Mu opioid receptor-dependent and independent components in effects of tramadol

Use of tramadol as analgesic alternative in Harris hawk (Parabuteo unicinctus)

BACKGROUND

The Harris hawk is a bird of prey susceptible to traumatic injuries because it is useful for several purposes such as conservancy, biological control and falconry. Once received in rehabilitation centres or specialized clinics, it is necessary to provide proper analgesia.

OBJECTIVES

The aim of this study is to demonstrate the analgesic efficacy of tramadol in Harris hawks (PISADOL 50 PiSA Agropecuaria, S.A. de C.V. Calle 1 Norte, Manzana 2-25 Parque Industrial Tula Atitalaquia, Hgo, México), by the assessment of nociceptive threshold.

METHODS

A total of 24 adult Harris hawks were selected from a rehabilitation centre. The birds were randomly divided into four groups: control (saline solution), 5.0, 15.0 and 30.0 mg/kg of intramuscular tramadol. Nociception was produced with electrical stimuli of 9 V, applied in propatagial skin at 1, 5, 10, 20, 30, 45, 60, 90, 120, 180, 240, 300 and 360 min, assessing the nociceptive threshold and sedative effects produced by each treatment.

RESULTS

No difference was observed between control and tramadol group 5 mg/kg. At 15 mg/kg, the pain threshold increased from 20 to 240 min, with minimal sedative effects. At 30 mg/kg, there was a marked increase in pain threshold from 10 to 300 min, and sedative effects like wing and head drooping for a period of 90 min.

CONCLUSIONS

Tramadol can be an analgesic alternative for Harris's hawks, as it decreases the response to painful stimuli in this species when administered by intramuscular route.

Neuropathic pain: From actual pharmacological treatments to new therapeutic horizons

Neuropathic pain, caused by a lesion or disease affecting the somatosensory system, affects between 3 and 17% of the general population. The treatment of neuropathic pain is challenging due to its heterogeneous etiologies, lack of objective diagnostic tools and resistance to classical analgesic drugs. First-line treatments recommended by the Special Interest Group on Neuropathic Pain (NeuPSIG) and European Federation of Neurological Societies (EFNS) include gabapentinoids, tricyclic antidepressants (TCAs) and selective serotonin noradrenaline reuptake inhibitors (SNRIs). Nevertheless these treatments have modest efficacy or dose limiting side effects. There is therefore a growing number of preclinical and clinical studies aim at developing new treatment strategies to treat neuropathic pain with better efficacy, selectivity, and less side effects. In this review, after a brief description of the mechanisms of action, efficacy, and limitations of current therapeutic drugs, we reviewed new preclinical and clinical targets currently under investigation, as well as promising non-pharmacological alternatives and their potential co-use with pharmacological treatments.

Tramadol and Tapentadol Induce Conditioned Place Preference with a Differential Impact on Rewarding Memory and Incubation of Craving

Tramadol and tapentadol, synthetic opioids commonly prescribed for moderate-to-severe pain, have a unique pharmacology that optimizes their analgesia and safety. However, they are not devoid of risks, presenting addictive, abuse, and dependence potential. While tramadol-reinforcing properties have been documented by various studies with human and animal models, including conditioned place preference (CPP) assays, no similar studies have been performed with tapentadol. In the present study, we performed CPP assays by intraperitoneally administering Wistar rats with a tramadol/tapentadol therapeutic dose. Animal permanence and the number of entries in the CPP compartments were recorded in the preconditioning phase and then 1 (T1), 7 (T7), and 14 (T14) days after conditioning. Both opioids induced a change in place preference (T1), suggesting that they have short-term reinforcing properties. However, only tramadol was associated with place preference retention (T7 and T14), with an increase in the number of entries in the opioid-paired compartment (T1 and T7), showing that it causes rewarding memory and incubation of craving. The results indicate that at therapeutic doses: (1) both drugs cause short-term rewarding effects and (2) as opposed to tramadol, tapentadol does not cause CPP retention, despite its higher central nervous system activity and stricter scheduling.

Effects of imidazoline agents in a rat conditioned place preference model of addiction

Agmatine (AG), idazoxan (IDZ), and efaroxan (EFR) are imidazoline receptor ligands with beneficial effects in central nervous system disorders. The present study aimed to evaluate the interaction between AG, IDZ, and EFR with an opiate, tramadol (TR), in a conditioned place preference (CPP) paradigm. In the experiment, we used five groups with 8 adult male Wistar rats each. During the condition session, on days 2, 4, 6, and 8, the rats received the drugs (saline, or TR, or IDZ and TR, or EFR and TR, or AG and TR) and were placed in their least preferred compartment. On days 1, 3, 5, and 7, the rats received saline in the preferred compartment. In the preconditioning, the preferred compartment was determined. In the postconditioning, the preference for one of the compartments was reevaluated. TR increased the time spent in the non-preferred compartment. AG decreased time spent in the TR-paired compartment. EFR, more than IDZ, reduced the time spent in the TR-paired compartment, but without statistical significance. AG reversed the TR-induced CPP, while EFR and IDZ only decreased the time spent in the TR-paired compartment, without statistical significance.

Biased, Bitopic, Opioid–Adrenergic Tethered Compounds May Improve Specificity, Lower Dosage and Enhance Agonist or Antagonist Function with Reduced Risk of Tolerance and Addiction

This paper proposes the design of combination opioid–adrenergic tethered compounds to enhance efficacy and specificity, lower dosage, increase duration of activity, decrease side effects, and reduce risk of developing tolerance and/or addiction. Combinations of adrenergic and opioid drugs are sometimes used to improve analgesia, decrease opioid doses required to achieve analgesia, and to prolong the duration of analgesia. Recent mechanistic research suggests that these enhanced functions result from an allosteric adrenergic binding site on opioid receptors and, conversely, an allosteric opioid binding site on adrenergic receptors. Dual occupancy of the receptors maintains the receptors in their high affinity, most active states; drops the concentration of ligand required for full activity; and prevents downregulation and internalization of the receptors, thus inhibiting tolerance to the drugs. Activation of both opioid and adrenergic receptors also enhances heterodimerization of the receptors, additionally improving each drug’s efficacy. Tethering adrenergic drugs to opioids could produce new drug candidates with highly desirable features. Constraints—such as the locations of the opioid binding sites on adrenergic receptors and adrenergic binding sites on opioid receptors, length of tethers that must govern the design of such novel compounds, and types of tethers—are described and examples of possible structures provided.

Analgesic and cardiopulmonary effects of premedication with tramadol in calves anesthetized with the infusion of guaifenesin and thiamylal

This study examined the analgesic and cardiopulmonary effects of intravenous (IV) tramadol during general intravenous anesthesia in calves. Calves were premedicated with diazepam (0.2 mg/kg, IV) with tramadol (2 mg/kg, IV) (group T) or saline (group S). Anesthesia was induced by thiamylal sodium (4 mg/kg, IV) and maintained with an infusion (2 ml/kg/hr) of 5% guaifenesin containing thiamylal sodium (2 mg/ml). Additional thiamylal sodium (1~2 mg/kg, IV) was administered when interference from the calves was observed during surgery. The total counts of additional thiamylal sodium administration, analgesia score using a visual analog scale, recovery time, and cardiopulmonary function in the different groups were assessed and compared. Group T showed significantly fewer counts of additional drug administration and a significantly higher analgesia score. Tramadol may provide adequate analgesia with minimal cardiopulmonary changes in calves during general anesthesia.

Combined toxic effects of aflatoxin B2 and the protective role of resveratrol in Swiss albino mice

In this study, the toxic effects of aflatoxin B₂ (AFB₂) on Swiss albino mice and the protective effects of resveratrol were investigated. Physiological (body weight, liver and kidney weight), biochemical (aspartate aminotransferase-AST, alanine transaminase-ALT, blood urea nitrogen-BUN, creatinine, malondialdehyde-MDA and glutathione-GSH) and cytogenetic parameters (micronucleus-MN in buccal epithelium, erythrocyte and leukocyte cells and chromosomal aberrations-CAs) were used to determine the toxic effects. Additionally, scavenging effects of resveratrol against superoxide, hydrogen peroxide (H₂O₂) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals were also investigated. In experimental period, mice were divided into six groups and the groups were treated with tap water, 10 mg/kg b.w resveratrol, 20 mg/kg b.w resveratrol, 20 µg/kg b.w. AFB₂, 10 mg/kg b.w resveratrol + 20 µg/kg b.w AFB₂, 20 mg/kg b.w resveratrol + 20 µg/kg b.w AFB₂, respectively. As a result, the scavenging effects of resveratrol increased with increasing dose and the superoxide, H₂O₂ and DPPH radical scavenging activity of resveratrol were 74.9%, 79.1% and 49.2%, respectively. AFB₂ administration caused a significant decrease in physiological parameters, and these decreases regressed in AFB₂ + resveratrol treated groups. Serum ALT and AST activities, BUN and creatinine levels were higher in the AFB₂ treated group compared to the control group and serious abnormalities were found in MDA and GSH levels in the kidney and liver. In the group treated with AFB₂ + 20 mg/kg resveratrol, ALT, AST, BUN and creatinine levels decreased significantly and GSH levels increased compared to only-AFB₂ treated group. AFB₂ triggered MN formation in buccal epithelium, erythrocyte and leukocyte cells and CAs in bone marrow cells. The application of 20 mg/kg resveratrol together with AFB₂ was decreased the MN and CAs frequency. Resveratrol exhibited a recovery effect in the range of 40.9-80.5% against AFB₂ toxicity in all tested parameters. In this study, it was determined that AFB₂ caused serious changes in selected physiological, biochemical and cytogenetic parameters while resveratrol displayed a protective role against these toxic effects.

In Vitro and In Vivo Pharmaco-Toxicological Characterization of 1-Cyclohexyl-x-methoxybenzene Derivatives in Mice: Comparison with Tramadol and PCP

1-cyclohexyl-x-methoxybenzene is a novel psychoactive substance (NPS), first discovered in Europe in 2012 as unknown racemic mixture of its three stereoisomers: ortho, meta and para. Each of these has structural similarities with the analgesic tramadol and the dissociative anesthetic phencyclidine. In light of these structural analogies, and based on the fact that both tramadol and phencyclidine are substances that cause toxic effects in humans, the aim of this study was to investigate the in vitro and in vivo pharmacodynamic profile of these molecules, and to compare them with those caused by tramadol and phencyclidine. In vitro studies demonstrated that tramadol, ortho, meta and para were inactive at mu, kappa and delta opioid receptors. Systemic administration of the three stereoisomers impairs sensorimotor responses, modulates spontaneous motor activity, induces modest analgesia, and alters thermoregulation and cardiorespiratory responses in the mouse in some cases, with a similar profile to that of tramadol and phencyclidine. Naloxone partially prevents only the visual sensorimotor impairments caused by three stereoisomers, without preventing other effects. The present data show that 1-cyclohexyl-x-methoxybenzene derivatives cause pharmaco-toxicological effects by activating both opioid and non-opioid mechanisms and suggest that their use could potentially lead to abuse and bodily harm.

Utilizing multimodal analgesia to evaluate postoperative analgesic requirements in kidney transplant recipients

The use of non-opioid analgesics following surgery has proven beneficial in managing pain and decreasing adverse outcomes following surgery. Data assessing outcomes related to opioid use is limited in kidney transplant recipients (KTRs). We evaluated the effectiveness of implementing a reduced to no opioid use protocol in KTRs. This retrospective cohort study included adult KTRs between January 2017 and July 2019 with a multimodal analgesic protocol (MAP), focused on limiting opioids, implemented in August 2018. We compared analgesic requirements in morphine milligram equivalents (MME) during transplant admissions between the MAP cohort and traditional cohort. There were 217 KTRs who met the criteria. Inpatient opioid use was significantly reduced in the MAP cohort (16.5 ± 19.2 MME/day vs 24.7 ± 19.7 MME/day; P <.05) with no significant difference in pain scores. No use of opioids within six months of discharge was significantly increased in the MAP cohort (50% vs 7%; P <.001), and there were no reported deaths at six months in either cohort. The use of multimodal analgesia is beneficial in KTRs to provide adequate pain control with limited to no exposure of opioids during admission or at discharge.

Comparison of intraoperative cardiorespiratory and behavioral responses to medetomidine combined with tramadol or butorphanol during standing laparoscopic ovariectomy in horses

The purpose of this study was to assess the cardiorespiratory and behavioral responses to the combination of medetomidine and tramadol (M-T) or butorphanol (M-B) in standing laparoscopic ovariectomy in horses. One ovary was removed under M-T and the contralateral ovary was removed under M-B with at least 4 weeks between operations at random. Horses were sedated using intravenous medetomidine (5 µg/kg) followed by tramadol (1 mg/kg) or butorphanol (10 µg/kg) after 5 min. Sedation was maintained through the repeated injection of medetomidine (1 µg/kg) and tramadol (0.4 mg/kg) or medetomidine (1 µg/kg) and butorphanol (4 µg/kg) every 15 min. Cardiorespiratory function and behavioral responses, including, sedation, ataxia, and analgesia, were assessed during the surgery. There were no significant differences in cardiorespiratory values and sedation and analgesia scores between M-T and M-B. Ataxia scores were significantly lower in M-T than in M-B. This result suggests that M-T could maintain smooth and stable standing surgery with minimal cardiorespiratory changes in horses.

Ketamine Versus Tramadol As an Adjunct To PCA Morphine for Postoperative Analgesia After Major Upper Abdominal Surgery: a Prospective, Comparative, Randomized Trial

Background and aims

Patient-controlled analgesia (PCA) with morphine is commonly used to provide analgesia following major surgery, but is not sufficient as a monotherapy strategy. This study aimed to compare the adjunctive analgesic effect of ketamine versus tramadol on postoperative analgesia provided via PCA-morphine in patients undergoing major upper abdominal surgeries.

Methods

Forty-two patients undergoing elective major upper abdominal surgery under general anesthesia were allocated to receive either ketamine (load dose of 0.5 mg kg⁻¹ followed by a continuous infusion of 0.12 mg kg⁻¹ h⁻¹ up to 48 postoperative hours; ketamine group, n = 21) or tramadol (load dose of 1 mg kg⁻¹ followed by a continuous infusion of 0.2 mg kg⁻¹ h⁻¹ up to 48 postoperative hours; tramadol group, n = 21) in addition to their standard postoperative analgesia with PCA-morphine. Postoperative data included morphine consumption, visual analog scale (VAS) scores, and side effects during the first 48 postoperative hours after PCA-morphine initiation.

Results

There were no significant differences in patient demographic and intraoperative data between the two groups. Tramadol group had significantly less total morphine consumption during the first 48 postoperative hours (28.905 [16.504] vs 54.524 [20.846] mg [p < 0.001]) and presented significantly lower VAS scores at rest and mobilization (p < 0.05) than the ketamine group. No statistical difference was recorded between the two groups (p > 0.05) regarding postoperative cough, sedation, hallucinations, pruritus, urine retention, and postoperative nausea and vomiting. However, patients in the ketamine group reported dry mouth more frequently than patients in the tramadol group (p = 0.032).

Conclusions

Postoperative administration of tramadol was superior to ketamine due to significantly reduced opioid consumption and better pain scores in patients receiving PCA-morphine after major upper abdominal surgery.

Toxicology of tramadol following chronic exposure based on metabolomics of the cerebrum in mice

Tramadol is an opioid used as an analgesic for treating moderate or severe pain. The long-term use of tramadol can induce several adverse effects. The toxicological mechanism of tramadol abuse is unclear. Metabolomics is a very useful method for investigating the toxicology of drug abuse. We investigated the impact of chronic tramadol administration on the cerebrum of mice, focusing on the metabolites after tramadol administration. The mice received 20 or 50 mg/kg body weight tramadol dissolved in physiological saline daily for 5 weeks via oral gavage. Compared with the control group, the low dose tramadol group showed seven potential biomarkers, including gamma-hydroxybutyric acid, succinate semialdehyde, and methylmalonic acid, which were either up- or down-regulated. Compared with the control group, the high dose tramadol group showed ten potential biomarkers, including gamma-hydroxybutyric acid, glutamine, and O-phosphorylethanolamine, which were either up- or down-regulated. The up-regulated gamma-hydroxybutyric acid and the down-regulated succinate semialdehyde revealed that the neurotransmitter system was disrupted after tramadol abuse. Compared with the low dose tramadol group, there were twenty-nine potential biomarkers in the high dose tramadol group, mainly related to the pentose phosphate pathway and glycerophospholipid metabolism. In conclusion, metabolomics in the tramadol abuse group demonstrated that long-term tramadol abuse can result in oxidative damage, inflammation, and disruption of the GABA neurotransmitter system, which will help to elucidate the toxicology of tramadol abuse.

ADME and toxicity considerations for tramadol: from basic research to clinical implications

INTRODUCTION

Tramadol is widely being used in chronic pain management for improving patients' life quality and reducing trauma. Although it is listed in several medicinal guidelines, its use is controversial because of the conflicting results obtained in pharmacokinetic/pharmacodynamic studies. This multi-receptor drug acts as µ₁ opioid receptor agonist, monoamine reuptake inhibitor, and inhibitor of ligand-gated ion channels and some special protein-coupled receptors.

AREAS COVERED

This review provides a comprehensive view on the pharmacokinetic, pharmacodynamic, and toxicity of tramadol with a deep look on its side effects, biochemical and pathological changes, and possible drug interactions. In addition, the main ways of tramadol poisoning management describe according to in vivo and clinical trial studies.

EXPERT OPINION

Given the broad spectrum of targets, increasing the cases of overdoses and toxicity, and probable drugs interaction, it is necessary to take another look at the pharmacology of tramadol. Regarding the adverse effects of tramadol on different tissues, especially the nervous system and liver tissue, more attentions to tramadol metabolites, their interaction with other drugs, and active agents seem critical. Seizure as the most cited effect of tramadol and its destructive effects on tissues would alleviate by co-administration with drugs with antioxidant properties.

Acute Tramadol-Induced Cellular Tolerance and Dependence of Ventral Tegmental Area Dopaminergic Neurons: An In Vivo Electrophysiological Study

Introduction

Ventral Tegmental Area (VTA) is a core region of the brainstem that contributes to different vital bio-responses such as pain and addiction. The Dopaminergic (DA) cellular content of VTA has major roles in different functions. This study aims to evaluate the cellular effect of tramadol on the putative VTA-DA neurons.

Methods

Wistar rats were assigned into three groups of control, sham, and tramadol-treated. The animals were anesthetized and their VTA-DA neuronal activity was obtained under controlled stereotaxic operation. The firing rate of the neurons was extracted according to principal component analysis by Igor Pro software and analyzed statistically considering P<0.05 as significant. Tramadol (20 mg/kg) was infused intraperitoneally.

Results

Overall, 121 putative VTA-DA neurons were isolated from all groups. In tramadol-treated rats, the inhibition of the neuronal firing was proposed as tolerance and the excitation period as dependence or withdrawal. The Mean±SD inhibition time lasted up to 50.34±10.17 minutes and 31% of neurons stopped firing and silenced after 24±3 min on average but the remaining neurons lowered their firing up to 43% to 67% of their baseline firing. All neurons showed the excitation period, lasted about 56.12±15.30 min, and the firing of neurons increased from 176% to 244% of their baseline or pre-injection period.

Conclusion

The tolerance and dependence effects of tramadol are related to the changes in the neuronal firing rate at the putative VTA-DA neurons. The acute injection of tramadol can initiate neuroadaptation on the opioid and non-opioid neurotransmission to mediate these effects.

Different rates of tramadol infusion for peri and postoperative analgesia in dogs undergoing orthopedic surgery

ABSTRACT The study aimed to determine the continuous rate infusion of tramadol associated with peri- and postoperative analgesia for orthopedic surgeries in dogs, as well as cardiorespiratory and adverse effects. Thirty dogs aged 4.2±1.2 years and weighing 15.1±0.9kg were enrolled in the study, premedicated intramuscularly with acepromazine (0.04mg kg-1) and tramadol (2mg kg-1); anesthesia was induced with propofol and maintained with isoflurane in oxygen. Three infusion rates were compared, comprising three experimental groups: G2: 2.0mg kg-1 h-1; G2.5: 2.5mg kg-1 h-1; and G3: 3.0mg kg-1 h-1. Surgery was initiated 15 minutes following the start of tramadol infusion. During anesthesia, animals were monitored in predefined time points: immediately after tracheal intubation and start of inhalation anesthesia (T0); surgical incision (TSI); final suture (TFS) and end of tramadol infusion (TEI), which was maintained for at least 120 minutes and prolonged according to the duration of surgery. Postoperative analgesia was evaluated through an interval pain scoring scale and the Melbourne pain scale. The mean time of tramadol infusion was greater than 120 minutes in all groups and no differences were found among them (141±27 minutes in G2, 137±27 minutes in G2.5 and 137±30 minutes in G3). Perioperative analgesia was regarded as short and did not correlate with infusion rates. Tramadol infusion provided adequate analgesia with cardiorespiratory stability Analgesia was not dose-dependent, however, and residual postoperative effects were short-lasting, which warrants proper postoperative analgesia following tramadol infusion. Additional studies are required using higher infusion rates and standardized nociceptive stimulation in order to determine how doses influence tramadol analgesia and whe therthereis a limit to its effect in dogs.

An overview of tramadol and its usage in pain management and future perspective

Patients with chronic non-malignant pain report impairment of physical and social life along with psychological state affecting their overall quality of life. The purpose of managing pain is to reduce the trauma and improve the patient comfort with better quality of life. Tramadol is a centrally acting weak μ-opioid receptor analgesic and is a racemic mixture of (+)-tramadol and (-)-tramadol enantiomers. Tramadol is used worldwide and is listed in many medical guidelines for pain management. The (+)-tramadol has greater affinity for μ-opioid receptor and provides additional prevention of 5- hydroxy tryptamine reuptake, while the (-)-tramadol is a successful noradrenaline reuptake inhibitor and intensifies its release by activating the auto receptor. Tramadol is prescribed to relieve moderate to severe pain management in patients. Tramadol does not show much serious adverse effects without any dependency potential in therapeutic doses as seen in other opioids, like morphine. Tramadol metabolite M1 also has μ-opioid receptor agonist activity, but it faces poor blood brain barrier permeability. In this review, we report the complete updated status of Tramadol along with its chemistry, synthesis, pharmacology, medicinal uses, adverse effects and its combinations available in the market. We have also covered Tramadol patents so that a complete overview provides a broader perspective for future designing of its derivatives and increase their potential use for pain management in terminal cancer patients.

Usefulness of knockout mice to clarify the role of the opioid system in chronic pain

Several lines of knockout mice deficient in the genes encoding each component of the endogenous opioid system have been used for decades to clarify the specific role of the different opioid receptors and peptide precursors in many physiopathological conditions. The use of these genetically modified mice has improved our knowledge of the specific involvement of each endogenous opioid component in nociceptive transmission during acute and chronic pain conditions. The present review summarizes the recent advances obtained using these genetic tools in understanding the role of the opioid system in the pathophysiological mechanisms underlying chronic pain. Behavioural data obtained in these chronic pain models are discussed considering the peculiarities of the behavioural phenotype of each line of knockout mice. These studies have identified the crucial role of specific components of the opioid system in different manifestations of chronic pain and have also opened new possible therapeutic approaches, such as the development of opioid compounds simultaneously targeting several opioid receptors. However, several questions still remain open and require further experimental effort to be clarified. The novel genetic tools now available to manipulate specific neuronal populations and precise genome editing in mice will facilitate in a near future the elucidation of the role of each component of the endogenous opioid system in chronic pain.

LINKED ARTICLES

This article is part of a themed section on Emerging Areas of Opioid Pharmacology. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.14/issuetoc.

Pain and Its Control in Reptiles

Reptiles have the anatomic and physiologic structures needed to detect and perceive pain. Reptiles are capable of demonstrating painful behaviors. Most of the available literature indicates pure μ-opioid receptor agonists are best to provide analgesia in reptiles. Multimodal analgesia should be practiced with every reptile patient when pain is anticipated. Further research is needed using different pain models to evaluate analgesic efficacy across reptile orders.

Tramadol differentially regulates M1 and M2 macrophages from human umbilical cord blood

Tramadol is an analgesic drug and relieves pain through activating μ-opioid receptors and inhibiting serotonin and noradrenaline reuptake. Emerging evidence shows that it also stimulates immune cells, including NK cells, splenocytes, and lymphocytes, and elevates IL-2 production. However, it remains unknown whether and how tramadol directly affects macrophages. To answer these questions, we collected human umbilical cord blood, isolated macrophages, and examined their responses to tramadol. Although tramadol did not alter resting macrophages and the antigen-presenting function in lipopolysaccharide-activated macrophages, it regulated M1 and M2 macrophages, which are, respectively, transformed by IFN-γ and IL-4. Interestingly, tramadol inhibits production and secretion of cytokines in M1 macrophages, but facilitates the production of inflammation-responding molecules, synthesized in M2 macrophages. We also found that STAT6 cascade pathway in M2 macrophages was significantly enhanced by tramadol. Therefore, this study reveals that tramadol regulates inflammation by inhibiting M1 macrophages (killing process), but promoting the function of M2 macrophages (healing process).

Pharmacology of Acetaminophen, Nonsteroidal Antiinflammatory Drugs, and Steroid Medications: Implications for Anesthesia or Unique Associated Risks

Acetaminophen, nonsteroidal antiinflammatory drugs (NSAIDs), and corticosteroids, historically used in perioperative management, are potent analgesic medications. They primarily inhibit the cyclooxygenase (COX) enzyme, decreasing the synthesis of prostaglandins, and modulating pain and temperature. Acetaminophen does not inhibit this synthesis at the inflammatory site. The primary mechanism of action of corticosteroids involves regulation of nuclear expression of genes involved in inflammatory pathways and other systemic effects. Metaanalyses have added purposeful perioperative indications, clarified misconceptions, and established protocols for administering these drugs. Some indications, doses, clinical considerations, and adverse effects need to be further studied.

Comparative Study of the Effect of Intravenous Paracetamol and Tramadol in Relieving of Postoperative Pain after General Anesthesia in Nephrectomy Patients

Aim:

The aim of this study was to compare the effect of intravenous paracetamol and tramadol in relieving of postoperative pain after general anesthesia for nephrectomy in prospective donor patients for kidney transplantation.

Materials and Methods:

A randomized study was conducted on 100 adult patients scheduled for nephrectomy aged from 35 to 55 years of both sexes and divided into two groups and were administered intravenous paracetamol and tramadol for postoperative pain relief and assessed with visual analog scale score and variations in vital parameters to assess extent of pain relief.

Results:

After statistical interpretation of collected data, the observations were extrapolated. There was a statistically significant difference in the pain intensity scores obtained between the paracetamol and tramadol groups.

Conclusion:

On the basis of the present study, it is concluded that tramadol due to its lesser onset of action time was superior to paracetamol in providing acute postoperative pain relief.

Cortical and subcortical modulation of pain

Pain is more than merely nociception and response, but rather it encompasses emotional, behavioral and cognitive components that make up the pain experience. With the recent advances in imaging techniques, we now understand that nociceptive inputs can result in the activation of complex interactions among central sites, including cortical regions that are active in cognitive, emotional and reward functions. These sites can have a bimodal influence on the serotonergic and noradrenergic descending pain modulatory systems via communications among the periaqueductal gray, rostral ventromedial medulla and pontine noradrenergic nuclei, ultimately either facilitating or inhibiting further nociceptive inputs. Understanding these systems can help explain the emotional and cognitive influences on pain perception and placebo/nocebo effects, and can help guide development of better pain therapeutics.

Comparison of pharmacokinetics of tramadol between young and middle-aged dogs

This study aimed to compare the pharmacokinetics of tramadol between young and middle-aged dogs. Tramadol (4 mg/kg) was administered intravenously (IV) to young and middle-aged dogs (2 and 8–10 years, respectively). Plasma concentrations of tramadol were measured using high-performance liquid chromatography (HPLC), and its pharmacokinetics best fit a two-compartment model. The volume of distribution (V_d), elimination half-life (t_1/2,β) and total body clearance (CL_tot) of the young group were 4.77 ± 1.07 l/kg, 1.91 ± 0.26 hr and 29.9 ± 7.3 ml/min/kg, respectively, while those of the middle-aged group were 4.73 ± 1.43 l/kg, 2.39 ± 0.97 hr and 23.7 ± 5.4 ml/min/kg, respectively. Intergroup differences in the t_1/2,β and CL_tot were significant (P<0.05). In conclusion, tramadol excretion was significantly prolonged in middle-aged dogs.

A comparative study of intravenous paracetamol and intravenous tramadol for postoperative analgesia in laparotomies

Background:

Pain in the perioperative setting or thereafter plays a significant role in delaying an otherwise successful recovery. Hence, mitigation of such postoperative pain assumes importance. Among the various agents employed for such mitigation, opioids and non-steroidal anti-inflammatory drugs have for some time taken center stage. However, alas they are not without their share of adverse effects. This study was undertaken with the purpose of elucidating the efficacy of intravenous (IV) paracetamol as compared to IV tramadol in mitigating postoperative pain while observing its effect on hemodynamic stability and the presence of adverse drug reactions, if any.

Materials and Methods:

A total of 60 randomized cases aged ranges from 20 to 60 years of both sexes divided into two groups (each for paracetamol and tramadol) scheduled for laparotomies were administered IV paracetamol and tramadol for postoperative pain relief and assessed with visual analog scale (VAS) score and variations in vital parameters to ascertain extent of pain relief and post-operative nausea vomiting (PONV).

Results:

Data so collected was statistically interpreted, and observations extrapolated. Save for a perceptible decline in PONV with paracetamol group compared with tramadol group with a statistically significant P < 0.001, nothing statistically significant was observed in any other parameter, including VAS scores between either group.

Conclusion:

IV paracetamol is a safer alternative to tramadol with lesser PONV in the postoperative period translates into the lesser duration of hospitalization and hence earlier discharge.

Comparison of carprofen and tramadol for postoperative analgesia in dogs undergoing enucleation

OBJECTIVE

To compare analgesia provided by carprofen and tramadol in dogs after enucleation.

DESIGN

Randomized, masked clinical trial.

ANIMALS

43 dogs.

PROCEDURES

Client-owned dogs admitted for routine enucleation were randomly assigned to receive either carprofen or tramadol orally 2 hours prior to surgery and 12 hours after the first dose. Dogs were scored for signs of pain at baseline (ie, before carprofen or tramadol administration) and at 0.25, 0.5, 1, 2, 4, 6, 8, 24, and 30 hours after extubation. Dogs received identical premedication and inhalation anesthesia regimens, including premedication with hydromorphone. If the total pain score was ≥ 9 (maximum possible score of 20), there was a score ≥ 3 in any of 5 behavioral categories (highest score possible per category was 3 or 4), or the visual analog scale (VAS) score was ≥ 35 (maximum possible score of 100) combined with a palpation score > 0, rescue analgesia (hydromorphone) was administered and treatment failure was recorded.

RESULTS

No differences were found in age, sex, or baseline pain scores between groups. Significantly more dogs receiving tramadol required rescue analgesia (6/21), compared with dogs receiving carprofen (1/22). Pain and VAS scores decreased linearly over time. No significant differences were found in pain or VAS scores between groups at any time point (dogs were excluded from analysis after rescue).

CONCLUSIONS AND CLINICAL RELEVANCE

Results of this study suggested that carprofen, with opioid premedication, may provide more effective postoperative analgesia than tramadol in dogs undergoing enucleation.

Amelioration of the reduced antinociceptive effect of morphine in the unpredictable chronic mild stress model mice by noradrenalin but not serotonin reuptake inhibitors

Background

Although alterations in not only the pain sensitivity but also the analgesic effects of opioids have been reported under conditions of stress, the influence of unpredictable chronic mild stress (UCMS) on the antinociceptive effects of opioid analgesics remains to be fully investigated. The present study examined the influence of UCMS on the thermal pain sensitivity and antinociceptive effects of two opioid analgesics, morphine (an agonist of opioid receptors) and tramadol (an agonist of μ-opioid receptor and an inhibitor of both noradrenaline and serotonin transporters). We also examined the effects of pretreatment with maprotiline (a noradrenaline reuptake inhibitor) and escitalopram (a serotonin reuptake inhibitor) on the antinociceptive action of morphine in mice under an UCMS condition.

Results

Unpredictable chronic mild stress did not affect the basal thermal pain sensitivity in a mouse hot-plate test. Although morphine dose-dependently induced thermal antinociceptive effects under both the UCMS and non-stress conditions, the thermal antinociceptive effect of 3 mg/kg morphine under the UCMS condition was significantly lower than under the non-stressed condition. Unlike the case with morphine, we observed no significant difference in the thermal antinociceptive effect of tramadol between the UCMS and non-stress conditions. Furthermore, the reduced thermal antinociceptive effect of 3 mg/kg morphine under the UCMS condition was significantly ameliorated by pretreatment with 10 mg/kg maprotiline but not 3 mg/kg escitalopram. Pretreatment with neither maprotiline nor escitalopram alone was associated with an antinociceptive effect under either condition.

Conclusions

We demonstrated that the antinociceptive effect of morphine but not tramadol was reduced in mice that had experienced UCMS. The reduced antinociceptive effect of morphine under the UCMS condition was ameliorated by pretreatment with maprotiline but not escitalopram. These results suggest that the reduced antinociceptive effects of morphine under conditions of chronic stress may be ameliorated by activation of the noradrenergic but not the serotonergic system.

Analgesia in the Perioperative Period

Untreated or undermanaged perioperative pain has systemic effects that may negatively impact a patient's welfare and return to function. A consistent analgesic plan that assesses a patient's pain and comfort at regular intervals during the perioperative period should be incorporated into practice. Validated pain assessment tools are available for use in dogs and cats. Multimodal analgesic plans should be created for individual patients and modified according to pain assessments. These plans, based on a thorough history, physical examination, and knowledge of the expected pain, should be combinations of an opioid, a nonsteroidal anti-inflammatory drug, a local anesthetic, and nonpharmacologic analgesic techniques.

Effects of tramadol on substantia gelatinosa neurons in the rat spinal cord: an in vivo patch-clamp analysis

Tramadol is thought to modulate synaptic transmissions in the spinal dorsal horn mainly by activating µ-opioid receptors and by inhibiting the reuptake of monoamines in the CNS. However, the precise mode of modulation remains unclear. We used an in vivo patch clamp technique in urethane-anesthetized rats to determine the antinociceptive mechanism of tramadol. In vivo whole-cell recordings of spontaneous inhibitory postsynaptic currents (sIPSCs) and spontaneous excitatory postsynaptic currents (sEPSCs) were made from substantia gelatinosa (SG) neurons (lamina II) at holding potentials of 0 mV and -70 mV, respectively. The effects of intravenous administration (0.5, 5, 15 mg/kg) of tramadol were evaluated. The effects of superfusion of tramadol on the surface of the spinal cord and of a tramadol metabolite (M1) were further analyzed. Intravenous administration of tramadol at doses >5 mg/kg decreased the sEPSCs and increased the sIPSCs in SG neurons. These effects were not observed following naloxone pretreatment. Tramadol superfusion at a clinically relevant concentration (10 µM) had no effect, but when administered at a very high concentration (100 µM), tramadol decreased sEPSCs, produced outward currents, and enhanced sIPSCs. The effects of M1 (1, 5 mg/kg intravenously) on sEPSCs and sIPSCs were similar to those of tramadol at a corresponding dose (5, 15 mg/kg). The present study demonstrated that systemically administered tramadol indirectly inhibited glutamatergic transmission, and enhanced GABAergic and glycinergic transmissions in SG neurons. These effects were mediated primarily by the activation of μ-opioid receptors. M1 may play a key role in the antinociceptive mechanisms of tramadol.

Noradrenergic modulation of itch transmission in the spinal cord

Inhibition of both itching and scratching is important in the treatment of chronic pruritic diseases, because itching has a negative impact on quality of life and vigorous scratching worsens skin conditions. Pharmacological modulation of itch transmission in the dorsal horn is an effective way to inhibit both itching and scratching in pruritic diseases. Pruriceptive transmission in the spinal dorsal horn undergoes inhibitory modulation by the descending noradrenergic system. The noradrenergic inhibition is mediated by excitatory α₁-adrenoceptors located on inhibitory interneurons and inhibitory α₂-adrenoceptors located on central terminals of primary sensory neurons. The descending noradrenergic system and α-adrenoceptors in the dorsal horn are potential targets for antipruritic drugs.

Proconvulsant effects of tramadol and morphine on pentylenetetrazol-induced seizures in adult rats using different routes of administration

Tramadol is frequently used as a pain reliever. However, it has been sometimes noted to have the potential to cause seizures. Because of its dual mechanism of action (both opioid and nonopioid), the adverse effect profile of tramadol can be different in comparison with single-mechanism opioid analgesics, such as morphine. In the present study, the facilitatory effects of tramadol and morphine on pentylenetetrazol-induced seizures using different routes of administration were compared in rats. Adult female rats were divided into six groups and continuously received saline, morphine, or tramadol on a daily basis for 15 days [gavage (PO) or intraperitoneal (IP)]. An increasing dose of morphine and tramadol was used to prevent resistance to repetitive dose (20-125 mg/kg). Following one week of withdrawal period and 30 min before the seizure induction (PTZ=80 mg/kg, IP), each group of rats was further divided into subgroups that received saline, morphine, or tramadol for the second time on the 22nd day of the experiment. Results showed that, while morphine, tramadol, and their administration had different effects on seizure behaviors, both acute and chronic administrations of morphine and tramadol potentiated PTZ-induced seizures. However, there was no significant difference between morphine and tramadol in terms of seizure severity. Effects of morphine and tramadol on PTZ-induced seizures were also stable following one week of withdrawal. In conclusion, this study indicated similar severity in the proconvulsant effect of morphine and tramadol on PTZ-induced seizures, which might depend on their similar effects on GABAergic pathways.

Chronic resveratrol treatment exerts antihyperalgesic effect and corrects co-morbid depressive like behaviors in mice with mononeuropathy: involvement of serotonergic system

Patients suffering from chronic neuropathic pain are at high risk of co-morbid depression, which burdens healthcare. This work aimed to investigate the effects of resveratrol, a phenolic monomer enriched in red wine and grapes, on pain-related and depressive-like behaviors in mice with mononeuropathy, and explored the mechanism(s). Mice received chronic constriction injury (CCI) of sciatic nerves, and sequentially developed pain-related and depressive-like behaviors, as evidenced by sensory hypersensitivity (thermal hyperalgesia in Hargreaves test and mechanical allodynia in von Frey test) and behavioral despair (prolonged immobility time in forced swim test). Chronic treatment of neuropathic mice with resveratrol (30 mg/kg, p.o., twice per day for three weeks) normalized their thermal hyperalgesia (but not mechanical allodynia) and depressive-like behaviors, and these actions were abolished by chemical depletion of central serotonin (5-HT) but potentiated by co-treatment with 5-HTP, a precursor of 5-HT. The anti-hyperalgesia and anti-depression exerted by resveratrol may be pharmacologically segregated, since intrathecal (i.t.) and intracerebroventricular (i.c.v.) injection of methysergide, a non-selective 5-HT receptor antagonist, separately abrogated the two actions. Furthermore, the antihyperalgesic action of resveratrol was preferentially counteracted by co-administration of the 5-HT7 receptor antagonist SB-258719, while the anti-depression was abrogated by 5-HT1A receptor antagonist WAY-100635. These results confirm that chronic resveratrol administration exerts curative-like effects on thermal hyperalgesia and co-morbid depressive-like behaviors in mice with mononeuropathy. Spinal and supraspinal serotonergic systems (coupled with 5-HT7 and 5-HT1A receptors, respectively) are differentially responsible for the antihyperalgesic and antidepressant-like properties of resveratrol.

Contributions of peripheral, spinal, and supraspinal actions to analgesia

Pain signaling involves several main compartments that can be considered as potential sites for analgesic drug actions. When drugs are given systemically, they can act at spinal, supraspinal and peripheral sites, and several methods have been developed for identifying where they act. These include (1) localized delivery of drugs to specific sites (via intracerebral, intrathecal, and intraplantar injections), (2) systemic delivery of drugs with localized delivery of antagonists for the receptor on which the drug acts or for a system recruited by the drug, (3) use of peripherally restricted analogs, and (4) use of conditional knockout technology to selectively deplete receptors on nociceptors. Delivery of drugs simultaneously to several sites (spinal/supraspinal, peripheral/spinal, and peripheral/supraspinal) reveals "self-synergy" between sites for some agents. Knowledge of peripheral contributions to drug actions is important because of the potential to develop peripherally restricted analgesics (with a diminished side effect profile due to not entering the central nervous system), the potential to deliver drugs peripherally (e.g. topically) to act on sensory nerve endings and adjacent tissue (with a diminished side effect profile due to limited systemic absorption), and the potential to use combinations of topical and oral drug regimens to obtain improved pain relief (without increasing the side effect burden). This review considers methods used for compartmental analysis, and results of such site analysis for several major classes of analgesic drugs that are in current use.

Spinal and peripheral adenosine A₁ receptors contribute to antinociception by tramadol in the formalin test in mice

Tramadol, an analgesic used alone or combined with acetaminophen, has a complex mechanism of action involving opioid and amine mechanisms. In this study, we explored the involvement of spinal and peripheral adenosine A1 receptors in antinociception by tramadol, and determined whether spinal serotonin 5-HT₇ receptors were linked to spinal A1 receptor actions. Antinociception was examined using the 2% formalin test in mice. Tramadol was administered systemically (intraperitoneal) or peripherally (intraplantar). Caffeine (non-selective A₁/A₂A receptor antagonist) and SCH58261 (selective A₂A receptor antagonist) were given systemically, while DPCPX (selective A₁ receptor antagonist) was given systemically, spinally (lumbar puncture), or peripherally. Systemic tramadol 35 mg/kg produced antinociception against phase 2 formalin-evoked flinching behaviors, particularly in the earlier parts (phase 2A). Systemic caffeine (10 mg/kg) and DPCPX (1 mg/kg), but not SCH58261 (3 mg/kg), inhibited antinociception by systemic tramadol. Spinal DPCPX 3 μg also inhibited the action of systemic tramadol. Spinal SB269970 (selective 5-HT₇ receptor antagonist) 3-10 μg did not alter the effect of systemic tramadol. Intraplantar tramadol produced antinociception against flinching behaviors, and this action was reversed by intraplantar DPCPX 4.5 μg administered on the ipsilateral, but not contralateral, side. Intraplantar DPCPX also reversed antinociception by systemic tramadol. These results indicate that adenosine A₁ receptors contribute to antinociception by tramadol in the mouse formalin model, and that spinal and peripheral sites are involved in these actions. 5HT₇ receptors in the spinal cord do not appear to be involved in the recruitment of A₁ receptor mechanisms when tramadol is given systemically in this model.

The perception and endogenous modulation of pain

Pain is often perceived an unpleasant experience that includes sensory and emotional/motivational responses. Accordingly, pain serves as a powerful teaching signal enabling an organism to avoid injury, and is critical to survival. However, maladaptive pain, such as neuropathic or idiopathic pain, serves no survival function. Genomic studies of individuals with congenital insensitivity to pain or paroxysmal pain syndromes considerable increased our understanding of the function of peripheral nociceptors, and especially of the roles of voltage-gated sodium channels and of nerve growth factor (NGF)/TrkA receptors in nociceptive transduction and transmission. Brain imaging studies revealed a "pain matrix," consisting of cortical and subcortical regions that respond to noxious inputs and can positively or negatively modulate pain through activation of descending pain modulatory systems. Projections from the periaqueductal grey (PAG) and the rostroventromedial medulla (RVM) to the trigeminal and spinal dorsal horns can inhibit or promote further nociceptive inputs. The "pain matrix" can explain such varied phenomena as stress-induced analgesia, placebo effect and the role of expectation on pain perception. Disruptions in these systems may account for the existence idiopathic pan states such as fibromyalgia. Increased understanding of pain modulatory systems will lead to development of more effective therapeutics for chronic pain.

Pharmacodynamic profile of tramadol in humans: influence of naltrexone pretreatment

RATIONALE

Tramadol is a prescription analgesic that activates mu opioid and monoamine receptor systems. Tramadol is thought to have limited abuse potential compared to mu opioid agonists, but laboratory data indicate that it shares some of their pharmacodynamic effects.

OBJECTIVES

This study evaluated the effect of mu opioid receptor blockade with naltrexone on the pharmacodynamic action of tramadol in humans.

METHODS

This inpatient, double-blind, randomized, within-subject study examined the effects of oral placebo, tramadol (87.5, 175, and 350 mg), and hydromorphone (4 and 16 mg; positive control) after 1 h pretreatment with oral naltrexone (0 and 50 mg). Ten recreational opioid users completed the study. Pharmacodynamic effects were measured before and for 7 h after initial drug administration.

RESULTS

Lower doses of tramadol and hydromorphone were generally placebo-like. Hydromorphone (16 mg) produced prototypic mu opioid agonist-like effects that were blocked by naltrexone. Tramadol (350 mg) produced miosis and increased ratings of "Good Effects" and "Liking" but also increased ratings of "Bad Effects." Naltrexone reversed tramadol-induced physiological effects and mydriasis emerged, but unlike results with hydromorphone, naltrexone only partially attenuated tramadol's positive subjective effects and actually enhanced several unpleasant subjective ratings.

CONCLUSIONS

Naltrexone can be used to disentangle the mixed neuropharmacological actions of tramadol. High-dose tramadol produces a mixed profile of effects. These data suggest that both mu and non-mu opioid actions play a role in tramadol's subjective profile of action.