Physical dependence potential of daily tramadol dosing in humans

Exploring the potential use of melatonin as a modulator of tramadol-induced rewarding effects in rats

Background

Melatonin is responsible for regulating the sleep-wake cycle and circadian rhythms in mammals. Tramadol, a synthetic opioid analgesic, is used to manage moderate to severe pain but has a high potential for abuse and dependence. Studies have shown that melatonin could be a potential modulator to reduce tramadol addiction.

Methods

Male Wistar rats were used to investigate the effect of melatonin on tramadol-induced place preference. The rats were divided into four groups: control, tramadol, tramadol + melatonin (single dose), and tramadol + melatonin (repeated doses). Tramadol was administered intraperitoneally at 40 mg/kg, while melatonin was administered at 50 mg/kg for both the single dose and repeated-dose groups. The study consisted of two phases: habituation and acquisition.

Results

Tramadol administration produced conditioned place preference (CPP) in rats, indicating rewarding effects. However, melatonin administration blocked tramadol-induced CPP. Surprisingly, repeated doses of melatonin were ineffective and did not reduce the expression of CPP compared to that of the single dose administration.

Conclusion

The study suggests that melatonin may be a potential therapeutic option for treating tramadol addiction. The results indicate that melatonin attenuates the expression of tramadol-induced CPP, supporting its uses as an adjunct therapy for managing tramadol addiction. However, further studies are needed to investigate its effectiveness in humans.

Tramadol poisoning and its management and complications: a scoping review

Tramadol (TR) is an opioid agonist (μ-opioid receptors) that also affects the noradrenergic and serotonergic systems. TR is a synthetic analgesic substance with opioid agonist properties that has been approved for pain management by affecting the central nervous system.

OBJECTIVE

The primary objective of this scoping review was to determine the poisoning consequences of TR and its associated symptom management techniques, as well as its effect on opioid and non-opioid receptors, metabolism, and complications on various organ systems.

DISCUSSION

Typically, acute overdose of TR is not considered life threatening, and most fatalities are attributed to polysubstance overdose. TR can cause drowsiness, headaches, seizures, respiratory depression, low heart rate, coma, and even death. Additionally, the prolonged use of TR can lead to addiction, with withdrawal resulting in both common and atypical symptoms.

CONCLUSIONS

Therefore, it is recommended that patients with TR poisoning receive close monitoring of their cardiovascular system, along with a comprehensive management plan for their levels of consciousness and respiratory function.

Comparative Study of the Neurotoxic Effects of Pregabalin Versus Tramadol in Rats

In Egypt, both pregabalin and tramadol misuse increased in the last decade. Although many studies have confirmed the neurotoxic effects of tramadol, those of pregabalin are understudied. The aim of the study is to evaluate the neurotoxic effects of pregabalin compared with tramadol. Thirty male albino rats were included in this experimental study, and they were randomly allocated into three equal groups: group I (normal saline), group II (tramadol misuse), and group III (pregabalin misuse). All rats received the commenced drugs for 1 month. Open field tests were performed on the day of scarification, and after that, cortical samples were taken for immunohistochemical analysis and quantification of dopamine receptors' gene expression. The drug misuse groups showed a significant decrease in weight gain at the end of the study. Open field testing showed the upper hand of controls regarding all of the tested parameters. Tramadol has a more negative impact on the locomotor parameters compared with pregabalin. Both drugs induced relatively low dopamine-1 receptor (D1Rs) expression to dopamine-2 receptors (D2Rs), mimicking the schizophrenia model. Both tramadol and pregabalin were associated with neurotoxic effects in male albino rats. These effects were less noticed with pregabalin. It is suggested that long-term abuse may end in psychosis.

Buprenorphine for High-dose Tramadol Dependence: A Case Report of Successful Outpatient Treatment

Introduction

During the coronavirus disease 2019 pandemic caused by the severe acute respiratory syndrome coronavirus 2, deaths from opiate drug overdoses reached their highest recorded annual levels in 2020. Medication-assisted treatment for opiate use disorder has demonstrated efficacy in reducing opiate overdoses and all-cause mortality and improving multiple other patient-centered outcomes. Treatment of tramadol dependence in particular poses unique challenges due to its combined action as opioid agonist and serotonin-norepinephrine reuptake inhibitor. Tramadol puts patients with dependence at risk for atypical withdrawal syndromes when attempting to reduce use. Little evidence is available to guide treatment of tramadol dependence.

Case Report

We present a case of high-dose tramadol addiction that began with misuse of medically prescribed tramadol for treatment of musculoskeletal back pain. The patient’s use reached oral consumption of 5000–6000 milligrams of illicit tramadol daily. She complained of common complications of tramadol use disorder including memory impairment, excessive sedation, and tramadol-induced seizures. The patient was referred to the emergency department in a withdrawal crisis seeking treatment where she was successfully managed with buprenorphine and phenobarbital and then linked to ongoing outpatient treatment.

Conclusion

Our report adds to the limited guidance currently available on the acute management of tramadol withdrawal and treatment of tramadol use disorder. Our case suggests the initiation of high-dose buprenorphine may be an effective and feasible option for emergency clinicians.

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.

Expert review and recommendations for the management of acute, chronic, and neuropathic pain in Qatar

BACKGROUND

Pain management is an evolving area of expertise in Qatar. Gaps in knowledge, inadequate training for physicians and nurses, and the absence of policies/guidelines are the main barriers to effective pain management in Qatar. In addition, the use of certain pain medication, especially opioids, is highly regulated, limiting their availability in outpatient pain management. These factors are responsible for the undertreatment of pain in Qatar. This study aimed to standardize evidence-based local recommendations for pharmacological treatment of pain in Qatar.

METHODS

An expert panel of physicians from different disciplines, with experience in diagnosis and treatment of the three pain types (i.e., acute, chronic, and neuropathic), was convened for two face-to-face meetings in Doha, Qatar, on November 29, 2019, and on February 22, 2020, with subsequent virtual meetings. A literature search was performed on Medline and Google Scholar databases from inception till December 2019, and all relevant articles were selected. Based on these articles and repeated feedback from the authors, the final pain treatment protocols were developed.

RESULTS

Recommendations for the treatment of acute pain, based on pain severity, followed three approaches: acetaminophen/paracetamol or non-steroidal anti-inflammatory drugs (NSAIDs) for mild pain and moderate pain and referral to a pain specialist for severe pain. Acetaminophen/paracetamol or NSAIDs is recommended for chronic pain, and the use of opioids was strongly discouraged because of its long-term side effects. For neuropathic pain, tricyclic antidepressants or gabapentin or pregabalin or serotonin-norepinephrine reuptake inhibitors were recommended first-line agents. Non-responders must be referred to neurologists or a pain specialist.

CONCLUSION

The expert panel provides recommendations for the management of acute, chronic, and neuropathic pain based on international guidelines adapted to local practice and treatment availability in Qatar. More importantly, the panel has recommended taking extreme caution in the use of opioids for long-term management of chronic pain and to refer the patient to a pain specialist clinician as required.

Chronic Exposure to Tramadol Induces Neurodegeneration in the Cerebellum of Adult Male Rats

Tramadol is a centrally acting synthetic opioid analgesic and SNRI (serotonin/norepinephrine reuptake-inhibitor) that structurally resembles codeine and morphine. Given the tramadol neurotoxic effect and the body of studies on the effect of tramadol on the cerebellum, this study aims to provide deeper insights into molecular and histological alterations in the cerebellar cortex related to tramadol administration. In this study, twenty-four adult male albino rats were randomly and equally divided into two groups: control and tramadol groups. The tramadol group received 50 mg/kg of tramadol daily for 3 weeks via oral gavage. The functional and structural change of the cerebellum under chronic exposure of tramadol were measured. Our data revealed that treating rats with tramadol not only lead to cerebellum atrophy but also resulted in the actuation of microgliosis, neuroinflammatoin, and apoptotic biomarkers. Our results illustrated a significant drop in VEGF (vascular endothelial growth factor) level in the tramadol group. Additionally, tramadol impaired motor coordination and neuromuscular activity. We also identified several signaling cascades chiefly related to neurodegenerative disease and energy metabolism that considerably deregulated in the cerebellum of tramadol-treated rats. Overall, the outcomes of this study suggest that tramadol administration has a neurodegeneration effect on the cerebellar cortex via several pathways consisting of microgliosis, apoptosis, necroptosis, and neuroinflammatoin.

Evaluation of vitamin C protective effect on the cerebrocortical antioxidant defense, histopathological, pro-apoptotic p53 and anti-apoptotic Bcl2 expressions against tramadol neurotoxicity in rats

BACKGROUND

Reported tramadol toxicity emphasizes the necessity to recognize its mechanism of toxicity, particularly to the brain tissue.

AIM

This study aimed to evaluate the protective effect of vitamin C (Vit C) in cerebrocortical toxicity mediated by tramadol in rats using biochemical and histological parameters.

MATERIAL AND METHODS

Forty-eight albino rats were randomly divided into eight groups, (n = 6/group) as follow: the control group received normal saline and vitamin C group received vitamin C (200 mg/kg per oral). Tramadol 50, 100, 150 groups received tramadol in doses of (50, 100 and 150 mg/kg per oral, respectively); Tramadol 50+ Vit C, 100+ Vit C, 150+ Vit C groups received vitamin C (200 mg/kg per oral) plus tramadol in doses of (50, 100 and 150 mg/kg per oral, respectively). Rats had received vitamin C and tramadol daily for 30 days. Blood and brain tissues samples were harvested for biochemical, histopathological, immunohistochemical and electron microscopic examinations.

RESULTS

Tramadol administration leads to a significant elevation of MDA, NO levels and a significant decrease in antioxidants parameters (CAT, SOD and GSH) in the tissues of cerebral cortices in rats which were directly proportional to the dose of tramadol. In histological investigations, tramadol-treated groups showed pyknotic pyramidal cells, multiple red neurons and shrinking red neurons with hallows around it and apoptotic cells were detected. These biochemical abnormalities and histological impairment were ameliorated in groups with tramadol low doses by the co-treatment with vitamin C.

CONCLUSION

vitamin C has antioxidant and anti-apoptotic potentials against tramadol neurotoxicity via suppression of oxidative stress, lipid peroxidation, structural abnormalities, and down-regulation of p53 and overexpression of Bcl2 in the nervous tissues.

Tramadol aggravates cardiovascular toxicity in a rat model of alcoholism: Involvement of intermediate microfilament proteins and immune-expressed osteopontin

Tramadol and alcohol are among commonly abused drugs. Although there are potential dangers reported upon their mixing, there are no previous reports describing this mixture's effects on the cardiovascular system (CVS). The aim was to study the effects of mixed alcohol and tramadol on the CVS of adult male rats. Fifty rats were divided into four groups: control, tramadol-treated group, alcohol-treated, and coadministration groups. Tramadol caused a significant increases in creatine kinase-MB, troponin I, malondialdehyde, protein carbonyl, 8-hydroxy-2'-deoxyguanosine, and a significant decrease in total antioxidant capacity with histological alterations in sections of the heart and aorta and a significant increase in the area% of collagen fibers while there was a nonsignificant difference in body weight, heart weight, heart weight/body weight ratio, lipid profile, tissue tumor necrosis factor-α and interferon-γ, intermediate microfilament proteins (IFPs) {desmin, vimentin, connexin43} gene expression, mean area% of elastic fibers in aortic tissue and osteopontin expression in cardiac and aortic tissue. Alcohol treatment caused a significant change in all the measured parameters and more damage in histological sections. The changes were highest in the coadministration group. There was a strong positive correlation between the area% of collagen fibers and vimentin gene expression, and the area% of osteopontin expression was positively correlated to connexin43 in cardiac and vascular tissue. Tramadol causes CVS injury mainly through oxidative stresses, while the alcohol effect is multifactorial; mixing both aggravates CVS injury. The study also highlights the role of IFPs and osteopontin-expression in inducing injury.

Tramadol use and public health consequences in Iran: a systematic review and meta-analysis

BACKGROUND AND AIMS

Misuse of tramadol, an opioid prescription analgesic, is known as a public health challenge globally. We aimed to systematically review studies on the prevalence of non-prescribed use, regular tramadol use and dependence, tramadol-induced poisoning and mortality in Iran.

METHODS

Consistent with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, international (Medline, Scopus, Web of Science) and Persian (SID) databases were systematically searched up to June 2019. Other relevant data were collected through personal contacts and review of reference lists. Pooled estimates of prevalence of tramadol use in subgroups of males and females, percentage of tramadol poisoning among admitted poisoning cases, tramadol-associated seizures and mortality among tramadol poisonings and percentage of tramadol as a cause of death among fatal drug-poisoning records were estimated through a random-effects model.

RESULTS

A total of 84 records were included. Pooled estimates of last 12-month use of tramadol in the Iranian general population were 4.9% [95% confidence interval (CI) = 4.1-5.9] and 0.8% (95% CI = 0.2-1.8) among males and females, respectively. The estimates for last 12-month use among Iranian male and female university students were 4.8% (95% CI = 1.9-8.9) and 0.7% (95% CI = 0.3-1.1), respectively. Six heterogeneous reports indicated the existence of regular use of tramadol and dependence in Iran. Sixty-two studies provided data on tramadol-induced poisoning, seizures and mortality. The pooled estimate of the percentage of tramadol poisoning among all drug-poisoning patients was 13.1% (95% CI = 5.7-22.9). The overall estimates of seizures and mortality among tramadol-poisoning patients were 34.6% (95% CI = 29.6-39.8) and 0.7% (95% CI = 0.0-1.9), respectively. The pooled percentage of tramadol-related fatalities among drug-poisoned cases was 5.7% (95% CI = 0.5-15.4).

CONCLUSION

Despite control policies, tramadol use is as prevalent as the use of illicit opioids in Iran. Numerous cases of tramadol abuse, dependence, poisonings, seizures and hundreds of tramadol-related deaths have been reported in recent years.

The role of cannabinoid 1 receptor in the nucleus accumbens on tramadol induced conditioning and reinstatement

AIMS

Previous investigations demonstrated that tramadol, as a painkiller, similar to morphine induces tolerance and dependence. Furthermore, the cannabinoid receptor 1 (CB1R) located in the nucleus accumbens (NAc) plays a critical role in morphine-induced conditioning. Therefore, the main objective of this study was to evaluate the role of NAc CB1R in tramadol induced conditioning and reinstatement.

MAIN METHODS

In the present experiment, the effect of NAc CB1 receptors on tramadol induced conditioning was tested by microinjecting of arachidonylcyclopropylamide (ACPA, CB1R agonist) and AM 251 (CB1R inverse agonist) in the NAc during tramadol-induced conditioning in the adult male Wistar rats. In addition, the role of NAc CB1R in the reinstatement was also evaluated by injecting ACPA and AM 251 after a 10-days extinction period.

KEY FINDINGS

The obtained data revealed that the administration of tramadol (1,2, and 4 mg/kg, ip) dose-dependently produced conditioned place preference (CPP). Moreover, intra-NAc administration of ACPA (0.25, 0.5, and 1 μg/rat) dose-dependently induced conditioning, while the administration of AM-251 (30, 60, and 120 ng/rat) induced a significant aversion. In addition, the administration of a non-effective dose of AM251 during tramadol conditioning inhibited conditioning induced by tramadol. On the other hand, the administration of ACPA after extinction induced a significant reinstatement. Notably, the locomotor activity did not change among groups.

SIGNIFICANCE

Previous studies have shown that tramadol-induced CPP occurs through μ-opioid receptors. The data obtained in the current study indicated that CB1R located in the NAc is involved in mediating conditioning induced by tramadol. Besides, CB1R also plays a vital role in the reinstatement of tramadol-conditioned animals. It might be due to the effect of opioids on enhancing the level of CB1R.

Tramadol for the Management of Opioid Withdrawal: A Systematic Review of Randomized Clinical Trials

The increase in the prescription of opioid medications has resulted in a wildfire of misuse of opioids, both for medical and non-medical reasons, with over 1.7 million people in the United States (US) suffering from distinct disorders owing to opioid use. While various medications, such as methadone, buprenorphine, and naloxone, among others, have been used in treating opioid withdrawal symptoms, concerns of the potential abuse of these drugs, the cost of procurement, legislations, and prescription policies have risen. In recent times, tramadol has been considered a viable replacement for some of these treatment regimes. Tramadol is a synthetic analgesic that acts centrally, possessing opioid-like effects due to the binding of its metabolite with the mu (µ)-opioid receptor, yet with low potential for abuse. Several clinical studies conducted in the past ten years have identified the effects of tramadol in opioid withdrawal cases. The results showed that it exhibits better efficacy and tolerance with fewer side effects in specific clinical scenarios as compared to existing available detox management. We aim to examine the properties of tramadol in opioid withdrawal through this systematic review of clinical studies on humans.

Tramadol Promotes Oxidative Stress, Fibrosis, Apoptosis, Ultrastructural and Biochemical alterations in the Adrenal Cortex of Adult Male Rat with Possible Reversibility after Withdrawal

Tramadol is a centrally acting analgesic drug, used for the management of moderate to severe pain in a variety of diseases. The long-term use of tramadol can induce endocrinopathy. This study aimed to evaluate the effect of tramadol dependence on the adrenal cortex and the effect of its withdrawal. Thirty adult male rats were divided into three experimental groups: the control group, the tramadol-dependent group that received increasing therapeutic doses of tramadol orally for 1 month, and the recovery group that received tramadol in a dose and duration similar to the previous group followed by a withdrawal period for another month. Specimens from the adrenal cortex were processed for histological, immunohistochemical, enzyme assay, and quantitative real-time PCR (RT-qPCR) studies. Tramadol induced a significant increase in malondialdehyde level and a significant decrease in the levels of glutathione peroxidase and superoxide dismutase. A significant decrease in the levels of adrenocorticotrophic hormones, aldosterone, cortisol, corticosterone, and dehydroepiandrosterone sulfate was also detected. Severe histopathological changes in the adrenal cortex were demonstrated in the form of disturbed architecture, swollen cells, and shrunken cells with pyknotic nuclei. Inflammatory cellular infiltration and variable-sized homogenized areas were also detected. A significant increase in P53 and Bax immunoreaction was detected and confirmed by RT-qPCR. The ultrastructural examination showed irregular, shrunken adrenocorticocytes with dense nuclei. Dilated smooth endoplasmic reticulum, mitochondria with disrupted cristae, and numerous coalesced lipid droplets were also demonstrated. All these changes started to return to normal after the withdrawal of tramadol. Thus, it was confirmed that the long-term use of tramadol can induce severe adrenal changes with subsequent insufficiency.

Risk of Seizure after Naloxone Therapy in Acute Tramadol Poisoning: A Systematic Review with Meta-Analysis

Background

Many studies have focused on the relationship between naloxone and seizure in tramadol poisoning but the results are in conflict. We performed a meta-analysis study to see whether naloxone prevents or increase the risk of seizure in tramadol poisoning.

Methods

Bibliographic literature searches were conducted in the ISI Web of Science, Excerpta Medica Database (EMBASE), PubMed, and Cochrane from January 1990 to December 2017 for relevant articles. Pooled data were analyzed by calculating odds ratios (ORs) with 95% confidence intervals (CIs). The outcome includes seizure. To investigate the publication bias, Begg's and Egger's tests were used along with funnel plot as a graphical test.

Results

Seven studies met the inclusion criteria. The meta-analysis showed I ², 27%, (P value, 0.23) indicating no significant heterogeneity. As a result, using the fixed effect, the OR was 1.14 (95% CI = 0.60-2.18, P value, 0.69) which was not significant, means naloxone did not increase the risk of seizure.

Conclusions

Naloxone therapy did not increase the risk of seizure significantly in the treatment of acute tramadol poisoning. We suggest considering the risk/benefit when administration naloxone, especially for the seizure risk factors including previous history of seizure, tramadol misuse, and co-ingestion.

Trends of Opioid Utilisation in Denmark: A Nationwide Study

Background

Opioid use has more than doubled over recent decades, and Denmark occupies fifth place in the global ranking. These increases have been partly attributed to the ageing population.

Objective

Our objective was to assess the impact of age over time on utilisation of the most commonly used opioids in Denmark.

Methods

We retrieved nationwide sales data on opioid sales in Denmark from 1999 to 2017. We investigated utilisation trends in age groups for the four opioids with the highest use. We used three volume-based metrics (defined daily doses/1000/day, oral morphine equivalents/1000/day, and packages dispensed/year) and one person-based metric (users/1000/year).

Results

The four opioids selected according to users/1000/year were tramadol (46.1), codeine and combination products (12.4 for codeine, 3.7 for codeine and acetylsalicylic acid, and 4.2 for codeine and paracetamol), morphine (17.0), and oxycodone (12.1). Overall utilisation according to volume and person metrics increased for all except codeine and combination products. Tramadol doses or strength increased, albeit less with increasing age. Oxycodone doses or strength decreased for all age groups but were nearly unchanged for the age group ≥ 80 years.

Conclusion

Tramadol is the most utilised opioid in Denmark and was prescribed at increasing doses or strengths over the study period, particularly in the younger (< 80 years) age groups. Overall, oxycodone was prescribed at decreasing doses or strengths over time but remained unchanged for the age group ≥ 80 years. There is a need to address the pharmacological treatment of pain in terms of age, with tramadol and oxycodone being possible targets for regulatory efforts.

Electronic supplementary material

The online version of this article (10.1007/s40801-019-00163-w) contains supplementary material, which is available to authorized users.

An integrated safety analysis of combined acetaminophen and ibuprofen (Maxigesic /Combogesic®) in adults

INTRODUCTION

Acetaminophen (APAP) and ibuprofen (IBP) are two analgesic compounds with a long history of use. Both are considered safe at recommended over-the-counter daily doses. Chronic use, high doses, or concomitant medication can produce safety risks for both drugs. APAP is associated with increased risk of hepatic injury, while IBP can produce gastric bleeding and thromboembolic events. Using a combination of APAP and IBP provides superior analgesia without transgressing daily dose limits of each individual drug.

METHODS

The present study aimed to determine if treatment with a fixed-dose combination (FDC) containing APAP and IBP results in any unexpected adverse events (AEs) and/or changes in the safety profiles of its two ingredients compared to monotherapy. The analysis will examine clinical safety data obtained from either single dose trials, multiple dose trials, a long-term exposure trial, and post-marketing surveillance data of APAP/IBP FDC tablets (Maxigesic®/Combogesic®, AFT Pharmaceuticals Ltd). The largest dataset was obtained by pooling the four randomized-controlled, multiple-dose clinical studies with either APAP 325 mg + IBP 97.5 mg (FDC 325/97.5, three tablets per dose) or APAP 500 mg + IBP 150 mg (FDC 500/150, two tablets per dose). At maximum doses, the two FDCs are bioequivalent, permitting the pooling of data for the analysis of safety.

RESULTS

A safety population of 922 patients who received full doses of either FDC, APAP alone, IBP alone, or placebo was compiled from the four studies. A total of 521 AEs were experienced with the incidence of FDC AEs similar to or below either monotherapy group or placebo. The FDC did not alter the incidence and percentage of the most common AEs, including gastrointestinal events and postoperative bleeding.

CONCLUSION

Overall, the FDC is well tolerated and has a strong safety profile at single and multiple doses with improved efficacy over monotherapy.

Tramadol induces changes in Δ-FosB, µ-opioid receptor, and p-CREB level in the nucleus accumbens and prefrontal cortex of male Wistar rat

BACKGROUND

Besides the analgesic effect of tramadol, prolonged exposure to tramadol can induce adaptive changes thereby leading to dependence and tolerance. Tramadol induces its effect via µ-opioid receptor (MOR). However, tramadol has other targets such as serotonin and epinephrine transporters.

OBJECTIVE

CREB and ΔFosB are transcriptional factors, which are involved in the behavioral abnormalities underlying drug abuse. In this study, the effects of acute and chronic tramadol treatments on MOR, ΔFosB, and CREB levels were studied.

METHODS

For this purpose, 36 male Wistar rats were used. The animals were divided into two main groups. A total of 18 animals received tramadol (0, 5, and 10 mg/kg) acutely and 18 animals received the same doses for the following 14 days. One hour after the last injection, the NAC and PFC were dissected and kept at -80°C in liquid nitrogen. Using western blotting technique, the levels of MOR, ΔFosB, and p-CREB were evaluated.

RESULTS

In the NAC, acute tramadol exposure increases the levels of MOR and p-CREB. Moreover, chronic tramadol administration in this region results in elevated levels of MOR, ΔFosB and p-CREB compared with saline-treated rats. The levels of MOR and p-CREB in the PFC increased in both acute and chronic tramadol exposure. Also, ΔFosB levels increased only following chronic tramadol administration. The results revealed that adaptive changes occurred during drug exposure.

CONCLUSION

We concluded that both CREB and ΔFosB played a role in tramadol dependence. Additionally, increased MOR levels during tramadol treatments might be due to receptor desensitization.

A Systematic Review of Laboratory Evidence for the Abuse Potential of Tramadol in Humans

Background: Tramadol is an opioid-analgesic that has shown epidemiological evidence of abuse. This review evaluates the evidence for tramadol abuse potential in humans. Methods: A systematic literature search for human abuse liability examinations of tramadol was conducted in September 2018 and yielded 13 total studies. Studies were all within-subject, double-blind, placebo-controlled human laboratory comparisons of tramadol to opioid comparators. Results are organized based upon the route of tramadol administration (oral, parenteral) and the participant population (persons with and without current opioid physical dependence). Outcomes were categorized into self-report ratings of positive and negative effects, observer-ratings of effects, time course of effects, likelihood tramadol was identified as an opioid, and tramadol self-administration. Results: Results indicated the relative abuse potential of tramadol was lower than the opioids to which it was compared. Tramadol produced highest positive effect ratings when administered orally to persons with no opioid physical dependence. Relative to other opioids, it produced substantial negative ratings, generally demonstrated a slower onset of effects, and was less likely to be identified by participants as an opioid, though it did produce a higher rate of self-administration relative to other opioids in the one study reporting that outcome. Results suggest that the abuse potential of tramadol is highest when it is administered orally to non-dependent individuals, and that it likely decreases as the dose increased and when it was administered parentally or to persons with opioid physical dependence. Conclusion: Taken together, individuals may be less likely than with other opioids to escalate tramadol doses, transition from oral to parenteral routes of administration, or continue using tramadol once opioid physical dependence develops. In that way, the human abuse potential of tramadol appears to be different from and lower than other opioid analgesic medications.

Cross state-dependency of learning between tramadol and MK-801 in the mouse dorsal hippocampus: involvement of nitric oxide (NO) signaling pathway

RATIONALE

Tramadol, an atypical μ-opioid receptor agonist, as a psychoactive drug, is frequently abused by human beings. Understanding the neurobiological mechanisms of drug-associated learning and memory formation may help prevent drug addiction and relapse. Previous study revealed that dorsal hippocampus (CA1) plays a crucial role in the retrieval of tramadol-associated memory and that its role depends on the expression of CA1 N-methyl-D-aspartate (NMDA) receptors (Jafari-Sabet et al. Can J Physiol Pharmacol 96:45-50, 2018).

OBJECTIVE

To clarify the exact mechanisms involved, the activation of CA1 nitric oxide (NO) signaling pathway by L-arginine (a nitric oxide precursor) on the interaction between tramadol and MK-801 in memory retrieval was examined. The dorsal hippocampal CA1 regions of adult male NMRI mice were bilaterally cannulated and a single-trial step-down inhibitory avoidance apparatus was used for the assessment of memory retrieval.

RESULTS

Post-training and/or pre-test microinjection of tramadol (0.5 and 1 μg/mouse) and/or a non-competitive NMDA receptor antagonist, MK-801 (0.25 and 0.5 μg/mouse), induced amnesia which were reversed when the same doses of the drugs were administered 24 h later in a pre-test session, suggesting tramadol state-dependent learning (SDL) and MK-801 SDL. The amnesia induced by post-training microinjection of tramadol (1 μg/mouse) was reversed by pre-test microinjection of MK-801 (0.25 and 0.5 μg/mouse). Pre-test microinjection of MK-801 (0.125 and 0.25 μg/mouse) with an ineffective dose of tramadol (0.25 μg/mouse) potentiated tramadol SDL. The amnesia induced by post-training microinjection of MK-801 (0.5 μg/mouse) was reversed by pre-test microinjection of tramadol (0.5 and 1 μg/mouse). Pre-test microinjection of tramadol (0.25 and 0.5 μg/mouse) with an ineffective dose of MK-801 (0.125 μg/mouse) potentiated MK-801 SDL. Pre-test microinjection of ineffective doses of L-arginine (0.125, 025, and 0.5 μg/mouse) improved amnesia induced by the co-administration of tramadol and MK-801. Pre-test microinjection of L-arginine (0.125, 025, and 0.5 μg/mouse) could not reverse amnesia induced by post-training microinjection of tramadol while same doses of L-arginine improved MK-801 response on tramadol SDL.

CONCLUSION

The results strongly propose that activation of CA1 NO signaling pathway has a pivotal role in cross SDL among tramadol and MK-801.

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.

NMDA receptors in the dorsal hippocampal area are involved in tramadol state-dependent memory of passive avoidance learning in mice

The precise neurobiological mechanisms of tramadol abuse underlying the cognitive function are still unknown. The aim of the present study was to examine the possible effects of intra-CA1 injections of N-methyl-d-aspartate (NMDA), a glutamate NMDA receptor (NMDAR) agonist, and d,l-2-amino-5-phosphonopentanoic acid (DL-AP5), a competitive NMDAR antagonist, on tramadol state-dependent memory. A single-trial step-down passive avoidance task was used for the assessment of memory retrieval in adult male NMRI mice. Post-training i.p. administration of an atypical μ-opioid receptor agonist, tramadol (2.5 and 5 mg/kg), dose-dependently induced impairment of memory retention. Pre-test injection of tramadol (2.5 and 5 mg/kg) induced state-dependent retrieval of the memory acquired under post-training administration of tramadol (5 mg/kg) influence. Pre-test intra-CA1 injection of NMDA (10−5 and 10−4 μg/mouse) 5 min before the administration of tramadol (5 mg/kg, i.p.) dose-dependently inhibited tramadol state-dependent memory. Pre-test intra-CA1 injection of DL-AP5 (0.25 and 0.5 μg/mouse) reversed the memory impairment induced by post-training administration of tramadol (5 mg/kg). Pre-test administration of DL-AP5 (0.25 and 0.5 μg/mouse) with an ineffective dose of tramadol (1.25 mg/kg) restored the retrieval and induced tramadol state-dependent memory. It can be concluded that dorsal hippocampal NMDAR mechanisms play an important role in the modulation of tramadol state-dependent memory.

1-cyclohexyl-x-methoxybenzene derivatives, novel psychoactive substances seized on the internet market. Synthesis and in vivo pharmacological studies in mice

INTRODUCTION

Among novel psychoactive substances notified to EMCDDA and Europol were 1-cyclohexyl-x-methoxybenzene stereoisomers (ortho, meta, and para). These substances share some structural characteristics with phencyclidine and tramadol. Nowadays, no information on the pharmacological and toxicological effects evoked by 1-cyclohexyl-x-methoxybenzene are reported. The aim of this study was to investigate the effect evoked by each one stereoisomer on visual stimulation, body temperature, acute thermal pain, and motor activity in mice.

METHODS

Mice were evaluated in behavioral tests carried out in a consecutive manner according to the following time scheme: observation of visual placing response, measures of core body temperature, determination of acute thermal pain, and stimulated motor activity.

RESULTS

All three stereoisomers dose-dependent inhibit visual placing response (rank order: meta > ortho > para), induce hyperthermia at lower and hypothermia at higher doses (meta > ortho > para) and cause analgesia to thermal stimuli (para > meta = ortho), while they do not alter motor activity.

CONCLUSIONS

For the first time, this study demonstrates that systemic administration of 1-cyclohexyl-x-methoxybenzene compounds markedly inhibit visual response, promote analgesia, and induce core temperature alterations in mice. This data, although obtained in animal model, suggest their possible hazard for human health (i.e., hyperthermia and sensorimotor alterations). In particular, these novel psychoactive substances may have a negative impact in many daily activities, greatly increasing the risk factors for workplace accidents and traffic injuries.

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).

Tramadol-induced hyperalgesia and its prevention by ketamine in rats: A randomised experimental study

BACKGROUND

Opioid analgesia not only reduces inhalational anaesthetic requirements but may also induce delayed hyperalgesia, with potential effects on the minimum alveolar concentration (MAC) of inhalational anaesthetics.

OBJECTIVES

The objective of this study was to evaluate the development of tramadol-induced hyperalgesia and the associated changes in MAC, and whether ketamine prevents both processes.

DESIGN

A randomised, experimental study.

SETTING

Experimental Surgery Unit, La Paz University Hospital, Madrid, Spain.

ANIMALS

Thirty-nine adult male Wistar rats.

INTERVENTIONS

Mechanical nociceptive thresholds (MNT) were determined up to 21 days after the intraperitoneal administration of a single dose of tramadol (50 mg kg) with or without ketamine (10 mg kg), or 0.9% saline. The MNT and the MAC of sevoflurane were also assessed in a second experiment before, early (30 min) and 7 days after drug administration with the same treatments.

MAIN OUTCOME MEASURES

The MAC and MNT were evaluated. The analysis of variance (ANOVA) test was employed to determine differences between treatments and times on MAC and MNT.

RESULTS

Tramadol, alone or combined with ketamine, produced an early increase in MNT. However, tramadol given alone decreased MNT from day 1 up to 3 weeks, which was associated with an increase in the MAC of sevoflurane (P < 0.05; day 7). Ketamine administration prevented both the reduction in MNT and the increase in MAC (P > 0.05).

CONCLUSION

Tramadol-induced hyperalgesia in the rat lasted for several weeks and was associated with an increase in the MAC of sevoflurane. Prior administration of ketamine blocked both phenomena.

Nigella sativa oil alleviates ultrastructural alterations induced by tramadol in rat motor cerebral cortex

Tramadol is an opioid analgesic used to alleviate acute and chronic pain. Nigella sativa oil is one of the traditional remedies with antioxidant activity. This study was designed in order to investigate the ultrastructural alterations induced by tramadol in the rat cerebral cortex and to find out any possible protective effect of N. sativa oil against these alterations. Twenty-four male albino rats were assigned to three groups. Group I received intraperitoneal and oral normal saline for 30 days. Group II received intraperitoneal injections of tramadol 20 mg/kg/day, 40 mg/kg/day and 80 mg/kg/day on the first, second and third 10 days of the study, respectively. Group III received intraperitoneal tramadol similar to Group II and oral N. sativa oil at a dose of 4 ml/kg/day for 30 days. Specimens from the motor area were obtained and processed for transmission electron microscopy. In the tramadol-treated group, pyramidal and granular cells appeared shrunken and showed ultrastructural features of apoptosis such as nuclear membrane invaginations, chromatin margination, dilated rough endoplasmic reticulum, dilated Golgi saccules, and mitochondria with disintegrated cristae. The myelinated axons showed disorganization and splitting of the myelin sheath and contained vacuoles and abnormal mitochondria. Administration of N. sativa oil partially protected the cortical neurons and myelinated axons against tramadol-induced changes. In conclusion, N. sativa oil alleviates ultrastructural apoptotic changes induced by tramadol in the rat motor cerebral cortex.

Effects of glucosamine-chondroitin combination on synovial fluid IL-1β, IL-6, TNF-α and PGE2 levels in internal derangements of temporomandibular joint

BACKGROUND

The aim of the present study was to evaluate the effects of glucosamine-chondroitin sulphate combination on internal derangements of temporomandibular joint in clinical and biochemical manners.

MATERIAL AND METHODS

This randomized clinical study included 31 cases reporting joint tenderness, in which disc displacement was detected on MR imaging. In all patients, synovial fluid sampling was performed under local anesthesia. In the study group, the patients were prescribed a combination of 1500 mg glucosamine and 1200 mg chondroitin sulphate, while patients in the control group were only prescribed 50 mg tramadol HCl (twice daily) for pain control. After 8 weeks, synovial fluid sampling was repeated in the same manner. The levels of pain, maximum mouth opening (MMO), synovial fluid IL-1ß, IL-6, TNF-α and PGE2 measured before and after pharmacological intervention were compared.

RESULTS

The reduction in pain levels was significant in both groups. There was no significant difference between two groups in terms of pain reduction. The improvement in MMO was significant in the study group but it was not in the control group. The MMO improvement was significantly higher in the study group compared to the control group. In the study group, significant decrease was observed in PGE2 level, while the decreases in IL-1β, IL-6 and TNF-α levels were not significant. In the control group, no significant decrease was observed in any of the inflammatory cytokines after 8 weeks, moreover IL-1ß and IL-6 levels were increased. Alterations of IL-1ß and IL-6 levels were significant in study group while TNF-α and PGE2 levels were not, compared to control group.

CONCLUSIONS

In conclusion, these results might suggest that glucosamine-chondroitin combination significantly increases the MMO and decreases the synovial fluid IL1β and IL6 levels in internal derangements of TMJ compared to tramadol. The modifications of synovial fluid TNF-α and PGE2 levels do not reach statistical significance. This combination also provides efficient pain relief in similar level with tramadol, a narcotic analgesic.

Acute-withdrawal restless legs syndrome following abrupt cessation of short-term tramadol

We report a young man who had received tramadol for pain control and experienced an uncomfortable sensation in both legs immediately after tramadol withdrawal that worsened at rest and at night, and which could be relieved only by moving the legs. He suffered from insomnia and paced up and down in his house every night. Readministration of tramadol dramatically resolved his symptoms of restless legs syndrome (RLS), but they reappeared after tramadol withdrawal. Tramadol was therefore replaced with ropinirole, which was discontinued after several weeks, and there was no recurrence of his RLS symptoms. This patient appeared to have developed tramadol-withdrawal-induced RLS, and this case report emphasizes the importance of monitoring for withdrawal-type symptoms like RLS when tramadol intake is being stopped.

A case of tramadol dependence and successful treatment with buprenorphine/naloxone

Tramadol, a synthetic, centrally acting analgesic with weak mu-opioid agonist activity, is often prescribed as an alternative to opioids due to its negligible abuse potential. Although the potential for the abuse of tramadol appeared low when the medication first became available, findings have demonstrated increased rates of abuse with extended time on the market. This case report details the addiction to tramadol of a 39-year-old female serving in the United States Army. At the height of her addiction, she was consuming an average of 1400mg tramadol daily. Eventually the patient entered into residential inpatient treatment for 28 days at our facility. During this time she was successfully titrated to buprenorphine 8mg/naloxone 2mg daily while maintaining abstinence. Patient care transitioned to the outpatient treatment center during which she maintained sobriety with the continued use of buprenorphine/naloxone. This case adds to previous reports of the increasing abuse of tramadol and the need for quality evidence on successful treatments for this escalating concern.

Efficacy of extended-release tramadol for treatment of prescription opioid withdrawal: a two-phase randomized controlled trial

BACKGROUND

Tramadol is an atypical analgesic with monoamine and modest mu opioid agonist activity. The purpose of this study was to evaluate: (1) the efficacy of extended-release (ER) tramadol in treating prescription opioid withdrawal and (2) whether cessation of ER tramadol produces opioid withdrawal.

METHODS

Prescription opioid users with current opioid dependence and observed withdrawal participated in this inpatient, two-phase double blind, randomized placebo-controlled trial. In Phase 1 (days 1-7), participants were randomly assigned to matched oral placebo or ER tramadol (200 or 600 mg daily). In Phase 2 (days 8-13), all participants underwent double blind crossover to placebo. Breakthrough withdrawal medications were available for all subjects. Enrollment continued until 12 completers/group was achieved.

RESULTS

Use of breakthrough withdrawal medication differed significantly (p<0.05) among groups in both phases; the 200mg group received the least amount in Phase 1, and the 600 mg group received the most in both phases. In Phase 1, tramadol 200mg produced significantly lower peak ratings than placebo on ratings of insomnia, lacrimation, muscular tension, and sneezing. Only tramadol 600 mg produced miosis in Phase 1. In Phase 2, tramadol 600 mg produced higher peak ratings of rhinorrhea, irritable, depressed, heavy/sluggish, and hot/cold flashes than placebo. There were no serious adverse events and no signal of abuse liability for tramadol.

CONCLUSIONS

ER tramadol 200mg modestly attenuated opioid withdrawal. Mild opioid withdrawal occurred after cessation of treatment with 600 mg tramadol. These data support the continued investigation of tramadol as a treatment for opioid withdrawal.

Abuse liability and reinforcing efficacy of oral tramadol in humans

BACKGROUND

Tramadol, a monoaminergic reuptake inhibitor, is hepatically metabolized to an opioid agonist (M1). This atypical analgesic is generally considered to have limited abuse liability. Recent reports of its abuse have increased in the U.S., leading to more stringent regulation in some states, but not nationally. The purpose of this study was to examine the relative abuse liability and reinforcing efficacy of tramadol in comparison to a high (oxycodone) and low efficacy (codeine) opioid agonist.

METHODS

Nine healthy, non-dependent prescription opioid abusers (6 male and 3 female) participated in this within-subject, randomized, double blind, placebo-controlled study. Participants completed 14 paired sessions (7 sample and 7 self-administration). During each sample session, an oral dose of tramadol (200 and 400 mg), oxycodone (20 and 40 mg), codeine (100 and 200 mg) or placebo was administered, and a full array of abuse liability measures was collected. During self-administration sessions, volunteers were given the opportunity to work (via progressive ratio) for the sample dose or money.

RESULTS

All active doses were self-administered; placebo engendered no responding. The high doses of tramadol and oxycodone were readily self-administered (70%, 59% of available drug, respectively); lower doses and both codeine doses maintained intermediate levels of drug taking. All three drugs dose-dependently increased measures indicative of abuse liability, relative to placebo; however, the magnitude and time course of these and other pharmacodynamic effects varied qualitatively across drugs.

CONCLUSIONS

This study demonstrates that, like other mu opioids, higher doses of tramadol function as reinforcers in opioid abusers, providing new empirical data for regulatory evaluation.

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).

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.

Duloxetine in the management of chronic musculoskeletal pain

Chronic musculoskeletal pain is among the most frequent painful complaints that healthcare providers address. The bulk of these complaints are chronic low back pain and chronic osteoarthritis. Osteoarthritis is the most common form of arthritis in the United States. It is a chronic degenerative disorder characterized by a loss of cartilage, and occurs most often in older persons. The management of osteoarthritis and chronic low back pain may involve both nonpharmacologic (eg, weight loss, resistive and aerobic exercise, patient education, cognitive behavioral therapy) and pharmacologic approaches. Older adults with severe osteoarthritis pain are more likely to take analgesics than those with less severe pain. The pharmacologic approaches to painful osteoarthritis remain controversial, but may include topical as well as oral nonsteroidal antiinflammatory drugs, acetaminophen, duloxetine, and opioids. The role of duloxetine for musculoskeletal conditions is still evolving.

Genetically polymorphic OCT1: another piece in the puzzle of the variable pharmacokinetics and pharmacodynamics of the opioidergic drug tramadol

We investigated whether tramadol or its active metabolite, O-desmethyltramadol, are substrates of the organic cation transporter OCT1 and whether polymorphisms in OCT1 affect tramadol and O-desmethyltramadol pharmacokinetics. Tramadol showed high permeability through parallel artificial membrane permeability assays (PAMPAs). Tramadol uptake in HEK293 cells did not change after OCT1 overexpression, and the concentrations of tramadol in the plasma of healthy volunteers were independent of their OCT1 genotypes. In contrast, O-desmethyltramadol showed low membrane permeability, and OCT1 overexpression increased O-desmethyltramadol uptake 2.4-fold. This increase in uptake was reversed by OCT1 inhibitors and absent when loss-of-function OCT1 variants were overexpressed. Volunteers carrying loss-of-function OCT1 polymorphisms had significantly higher plasma concentrations of O-desmethyltramadol (P = 0.002, n = 41) and significantly prolonged miosis, a surrogate marker of opioidergic effects (P = 0.005, n = 24). In conclusion, polymorphisms in OCT1 influence the pharmacokinetics of O-desmethyltramadol, presumably by affecting its uptake into liver cells, and thus may modulate the efficacy of tramadol treatment.

Discriminative stimulus effects of tramadol in humans

Tramadol is an unscheduled atypical analgesic that acts as an agonist at μ-opioid receptors and inhibits monoamine reuptake. Tramadol can suppress opioid withdrawal, and chronic administration can produce opioid physical dependence; however, diversion and abuse of tramadol is low. The present study further characterized tramadol in a three-choice discrimination procedure. Nondependent volunteers with active stimulant and opioid use (n = 8) participated in this residential laboratory study. Subjects were trained to discriminate between placebo, hydromorphone (8 mg), and methylphenidate (60 mg), and tests of acquisition confirmed that all volunteers could discriminate between the training drugs. The following drug conditions were then tested during discrimination test sessions: placebo, hydromorphone (4 and 8 mg), methylphenidate (30 and 60 mg), and tramadol (50, 100, 200, and 400 mg). In addition to discrimination measures, which included discrete choice, point distribution, and operant responding, subjective and physiological effects were measured for each test condition. Both doses of hydromorphone and methylphenidate were identified as hydromorphone- and methylphenidate-like, respectively. Lower doses of tramadol were generally identified as placebo, with higher doses (200 and 400 mg) identified as hydromorphone, or opioid-like. The highest dose of tramadol increased ratings on the stimulant scale, but was not significantly identified as methylphenidate-like. Tramadol did not significantly increase subjective ratings associated with reinforcement. Taken together, these results extend previous work with tramadol as a potential medication for the treatment of opioid dependence and withdrawal, showing acute doses of tramadol exhibit a profile of effects similar to opioid agonists and may have abuse liability in certain populations.

Advances in perioperative pain management: use of medications with dual analgesic mechanisms, tramadol & tapentadol

Recovery from ambulatory surgical procedures can be limited by postoperative pain. Inadequate analgesia may delay or prevent patient discharge and can result in readmission. More frequently, postoperative pain produces discomfort and interrupts sleep, contributing to postoperative fatigue. The development of effective analgesic regimens for the management of postoperative pain is a priority especially in patients with impaired cardiorespiratory, hepatic, or renal function. Tramadol and tapentadol hydrochloride are novel in that their analgesic actions occur at multiple sites. Both agents are reported to be mu-opioid receptor agonists and monoamine-reuptake inhibitors. In contrast to pure opioid agonists, both drugs are believed to have lower risks of respiratory depression, tolerance, and dependence. The Food and Drug Administration has approved both drugs for the treatment of moderate-to-severe acute pain in adults. This article provides an evidence-based account of the role of tramadol and tapentadol in modern clinical practice.