Tapentadol increases levels of noradrenaline in the rat spinal cord as measured by in vivo microdialysis

Zinc oxide-aluminum oxide nanocomposite solid phase microextraction for diazepam and oxazepam trace determination

A new efficient ZnO-Al2O3 nanocomposite (ZANC) was synthesized to form solid-phase microextraction (SPME) fiber. The prepared fiber was used for trace determination of benzodiazepines by gas chromatography-flame ionization detector in urine samples. The effective parameters on the extraction process including extraction time, salt percentage, desorption time and sample pH were optimized by a factorial design method. The method was evaluated at the optimum conditions and limits of detection (LODs) were calculated 20 µg/L for diazepam and oxazepam. The method repeatability for oxazepam and diazepam (50 µg/L, n = 4) was calculated at 8.8 % and 6.4 %. Also, the method reproducibility was obtained, 7.45 % and 6.61 % for oxazepam and diazepam (50 µg/L, n = 4). Also, fiber-to-fiber relative standard deviation (RSDs%) for the target analytes were less than 15.5 %. The method linearity is within the range of 62-500 µg/L for diazepam and oxazepam. The ZANC-SPME fiber showed a good lifetime (60 times) with high chemical stability. The high thermal stability of ZANC-SPME fiber was attained at 280 °C. The extraction results of poly dimethylsiloxan/divinyl benzene (PDMS/DVB) fiber were compared by ZANC-SPME fiber. Therefore, the method is proposed as a suitable technique for benzodiazepines detection in the urine sample.

Oral morphine induces spinal 5-hydroxytryptamine (5-HT) release using an opioid receptor-independent mechanism

Morphine induces spinal 5-hydroxytryptamine (5-HT) release, but the role and mechanism of the spinal 5-HT release induced by morphine are not well understood. The purpose of this study was to define the role and mechanism of spinal 5-HT release induced by oral morphine. We also examined whether persistent pain affected the spinal 5-HT release induced by oral morphine. Spinal 5-HT release was measured using microdialysis of lumbar cerebrospinal fluid (CSF). Two opioids, morphine and oxycodone, were orally administered and 5-HT release was measured in awake rats. Naloxone and β-funaltrexamine (β-FNA) were used to determine whether the effect of morphine on 5-HT release was mediated by opioid receptor activation. To study persistent pain, a formalin test was used. At 45 min after oral morphine administration, the formalin test was started and spinal 5-HT release was measured. Oral morphine, but not oral oxycodone, increased 5-HT release at the spinal cord to approximately 4000% of the baseline value. This effect of morphine was not antagonized by either naloxone or β-FNA at a dose that antagonized the antinociceptive effect of morphine. Formalin-induced persistent pain itself had no effect on spinal 5-HT release but enhanced the oral morphine-induced spinal 5-HT release. Oral morphine-induced spinal 5-HT release was not mediated by opioid receptor activation. Spinal 5-HT induced by oral morphine did not play a major role in the antinociceptive effect of morphine in the hot plate test. Persistent pain increased oral morphine-induced spinal 5-HT release.

Tapentadol prolonged release for managing moderate to severe chronic neck pain with or without a neuropathic component

Background: Despite the high prevalence of neck pain, few studies have addressed the pharmacological treatment of this condition.Purpose: We evaluated the effectiveness of tapentadol prolonged-release (PR) in patients with or without a neuropathic pain component, with a focus on functional movements, disability and Quality of Life (QoL).Study design/setting: Observational, retrospective study.Patient sample: Ninety-four adult patients with severe neck pain not responsive to opioid step III treatment.Outcome measures: The primary endpoint was a ≥ 30% improvement of pain intensity at 4 weeks (W4). Several secondary outcomes were evaluated, including neck disability index (NDI), range of motion (ROM), and QoL.Methods: Patients received tapentadol PR at the starting dose of 100 mg/day. Dose titration was allowed in 50 mg increments, up to 500 mg daily.Results: At W4, the primary endpoint of ≥30% improvement of pain was reported in 70% (n = 35; 95% confidence interval [CI]: 55-82%) of patients with a neuropathic pain component and in 69% (n = 20; 95% CI: 49-85%) of those without a neuropathic component. The percentage of patients reporting a neuropathic pain component significantly decreased from baseline (64.2%) to W4 (27.8%). NDI significantly improved in both groups at W12. ROM significantly improved in all three planes of motion (p < .01), with no difference between the two groups. Interference of pain with sleep and QoL also improved.Conclusions: The reduction in pain provided by tapentadol is associated with functional recovery, which may in turn be linked to an improvement in QoL.

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.

Tapentadol: an effective option for the treatment of back pain

Back pain, including low back pain and neck pain, is the leading cause of disability worldwide. This type of pain is challenging to treat, since it presents both a nociceptive and a neuropathic component. The latter also contributes to the evolution of pain toward chronification. Treatment selection should therefore consider the ability to prevent this event. Tapentadol is characterized by a unique and innovative peculiar mechanism of action that makes it the first representative of a new class of central strong analgesics referred to as MOR-NRI. This molecule acts both on the nociceptive and neuropathic components of pain, and it can therefore be effective in the treatment of a mixed pain condition such as back pain. This narrative review discusses the rationale for the use of tapentadol in both low back pain and neck pain and presents available clinical data. Overall, data show that tapentadol prolonged release is a well-grounded treatment for chronic back pain, sustained by a strong mechanistic rationale and robust evidence. Given also the availability of long-term efficacy and safety data, we believe that this molecule should be considered as an elective therapy for chronic back pain.

Pharmacological rationale for tapentadol therapy: a review of new evidence

Chronic pain could be considered as a neurological disorder. Therefore, appropriate selection of the therapy, which should consider the pathophysiological mechanisms of pain, can result in a successful analgesic outcome. Tapentadol is an analgesic drug which acts both as a μ-opioid receptor (MOR) agonist and as a noradrenaline reuptake inhibitor (NRI), thereby generating a synergistic action in terms of analgesic efficacy, but not for the burden of adverse effects. Therefore, tapentadol can be defined as the first “MOR-NRI” drug. This molecule holds the potential to address at least some of the current limitations of analgesic therapy due to its unique mechanism of action and has shown to be safe and effective in the treatment of chronic pain of cancer and noncancer etiologies including nociceptive, neuropathic and mixed pain. In particular, the MOR component of tapentadol activity predominantly allows for analgesia in nociceptive pain; on the other hand, the NRI component contributes, now in a predominant manner, for analgesic efficacy in cases of neuropathic pain states. This paper will discuss recent pieces of evidence on the pathophysiology of pain, the background on tapentadol and then present some new studies on how the unique mechanism of action of tapentadol provides a key role in its analgesic efficacy in a number of pain states and with a favorable safety profile.

Where should analgesia lead to? Quality of life and functional recovery with tapentadol

Chronic pain is a major health-care problem worldwide, affecting more than one out of five adults in Europe. Although multiple analgesic agents have been extensively investigated in terms of clinical response and tolerability profile, few studies have focused on the impact of these therapies on patients' quality of life (QoL). Of note, improvement in QoL, together with functional recovery, has been recognized since the late 1990s as two main goals of analgesic therapy. Tapentadol is a novel analgesic molecule that synergistically combines two mechanisms of action, µ-opioid receptor agonism and norepinephrine reuptake inhibition, and for which multiple literature data are available that confirm its efficacy and safety in controlling pain. This narrative review summarizes the information available on the impact of tapentadol on QoL, with the aim to provide clinicians with a comprehensive overview of the analgesic effects of tapentadol prolonged release beyond the reduction of pain.

Tapentadol in the treatment of osteoarthritis: pharmacological rationale and clinical evidence

Osteoarthritis (OA) is the most prevalent joint disease in older people worldwide. Pain owing to OA is considered one of the most frequent causes of chronic pain; however, current pharmacological approaches have some limitations in terms of efficacy and safety. Of note, descending inhibitory pain pathways are often disrupted in chronic OA pain, and pharmacotherapies targeting those pathways – eg, those that block norepinephrine reuptake may be more appropriate for managing chronic pain than pure μ-opioid receptor (MOR) agonists. Tapentadol is an analgesic molecule, which combines two synergistic mechanisms of action, MOR, and norepinephrine reuptake inhibition. This narrative review will briefly discuss the mechanisms contributing to the onset and maintenance of pain in OA patients; clinical data on the use of tapentadol in this setting will then be presented and commented.

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.

Tapentadol Extended Release in the Treatment of Severe Chronic Low Back Pain and Osteoarthritis Pain

Tapentadol is a novel pain reliever with apparently synergistic dual mechanisms of action, capable of addressing both nociceptive and neuropathic components of chronic pain. As an effective analgesic with good tolerability, tapentadol may be appropriate for patients suffering from severe chronic pain associated with low back pain (LBP) or osteoarthritis (OA). Efficacy studies of tapentadol in populations of patients with severe chronic LBP or OA pain suggest that tapentadol is non-inferior to oxycodone. Its tolerability, especially with respect to gastrointestinal (GI) side effects, may be better than that of other strong opioids in clinical trials and analyses of multiple trials. Patient satisfaction with tapentadol extended release for chronic noncancer pain syndromes is good. Although tapentadol has an opioid component with abuse liability, it appears to be a difficult opioid for tampering with less appeal to abusers than other opioids. For patients with severe LBP and OA pain, tapentadol appears to hold promise as a safe, effective therapeutic option.

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.

Tapentadol in neuropathic pain cancer patients: a prospective open label study

Many chemotherapy treatments induce peripheral neuropathy (CIPN). These patients often experience neuropathic pain (NP) that reduces the quality of life. The aim of this prospective, open label study was to evaluate the efficacy and tolerability of tapentadol (TP) in patients affected by CIPN. CIPN were consecutively enrolled in a prospective open label study at the Neuro-Oncology Unit of the Regina Elena National Cancer Institute in Rome. During the titration phase, each patient initially received doses of TP 50 mg twice a day. All patients underwent pain intensity (NRS) and DN4. For evaluation of quality of life, patients underwent EORTC QLQ-C30 and EORTC QLQ-CIPN2 QLQ-CIPN20. We enrolled 31 patients, 19 were females with a median age of 60 years. After 3 months of treatment with TP, 22 patients completed the statistical package for social sciences (SPSS). Nineteen patients out of 22 showed a response to treatment (86%). We also observed that TP reduced the NRS and DN4 values from baseline to the last visit in a significant way (p < 0.001, respectively). Seven patients (22.5%) discontinued the TP therapy after the first week of occurrence of side effects. Furthermore, we observed that TP improved also the global health status measured by EORT QLQ-C30. TP is well tolerated and efficacy in the treatment of NP. The important reduction of neuropathic pain, the improvement in NRS and QoL scores after therapy with TP makes it a candidate in the management of patients suffering from neuropathic pain of CIPN also as a first line of therapy.

Mechanistic evaluation of tapentadol in reducing the pain perception using in-vivo brain and spinal cord microdialysis in rats

Role of monoamine neurotransmitters in the modulation of emotional and pain processing in spinal cord and brain regions is not well known. Tapentadol, a norepinephrine reuptake inhibitor with µ-opioid receptor agonistic activity has recently been introduced for the treatment of moderate to severe pain. The objective of the present study was to examine the effects of tapentadol on modulation of monoamines in the prefrontal cortex and dorsal horn using brain microdialysis. Tapentadol was administered intraperitoneally at 4.64-21.5mg/kg to male Wistar rats. Based on these results, 10mg/kg i.p. was chosen for spinal microdialysis in freely moving rats. Tapentadol produced significant and dose-dependent increase in cortical dopamine and norepinephrine levels with mean maximum increase of 600% and 300%, respectively. Treatment had no effect on cortical serotonin levels. In the dorsal horn, serotonin, dopamine and norepinephrine levels were significantly increased with mean maximum increases of 220%, 190% and 280%, respectively. Although the density of dopamine transporter is low in cortex, the increase of dopamine and norepinephrine levels in cortex could be mediated through the inhibition of norepinephrine transporter. In the dorsal horn, increase in norepinephrine levels could be due to inhibition of norepinephrine transporter in the spinal cord. Whereas, activation of opioids receptors in non-spinal regions might be responsible for increase in dopamine and serotonin levels. The results from current investigation suggest that clinical efficacy of tapentadol in neuropathic pain is mediated through the enhanced monoaminergic neurotransmission in the spinal cord and regions involved with emotional processing in brain.

Tapentadol: Can It Kill Two Birds with One Stone without Breaking Windows?

Tapentadol is a novel oral analgesic with a dual mode of action as an agonist of the µ-opioid receptor (MOR), and as a norepinephrine reuptake inhibitor (NRI) all in a single molecule. Immediate release (IR) tapentadol shows its analgesic effect quickly, at around 30 minutes. Its MOR agonistic action produces acute nociceptive pain relief; its role as an NRI brings about chronic neuropathic pain relief. Absorption is rapid, with a mean maximal serum concentration at 1.25-1.5 h after oral intake. It is present primarily in the form of conjugated metabolites after glucuronidation, and excretes rapidly and completely via the kidneys. The most common adverse reactions are nausea, dizziness, vomiting, and somnolence. Constipation is more common in use of the ER formulation. Precautions against concomitant use of central nervous system depressants, including sedatives, hypnotics, tranquilizers, general anesthetics, phenothiazines, other opioids, and alcohol, or use of tapentadol within 14 days of the cessation of monoamine oxidase inhibitors, are advised. The safety and efficacy have not been established for use during pregnancy, labor, and delivery, or for nursing mothers, pediatric patients less than 18 years of age, and cases of severe renal impairment and severe hepatic impairment. The major concerns for tapentadol are abuse, addiction, seeking behavior, withdrawal, and physical dependence. The presumed problem for use of tapentadol is to control the ratio of MOR agonist and NRI. In conclusion, tapentadol produces both nociceptive and neuropathic pain relief, but with worries about abuse and dependence.

Peripheral Nerve Injury Reduces Analgesic Effectsof Systemic Morphine via Spinal 5-Hydroxytryptamine 3 Receptors

Background:

Morphine produces powerful analgesic effects against acute pain, but it is not effective against neuropathic pain, and the mechanisms underlying this reduced efficacy remain unclear. Here, the authors compared the efficacy of systemic morphine between normal rats and rats with peripheral nerve injury, with a specific focus on descending serotonergic mechanisms.

Methods:

After L5 spinal nerve ligation injury, male Sprague–Dawley rats were subjected to behavioral testing, in vivo microdialysis of the spinal dorsal horn to determine serotonin (5-hydroxytryptamine [5-HT]) and noradrenaline release, and immunohistochemistry (n = 6 in each group).

Results:

Intraperitoneal administration of morphine (1, 3, or 10 mg/kg) produced analgesic effects in normal and spinal nerve ligation rats, but the effects were greater in normal rats (P &lt; 0.001). Morphine increased 5-HT release (450 to 500% of the baseline), but not noradrenaline release, in the spinal dorsal horn via activation of serotonergic neurons in the rostral ventromedial medulla. Intrathecal pretreatment with ondansetron (3 μg), a 5-HT3 receptor antagonist, or 5,7-dihydroxytryptamine creatinine sulfate (100 μg), a selective neurotoxin for serotonergic terminals, attenuated the analgesic effect of morphine (10 mg/kg) in normal rats but increased the analgesic effect of morphine in spinal nerve ligation rats (both P &lt; 0.05).

Conclusions:

Systemic administration of morphine increases 5-HT levels in the spinal cord, and the increase in 5-HT contributes to morphine-induced analgesia in the normal state but attenuates that in neuropathic pain through spinal 5-HT3 receptors. The plasticity of the descending serotonergic system may contribute to the reduced efficacy of systemic morphine in neuropathic pain.

μ-Opioid receptor activation and noradrenaline transport inhibition by tapentadol in rat single locus coeruleus neurons

BACKGROUND AND PURPOSE

Tapentadol is a novel analgesic that combines moderate μ-opioid receptor agonism and noradrenaline reuptake inhibition in a single molecule. Both mechanisms of action are involved in producing analgesia; however, the potency and efficacy of tapentadol in individual neurons has not been characterized.

EXPERIMENTAL APPROACH

Whole-cell patch-clamp recordings of G-protein-coupled inwardly rectifying K(+) (KIR 3.x) currents were made from rat locus coeruleus neurons in brain slices to investigate the potency and relative efficacy of tapentadol and compare its intrinsic activity with other clinically used opioids.

KEY RESULTS

Tapentadol showed agonist activity at μ receptors and was approximately six times less potent than morphine with respect to KIR 3.x current modulation. The intrinsic activity of tapentadol was lower than [Met]enkephalin, morphine and oxycodone, but higher than buprenorphine and pentazocine. Tapentadol inhibited the noradrenaline transporter (NAT) with potency similar to that at μ receptors. The interaction between these two mechanisms of action was additive in individual LC neurons.

CONCLUSIONS AND IMPLICATIONS

Tapentadol displays similar potency for both µ receptor activation and NAT inhibition in functioning neurons. The intrinsic activity of tapentadol at the μ receptor lies between that of buprenorphine and oxycodone, potentially explaining the favourable profile of side effects, related to μ receptors.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

Tapentadol potentiates descending pain inhibition in chronic pain patients with diabetic polyneuropathy

BACKGROUND

Tapentadol is an analgesic agent for treatment of acute and chronic pain that activates the µ-opioid receptor combined with inhibition of neuronal norepinephrine reuptake. Both mechanisms are implicated in activation of descending inhibitory pain pathways. In this study, we investigated the influence of tapentadol on conditioned pain modulation (CPM, an experimental measure of endogenous pain inhibition that gates incoming pain signals as a consequence of a preceding tonic painful stimulus) and offset analgesia (OA, a test in which a disproportionally large amount of analgesia becomes apparent upon a slight decrease in noxious heat stimulation).

METHODS

Twenty-four patients with diabetic polyneuropathy (DPN) were randomized to receive daily treatment with tapentadol sustained-release (SR) [average daily dose 433 (31) mg] or placebo for 4 weeks. CPM and OA were measured before and on the last day of treatment.

RESULTS

Before treatment, none of the patients had significant CPM or OA responses. At week 4 of treatment, CPM was significantly activated by tapentadol SR and coincided with significant analgesic responses. CPM increased from 9.1 (5.4)% (baseline) to 14.3 (7.2)% (placebo) and 24.2 (7.7)% (tapentadol SR, P<0.001 vs placebo); relief of DPN pain was also greater in patients treated with tapentadol than placebo (P=0.028). Neither placebo nor tapentadol SR treatment had an effect on the magnitude of the OA responses (P=0.78).

CONCLUSIONS

Tapentadol's analgesic effect in chronic pain patients with DPN is dependent on activation of descending inhibitory pain pathways as observed by CPM responses.

CLINICAL TRIAL REGISTRATION

The study was registered at trialregister.nl under number NTR2716.

The mu-opioid receptor agonist/noradrenaline reuptake inhibition (MOR-NRI) concept in analgesia: the case of tapentadol

Tapentadol is a novel, centrally-acting analgesic drug, with an analgesic efficacy comparable to that of strong opioids such as oxycodone and morphine. Its high efficacy has been demonstrated in a range of animal models of acute and chronic, nociceptive, inflammatory, and neuropathic pain as well as in clinical studies with moderate to severe pain arising from a number of different etiologies. At the same time, a favorable gastrointestinal tolerability has been demonstrated in rodents and humans, and advantages over morphine regarding tolerance development and physical dependence were shown in animal studies. Furthermore, a low level of abuse and diversion is beginning to emerge from first post-marketing data. Tapentadol acts as a μ-opioid receptor (MOR) agonist and noradrenaline reuptake inhibitor (NRI). Both mechanisms of action have been shown to contribute to the analgesic activity of tapentadol and to produce analgesia in a synergistic manner, such that relatively moderate activity at the two target sites (MOR and noradrenaline reuptake transporter) is sufficient to produce strong analgesic effects. It has been suggested that tapentadol is the first representative of a proposed new class of analgesics, MOR-NRI. This review presents the evidence that has led to this suggestion, and outlines how the pharmacology of tapentadol can explain its broad analgesic activity profile and high analgesic potency as well as its favorable tolerability.

Endogenous opiates and behavior: 2012

This paper is the thirty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2012 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Opioid and noradrenergic contributions of tapentadol in experimental neuropathic pain

Tapentadol is a dual action molecule with mu opioid agonist and norepinephrine (NE) reuptake blocking activity that has recently been introduced for the treatment of moderate to severe pain. The effects of intraperitoneal (i.p.) morphine (10mg/kg), tapentadol (10 or 30 mg/kg) or duloxetine (30 mg/kg), a norepinephrine/serotonin (NE/5HT) reuptake inhibitor, were evaluated in male, Sprague-Dawley rats with spinal nerve ligation (SNL) or sham surgery. Additionally, the effects of these drugs on spinal cerebrospinal fluid (CSF) NE levels were quantified. Response thresholds to von Frey filament stimulation decreased significantly from baseline in SNL, but not sham, operated rats. Duloxetine, tapentadol and morphine produced significant and time-related reversal of tactile hypersensitivity. Duloxetine significantly increased spinal CSF NE levels in both sham and SNL rats and no significant differences were observed in these groups. Tapentadol (10 mg/kg) produced a significant increase in spinal NE levels in SNL, but not in sham, rats. At the higher dose (30 mg/kg), tapentadol produced a significant increase in spinal CSF NE levels in both SNL and sham groups; however, spinal NE levels were elevated for an extended period in the SNL rats. This could be detected 30 min following tapentadol (30 mg/kg) in both sham and SNL groups. Surprisingly, while the dose of morphine studied reversed tactile hypersensitivity in nerve-injured rats, CSF NE levels were significantly reduced in both sham- and SNL rats. The data suggest that tapentadol elicits enhanced elevation in spinal NE levels in a model of experimental neuropathic pain offering a mechanistic correlate to observed clinical efficacy in this pain state.

Miotic and subject-rated effects of therapeutic doses of tapentadol, tramadol, and hydromorphone in occasional opioid users

RATIONALE

Tapentadol is a novel analgesic that activates mu-opioid receptors and blocks norepinephrine reuptake. There is very little information available regarding the non-analgesic pharmacodynamic effects of tapentadol.

OBJECTIVES

This outpatient study evaluated the physiological, subject-rated, and performance effects of therapeutic doses of tapentadol compared to two control drugs in humans.

METHODS

This double-blind, within-subject study examined the effects of oral placebo, tapentadol (25, 50, and 75 mg), tramadol (50, 100, and 150 mg), and hydromorphone (2, 4, and 6 mg). Nine occasional opioid users completed the study. Pharmacodynamic drug effects were measured before and for 6 h after drug administration.

RESULTS

All three doses of the tested drugs produced comparable, time-dependent decreases in pupil diameter, but the effects were generally not dose dependent. The high dose of tapentadol, as well as all three doses of tramadol and hydromorphone, increased positive subject-rated effects (e.g., "Good Effects" and "Like the Drug") as a function of time. Only tramadol increased negative subject-rated effects (e.g., "Bad Effects" and "Nauseous"); however, these were of low magnitude.

CONCLUSIONS

The highest tested dose of tapentadol produced a profile of positive effects comparable to that of hydromorphone, whereas tramadol produced positive and negative subject-rated effects. The mixed findings for tramadol are consistent with previous findings indicating that it has a distinct profile of effects relative to prototypic opioids. Future research should examine the effects of higher tapentadol doses, as well as the factors contributing to the different subject-rated profile of effects observed for tramadol relative to tapentadol and hydromorphone.

Effects of tapentadol on mechanical hypersensitivity in rats with ligatures of the infraorbital nerve versus the sciatic nerve

BACKGROUND

Convergent data showed that neuropathic pain has specific characteristics at cephalic versus extra-cephalic level, where single-targeted drugs differentially alleviate pain. Because the novel analgesic drug, tapentadol, is acting at two targets, μ-opioid receptors (as agonist) and noradrenaline reuptake (as inhibitor), we tested its effects on neuropathic pain at both cephalic and extra-cephalic levels.

METHODS

Sprague-Dawley rats underwent unilateral constriction injury (CCI) to the infraorbital nerve (ION; cephalic territory) or the sciatic nerve (SN; extra-cephalic territory), and alleviation of nerve lesion-induced mechanical allodynia/hyperalgesia was assessed after acute or repeated (for 4 days) treatment with tapentadol compared with morphine and/or reboxetine (noradrenaline reuptake inhibitor) 2 weeks after surgery. Possible changes in the expression of the neuroinflammatory markers activating transcription factor 3 (ATF3), interleukin-6 (IL-6) and brain-derived neurotrophic factor (BDNF) by repeated tapentadol treatment were quantified by real-time reverse transcription polymerase chain reaction in ganglia and central tissues.

RESULTS

Acute administration of tapentadol (1-10 mg/kg, i.p.) significantly reduced allodynia in both CCI-SN and CCI-ION rats. Although morphine (3 mg/kg, s.c.) or reboxetine (10 mg/kg, i.p.) alone was only marginally active, the combination of both drugs produced supra-additive effects like those observed with tapentadol. In contrast to repeated morphine whose effects vanished, the anti-allodynic effects of tapentadol remained unchanged after a 4-day treatment. However, the latter treatment with tapentadol did not affect nerve lesion-evoked overexpression of ATF3, IL-6 and BDNF transcripts.

CONCLUSIONS

The dual synergistic pharmacological properties of tapentadol, which result in clear-cut anti-neuropathic pain effects at both cephalic and extra-cephalic levels, probably involve mechanisms downstream of nerve injury-induced neuroinflammatory reaction.

Endogenous opiates and behavior: 2011

This paper is the thirty-fourth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2011 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).

Tapentadol extended-release: a recent addition to our analgesic armamentarium

SUMMARY In the never-ending process of providing therapy with diminishing side effects, pain medicine stands out as an important area of work. Ever since the introduction of opioids and elucidation of their mechanisms pharmaceutical researchers have sought a compound that provides long-term analgesia with none of the side effects that include somnolence, lethargy, tolerance, addiction, gastrointestinal symptoms and so on. This article reviews one of the latest improvements in analgesia, the formulation of tapentadol as an extended-release medication. Despite not claiming to have eliminated all the negatives of narcotics tapentadol extended-release seems to have made inroads to that goal.