Metabolism of the analgesic drug ULTRAM (tramadol hydrochloride) in humans: API-MS and MS/MS characterization of metabolites

Influence of cytochrome P450 2D6*10/*10 genotype on the risk for tramadol associated adverse effects: a retrospective cohort study

Background: Tramadol is primarily metabolized by the highly polymorphic CYP2D6 enzyme, leading to a large spectrum of adverse events and clinical response. Ample evidence pointed a reduced CYPD26 activity score in individuals harboring the CYP2D6*10/*10 genotype, nevertheless, there is scarce studies on the impact of CYP2D6*10/*10 genetic polymorphism on long-term tramadol's adverse effects. Aim: To test the correlation between CYP2D6*10/*10 expression and the risk for tramadol-associated adverse effects. Method: Using a database of Leumit Healthcare Services in Israel, we retrospectively assessed the occurrence of adverse events in patients who were prescribed tramadol. A binary logistic regression model was applied to model the relationship between CYP2D6*10/*10 genotype and the occurrence of adverse effects. Results: Data from four hundred ninety-three patients were included in this study. Only 25 (5.1%) patients were heterozygous for the CYP2D6*10 variant, while 56 patients (11%) were tested positive to the CYP2D6*10/*10 genotype. Compared to carriers of other variants, patients with the CYP2D6*10/*10 variant exhibited a higher occurrence of adverse events (odds ratio [OR] = 6.14, 95% confidence interval 3.18-11.83); the odds ratio for central nervous system adverse events and gastrointestinal adverse events were 5.13 (95% CI 2.84-9.28), and 3.25 (95% CI 1.78-5.93), respectively. Conclusion: Among the different CYP2D6 genotypes, CYP2D6*10/*10 genotype carries the higher risk of tramadol related adverse events. Appreciating the frequency of this specific allele it seems prudent to pharmacogenetically screen patients considered for long term tramadol treatment for better tolerability and efficacy outcomes.

Effect of apatinib on the pharmacokinetics of tramadol and O-desmethyltramadol in rats

Since the combination of anticancer drugs and opioids is very common, apatinib and tramadol are likely to be used in combination clinically. This study evaluated the effects of apatinib on the pharmacokinetics of tramadol and its main metabolite O-desmethyltramadol in Sprague-Dawley (SD) rats and the inhibitory effects of apatinib on tramadol in rat liver microsomes (RLMs), human liver microsomes (HLMs) and recombinant human CYP2D6.1. The samples were determined by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The in vivo results showed that compared with the control group, apatinib increased the AUC(0-t), AUC(0-∞) and Cmax values of tramadol and O-desmethyltramadol, and decreased the values of VZ/F and CLz/F. In addition, the MRT(0-t), MRT(0-∞) values of O-desmethyltramadol were increased. In vitro, apatinib inhibited the metabolism of tramadol by a mixed way with IC50 of 1.927 µM in RLMs, 2.039 µM in HLMs and 15.32 µM in CYP2D6.1. In summary, according to our findings, apatinib has a strong in vitro inhibitory effect on tramadol, and apatinib can increase the analgesic effect of tramadol and O-desmethyltramadol in rats.

Tramadol for chronic pain in adults: protocol for a systematic review with meta-analysis and trial sequential analysis of randomised clinical trials

BACKGROUND

Chronic pain in adults is a frequent clinical symptom with a significant impact on patient well-being. Therefore, sufficient pain management is of utmost importance. While tramadol is a commonly used pain medication, the quality of evidence supporting its use has been questioned considering the observed adverse events. Our objective will be to assess the benefits and harms of tramadol compared with placebo or no intervention for chronic pain.

METHODS/DESIGN

We will conduct a systematic review of randomised clinical trials with meta-analysis and trial sequential analysis to assess the beneficial and harmful effects of tramadol in any dose, formulation, or duration. We will accept placebo or no intervention as control interventions. We will include adult participants with any type of chronic pain, including cancer-related pain. We will systematically search the Cochrane Library, MEDLINE, EMBASE, Science Citation Index, and BIOSIS for relevant literature. We will follow the recommendations by Cochrane and the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) statement. The risk of systematic errors ('bias') and random errors ('play of chance') will be assessed. The certainty of evidence will be evaluated using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach.

DISCUSSION

Although tramadol is often being used to manage chronic pain conditions, the beneficial and harmful effects of this intervention are unknown. The present review will systematically assess the current evidence on the benefits and harms of tramadol versus placebo or no intervention to inform clinical practice and future research.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42019140334.

Persistence of N-oxides transformation products of tertiary amine drugs at lab and field studies

This work aimed at studying the formation and persistence of N-oxides transformation products (TPs) of tertiary amine drugs by combining laboratory and field studies relevant for surface water. A monitoring study using passive samplers was first achieved for assessing attenuation of selected pharmaceuticals and their related N-oxides and N-, O-dealkylated TPs (i.e., venlafaxine, tramadol, amisulpride and sulpiride) along a 1.7 km river stretch between two sampling sites. This study revealed the stability of tramadol-N-oxide, amisulpride-N-oxide and the fast dissipation of O-desmethylvenlafaxine-N-oxide, as well as the significance of N-oxidized TPs in comparison to N-dealkylated TPs and parent compounds in river. Lab-scale experiments were then implemented for a better understanding of their mechanisms of formation and degradation under aerobic water/sediment testing and under simulated solar photochemistry. N-oxidation reactions were always a minor transformation pathway under both degradation conditions with respect to N-and O-dealkylation reactions. The amount of generated N-oxides were similar for venlafaxine, tramadol and sulpiride and peaked in the 8.4-12.8% and <4% of their initial concentration (100 μg/L), during photodegradation and biodegradation experiments, respectively. Other transformation pathways such as hydroxylation and α-C-hydroxylation followed by oxidation to amide or dehydration were also identified. Investigated N-oxides TPs (except O-desmethylvenlafaxine-N-oxide) were found stable under solar photolysis and aerobic biodegradation with a very slight reverse reaction to parent compound observed for tramadol-N-oxide and amisulpride-N-oxide. Lab-scale degradation experiments were not able to anticipate the high occurrence levels of N-oxide compounds in the environment. This was most likely due to faster degradation kinetics and/or higher sorption to sediment of parent compounds and dealkylated TPs over N-oxide TPs, resulting in higher relative accumulation of the latter.

Molecular Network-Based Identification of Tramadol Metabolites in a Fatal Tramadol Poisoning

Identification of xenobiotics and their phase I/II metabolites in poisoned patients remains challenging. Systematic approaches using bioinformatic tools are needed to detect all compounds as exhaustively as possible. Here, we aimed to assess an analytical workflow using liquid chromatography coupled to high-resolution mass spectrometry with data processing based on a molecular network to identify tramadol metabolites in urine and plasma in poisoned patients. The generated molecular network from liquid chromatography coupled to high-resolution tandem mass spectrometry data acquired in both positive and negative ion modes allowed for the identification of 25 tramadol metabolites in urine and plasma, including four methylated metabolites that have not been previously reported in humans or in vitro models. While positive ion mode is reliable for generating a network of tramadol metabolites displaying a dimethylamino radical in their structure, negative ion mode was useful to cluster phase II metabolites. In conclusion, the combined use of molecular networks in positive and negative ion modes is a suitable and robust tool to identify a broad range of metabolites in poisoned patients, as shown in a fatal tramadol-poisoned patient.

HPLC-UV assay of tramadol and O-desmethyltramadol in human plasma containing other drugs potentially co-administered to participants in a paediatric population pharmacokinetic study

Multimodal analgesia is employed in paediatric pain management to maximise analgesia and minimise side effects. Tramadol is dosed at 1-1.5 mg/kg to treat severe pain in children but the assay for tramadol in plasma samples for pharmacokinetic and toxicology studies does not often consider concurrently administered medications. In this study we developed and validated an HPLC-UV method to quantify tramadol and its main metabolite (O-desmethyltramadol) in human plasma in the presence of seven potentially interfering drugs. Sample preparation method was developed by combining liquid-liquid extraction and protein precipitation. Chromatographic separation was achieved on a BDS-Hypersil-C18 column (5 µm, 250 × 4.6 mm) using a double gradient method. The limit of quantification was 6.7 ng/ml for both tramadol and ODT. The precision and accuracy were in compliance with ICH guidelines. This method was successfully employed to analyse the blood samples of 137 paediatric participants in a tramadol pharmacokinetic trial.

ANALGESIC EFFECT OF TRAMADOL IS NOT ALTERED BY POSTOPERATIVE SYSTEMIC INFLAMMATION AFTER MAJOR ABDOMINAL SURGERY

Tramadol is a commonly used analgesic in intensive care units (ICUs) for acute postoperative pain. Conversion of tramadol into active metabolites may be impaired in inflammatory states. Catechol-O-methyltransferase may influence pain. The aim of the study was to examine differences in the analgesic effect of tramadol between ICU patients with and without signs of systemic inflammation. Forty-three patients were admitted to ICU after a major abdominal surgery. The patients received a dose of 100 mg of tramadol intravenously every 6 hours during the first 24 hours after surgical procedure. Pain scores were measured by the Numeric Rating Scale before and 30 minutes after tramadol administration in awake patients. Systemic inflammation was considered when at least two of the following postoperative parameters were present in the first 24 hours of ICU admission: fever or hypothermia, tachycardia, pCO₂ <4.3 kPa, white blood cells >12000/mm³ or <4000/mm³, or preoperative value of C-reactive protein (CRP) >50 mg/L or/and procalcitonin (PCT) >0.5 mg/L. Catechol-O-methyltransferase was analyzed postoperatively. Fifteen (34.8%) patients met the criteria for systemic inflammation. Tramadol was proven to be an effective analgesic for the treatment of postoperative pain regardless of the presence of systemic inflammation (p<0.05). Lower perception of pain before tramadol application was observed in patients with systemic inflammation, but the difference was not significant. A negative correlation was observed between the preoperative values of CRP and PCT and the analgesic effect of tramadol assessed at the second measurement point (r=-0.358, p=0.03, and r=-0.364, p=0.02, respectively). Catechol-O-methyltransferase variants were not in correlation with pain and opioid consumption. Based on our findings, tramadol is effective in lowering pain scores after major abdominal surgery irrespective of the presence of systemic inflammation.

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.

Centrally administered CYP2D inhibitors increase oral tramadol analgesia in rats

Cytochrome P450 2D (CYP2D) mediates the activation and inactivation of several classes of psychoactive drugs, including opioids, which can alter drug response. Tramadol is a synthetic opioid with analgesic activity of its own as well as being metabolically activated by CYP2D to O-desmethyltramadol (ODMST) an opioid receptor agonist. We investigated the impact of brain CYP2D metabolism on central tramadol and ODSMT levels, and resulting analgesic response after oral tramadol administration in rats. CYP2D inhibitors propranolol and propafenone were administered intracerebroventricularly prior to oral tramadol administration and analgesia was measured by tail-flick latency. Drug levels of tramadol and its metabolites, ODSMT and N-desmethyltramadol, were assessed in plasma and in brain by microdialysis using LC-ESI-MS/MS. Inhibiting brain CYP2D with propafenone pretreatment increased analgesia after oral tramadol administration (ANOVA p = 0.02), resulting in a 1.5-fold increase in area under the analgesia-time curve (AUC_0-60, p < 0.01). This effect was associated with changes in the brain levels of tramadol and its metabolites consistent with brain CYP2D inhibition. In conclusion, under oral tramadol dosing pretreatment with a central administration of the CYP2D inhibitor propafenone increased analgesia (without altering plasma drug or metabolite levels), indicating that tramadol itself (and activity of CYP2D within the brain) contributed to analgesia.

Desmetramadol Has the Safety and Analgesic Profile of Tramadol Without Its Metabolic Liabilities: Consecutive Randomized, Double-Blind, Placebo- and Active Comparator-Controlled Trials

Desmetramadol is an investigational analgesic consisting of (+) and (-) enantiomers of the tramadol metabolite O-desmethyltramadol (M1). Tramadol is racemic and exerts analgesia by monoaminergic effects of (-)-tramadol and (-)-M1, and by the opioid (+)-M1. Tramadol labeling indicates cytochrome P450 (CYP) isozyme 2D6 ultrarapid metabolizer can produce dangerous (+)-M1 levels, and CYP2D6 poor metabolizers insufficient (+)-M1 for analgesia. We hypothesized that desmetramadol could provide the safety and analgesia of tramadol without its metabolic liabilities. We conducted consecutive double-blind, randomized, placebo-controlled, 3 segment cross-over trials A and B to investigate the steady-state pharmacokinetics and analgesia of 20 mg desmetramadol and 50 mg tramadol in 103 healthy participants without (n = 43) and with (n = 60) cotreatment with the CYP inhibitor paroxetine. In the absence of CYP inhibition (trial A), 20 mg desmetramadol and 50 mg tramadol dosed every 6 hours gave equivalent steady-state (+)-M1, similar adverse events, and analgesia significantly greater than placebo, but equal to each other. In trial B, CYP inhibition significantly depressed tramadol steady-state (+)-M1, reduced its adverse events, and led to insignificant analgesia comparable with placebo. In contrast, CYP inhibition in trial B had no deleterious effect on desmetramadol (+)-M1 or (-)-M1, which gave significant analgesia as in trial A and superior to tramadol (P = .003). Desmetramadol has the safety and efficacy of tramadol without its metabolic liabilities. CLINICALTRIALS.GOV REGISTRATIONS: NCT02205554, NCT03312777 PERSPECTIVE: To our knowledge, this is the first study of desmetramadol in humans and the first to show it provides the same safety and analgesia as tramadol, but without tramadol's metabolic liabilities and related drug-drug interactions. Desmetramadol could potentially offer expanded safety and usefulness to clinicians seeking an alternative to schedule II opioids.

Population pharmacokinetic analysis of tramadol and O-desmethyltramadol with genetic polymorphism of CYP2D6

Aim: Tramadol is widely used to treat acute, chronic, and neuropathic pain. Its primary active metabolite, O-desmethyltramadol (M1), is mainly responsible for its µ-opioid receptor-related analgesic effect. Tramadol is metabolized to M1 mainly by the cytochrome P450 (CYP) 2D6 enzyme, and to other metabolites by CYP3A4 and CYP2B6. The aim of this study was to develop a population pharmacokinetic (PK) model of tramadol and its metabolite using healthy Korean subjects.

Methods: Data on plasma concentrations of tramadol and M1 were obtained from 23 healthy Korean male subjects after a twice-daily oral dose of 100 mg of tramadol, every 12 hrs, for a total of 5 times. Blood samples were collected at 0 (pre-dose), 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 10, 12, 24, 48 and 72 hrs after last administration. Plasma tramadol concentrations were then analyzed using LC/MS. Population PK analysis of tramadol and its metabolite was performed using a nonlinear mixed-effects modeling (NONMEM).

Results: A one-compartment model with combined first-order and zero-order absorption was well fitted to the concentration–time curve of tramadol. M1 was well described by the one-compartment model as an extension of the parent drug (tramadol) model. Genetic polymorphisms of CYP2D6 correlated with the clearance of tramadol, and clearance from the central compartment to the metabolite compartment.

Conclusion: The parent-metabolite model successfully characterized the PK of tramadol and its metabolite M1 in healthy Korean male subjects. These results could be applied to evaluate plasma tramadol concentrations after various dosing regimens.

Disinfection by-Products and Ecotoxic Risk Associated with Hypochlorite Treatment of Tramadol

In recent years, many studies have highlighted the consistent finding of tramadol (TRA) in the effluents from wastewater treatment plants (WTPs) and also in some rivers and lakes in both Europe and North America, suggesting that TRA is removed by no more than 36% by specific disinfection treatments. The extensive use of this drug has led to environmental pollution of both water and soil, up to its detection in growing plants. In order to expand the knowledge about TRA toxicity as well as the nature of its disinfection by-products (DBPs), a simulation of the waste treatment chlorination step has been reported herein. In particular, we found seven new by-products, that together with TRA, have been assayed on different living organisms (Aliivibrio fischeri, Raphidocelis subcapitata and Daphnia magna), to test their acute and chronic toxicity. The results reported that TRA may be classified as a harmful compound to some aquatic organisms whereas its chlorinated product mixture showed no effects on any of the organisms tested. All data suggest however that TRA chlorination treatment produces a variety of DBPs which can be more harmful than TRA and a risk for the aquatic environment and human health.

Tramadol Hydrochloride at Steady State Lacks Clinically Relevant QTc Interval Increases in Healthy Adults

We evaluated the effects of therapeutic and supratherapeutic doses of tramadol hydrochloride on the corrected QT (QTc) interval in healthy adults (aged 18‐55 years) in a randomized, phase I, double‐blind, placebo‐ and positive‐controlled, multiple‐dose, 4‐way crossover study. Participants were randomized to receive 1 of 4 treatments (A‐D), 1 each in 4 treatment periods (1‐4), separated by a washout period (7‐15 days). Treatment A comprised tramadol 400 mg (therapeutic dose) on days 1 through 3, tramadol 100 mg and moxifloxacin‐matched placebo on day 4, and placebo on all 4 days. Treatment B comprised tramadol 600 mg (supratherapeutic dose) on days 1 through 3, and tramadol 150 mg and moxifloxacin‐matched placebo on day 4. Treatment C comprised placebo on days 1 through 4 and moxifloxacin‐matched placebo on day 4. Treatment D comprised placebo on days 1 through 4 and moxifloxacin 400 mg on day 4. Of 68 participants enrolled, 57 (83.8%) completed the study. Both therapeutic and supratherapeutic doses of tramadol were shown to be noninferior to placebo regarding their effect on QTc prolongation. Sixty‐one of 68 (89.7%) participants reported at least 1 treatment‐emergent adverse event (mild); nausea was the most frequently reported treatment‐emergent adverse event. Summarizing, tramadol at doses up to 600 mg/day did not cause clinically relevant QTc interval prolongation in healthy adults.

Effects of human SULT1A3/SULT1A4 genetic polymorphisms on the sulfation of acetaminophen and opioid drugs by the cytosolic sulfotransferase SULT1A3

Sulfoconjugation has been shown to be critically involved in the metabolism of acetaminophen (APAP), morphine, tapentadol and O-desmethyl tramadol (O-DMT). The objective of this study was to investigate the effects of single nucleotide polymorphisms (SNPs) of human SULT1A3 and SULT1A4 genes on the sulfating activity of SULT1A3 allozymes toward these analgesic compounds. Twelve non-synonymous coding SNPs (cSNPs) of SULT1A3/SULT1A4 were investigated, and the corresponding cDNAs were generated by site-directed mutagenesis. SULT1A3 allozymes, bacterially expressed and purified, exhibited differential sulfating activity toward each of the four analgesic compounds tested as substrates. Kinetic analyses of SULT1A3 allozymes further revealed significant differences in binding affinity and catalytic activity toward the four analgesic compounds. Collectively, the results derived from the current study showed clearly the impact of cSNPs of the coding genes, SULT1A3 and SULT1A4, on the sulfating activity of the coded SULT1A3 allozymes toward the tested analgesic compounds. These findings may have implications in the pharmacokinetics as well as the toxicity profiles of these analgesics administered in individuals with distinct SULT1A3 and/or SULT1A4 genotypes.

New Findings on Local Tramadol Use in Oral Surgery

In modern times, all procedures in oral surgery need to be painless and management of postoperative pain needs to be adequate. The surgical extraction of the third molar or alveolectomy of the wisdom tooth is one of the most common surgical procedures carried out in oral surgery and it includes rising a flap, bone removal and suturing. These surgical procedures usually cause swelling, trismus and moderate to severe pain. Third molar surgery is often used as a model in clinical trials that are directed toward reducing postoperative pain and improving its management. Tramadol is a well-known central acting opioid analgesic that produces analgesia against multiple pain conditions such as postsurgical pain, obstetric pain, terminal cancer pain, pain of coronary origin and neuropathic pain. Tramadol is an atypical opioid. When administered locally, it has both analgesic and anesthetic properties. The aim of this paper was to present new findings on local effects of tramadol in oral surgery.

Uptake and Metabolism of Human Pharmaceuticals by Fish: A Case Study with the Opioid Analgesic Tramadol

Recent species-extrapolation approaches to the prediction of the potential effects of pharmaceuticals present in the environment on wild fish are based on the assumption that pharmacokinetics and metabolism in humans and fish are comparable. To test this hypothesis, we exposed fathead minnows to the opiate pro-drug tramadol and examined uptake from the water into the blood and brain and the metabolism of the drug into its main metabolites. We found that plasma concentrations could be predicted reasonably accurately based on the lipophilicity of the drug once the pH of the water was taken into account. The concentrations of the drug and its main metabolites were higher in the brain than in the plasma, and the observed brain and plasma concentration ratios were within the range of values reported in mammalian species. This fish species was able to metabolize the pro-drug tramadol into the highly active metabolite O-desmethyl tramadol and the inactive metabolite N-desmethyl tramadol in a similar manner to that of mammals. However, we found that concentration ratios of O-desmethyl tramadol to tramadol were lower in the fish than values in most humans administered the drug. Our pharmacokinetic data of tramadol in fish help bridge the gap between widely available mammalian pharmacological data and potential effects on aquatic organisms and highlight the importance of understanding drug uptake and metabolism in fish to enable the full implementation of predictive toxicology approaches.

Safety, Tolerability, and Pharmacokinetics of Therapeutic and Supratherapeutic Doses of Tramadol Hydrochloride in Healthy Adults: A Randomized, Double-Blind, Placebo-Controlled Multiple-Ascending-Dose Study

This randomized, double-blind, parallel-group multiple-ascending-dose study evaluated the safety, tolerability, and pharmacokinetics of tramadol hydrochloride in healthy adults to inform dosage and design for a subsequent QT/QTc study. Healthy men and women, 18 to 45 years old (inclusive), were sequentially assigned to the tramadol 200, 400, or 600 mg/day treatment cohort and within each cohort, randomized (4:1) to either tramadol or placebo every 6 hours for 9 oral doses. Of the 24 participants randomized to tramadol (n = 8/cohort), 22 (91.7%) completed the study. The AUC_tau,ss of tramadol increased approximately 2.2- and 3.6-fold for the (+) enantiomer and 2.0- and 3.5-fold for the (-) enantiomer with increasing dose from 200 to 400  and 600 mg/day, whereas the C_max,ss increased 2.1- and 3.3-fold for the (+) enantiomer and 2.0- and 3.2-fold for the (-) enantiomer. Overall, 21 participants (87.5%) participants reported ≥1 treatment-emergent adverse event; most frequent were nausea (17 of 24, 70.8%) and vomiting (7 of 24, 29.2%). Vomiting (affected participants and events) increased with increasing dose from 200 to 600 mg/day but was mild (5 of 24) or moderate (2 of 24) in severity. All tested dosage regimens of tramadol showed acceptable safety and tolerability profile for further investigation in a thorough QT/QTc study.

The impact of black seed oil on tramadol-induced hepatotoxicity: Immunohistochemical and ultrastructural study

The natural herb, black seed (Nigella Sativa; NS) is one of the most important elements of folk medicine. The aim was to evaluate the impact of Nigella Sativa Oil (NSO) on the changes induced by tramadol in rat liver. Twenty four albino rats were used.

CONTROL GROUP

given intraperitoneal and oral saline for 30days. TR-group: given intraperitoneal tramadol (20, 40, 80mg/kg/day) in the first, middle and last 10days of the experiment, respectively. TR+NS group: administered intraperitoneal tramadol in similar doses to TR-group plus oral NSO (4ml/kg/day) for 30days. Immunohistochemical, electron microscopic, biochemical and statistical studies were performed. TR-group displayed disarranged hepatic architecture, hepatic congestion, hemorrhage and necrosis. Apoptotic hepatocytes, mononuclear cellular infiltration and a significant increase in the number of anti-CD68 positive cells were observed. Ultrastructurally, hepatocytes showed shrunken nuclei, swollen mitochondria, many lysosomes and autophagic vacuoles. Activated Ito and Von Kupffer cells were also demonstrated. Elevated serum levels of AST, ALT, ALP and bilirubin were noticed. NSO administration resulted in preservation of hepatic histoarchitecture and ultrastructure and significant reductions in the number of anti-CD68 positive cells and serum levels of liver seromarkers. In conclusion, NSO administration could mitigate the alterations induced by tramadol in rat liver.

On the sulfation of O-desmethyltramadol by human cytosolic sulfotransferases

BACKGROUND

Previous studies have demonstrated that sulfate conjugation is involved in the metabolism of the active metabolite of tramadol, O-desmethyltramadol (O-DMT). The current study aimed to systematically identify the human cytosolic sulfotransferases (SULTs) that are capable of mediating the sulfation of O-DMT.

METHODS

The sulfation of O-DMT under metabolic conditions was demonstrated using HepG2 hepatoma cells and Caco-2 human colon carcinoma cells. O-DMT-sulfating activity of thirteen known human SULTs and four human organ specimens was examined using an established sulfotransferase assay. pH-Dependency and kinetic parameters were also analyzed using, respectively, buffers at different pHs and varying O-DMT concentrations in the assays.

RESULTS

Of the thirteen human SULTs tested, only SULT1A3 and SULT1C4 were found to display O-DMT-sulfating activity, with different pH-dependency profiles. Kinetic analysis revealed that SULT1C4 was 60 times more catalytically efficient in mediating the sulfation of O-DMT than SULT1A3 at respective optimal pH. Of the four human organ specimens tested, the cytosol prepared from the small intestine showed much higher O-DMT-sulfating activity than cytosols prepared from liver, lung, and kidney. Both cultured HepG2 and Caco-2 cells were shown to be capable of sulfating O-DMT and releasing sulfated O-DMT into cultured media.

CONCLUSION

SULT1A3 and SULT1C4 were the major SULTs responsible for the sulfation of O-DMT. Collectively, the results obtained provided a molecular basis underlying the sulfation of O-DMT and contributed to a better understanding about the pharmacokinetics and pharmacodynamics of tramadol in humans.

Evaluation of the route dependency of the pharmacokinetics and neuro-pharmacokinetics of tramadol and its main metabolites in rats

Tramadol hydrochloride is a centrally acting analgesic used for the treatment of moderate-to-severe pain. It has three main metabolites: O-desmethyltramadol (M1), N-desmethyltramadol (M2), and N,O-didesmethyltramadol (M5). Because of the frequent use of tramadol by patients and drug abusers, the ability to determine the parent drug and its metabolites in plasma and cerebrospinal fluid is of great importance. In the present study, a pharmacokinetic approach was applied using two groups of five male Wistar rats administered a 20mg/kg dose of tramadol via intravenous (i.v.) or intraperitoneal (i.p.) routes. Plasma and CSF samples were collected at 5-360min following tramadol administration. Our results demonstrate that the plasma values of Cmax (C0 in i.v. group) and area under the curve (AUC)0-t for tramadol were 23,314.40±6944.85 vs. 3187.39±760.25ng/mL (Cmax) and 871.15±165.98 vs. 414.04±149.25μg·min/mL in the i.v. and i.p. groups, respectively (p<0.05). However, there were no significant differences between i.v. and i.p. plasma values for tramadol metabolites (p>0.05). Tramadol rapidly penetrated the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSFB) (5.00±0.00 vs. 10.00±5.77min in i.v. and i.p. groups, respectively). Tramadol and its metabolites (M1 and M2) were present to a lesser extent in the cerebrospinal fluid (CSF) than in the plasma. M5 hardly penetrated the CSF, owing to its high polarity. There was no significant difference between the AUC0-t of tramadol in plasma (414.04±149.25μg·min/mL) and CSF (221.81±83.02μg·min/mL) in the i.p. group. In addition, the amounts of metabolites (M1 and M2) in the CSF showed no significant differences following both routes of administration. There were also no significant differences among the Kp,uu,CSF(0-360) (0.51±0.12 vs. 0.63±0.04) and Kp,uu,CSF(0-∞) (0.61±0.10 vs. 0.62±0.02) for i.v. and i.p. pathways, respectively (p>0.05). Drug targeting efficiency (DTE) values of tramadol after i.p. injection were more than unity for all scheduled time points. Considering the main analgesic effect of M1, it is hypothesized that both routes of administration may produce the same amount of analgesia.

Photocatalytic degradation kinetics, mechanism and ecotoxicity assessment of tramadol metabolites in aqueous TiO2 suspensions

This study investigated for the first time the photocatalytic degradation of three well-known transformation products (TPs) of pharmaceutical Tramadol, N-desmethyl-(N-DES), N,N-bidesmethyl (N,N-Bi-DES) and N-oxide-tramadol (N-OX-TRA) in two different aquatic matrices, ultrapure water and secondary treated wastewater, with high (10 mg L(-1)) and low (50 μg L(-1)) initial concentrations, respectively. Total disappearance of the parent compounds was attained in all experiments. For initial concentration of 10 mg L(-1), the target compounds were degraded within 30-40 min and a mineralization degree of more than 80% was achieved after 240 min of irradiation, while the contained organic nitrogen was released mainly as NH4(+) for N-DES, N,N-Bi-DES and NO3(-) for N-OX-TRA. The degradation rates of all the studied compounds were considerably decreased in the wastewater due to the presence of inorganic and organic constituents typically found in effluents and environmental matrices which may act as scavengers of the HO(•). The effect of pH (4, 6.7, 10) in the degradation rates was studied and for N-DES-TRA and N,N-Bi-DES-TRA, the optimum pH value was 6.7. In contrast, N-OX-TRA showed an increasing trend in the photocatalytic degradation kinetic in alkaline solutions (pH 10). The major transformation products were identified by high resolution accurate mass spectrometry coupled with liquid chromatography (HR-LC-MS). Scavenging experiments indicated for all studied compounds the important role of HO(•) in the photocatalytic degradation pathways that included mainly hydroxylation and further oxidation of the parent compounds. In addition, Microtox bioassay (Vibrio fischeri) was employed for evaluating the ecotoxicity of photocatalytically treated solutions. Results clearly demonstrate the progressive decrease of the toxicity and the efficiency of the photocatalytic process in the detoxification of the irradiated solutions.

Detection and quantification of the opioid tramadol in urine using surface enhanced Raman scattering

There is an on going requirement for the detection and quantification of illicit substances. This is in particular the case for law enforcement where portable screening methods are needed and there has been recent interest in breath tests for a range of narcotics. In this study we first developed surface enhanced Raman scattering (SERS) for the detection of tramadol in water and establish robust and reproducible methods based on silver hydroxylamine colloid. We used 0.5 M NaCl as the aggregating agent, with the pH ∼ 7.0 and SERS data were collected immediately (i.e., the analyte association and colloid aggregation times were zero). The limit of detection was rather high and calculated to be 5 × 10(-4) M which would not be practical in the field. Undeterred we continued with spiking tramadol in artificial urine and found that no aggregating agent or modification of pH was necessary. Indeed aggregation occurred spontaneously due to the complexity of the medium which is rich in multiple salts, which are commonly used for SERS. We estimated the limit of detection in artificial urine to be 2.5 × 10(-6) M which is equivalent to 657.5 ng mL(-1) and very close to the levels typically found in individuals who use tramadol for pain relief. We believe this opens up opportunities for testing SERS in real world samples and this will be an area of future study.

Differential Consequences of Tramadol in Overdosing: Dilemma of a Polymorphic Cytochrome P450 2D6-Mediated Substrate

Tramadol is a centrally acting opioid analgesic that is prone to polymorphic metabolism via cytochrome P450 (CYP) 2D6. The generation of the active metabolite, O-desmethyltramadol, which occurs through the CYP 2D6 pathway, significantly contributes to the drug's activity. However, dosage adjustments of tramadol are typically not practiced in the clinic when treating patients who are homozygous extensive metabolizers, heterozygous extensive metabolizers, or poor metabolizers. In the event of a tramadol overdose, the consequences may be influenced importantly by the genotype or phenotype status of the subject. Depending on the individual subject's CYP 2D6 status, one may see excessive miotic-related toxicity driven by the excessive availability of O-desmethyltramadol or one may manifest mydriatic-related toxicity driven by the excessive availability of tramadol. This report provides pharmacokinetic perspectives in situations of tramadol overdosing.

Physiologically Based Pharmacokinetic Predictions of Tramadol Exposure Throughout Pediatric Life: an Analysis of the Different Clearance Contributors with Emphasis on CYP2D6 Maturation

This paper focuses on the retrospective evaluation of physiologically based pharmacokinetic (PBPK) techniques used to mechanistically predict clearance throughout pediatric life. An intravenous tramadol retrograde PBPK model was set up in Simcyp® using adult clearance values, qualified for CYP2D6, CYP3A4, CYP2B6, and renal contributions. Subsequently, the model was evaluated for mechanistic prediction of total, CYP2D6-related, and renal clearance predictions in very early life. In two in vitro pediatric human liver microsomal (HLM) batches (1 and 3 months), O-desmethyltramadol and N-desmethyltramadol formation rates were compared with CYP2D6 and CYP3A4 activity, respectively. O-desmethyltramadol formation was mediated only by CYP2D6, while N-desmethyltramadol was mediated in part by CYP3A4. Additionally, the clearance maturation of the PBPK model predictions was compared to two in vivo maturation models (Hill and exponential) based on plasma concentration data, and to clearance estimations from a WinNonlin® fit of plasma concentration and urinary excretion data. Maturation of renal and CYP2D6 clearance is captured well in the PBPK model predictions, but total tramadol clearance is underpredicted. The most pronounced underprediction of total and CYP2D6-mediated clearance was observed in the age range of 2-13 years. In conclusion, the PBPK technique showed to be a powerful mechanistic tool capable of predicting maturation of CYP2D6 and renal tramadol clearance in early infancy, although some underprediction occurs between 2 and 13 years for total and CYP2D6-mediated tramadol clearance.

Role of CYP2D6 Polymorphisms in the Outcome of Postoperative Pain Treatment

OBJECTIVE

To investigate the role of CYP2D6 phenotype in the outcome of postoperative (PO) pain (POP) treatment.

DESIGN

Longitudinal cohort study. Open-label trial with post hoc analysis.

SETTING

General Hospital Surgery and Recovery Units.

PATIENTS

Ninety unrelated Caucasians submitted to abdominal/thoracic surgery.

INTERVENTIONS

Standard multimodal POP treatment including opioids (tramadol) and nonsteroidal anti-inflammatory drugs (ketoprofen) at different dosages and infusion rates according to the predicted mild, moderate, or severe POP.

OUTCOME MEASURES

Pain (Numeric Rating Scale-NRS) and sedation (Ramsay Sedation Scale-RSS) up to 24 hours after surgery. By genotyping 16 CYP2D6 alleles, the four CYP2D6 phenotypes poor metabolizer (PM), intermediate metabolizers (IM), extensive metabolizers (EM) and ultrarapid metabolizers (UM) were predicted.

RESULTS

As compared with the CYP2D6-EM phenotype, in the early PO time (30 min) a higher RSS mean score in IM was observed (P = 0.035). A suggestion towards higher mean score in PM (P = 0.091) and a minor mean score in UM (P = 0.091) was also detected. No difference in the outcome of pain across the CYP2D6 phenotypes was observed.

CONCLUSIONS

In respect to the normal CYP2D6 phenotype, our results suggested that slowly metabolizers (IMs and PMs) might have a major sedation, whereas more rapid metabolizers (UM) a minor sedation, in the early time after surgery. A minor role of CYP2D6 phenotype in PO analgesia may be suggested.

Fluorescence detection of tramadol in healthy Chinese volunteers by high-performance liquid chromatography and bioequivalence assessment

This study developed a revised high-performance liquid chromatography fluorescence method to determine plasma tramadol concentration, and thereby to examine the bioequivalence of two tramadol formulations among healthy male Chinese volunteers. The study used a double-blind, randomized, 2×2 crossover-design principle. Calculated pharmacokinetic parameters for both formulations were consistent with previous reports. According to the observation of vital signs and laboratory measurement, no subjects had any adverse reactions. The geometric mean ratios (90% confidence interval) of the test drug/reference drug for tramadol were 100.2% (95.3%-103.4%) for the area under the plasma concentration-time curve (AUC) from time zero to the last measurable concentration, 99.6% (94.2%-102.7%) for the AUC from administration to infinite time, and 100.8% (93.1%-106.4%) for maximum concentration. For the 90% confidence intervals of the test/reference AUC ratio and maximum concentration ratio of tramadol, both were in the acceptance range for bioequivalence. According to the two preparations by pharmacokinetic parameter statistics, the half-life, mean residence time, and clearance values showed no significant statistical differences. Therefore, the conclusion of this study was that the two tramadol formulations (tablets and capsules) were bioequivalent.

Effects of terbinafine and itraconazole on the pharmacokinetics of orally administered tramadol

BACKGROUND

Tramadol is widely used for acute, chronic, and neuropathic pain. Its primary active metabolite is O-desmethyltramadol (M1), which is mainly accountable for the μ-opioid receptor-related analgesic effect. Tramadol is metabolized to M1 mainly by cytochrome P450 (CYP)2D6 enzyme and to other metabolites by CYP3A4 and CYP2B6. We investigated the possible interaction of tramadol with the antifungal agents terbinafine (CYP2D6 inhibitor) and itraconazole (CYP3A4 inhibitor).

METHODS

We used a randomized placebo-controlled crossover study design with 12 healthy subjects, of which 8 were extensive and 4 were ultrarapid CYP2D6 metabolizers. On the pretreatment day 4 with terbinafine (250 mg once daily), itraconazole (200 mg once daily) or placebo, subjects were given tramadol 50 mg orally. Plasma concentrations of tramadol and M1 were determined over 48 h and some pharmacodynamic effects over 12 h. Pharmacokinetic variables were calculated using standard non-compartmental methods.

RESULTS

Terbinafine increased the area under plasma concentration-time curve (AUC0-∞) of tramadol by 115 % and decreased the AUC0-∞ of M1 by 64 % (P < 0.001). Terbinafine increased the peak concentration (C max) of tramadol by 53 % (P < 0.001) and decreased the C max of M1 by 79 % (P < 0.001). After terbinafine pretreatment the elimination half-life of tramadol and M1 were increased by 48 and 50 %, respectively (P < 0.001). Terbinafine reduced subjective drug effect of tramadol (P < 0.001). Itraconazole had minor effects on tramadol pharmacokinetics.

CONCLUSIONS

Terbinafine may reduce the opioid effect of tramadol and increase the risk of its monoaminergic adverse effects. Itraconazole has no meaningful interaction with tramadol in subjects who have functional CYP2D6 enzyme.

Pharmacokinetics of tramadol following intravenous and oral administration in male rhesus macaques (Macaca mulatta)

Recently, tramadol and its active metabolite, O-desmethyltramadol (M1), have been studied as analgesic agents in various traditional veterinary species (e.g., dogs, cats, etc.). This study explores the pharmacokinetics of tramadol and M1 after intravenous (IV) and oral (PO) administration in rhesus macaques (Macaca mulatta), a nontraditional veterinary species. Rhesus macaques are Old World monkeys that are commonly used in biomedical research. Effects of tramadol administration to monkeys are unknown, and research veterinarians may avoid inclusion of this drug into pain management programs due to this limited knowledge. Four healthy, socially housed, adult male rhesus macaques (Macaca mulatta) were used in this study. Blood samples were collected prior to, and up to 10 h post-tramadol administration. Serum tramadol and M1 were analyzed using liquid chromatography-mass spectrometry. Noncompartmental pharmacokinetic analysis was performed. Tramadol clearance was 24.5 (23.4-32.7) mL/min/kg. Terminal half-life of tramadol was 111 (106-127) min IV and 133 (84.9-198) min PO. Bioavailability of tramadol was poor [3.47% (2.14-5.96%)]. Maximum serum concentration of M1 was 2.28 (1.88-2.73) ng/mL IV and 11.2 (9.37-14.9) ng/mL PO. Sedation and pruritus were observed after IV administration.

Tramadol can selectively manage moderate pain in children following European advice limiting codeine use

The European Medicine Agency recommendations limiting codeine use in children have created a void in managing moderate pain. We review the evidence on the pharmacokinetic, pharmacodynamic and safety profile of tramadol, a possible substitute for codeine.

CONCLUSION

Tramadol appears to be safe in both paediatric inpatients and outpatients. It may be appropriate to limit the current use of tramadol to monitored settings in children with risk factors for respiratory depression, subject to further safety evidence.

Tramadol--a true natural product?

We have independently investigated the source of tramadol, a synthetic analgesic largely used for treating moderate to severe pain in humans, recently found in the roots of the Cameroonian medicinal plant, Nauclea latifolia. We found tramadol and its three major mammalian metabolites (O-desmethyltramadol, N-desmethyltramadol, and 4-hydroxycyclohexyltramadol) in the roots of N. latifolia and five other plant species, and also in soil and local water bodies only in the Far North region of Cameroon. The off-label administration of tramadol to cattle in this region leads to cross-contamination of the soil and water through feces and urine containing parent tramadol as well as tramadol metabolites produced in the animals. These compounds can then be absorbed by the plant roots and also leached into the local water supplies. The presence of tramadol in roots is, thus, due to an anthropogenic contamination with the synthetic compound.

Tramadol toxicity in a cat: case report and literature review of serotonin syndrome

Overview:

Tramadol toxicity has not previously been reported in a cat.

Case summary:

This report describes the clinical signs, diagnosis and treatment of tramadol toxicity, manifesting as serotonin syndrome, in a cat in Australia.

Practical relevance:

For any cat with suspicion of serotonin syndrome, in particular secondary to tramadol overdose, it is recommended that decontamination, monitoring and supportive care are instituted as soon as clinical signs develop. Prolonged hospitalisation may be required in the event of a severe overdose.

Literature review:

The literature relating to the pharmacology of tramadol and tramadol overdose, clinical manifestations of tramadol overdose, and serotonin syndrome in cats, humans and dogs is reviewed. Recommended treatment for tramadol overdose and serotonin syndrome is also discussed.

A cytochrome P450 phenotyping cocktail causing unexpected adverse reactions in female volunteers

BACKGROUND

A four-drug cytochrome P450 (CYP) phenotyping cocktail was developed to rapidly and safely determine CYP2D6, CYP2C19, CYP2C9 and CYP1A2 enzyme activity and phenotype.

METHODS

The cocktail consisted of the single CYP phenotyping probes of 50 mg tramadol (CYP2D6), 20 mg omeprazole (CYP2C19), 25 mg losartan (CYP2C9) and 200 mg caffeine (CYP1A2) and was administered as a single oral dose. For enzyme activity measurements, urine was collected as 8 h post-administration and blood was sampled at 4 h. The enzyme activity was determined by metabolic ratios of molar concentrations of the drugs and their enzyme catalyzed metabolites and was correlated to the relevant genotypes.

RESULTS

In a pilot study in 12 healthy male volunteers the CYP genotype-phenotype correlation and robustness of the cocktail was successfully determined without detection of any adverse drug reactions. In the subsequent population study, four female volunteers experienced unexpected and unacceptable moderate and severe adverse reactions (ARs) of headache, dizziness, nausea, vomiting, blue fingers, nails and lips and difficulties in urinating, which led to the study being prematurely terminated after inclusion of only 22 subjects (15 males, 7 females) [corrected].

CONCLUSION

Attention must be paid to adverse reactions when designing new combinations of phenotype cocktails regardless of the doses and drugs involved. We specifically warn against the combination of tramadol, omeprazole, losartan and caffeine.

Comparative toxicokinetics of organic micropollutants in freshwater crustaceans

Exposure and depuration experiments for Gammarus pulex and Daphnia magna were conducted to quantitatively analyze biotransformation products (BTPs) of organic micropollutants (tramadol, irgarol, and terbutryn). Quantification for BTPs without available standards was performed using an estimation method based on physicochemical properties. Time-series of internal concentrations of micropollutants and BTPs were used to estimate the toxicokinetic rates describing uptake, elimination, and biotransformation processes. Bioaccumulation factors (BAF) for the parents and retention potential factors (RPF), representing the ratio of the internal amount of BTPs to the parent at steady state, were calculated. Nonlinear correlation of excretion rates with hydrophobicity indicates that BTPs with lower hydrophobicity are not always excreted faster than the parent compound. For irgarol, G.pulex showed comparable elimination, but greater uptake and BAF/RPF values than D.magna. Further, G. pulex had a whole set of secondary transformations that D. magna lacked. Tramadol was transformed more and faster than irgarol and there were large differences in toxicokinetic rates for the structurally similar compounds irgarol and terbutryn. Thus, predictability of toxicokinetics across species and compounds needs to consider biotransformation and may be more challenging than previously thought because we found large differences in closely related species and similar chemical structures.

A suicidal poisoning due to tramadol. A metabolic approach to death investigation

Tramadol is a synthetic opioid, widely used for post-surgical and chronic pain. Lethal overdose due only to tramadol is not common; more often the poisoning is due to tramadol in combination with other substances. Reported is a suicidal case of lethal tramadol poisoning in a 48-year-old woman. Tramadol and its metabolites O-desmethyltramadol (M1), N-desmethyltramadol (M2), N,N-didesmethyltramadol (M3), N,O-didesmethyltramadol (M5) were detected by GC/MS in biological fluids (femoral blood, bile, urine, gastric content) and viscera (brain, lung, liver and kidney). The tramadol concentration in femoral blood was 61.83 mcg/ml which is approximately 30 times higher than that believed to be lethal. According with other Authors, a preferential formation of M1 over M2 (M1/M2 ratio >1) is indicative of acute death, while M1/M2 ratio <1 suggests that death occurred after a longer time lapse from ingestion.

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.

Study of the pharmacokinetic changes of Tramadol in diabetic rats

Background

Besides the pathological states, diabetes mellitus may also alter the hepatic biotransformation of pharmaceutical agents. It is advantageous to understand the effect of diabetes on the pharmacokinetic of drugs. The objective of this study was to define the pharmacokinetic changes of tramadol and its main metabolites after in vivo intraperitoneal administration and ex vivo perfused liver study in diabetic rat model.

Tramadol (10 mg/kg) was administered to rats (diabetic and control groups of six) intraperitoneally and blood samples were collected at different time points up to 300 min. In a parallel study, isolated liver perfusion was done (in diabetic and control rats) by Krebs-Henseleit buffer (containing 500 ng/ml tramadol). Perfusate samples were collected at 10 min intervals up to 180 min. Concentration of tramadol and its metabolites were determined by HPLC.

Results

Tramadol reached higher concentrations after i.p. injection in diabetics (C_max of 1607.5 ± 335.9 ng/ml) compared with control group (C_max of 561.6 ± 111.4). M1 plasma concentrations were also higher in diabetic rats compared with control group. M2 showed also higher concentrations in diabetic rats. Comparing the concentration levels of M1 in diabetic and control perfused livers, showed that in contrast to intact animals, the metabolic ratios of M1 and M5 (M/T) were significantly higher in diabetic perfused liver compared to those of control group.

Conclusions

The pharmacokinetic of tramadol and its three metabolites are influenced by diabetes. As far as M1 is produced by Cyp2D6, its higher concentration in diabetic rats could be a result of induction in Cyp2D6 activity, while higher concentrations of tramadol can be explained by lower volume of distribution.

Ticlopidine inhibits both O-demethylation and renal clearance of tramadol, increasing the exposure to it, but itraconazole has no marked effect on the ticlopidine-tramadol interaction

PURPOSE

We assessed possible drug interactions of tramadol given concomitantly with the potent CYP2B6 inhibitor ticlopidine, alone or together with the potent CYP3A4 and P-glycoprotein inhibitor itraconazole.

METHODS

In a randomized, placebo-controlled cross-over study, 12 healthy subjects ingested 50 mg of tramadol after 4 days of pretreatment with either placebo, ticlopidine (250 mg twice daily) or ticlopidine plus itraconazole (200 mg once daily). Plasma and urine concentrations of tramadol and its active metabolite O-desmethyltramadol (M1) were monitored over 48 h and 24 h, respectively.

RESULTS

Ticlopidine increased the mean area under the plasma concentration-time curve (AUC0-∞) of tramadol by 2.0-fold (90 % confidence interval (CI) 1.6-2.4; p < 0.001) and Cmax by 1.4-fold (p < 0.001), and reduced its oral and renal clearance (p < 0.01). Ticlopidine reduced the AUC0-3 of M1 (p < 0.001) and the ratio of the AUC0-∞ of M1 to that of tramadol, but did not influence the AUC0-∞ of M1. Tramadol or M1 pharmacokinetics did not differ between the ticlopidine alone and ticlopidine plus itraconazole phases.

CONCLUSIONS

Ticlopidine increased exposure to tramadol, reduced its renal clearance and inhibited the formation of M1, most likely via inhibition of CYP2B6 and/or CYP2D6. The addition of itraconazole to ticlopidine did not modify the outcome of the drug interaction. Concomitant clinical use of ticlopidine and tramadol may enhance the risk of serotonergic effects, especially when higher doses of tramadol are used.

Pharmacokinetics of tramadol in a diverse healthy Chinese population

WHAT IS KNOWN AND OBJECTIVES

Drug disposition may show ethnicity and gender differences. The objective of this study is to assess whether there are gender and ethnic differences in the pharmacokinetics of tramadol.

METHODS

Fifty healthy volunteers from five different ethnic Chinese groups (Han, Mongolian, Korean, Uygur and Hui) were recruited, and blood samples were obtained for up to 36 h after oral administration of a single 100 mg capsule of tramadol. The plasma concentration-time course of tramadol was measured by high-performance liquid chromatography and the pharmacokinetic estimated.

RESULTS AND DISCUSSION

The mean maximum plasma concentration (C(max)) of tramadol was different between Chinese males and females. There were also statistically significant differences between Hui and the other ethnic groups in tramadol's clearance (CL/F), volume of distribution (V(d) /F), C(max) and area under the plasma concentration time curve (AUC(0-∞)) (P < 0·05).

WHAT IS NEW AND CONCLUSION

The pharmacokinetics of tramadol was different in Hui subjects compared to the other Chinese ethnic groups. Tramadol CL/F may also show gender differences.