1-2 by the Common Terminology Criteria for Adverse Events v4.03.

Conclusions

Tapentadol appears to have an acceptable safety margin and promising efficacy to relieve cancer-related neuropathic pain that is refractory to first-line opioid treatment.

Pharmacokinetics and pharmacodynamics after oral administration of tapentadol hydrochloride in dogs

OBJECTIVE To evaluate pharmacokinetic and pharmacodynamic characteristics of 3 doses of tapentadol hydrochloride orally administered in dogs.

ANIMALS 6 healthy adult mixed-breed dogs.

PROCEDURES In a prospective, randomized crossover study, dogs were assigned to receive each of 3 doses of tapentadol (10, 20, and 30 mg/kg, PO); there was a 1-week washout period between subsequent administrations. Plasma concentrations and physiologic variables were measured for 24 hours. Samples were analyzed by use of high-performance liquid chromatography–tandem mass spectrometry.

RESULTS Tapentadol was rapidly absorbed after oral administration. Mean maximum plasma concentrations after 10, 20, and 30 mg/kg were 10.2, 19.7, and 31 ng/mL, respectively. Geometric mean plasma half-life of the terminal phase after tapentadol administration at 10, 20, and 30 mg/kg was 3.5 hours (range, 2.7 to 4.5 hours), 3.7 hours (range, 3.1 to 4.0 hours), and 3.7 hours (range, 2.8 to 6.5 hours), respectively. Tapentadol and its 3 quantified metabolites (tapentadol sulfate, tapentadol-O-glucuronide, and desmethyltapentadol) were detected in all dogs and constituted 0.16%, 2.8%, 97%, and 0.04% of the total area under the concentration-time curve (AUC), respectively. Plasma AUCs for tapentadol, tapentadol sulfate, and tapentadol-O-glucuronide increased in a dose-dependent manner. Desmethyltapentadol AUC did not increase in a linear manner at the 30-mg/kg dose. Sedation scores and heart and respiratory rates were not significantly affected by dose or time after administration.

CONCLUSIONS AND CLINICAL RELEVANCE Oral administration of tapentadol was tolerated well, and the drug was rapidly absorbed. Adverse events were not apparent in any dogs at any doses in this study.

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."

Comparative pharmacology and toxicology of tramadol and tapentadol

Moderate-to-severe pain represents a heavy burden in patients' quality of life, and ultimately in the society and in healthcare costs. The aim of this review was to summarize data on tramadol and tapentadol adverse effects, toxicity, potential advantages and limitations according to the context of clinical use. We compared data on the pharmacological and toxicological profiles of tramadol and tapentadol, after an extensive literature search in the US National Library of Medicine (PubMed). Tramadol is a prodrug that acts through noradrenaline and serotonin reuptake inhibition, with a weak opioid component added by its metabolite O-desmethyltramadol. Tapentadol does not require metabolic activation and acts mainly through noradrenaline reuptake inhibition and has a strong opioid activity. Such features confer tapentadol potential advantages, namely lower serotonergic, dependence and abuse potential, more linear pharmacokinetics, greater gastrointestinal tolerability and applicability in the treatment of chronic and neuropathic pain. Although more studies are needed to provide clear guidance on the opioid of choice, tapentadol shows some advantages, as it does not require CYP450 system activation and has minimal serotonergic effects. In addition, it leads to less side effects and lower abuse liability. However, in vivo and in vitro studies have shown that tramadol and tapentadol cause similar toxicological damage. In this context, it is important to underline that the choice of opioid should be individually balanced and a tailored decision, based on previous experience and on the patient's profile, type of pain and context of treatment.

SIGNIFICANCE

This review underlines the need for a careful prescription of tramadol and tapentadol. Although both are widely prescribed synthetic opioid analgesics, their toxic effects and potential dependence are not completely understood yet. In particular, concerning tapentadol, further research is needed to better assess its toxic effects.

Improved therapeutic potential of tapentadol employing cationic exchange resins as carriers in neuropathic pain: evidence from pharmacokinetic and pharmacodynamics study

Current investigation was endeavoured to overcome problem of poor palatability and bioavailability of centrally acting analgesic, tapentadol (TAP) by formulating controlled release drug-resin complexes (DRCs). The technology encompassed in preparation of DRCs involved chemisorption of TAP to weak cationic resins (KyronT-134 and Tulsion335) by batch method. Various formulation variables like drug-resin ratio, pH, resin activation and swelling time were optimized to achieve maximum drug loading in DRCs. FT-IR, DSC, pXRD, in vitro release study under bio-relevant condition of mouth and in vivo sensory taste evaluation established formation of taste masked DRC whereas dissolution study assured prolonged drug release behaviour of optimized DRC. Among DRCs, TAP-KyronT-134 complex exhibited higher drug loading (80.89 ± 4.56%), stability and prolonged release profile (10 h) without any detectable amount of drug release under salivary conditions. Pharmacokinetic studies in wistar rats revealed increased Tmax (2.67-fold), MRT (1.94-fold), elimination half-life (2.79-fold) and relative oral bioavailability (2.62-fold) of TAP on oral administration of optimized formulation compared to TAP solution. Furthermore, pharmacodynamics study confessed higher potential of DRC in attenuating chronic injury induced tactile allodynia for prolonged duration. In conclusion, the method developed is easily scalable and holds potential for commercialization with an evidence of obtaining more efficacious neuropathic pain management therapy.

Mu-opioid peptide (MOP) and nociceptin/orphanin FQ peptide (NOP) receptor activation both contribute to the discriminative stimulus properties of cebranopadol in the rat

The novel potent analgesic cebranopadol is an agonist at nociceptin/orphanin FQ peptide (NOP) and classical opioid receptors, with the highest in-vitro activity at NOP and mu-opioid peptide (MOP) receptors, and somewhat lower activity at kappa-opioid peptide (KOP) and delta-opioid peptide (DOP) receptors. We addressed the question of which of these pharmacological activities contribute to the stimulus properties of cebranopadol using a rat drug discrimination procedure. First, cebranopadol was tested in generalization tests against a morphine cue, including receptor-specific antagonism. Second, cebranopadol was established as a cue, and MOP, NOP, KOP and DOP receptor-selective agonists were tested in generalization tests. Third, cebranopadol in combination with receptor-selective antagonists was tested against the cebranopadol cue. Cebranopadol generalized to the morphine cue. Full generalization was only seen at clearly supra-analgesic doses. The effect of cebranopadol was reduced by naloxone, but was enhanced by the NOP receptor antagonist J-113397. In cebranopadol-trained rats, cebranopadol as well as morphine produced generalization. A NOP receptor agonist did not, while a DOP receptor agonist and a KOP receptor agonist weakly generalized to the cebranopadol cue. Conversely, generalization of cebranopadol was reduced by naloxone and J-113397, but not by a DOP or a KOP receptor antagonist. These results suggest a contribution of MOP receptor activity and a relative lack of contribution of DOP and KOP receptor activity to cebranopadol's stimulus properties. The findings regarding the contribution of NOP receptor activity were equivocal, but interestingly, the morphine-like stimulus property of cebranopadol appears to be reduced by its intrinsic NOP receptor activity.

The standardized Withania somnifera Dunal root extract alters basal and morphine-induced opioid receptor gene expression changes in neuroblastoma cells

Background

Behavioral studies demonstrated that the administration of Withania somnifera Dunal roots extract (WSE), prolongs morphine-elicited analgesia and reduces the development of tolerance to the morphine’s analgesic effect; however, little is known about the underpinning molecular mechanism(s). In order to shed light on this issue in the present paper we explored whether WSE promotes alterations of μ (MOP) and nociceptin (NOP) opioid receptors gene expression in neuroblastoma SH-SY5Y cells.

Methods

A range of WSE concentrations was preliminarily tested to evaluate their effects on cell viability. Subsequently, the effects of 5 h exposure to WSE (0.25, 0.50 and 1.00 mg/ml), applied alone and in combination with morphine or naloxone, on MOP and NOP mRNA levels were investigated.

Results

Data analysis revealed that morphine decreased MOP and NOP receptor gene expression, whereas naloxone elicited their up-regulation. In addition, pre-treatment with naloxone prevented the morphine-elicited gene expression alterations. Interestingly, WSE was able to: a) alter MOP but not NOP gene expression; b) counteract, at its highest concentration, morphine-induced MOP down-regulation, and c) hamper naloxone-induced MOP and NOP up-regulation.

Conclusion

Present in-vitro data disclose novel evidence about the ability of WSE to influence MOP and NOP opioid receptors gene expression in SH-SY5Y cells. Moreover, our findings suggest that the in-vivo modulation of morphine-mediated analgesia by WSE could be related to the hindering of morphine-elicited opioid receptors down-regulation here observed following WSE pre-treatment at its highest concentration.

Opioid-induced inhibition of the human 5-HT and noradrenaline transporters in vitro: link to clinical reports of serotonin syndrome

Background and Purpose

Opioids may inhibit the 5‐HT transporter (SERT) and the noradrenaline transporter (NET). NET inhibition may contribute to analgesia, and SERT inhibition or interactions with 5‐HT receptors may cause serotonergic toxicity. However, the effects of different opioids on the human SERT, NET and 5‐HT receptors have not been sufficiently studied.

Experimental Approach

We determined the potencies of different opioids to inhibit the SERT and NET in vitro using human transporter‐transfected HEK293 cells. We also tested binding affinities at 5‐HT_1A, 5‐HT_2A and 5‐HT_2C receptors. Additionally, we assessed clinical cases of the serotonin syndrome associated with each opioid reported by PubMed and a World Health Organization database.

Key Results

Dextromethorphan, l(R)‐methadone, racemic methadone, pethidine, tramadol and tapentadol inhibited the SERT at or close to observed drug plasma or estimated brain concentrations in patients. Tapentadol was the most potent NET inhibitor. Pethidine, tramadol, l(R)‐methadone, racemic methadone, dextromethorphan and O‐desmethyltramadol also inhibited the NET. 6‐Monoacetylmorphine, buprenorphine, codeine, dihydrocodeine, heroin, hydrocodone, hydromorphone, morphine, oxycodone and oxymorphone did not inhibit the SERT or NET. Fentanyl interacted with 5‐HT_1A receptors and methadone, pethidine and fentanyl with 5‐HT_2A receptors, in the low micromolar range. Opioids most frequently associated with the serotonin syndrome are tramadol, fentanyl, tapentadol, oxycodone, methadone and dextromethorphan.

Conclusions and Implications

Some synthetic opioids interact with the SERT and NET at potentially clinically relevant concentrations. SERT inhibition by tramadol, tapentadol, methadone, dextromethorphan and pethidine may contribute to the serotonin syndrome. Direct effects on 5‐HT_1A and/or 5‐HT_2A receptors could be involved with methadone and pethidine.

Review of Post-Marketing Safety Data on Tapentadol, a Centrally Acting Analgesic

Introduction

Tapentadol is a centrally acting analgesic that has been available for the management of acute and chronic pain in routine clinical practice since 2009.

Methods

This is the first integrated descriptive analysis of post-marketing safety data following the use of tapentadol in a broad range of pain conditions relating to the topics overall safety, dose administration above approved dosages, administration during pregnancy, serotonin syndrome, respiratory depression, and convulsion. The data analyzed pertain to spontaneous reports from healthcare and non-healthcare professionals and were put in the context of safety information known from interventional and non-interventional trials.

Results

The first years of routine clinical practice experience with tapentadol have confirmed the tolerability profile that emerged from the clinical trials. Moreover, the reporting of expected side effects such as respiratory depression and convulsion was low and no major risks were identified. The evaluation of available post-marketing data did not confirm the theoretical risk of serotonin syndrome nor did it reveal unexpected side effects with administration of higher than recommended doses.

Conclusion

More than 8 years after its first introduction, the favorable overall safety profile of tapentadol in the treatment of various pain conditions is maintained in the general population.

Funding

Grünenthal GmbH.

Electronic supplementary material

The online version of this article (10.1007/s12325-017-0654-0) contains supplementary material, which is available to authorized users.

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 beneficial use of ultramicronized palmitoylethanolamide as add-on therapy to Tapentadol in the treatment of low back pain: a pilot study comparing prospective and retrospective observational arms

Background

This pilot study was designed to compare the efficacy of ultramicronized palmitoylethanolamide (um-PEA) as add-on therapy to tapentadol (TP) with TP therapy only in patients suffering from chronic low back pain (LBP).

Methods

This pilot observational study consists in two arms: the prospective arm and the retrospective one. In the prospective arm patients consecutively selected received um-PEA as add-on therapy to TP for 6 months; in the retrospective arm patients were treated with TP only for 6 months. Pain intensity and neuropathic component were evaluated at baseline, during and after 6 months. The degree of disability and TP dosage assumption were evaluated at baseline and after 6 months.

Results

Statistical analysis performed with generalized linear mixed model on 55 patients (30 in the prospective group and 25 in the retrospective group) demonstrated that um-PEA as add-on treatment to TP in patients with chronic LBP, in comparison to TP alone, led to a significantly higher reduction in pain intensity, in the neuropathic component, the degree of disability and TP dosage assumption. No serious side effects were observed.

Conclusion

Overall, the present findings suggest that um-PEA may be an innovative therapeutic intervention as add-on therapy to TP for the management of chronic LBP with a neuropathic component, as well as to improve patient quality of life. Additionally, this combination treatment allowed a reduction in TP dose over time and did not show any serious side effects.

Pharmacokinetics of tapentadol in laying hens and its residues in eggs after multiple oral dose administration

1. The aim of the study was to evaluate the pharmacokinetics (PKs) of tapentadol (TAP), a novel opioid analgesic, in laying hens after intravenous (IV) and oral (PO) administration and to quantify the concentrations of TAP residues in eggs. 2. Twenty healthy laying hens were divided into three groups: A (n = 6), B (n = 6) and C (n = 8). The study was conducted in two phases. Groups A and B received TAP by IV and PO routes at the dose of 1 and 5 mg/kg, respectively. 3. No visible adverse effects were observed after administration of the drug. TAP plasma concentrations were detectable up to 4 h following administration. Following IV administration, TAP plasma concentrations were only higher than the minimal effective concentration (148 ng/ml) reported for humans for 1 h. After single PO administration, plasma concentrations of TAP would not conform to software algorithms and the PK parameters were not calculated. TAP concentration following multiple PO doses at 5 mg/kg for 5 d was found to be higher and more persistent (12 h vs. 7 h) in yolk compared with albumen. 4. This is the first PK study on the novel atypical opioid TAP in laying hens. Further studies are required to investigate the analgesic efficacy and actual effective plasma concentration of TAP in this species.

Chronic pain and adult hippocampal neurogenesis: translational implications from preclinical studies

Adult hippocampal neurogenesis (ahNG) occurs in the human brain. Adult generated neurons have been proposed to functionally contribute to relevant hippocampal functions such as learning and memory, mood regulation, and stress response. Learning, environmental enrichment, and physical exercise exert positive effects on ahNG. In parallel, these proneurogenic stimuli have been shown to ameliorate cognitive performance and/or depressive-like behavior in animal models. Conversely, aging, social isolation, and chronic stress exert negative effects on ahNG. Interestingly, reduction of hippocampal neurogenesis is suggested to potentially contribute to cognitive decline and mood alterations associated with aging and several neuropsychiatric disorders. Clinical observation demonstrates that patients affected by chronic pain often exhibit increased anxiety and depression, impaired cognitive flexibility, and memory capacities. As of today, our understanding of the molecular and cellular events that may underlie the comorbidity of chronic pain, depression, and cognitive impairment is limited. Herein we review recent preclinical data suggesting that chronic pain may induce profound changes in hippocampal plasticity, including reduced ahNG. We discuss the possibility that deregulated hippocampal neurogenesis in chronic pain may, at least in part, contribute to cognitive and mood alterations. Based on this hypothesis, the mechanisms underlying chronic pain-associated changes in hippocampal neurogenesis and related functions need to be addressed experimentally. One interesting feature of ahNG is its susceptibility to pharmacological modulation. Again, based on preclinical data we discuss the possibility that, at least in principle, distinct analgesic drugs commonly used in chronic pain states (typical and atypical opiates, α2δ ligands, and acetyl-l-carnitine) may differentially impact ahNG and that this aspect could be taken into account to reduce and/or prevent the potential risk of cognitive and emotional side effects in the clinical setting.

Antinociception induced by a novel α2A adrenergic receptor agonist in rodents acute and chronic pain models

The mechanisms and antinociceptive effects of a novel α_2A adrenoceptor agonist, 3-(2-chloro-6-fluorobenzil)-imidazolinide-2,4-dione (PT-31) were investigated using animal models of acute and chronic pain. The effects of PT-31 on pain responses were examined using hot plate and formalin tests in mice and spinal nerve ligation (SNL)-induced hyperalgesia in rats. The effects of antagonists acting on α adrenoceptor were assessed to investigate the interaction of these pathways upon PT-31 induced antinociception. PT-31 effects on motor activity/skills and on hemodynamic parameters were also evaluated. PT-31 had dose-dependent antinociception effects on hot-plate and formalin-injection induced pain responses. Thermal hyperalgesia and mechanical allodynia were reduced following a 7 d treatment with PT-31 (1, 5, and 10mg/kg/d, p.o.), and those effects were attenuated by yohimbine (5mg/kg), atropine (2mg/kg), L-nitro arginine methyl ester (L-NAME; 30mg/kg), or naloxone (2mg/kg). In contrast to clonidine, PT-31 did not have locomotor or hemodynamic effects in rats. The present results suggest that PT-31 represents a candidate for pain treatment with advantages over clonidine, namely no locomotor or hemodynamic impairments.

Intranasal delivery of tapentadol hydrochloride-loaded chitosan nanoparticles: formulation, characterisation and its in vivo evaluation

The aim of the present investigation was to formulate tapentadol hydrochloride-loaded chitosan nanoparticles (CS-NPs) for nose to brain delivery. Chitosan nanoparticles were prepared using ionotropic gelation technique. Optimisation of the formulation and process parameters was done using Box-Behnken Design. The entrapment efficiency, drug loading, Z-average size and zeta potential of the optimised batch were 63.49 ± 1.61%, 17.25 ± 1.38%w/w, 201.2 ± 1.5 nm and +49.3 mV, respectively. In-vitro release study showed 84.04 ± 1.53% drug release after 28 h, while ex vivo studies indicated higher permeation of CS-NPs through nasal mucosa. The nanoparticles exhibited good mucoadhesiveness, haemocompatibility and safety as evidenced by histopathology. The results of the pharmacodynamic study revealed prolongation of the analgesic activity. The intranasal instillation of CS-NPs resulted in the higher concentrations in brain compared to the drug solution and intravenous administration of CS-NPs. In a nutshell, intranasal administration of tapentadol hydrochloride-loaded CS-NPs is a promising approach for effective pain management.

Tapentadol prolonged-release for moderate-to-severe chronic osteoarthritis knee pain: a double-blind, randomized, placebo- and oxycodone controlled release-controlled study

OBJECTIVE

To assess efficacy and safety of tapentadol prolonged release (PR) for moderate-to-severe chronic osteoarthritis knee pain.

METHODS

Patients (n = 990) were randomized (1:1:1) to tapentadol PR, oxycodone controlled release (CR; reference compound for assay sensitivity), or placebo for a double-blind 3-week titration and 12-week maintenance period. Primary efficacy end-points were change from baseline in average pain intensity at week 12 of maintenance (US end-point) and over the entire maintenance period (non-US end-point) with "last observation carried forward" as imputation method for missing scores.

RESULTS

Both primary end-points were not significantly different for tapentadol PR nor for oxycodone CR vs placebo at week 12 (least squares [LS] mean difference = -0.3 [95% CI = -0.61-0.09]; p = 0.152 and 0.2 [95% CI = -0.16-0.54]; p = 0.279, respectively) and over the maintenance period (LS mean difference = -0.2 [95% CI = -0.55-0.07]; p = 0.135 and 0.1 [95% CI = -0.18-0.44]; p = 0.421, respectively). Considerably more patients receiving tapentadol PR than oxycodone CR completed the trial (58.3% vs 36.6%). This is consistent with better results with tapentadol PR on the overall health status (PGIC) compared to oxycodone CR. Indeed, respectively, 56% and 42.5% rated at least "much improved" at the end of treatment. Incidences of gastrointestinal adverse events were higher for both active treatments compared to placebo. Tapentadol PR was associated with a better gastrointestinal tolerability profile with incidences of constipation (17.9% vs 35%) and of the composite of nausea and/or vomiting (23.8% vs 46.8%) significantly lower vs oxycodone CR (p < 0.001).

CONCLUSIONS

The study did not demonstrate assay sensitivity. The finding that both primary end-points for tapentadol PR were not met can, thus, not be interpreted. Tapentadol PR was better tolerated than oxycodone CR, largely due to fewer gastrointestinal side-effects.

Acute administration of tramadol and tapentadol at effective analgesic and maximum tolerated doses causes hepato- and nephrotoxic effects in Wistar rats

Tramadol and tapentadol are two atypical synthetic opioid analgesics, with monoamine reuptake inhibition properties. Mainly aimed at the treatment of moderate to severe pain, these drugs are extensively prescribed for multiple clinical applications. Along with the increase in their use, there has been an increment in their abuse, and consequently in the reported number of adverse reactions and intoxications. However, little is known about their mechanisms of toxicity. In this study, we have analyzed the in vivo toxicological effects in liver and kidney resulting from an acute exposure of a rodent animal model to both opioids. Male Wistar rats were intraperitoneally administered with 10, 25 and 50mg/kg tramadol and tapentadol, corresponding to a low, effective analgesic dose, an intermediate dose and the maximum recommended daily dose, respectively, for 24h. Toxicological effects were assessed in terms of oxidative stress, biochemical and metabolic parameters and histopathology, using serum and urine samples, liver and kidney homogenates and tissue specimens. The acute exposure to tapentadol caused a dose-dependent increase in protein oxidation in liver and kidney. Additionally, exposure to both opioids led to hepatic commitment, as shown by increased serum lipid levels, decreased urea concentration, increased alanine aminotransferase and decreased butyrylcholinesterase activities. It also led to renal impairment, as reflected by proteinuria and decreased glomerular filtration rate. Histopathological findings included sinusoidal dilatation, microsteatosis, vacuolization, cell infiltrates and cell degeneration, indicating metabolic changes, inflammation and cell damage. In conclusion, a single effective analgesic dose or the maximum recommended daily dose of both opioids leads to hepatotoxicity and nephrotoxicity, with tapentadol inducing comparatively more toxicity. Whether these effects reflect risks during the therapeutic use or human overdoses requires focused attention by the medical community.