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

A consideration of CYP2D6 genetic variations in the Ghanaian population as a potential 'culprit' for the tramadol 'abuse crisis'

BACKGROUND

Cytochrome P450 2D6 is involved in the metabolism of several important medicines including opioids. Variations in CYP2D6 have been implicated in drug response and according to the Clinical Pharmacogenetics Implementation Consortium Guideline (CPIC) for CYP2D6, dosing for CYP2D6 substrates should be based on variants carried by individuals. Although CYP2D6 variations in Ghana had been previously recorded, not all variants have been reported in the Ghanaian population. In this exploratory study we set to investigate certain unreported variations in the Ghanaian population in addition to the previously reported ones and use that to understand the tramadol 'abuse' crisis that is currently being experienced in Ghana.

METHODS

This study employed a convenience sampling approach to include 106 unrelated participants who were recruited as part of the PHARMABIOME project. We successfully genotyped 106 samples using Iplex GOLD SNP genotyping protocol after extracting DNA from these individuals. Allele and diplotype frequencies were undertaken by counting from observed genotypes. Comparison of alleles reported from various studies were done.

RESULTS

Unreported alleles such as *3, *9 and *41 which are classified as no function and decreased function were observed in our study cohort. In addition, variants such as (*1, *2, *4, *5, *10, *17 and *29 were observed with different frequencies. Our study showed 26% representation of intermediate metabolizers (IM) and 2% poor metabolizers (PM) in the study population.

CONCLUSION

The implications for informal sector workers who use tramadol for recreational purposes, is that IMs and PMs will overdose as they may have reduced analgesic effects which will translate into increased risks of unforeseen adverse events. We therefore propose that CYP2D6 should be considered in opioid dosage while making use of these observed variations to implement new approaches to tackle the tramadol 'abuse crisis' in Ghana.

The toxic profile of tramadol combined with nicotine on the liver and testicles: evidence from endoplasmic reticulum stress

BACKGROUND

Tramadol is one of the most commonly abused substances in the Middle East. Furthermore, smoking is extremely common among the population.

METHODS

An experimental study was performed on Sprague-Dawley rats to explore the effects of both nicotine and tramadol on the liver and testes. The tramadol was administered at 10 and 20 mg/kg, respectively, while the nicotine was administered at 125 mg/kg. Histological examination and androgen receptor ELISA assay showed mild effects on the liver and proofed safety on the testis. Western blot analysis of BIP (immunoglobulin heavy-chain binding protein) and CHOP (CCAAT-enhancer-binding protein homologous protein) revealed that fewer problems were induced by adding nicotine to tramadol. Autophagy marker LCIII and apoptosis marker caspase-8 showed similar effects to CHOP and BIP on liver samples. The real-time PCR of BIP expression showed similar but not identical results.

CONCLUSIONS

The results showed mild endoplasmic reticulum stress, autophagy, and apoptosis in the liver samples. Histological examination revealed stable spermatogenesis with average androgen receptor blood levels in the different groups.

Massive tramadol ingestion resulting in fatal brain injury - a pharmacokinetic study with discussion on the involved mechanisms of toxicity

BACKGROUND

Tramadol-attributed toxicity may involve opioid-like, serotoninergic, and noradrenergic mechanisms. We investigated the mechanisms of toxicity in a massive tramadol ingestion case by examining serial clinical, imaging, electroencephalography, pharmacokinetics, and genotyping data.

CASE REPORT

A 32-year-old female who presumably ingested 9000 mg sustained-release tramadol was found comatose without hypoglycemia, bradypnea, hypotension, marked hypoxemia or seizures. She developed eyelid myoclonus and non-reactive mydriasis. Electroencephalogram showed non-reactive encephalopathy. MRI showed extensive brain injury. Despite supportive care and ventricular derivation, brain death occurred on day 12.

METHODS

Plasma concentrations of tramadol and metabolites were measured using a liquid chromatography-tandem mass spectrometry assay. Genotyping for the presence of metabolizing cytochrome P450 (CYP) gene polymorphisms was performed.

RESULTS

Plasma concentrations of tramadol and metabolites were extremely high (∼70-fold the therapeutic concentrations) and slowly decreased during the first ∼146 h post-admission, possibly due to prolonged gastrointestinal absorption. Elimination half-lives were 2-3-fold longer than usual values. The patient was an intermediate CYP2D6 metabolizer with decreased CYP3A4 and CYP2B6 activities. Clinical and electroencephalographic data did not support the hypotheses of opioid or serotoninergic toxicity nor prolonged/repeated seizures. Based on serial imaging showing progressive extension of ischemic edema in the context of prolonged high plasma concentrations, we hypothesized a cerebral vasospasm as mechanism of injury.

CONCLUSION

Massive tramadol ingestion with prolonged high plasma concentrations can result in severe brain injury, possibly involving vasospasm.

Glycosides for Peripheral Neuropathic Pain: A Potential Medicinal Components

Neuropathic pain is a refractory disease that occurs across the world and pharmacotherapy has limited efficacy and/or safety. This disease imposes a significant burden on both the somatic and mental health of patients; indeed, some patients have referred to neuropathic pain as being ‘worse than death’. The pharmacological agents that are used to treat neuropathic pain at present can produce mild effects in certain patients, and induce many adverse reactions, such as sedation, dizziness, vomiting, and peripheral oedema. Therefore, there is an urgent need to discover novel drugs that are safer and more effective. Natural compounds from medical plants have become potential sources of analgesics, and evidence has shown that glycosides alleviated neuropathic pain via regulating oxidative stress, transcriptional regulation, ion channels, membrane receptors and so on. In this review, we summarize the epidemiology of neuropathic pain and the existing therapeutic drugs used for disease prevention and treatment. We also demonstrate how glycosides exhibit an antinociceptive effect on neuropathic pain in laboratory research and describe the antinociceptive mechanisms involved to facilitate the discovery of new drugs to improve the quality of life of patients experiencing neuropathic pain.

Comparative Multimodal Palliative efficacy of gabapentin and tramadol By Using Two Pain Scoring Systems in Cats Undergoing Ovariohysterectomy

The analgesic efficacy of the gabapentin-tramadol combination was compared with meloxicam-tramadol and tramadol perioperative analgesic regimens in cats brought to the clinic for ovariohysterectomy. Thirty adult cats belonging to comparable demographics (age, body weight), were enrolled into a randomized, blinded study after due consent from their owners into four treatment groups. A Gabapentin-Tramadol group (GT-group, n = 10), Meloxicam-Tramadol group (MT-group, n = 10), and a Tramadol group (T-group, n = 10) were formed. Gabapentin capsules at 50 mg were administered orally 2 hours before surgery while the rest received a placebo dose. Tramadol (2 mg/kg, IM) and meloxicam at (0.2 mg/kg, SC) were injected immediately prior to anesthetic premedication. Anesthetic protocol involved premedication with ketamine and xylazine, while anesthesia was induced using propofol. Inhalant isoflurane anesthesia was used to maintain a surgical plane. GT group scored lower on IVAS as well as CPS than MT group, and T group for up to 8 hours after surgery. The mechanical nociceptive threshold remained higher (98±0) for up to 12 hours postoperatively a nd serum cortisol concentrations remained significantly lower during the 24hr period. The addition of gabapentin to the tramadol regimen significantly improved analgesia and mechanical nociceptive threshold than when used on its own.

Evaluation of mitochondrial dysfunction due to oxidative stress in therapeutic, toxic and lethal concentrations of tramadol

Tramadol (TR) is a centrally acting analgesic drug that is used to relieve pain. The therapeutic (0.1-0.8 mg/l), toxic (1-2 mg/l) and lethal (>2 mg/l) ranges were reported for TR. The present study was designed to evaluate which doses of TR can induce liver mitochondrial toxicity. Mitochondria were isolated from the five rats' liver and were incubated with therapeutic to lethal concentrations (1.7-600 μM) of TR. Biomarkers of oxidative stress including: reactive oxygen species (ROS), lipid peroxidation (LPO), protein carbonyl content, glutathione (GSH) content, mitochondrial function, mitochondrial membrane potential (MMP) and mitochondrial swelling were assessed. Our results showed that ROS and LPO at 100 μM and protein carbonylation at 600 μM concentrations of TR were significantly increased. GSH was decreased specifically at 600 μM concentration. Mitochondrial function, MMP and mitochondrial swelling decreased in isolated rat liver mitochondria after exposure to 100 and 300 μM, respectively. This study suggested that TR at therapeutic and toxic levels by single exposure could not induce mitochondrial toxicity. But, in lethal concentration (≥100 μM), TR induced oxidative damage and mitochondria dysfunction. This study suggested that ROS overproduction by increasing of TR concentration induced mitochondrial dysfunction and caused mitochondrial damage via Complex II and membrane permeability transition pores disorders, MMP collapse and mitochondria swelling.

Effects of naloxone and diazepam on blood glucose levels in tramadol overdose using generalized estimating equation (GEE) model; (an experimental study)

BACKGROUND

Tramadol is a synthetic opioid and poisoning is increasing around the world day by day. Various treatments are applied for tramadol poisoning. Due to the unknown effects of tramadol poisoning and some of its treatments on blood glucose levels, this study was conducted to investigate the overdose of tramadol and its common treatments (naloxone, diazepam), and their combination on blood glucose levels in male rats.

METHODS

This study was conducted in 45 male Wistar rats. The animals were randomly divided into five groups of 9. They received a 75 mg/kg dose of tramadol alone with naloxone, diazepam, and a combination of both of these two drugs. On the last day, animals' tail vein blood glucose levels (BGL) were measured using a glucometer at different times, including before the tramadol injection (baseline) and 1 hour, 3 hours, and 6 hours after wards. The rats were anesthetized and sacrificed 24 h after the last injection. Blood samples were then taken, and the serum obtained was used to verify the fasting glucose concentration. Data were analyzed using SPSS software at a significance level of 0.05 using a one-way analysis of variance (ANOVA) and a generalized estimating equation (GEE).

RESULTS

According to the GEE model results, the diazepam-tramadol and naloxone-diazepam-tramadol groups showed blood glucose levels five units higher than the tramadol group (p < 0.05). The diazepam-tramadol group had significantly higher blood glucose levels than the naloxone-tramadol group (p < 0.05). The mean blood glucose levels before the intervention, 3 hours and 6 hours after the injection of tramadol did not differ between the groups, but the blood glucose levels 1 hour after the injection of tramadol in the group of naloxone-tramadol were significantly lower than in the control group (p < 0.05). Blood glucose levels did not differ between the groups 24 h after injection of tramadol.

CONCLUSION

The results of the present study showed tramadol overdose does not affect blood glucose levels. The diazepam-tramadol combination and the diazepam-naloxone-tramadol combination caused an increase in blood glucose levels.

Marked and prolonged serotonin toxicity in a tramadol-poisoned patient with a pharmacokinetic study

BACKGROUND

Tramadol poisoning rarely causes serotonin toxicity, which mechanisms remain poorly understood. We investigated alterations in tramadol pharmacokinetics in a tramadol-poisoned patient who presented with marked and prolonged serotonin toxicity.

CASE REPORT

A 21-year-old male self-ingested 750 mg-tramadol, 200 mg-sotalol, 400 mg-propranolol and 6 mg-lorazepam. He was a kidney transplant patient treated with mycophenolate, tacrolimus, prednisone, and paroxetine. He developed transitory cardiovascular failure and prolonged serotonin toxicity requiring sedation, muscle paralysis, and cyproheptadine, with a favorable outcome.

METHODS

We measured plasma concentrations of tramadol, M1, M2, and M5 using liquid-chromatography-tandem mass spectrometry, calculated elimination half-lives and metabolic ratios of the compounds, and genotyped cytochromes involved in tramadol metabolism.

RESULTS

Elimination half-lives of tramadol (6.1 h) and M1 (7.1 h) were normal while those of M2 (26.5 h) and M5 (16.7 h) prolonged. M1 metabolic ratio (0.12) was 2-fold reduced, M2 metabolic ratio (197) 1000-fold increased and M5 metabolic ratio (0.12) normal. This metabolic profile in a patient with normal CYP2D6-metabolizer status based on genotyping supports CYP2D6 inhibition by paroxetine and propranolol, two strong mechanism-based inhibitors. Only M2 present in sufficient concentrations up to 48 h could explain the prolonged serotonin toxicity.

CONCLUSION

Marked and prolonged serotonin toxicity was attributed to increased M2 production due to paroxetine- and propranolol-related CYP2D6 inhibition of tramadol metabolism.

A review on tramadol toxicity: mechanism of action, clinical presentation, and treatment

Aims

As an analgesic that acts upon the central nervous system (CNS), tramadol has gained popularity in treating moderate to severe pain. Recently, it has been increasingly reported as a drug of misuse with intentional overdoses or intoxications. This review focuses on tramadol intoxication in humans and its effects on different systems.

Subject and method

This narrative review provides a comprehensive view of the pharmacokinetics, mechanism of action, and incidence of tramadol toxicity with an in-depth look at its side effects. In addition, the main approaches to the management of tramadol poisoning are described.

Results

Tramadol poisoning can affect multiple organ systems: gastrointestinal, central nervous system (seizure, CNS depression, low-grade coma, anxiety, and over time anoxic brain damage), cardiovascular system (palpitation, mild hypertension to life-threatening complications such as cardiopulmonary arrest), respiratory system, renal system (renal failure with higher doses of tramadol intoxication), musculoskeletal system (rhabdomyolysis), endocrine system (hypoglycemia), as well as, cause serotonin syndrome. Seizure, a serious nervous disturbance, is more common in tramadol intoxication than with other opioids. Fatal tramadol intoxications are uncommon, except in ingestion cases concurrent with other medications, particularly CNS depressants, most commonly benzodiazepines, and ethanol.

Conclusion

With the increasing popularity of tramadol, physicians must be aware of its adverse effects, substantial abuse potential, and drug interactions, to weigh its risk–benefit ratio for pain management. Alternative therapies might be considered in patients with a previous overdose history to reduce risks for adverse outcomes.

Zebrafish early life stages as alternative model to study 'designer drugs': Concordance with mammals in response to opioids

The number of new psychoactive substances (NPS) on the illicit drug market increases fast, posing a need to urgently understand their toxicity and behavioural effects. However, with currently available rodent models, NPS assessment is limited to a few substances per year. Therefore, zebrafish (Danio rerio) embryos and larvae have been suggested as an alternative model that would require less time and resources to perform an initial assessment and could help to prioritize substances for subsequent evaluation in rodents. To validate this model, more information on the concordance of zebrafish larvae and mammalian responses to specific classes of NPS is needed. Here, we studied toxicity and behavioural effects of opioids in zebrafish early life stages. Synthetic opioids are a class of NPS that are often used in pain medication but also frequently abused, having caused multiple intoxications and fatalities recently. Our data shows that fentanyl derivatives were the most toxic among the tested opioids, with toxicity in the zebrafish embryo toxicity test decreasing in the following order: butyrfentanyl>3-methylfentanyl>fentanyl>tramadol> O-desmethyltramadol>morphine. Similar to rodents, tramadol as well as fentanyl and its derivatives led to hypoactive behaviour in zebrafish larvae, with 3-methylfentanyl being the most potent. Physico-chemical properties-based predictions of chemicals' uptake into zebrafish embryos and larvae correlated well with the effects observed. Further, the biotransformation pattern of butyrfentanyl in zebrafish larvae was reminiscent of that in humans. Comparison of toxicity and behavioural responses to opioids in zebrafish and rodents supports zebrafish as a suitable alternative model for rapidly testing synthetic opioids.

Physiologically based pharmacokinetic modeling of tramadol to inform dose adjustment and drug-drug interactions according to CYP2D6 phenotypes

OBJECTIVES

The objective of this study was to establish physiologically based pharmacokinetic (PBPK) models of tramadol and its active metabolite O-desmethyltramadol (M1) and to explore the influence of CYP2D6 gene polymorphism on the pharmacokinetics of tramadol and M1. Furthermore, we used PBPK modeling to prospectively predict the extent of drug-drug interactions (DDIs) in the presence of genetic polymorphisms when tramadol was co-administered with the CYP2D6 inhibitors duloxetine and paroxetine.

METHODS

Plasma concentrations of tramadol and M1 were used to adjust the turnover frequency (K_cat ) of CYP2D6 for phenotype populations with different CYP2D6 genotypes. PBPK models were developed to capture the pharmacokinetics between CYP2D6 extensive metabolizers (EMs), intermediate metabolizers (IMs), poor metabolizers (PMs), and ultra-rapid metabolizers (UMs). The validated models were then used to support dose adjustment in different CYP2D6 phenotypes and to predict the extent of CYP2D6-mediated DDIs when tramadol was co-administered with paroxetine or duloxetine.

RESULTS

The PBPK models we built accurately describe tramadol and M1 exposure in the population with different CYP2D6 phenotypes. In our prediction, the area under the concentration-time curve (AUC_inf-tDlast ) of M1 is 70% lower in PMs than in EMs, 27% lower in IMs, and 15% higher in UMs. Based on the models we built, we suggest that the oral dose of tramadol should be 50% higher for IMs and 25% lower for UMs to achieve an approximately equivalent plasma exposure of M1 as in EMs. When tramadol was co-administered with paroxetine or duloxetine, the magnitude of the inhibitor-substrate interaction was lowest in EMs (0.45), secondary in IMs (0.39), and highest in PMs (0.18) in terms of M1.

CONCLUSION

The current example uses the PBPK model to guide dose adjustment of tramadol and to predict the effect of CYP2D6 genetic polymorphisms on DDIs for rational clinical use of tramadol in the future.

Repeated Administration of Clinically Relevant Doses of the Prescription Opioids Tramadol and Tapentadol Causes Lung, Cardiac, and Brain Toxicity in Wistar Rats

Tramadol and tapentadol, two structurally related synthetic opioid analgesics, are widely prescribed due to the enhanced therapeutic profiles resulting from the synergistic combination between μ-opioid receptor (MOR) activation and monoamine reuptake inhibition. However, the number of adverse reactions has been growing along with their increasing use and misuse. The potential toxicological mechanisms for these drugs are not completely understood, especially for tapentadol, owing to its shorter market history. Therefore, in the present study, we aimed to comparatively assess the putative lung, cardiac, and brain cortex toxicological damage elicited by the repeated exposure to therapeutic doses of both prescription opioids. To this purpose, male Wistar rats were intraperitoneally injected with single daily doses of 10, 25, and 50 mg/kg tramadol or tapentadol, corresponding to a standard analgesic dose, an intermediate dose, and the maximum recommended daily dose, respectively, for 14 consecutive days. Such treatment was found to lead mainly to lipid peroxidation and inflammation in lung and brain cortex tissues, as shown through augmented thiobarbituric acid reactive substances (TBARS), as well as to increased serum inflammation biomarkers, such as C reactive protein (CRP) and tumor necrosis factor-α (TNF-α). Cardiomyocyte integrity was also shown to be affected, since both opioids incremented serum lactate dehydrogenase (LDH) and α-hydroxybutyrate dehydrogenase (α-HBDH) activities, while tapentadol was associated with increased serum creatine kinase muscle brain (CK-MB) isoform activity. In turn, the analysis of metabolic parameters in brain cortex tissue revealed increased lactate concentration upon exposure to both drugs, as well as augmented LDH and creatine kinase (CK) activities following tapentadol treatment. In addition, pneumo- and cardiotoxicity biomarkers were quantified at the gene level, while neurotoxicity biomarkers were quantified both at the gene and protein levels; changes in their expression correlate with the oxidative stress, inflammatory, metabolic, and histopathological changes that were detected. Hematoxylin and eosin (H & E) staining revealed several histopathological alterations, including alveolar collapse and destruction in lung sections, inflammatory infiltrates, altered cardiomyocytes and loss of striation in heart sections, degenerated neurons, and accumulation of glial and microglial cells in brain cortex sections. In turn, Masson's trichrome staining confirmed fibrous tissue deposition in cardiac tissue. Taken as a whole, these results show that the repeated administration of both prescription opioids extends the dose range for which toxicological injury is observed to lower therapeutic doses. They also reinforce previous assumptions that tramadol and tapentadol are not devoid of toxicological risk even at clinical doses.