Tramadol, M1 metabolite and enantiomer affinities for cloned human opioid receptors expressed in transfected HN9.10 neuroblastoma cells

Assessment of tramadol pharmacokinetics in correlation with CYP2D6 and clinical symptoms

Objectives Due to lack of adequate data on tramadol kinetic in relevance of CYP2D6 toxicity, this study was designed to investigate the effect of CYP2D6 phenotype in tramadol poisoning. The saliva, urine and blood samples were taken at the admission time. Consequently, concentration of tramadol and its major metabolites were measured. Methods A pharmacokinetic and metabolic study was developed in cases of tramadol poisoned (n=96). Cases of tramadol poisoned evidenced seizure, hypertension, dizziness, nausea and vomiting symptoms participated. Results Female cases showed higher N-desmethyltramadol (M2) tramadol concentrations than male cases: in urine (40.12 ± 124.53 vs. 7.3 ± 7.13), saliva (16.91 ± 26.03 vs. 5.89 ± 7.02), and blood (1.11 ± 1.56 vs. 0.3 ± 0.38) samples. Significant correlation between blood, saliva, and urine concentrations were found (r = 0.5). Based on the metabolic ratio of O-desmethyltramadol (M1) of male (0.53 ± 0.22) and female (0.43 ± 0.26), poisoning and severe symptoms like seizure in female occurs statistically fewer (13.04%) than in male (50.6%). Assessment of CYP2D6 phenotype showed all of the participants were extensive metabolizers (EM) and their phenotype was associated with clinical symptoms. Conclusions According to our results, M1 as a high potent metabolite has an important role in toxicity and the likelihood of poisoning in people with EM phenotype. Finally, tramadol metabolic ratio may justify the cause of various symptoms in human tramadol poisoning.

Assessment of tramadol pharmacokinetics in correlation with CYP2D6 and clinical symptoms

Objectives Due to lack of adequate data on tramadol kinetic in relevance of CYP2D6 toxicity, this study was designed to investigate the effect of CYP2D6 phenotype in tramadol poisoning. The saliva, urine and blood samples were taken at the admission time. Consequently, concentration of tramadol and its major metabolites were measured. Methods A pharmacokinetic and metabolic study was developed in cases of tramadol poisoned (n=96). Cases of tramadol poisoned evidenced seizure, hypertension, dizziness, nausea and vomiting symptoms participated. Results Female cases showed higher N-desmethyltramadol (M2) tramadol concentrations than male cases: in urine (40.12 ± 124.53 vs. 7.3 ± 7.13), saliva (16.91 ± 26.03 vs. 5.89 ± 7.02), and blood (1.11 ± 1.56 vs. 0.3 ± 0.38) samples. Significant correlation between blood, saliva, and urine concentrations were found (r = 0.5). Based on the metabolic ratio of O-desmethyltramadol (M1) of male (0.53 ± 0.22) and female (0.43 ± 0.26), poisoning and severe symptoms like seizure in female occurs statistically fewer (13.04%) than in male (50.6%). Assessment of CYP2D6 phenotype showed all of the participants were extensive metabolizers (EM) and their phenotype was associated with clinical symptoms. Conclusions According to our results, M1 as a high potent metabolite has an important role in toxicity and the likelihood of poisoning in people with EM phenotype. Finally, tramadol metabolic ratio may justify the cause of various symptoms in human tramadol poisoning.

Suppression of Human Natural Killer Cells by Different Classes of Opioids

BACKGROUND

The use of regional and other opioid-sparing forms of anesthesia has been associated with a decrease in the recurrence of certain malignancies. Direct suppression of human natural killer cells by opioids has been postulated to explain this observation. However, the effect of different classes of opioids on suppression of natural killer cell cytotoxicity has not been systematically characterized.

METHODS

After confirming that freshly isolated natural killer cells from peripheral human blood express opioid receptors, cells were incubated with increasing concentrations of clinically used or receptor-specific opioid agonists. We also evaluated the effect of pretreatment with receptor-specific antagonists or naloxone. Treated natural killer cells were then coincubated with a carboxyfluorescein succinimidyl ester-labeled target tumor cell line, K562. Annexin V staining was used to compare the percent of tumor cell apoptosis in the presence of opioid-pretreated and untreated natural killer cells. Treated samples were compared to untreated samples using Kruskal-Wallis tests with a post hoc Dunn correction.

RESULTS

Morphine, methadone, buprenorphine, loperamide, [D-Ala2, N-MePhe4, Gly-ol]-enkephalin, and U-50488 significantly decreased natural killer cell cytotoxicity. When natural killer cells were pretreated with naloxone, cyprodime, and nor-binaltorphimine before exposure to morphine, there was no difference in natural killer cytotoxicity, compared to the amount observed by untreated natural killer cells. Fentanyl, O-desmethyltramadol, and [D-Pen2,D-Pen5] enkephalin did not change natural killer cell cytotoxicity compare to untreated natural killer cells.

CONCLUSIONS

Incubation of isolated natural killer cells with certain opioids causes a decrease in activity that is not observed after naloxone pretreatment. Suppression of natural killer cell cytotoxicity was observed with μ- and κ-receptor agonists but not δ-receptor agonists. These data suggest that the effect is mediated by μ- and κ-receptor agonism and that suppression is similar with many clinically used opioids.

A Reversed-Phase Mode LC-MS/MS Method Using a Polysaccharide Chiral Selector for Simultaneous Quantitation of Each Enantiomer of Tramadol and its Metabolites in Human Plasma and Evaluation of CYP-Mediated Stereoselective Demethylation

BACKGROUND

The enantiomeric pharmacokinetics and metabolism of tramadol and its metabolites have not fully been understood. This study aimed to develop a reversed-phase mode liquid chromatography coupled to a tandem mass spectrometry method for the enantiomeric quantitation of tramadol and its metabolites in human plasma and to evaluate the stereoselective demethylation.

METHODS

Racemic tramadol and its metabolites in plasma specimens were separated using a chiral selector coated with cellulose tris(3,5-dimethylphenylcarbamate) on silica gel under a reversed-phase mode. The mass spectrometer ran in the positive ion multiple-reaction monitoring mode. This method was performed to quantify plasma samples from 20 cancer patients treated with oral tramadol. The stereoselective demethylation was evaluated using recombinant cytochrome P450 (CYP) enzymes.

RESULTS

The calibration curves of (+)- and (-)-tramadol, (+)- and (-)-O-desmethyltramadol (ODT), and (+)- and (-)-N-desmethyltramadol (NDT) were linear over the plasma concentration ranges of 6.25-800, 1.25-160, and 3.13-400 ng/mL for the respective enantiomers. In the present method, the intra- and inter-day accuracies and imprecisions were 94.2%-108.3% and 0.5%-6.0% for all analytes. The plasma concentrations of (+)-tramadol and NDT were higher than those of (-)-enantiomers. In contrast, no differences were observed between the plasma concentrations of (+)- and (-)-ODT. In the demethylation assay, the O-demethylations of tramadol and NDT by CYP2D6 were (-)-form-selective.

CONCLUSIONS

The present method can be useful in the enantiomeric evaluation of tramadol and its metabolites in human plasma. Although CYP2D6 contributed to the stereoselective demethylation of tramadol, remarkable differences between (+)- and (-)-ODT were not observed in the plasma of the cancer patients.

A Time-Embedding Network Models the Ontogeny of 23 Hepatic Drug Metabolizing Enzymes

Pediatric patients are at elevated risk of adverse drug reactions, and there is insufficient information on drug safety in children. Complicating risk assessment in children, there are numerous age-dependent changes in the absorption, distribution, metabolism, and elimination of drugs. A key contributor to age-dependent drug toxicity risk is the ontogeny of drug metabolism enzymes, the changes in both abundance and type throughout development from the fetal period through adulthood. Critically, these changes affect not only the overall clearance of drugs but also exposure to individual metabolites. In this study, we introduce time-embedding neural networks in order to model population-level variation in metabolism enzyme expression as a function of age. We use a time-embedding network to model the ontogeny of 23 drug metabolism enzymes. The time-embedding network recapitulates known demographic factors impacting 3A5 expression. The time-embedding network also effectively models the nonlinear dynamics of 2D6 expression, enabling a better fit to clinical data than prior work. In contrast, a standard neural network fails to model these features of 3A5 and 2D6 expression. Finally, we combine the time-embedding model of ontogeny with additional information to estimate age-dependent changes in reactive metabolite exposure. This simple approach identifies age-dependent changes in exposure to valproic acid and dextromethorphan metabolites and suggests potential mechanisms of valproic acid toxicity. This approach may help researchers evaluate the risk of drug toxicity in pediatric populations.

The human endogenous metabolome as a pharmacology baseline for drug discovery

We have limited understanding of the variation in in vitro affinities of drugs for their targets. An analysis of a highly curated set of 815 interactions between 566 drugs and 129 primary targets reveals that 71% of drug-target affinities have values above that of the corresponding endogenous ligand, 96% of them fitting within a range of two orders of magnitude. Our findings suggest that the evolutionary optimised affinity of endogenous ligands for their native proteins can serve as a baseline for the primary pharmacology of drugs. We show that the degree of off-target selectivity and safety risks of drugs derived from their secondary pharmacology depend very much on that baseline. Thus, we propose a new approach for estimating safety margins.

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.

Status Epilepticus Decreases Brain Cytochrome P450 2D4 Expression in Rats

Status epilepticus (SE) is a life-threatening neurological emergency characterized by frequent seizures. The present study aims at elucidating the effect of SE on CYP2D4 expression in the rat brain. To create a rat model of SE, Sprague-Dawley rats were intraperitoneally administered 10 mg/kg kainic acid. The CYP2D4 mRNA levels in the cortex and hippocampus of the SE rats were decreased by 0.38- and 0.39-fold, respectively. The protein level of octamer transcription factor 1 (Oct-1), which is involved in the transcriptional activation of CYP2D4 by binding to the CYP2D4 regulatory element, was also attenuated by 0.64- and 0.51-fold in these regions of the SE rat, suggesting that a reduction in Oct-1 may be involved in the CYP2D4 suppression. Yin yang 1 can function as a cofactor of histone deacetylase 1 and inhibit the binding of Oct-1 to the CYP2D4 regulatory element. The coimmunoprecipitation assay revealed that the interaction between yin yang 1 and histone deacetylase 1 in the cortex and hippocampus was enhanced during SE, indicating that this interaction is also responsible for the CYP2D4 suppression. This study clarified that SE led to a decrease in the expression of CYP2D4, thus altering the pharmacokinetics and efficacy of the drugs in the brain.

Tramadol metabolism to O-desmethyl tramadol (M1) and N-desmethyl tramadol (M2) by dog liver microsomes: Species comparison and identification of responsible canine cytochrome P-450s (CYPs)

Tramadol is widely used to manage mild to moderately painful conditions in dogs. However, this use is controversial since clinical efficacy studies in dogs showed conflicting results, while pharmacokinetic studies demonstrated relatively low circulating concentrations of O-desmethyltramadol (M1). Analgesia has been attributed to the opioid effects of M1, while tramadol and the other major metabolite (N-desmethyltramadol, M2) are considered inactive at opioid receptors. The aims of this study were to determine whether cytochrome P450 (CYP) dependent M1 formation by dog liver microsomes is slower compared with cat and human liver microsomes; and identify the CYPs responsible for M1 and M2 formation in canine liver. Since tramadol is used as a racemic mixture of (+)- and (-)-stereoisomers, both (+)-tramadol and (-)- tramadol were evaluated as substrates. M1 formation from tramadol by liver microsomes from dogs was slower than from cats (3.9-fold), but faster than humans (7-fold). However, M2 formation by liver microsomes from dogs was faster than from cats (4.8-fold) and humans (19-fold). Recombinant canine CYP activities indicated that M1 was formed by CYP2D15, while M2 was largely formed by CYP2B11 and CYP3A12. This was confirmed by dog liver microsomes studies that showed selective inhibition of M1 formation by quinidine and M2 formation by chloramphenicol and CYP2B11 antiserum, and induction of M2 formation by phenobarbital. Findings were similar for both (+)-tramadol and (-)-tramadol. In conclusion, low circulating M1 concentrations in dogs is explained in part by low M1 formation and high M2 formation, which are mediated by CYP2D15 and CYP2B11/CYP3A12, respectively.

Latarjet Procedure for Anterior Shoulder Instability Due to Tramadol-Induced Seizures: A Multicenter Study

BACKGROUND

Seizures, commonly due to epilepsy, are known to cause shoulder instability. Tramadol addiction has recently been found to induce seizures in patients who exceed the recommended dose. Because of the easy accessibility and low cost of tramadol, an increasingly alarming phenomenon of tramadol abuse has been demonstrated in recent years.

PURPOSE/HYPOTHESIS

The purpose of this multicenter study was to investigate shoulder instability resulting from tramadol-induced seizure (TIS) as well as to recommended management for such shoulder instability. The hypothesis was that TIS leads to anterior shoulder dislocations with major bony defects, which favors bony reconstructive procedures as a suitable method of treatment.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

This prospective case series study was conducted on 73 patients (78 shoulders) who presented with anterior shoulder dislocations and a clear history of tramadol abuse. The mean age of the patients was 26.8 years, and the mean number of dislocations was 14. The mean duration of addiction was 17 months, with a mean dose of 752 mg of tramadol hydrochloride per day. Glenoid and humeral bone loss ranged from 15% to 35% and from 15% to 40%, respectively. The mean follow-up period was 28 months. All patients underwent an open Latarjet procedure.

RESULTS

Postoperative mean Rowe score and American Shoulder and Elbow Surgeons score at final follow-up (24 months) improved significantly from 20 to 84 and from 44 to 91, respectively (P < .05). The patient satisfaction rate reached 95%, and the mean period of return to work was 12.8 weeks. Five patients (9%) had postoperative seizures due to relapse of the tramadol abuse, but only 3 patients (5%) had redislocations with nonunion or breakage of the graft or hardware.

CONCLUSION

Tramadol addiction has evolved as an important cause of seizures that can result in shoulder dislocation. Anterior shoulder instability with TIS occurs mainly with higher levels of addiction and results in significant humeral and/or glenoid bone defects. The Latarjet procedure is recommended for these patients, after control of addiction, and provides 95% satisfaction at midterm follow-up.

Pain management of the cancer patient

INTRODUCTION

Cancer pain is one of the most important symptoms of malignant disease, which has a major impact on the quality of life of cancer patients. Therefore, it needs to be treated appropriately after a careful assessment of the types and causes of pain.

AREAS COVERED

The mainstay of cancer pain management is systemic pharmacotherapy. This is, in principle, still based on the WHO guidelines initially published in 1986. Although these have been validated, they are not evidence-based. The principles are a stepladder approach using non-opioids, weak and then strong opioids. In addition, adjuvants can be added at any step to address specific situations such as bone or neuropathic pain. Patients, even if they are on long-acting opioids, need to be provided with immediate-release opioids for breakthrough pain. In case of inefficacy or severe adverse effects of one opioid, rotation to another opioid is recommended.

EXPERT OPINION

There is a major need for more and better randomized controlled trials in the setting of cancer pain as the lack of evidence is hampering the improvement of current treatment guidelines.

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.

Pharmacologically active drug metabolites: impact on drug discovery and pharmacotherapy

Metabolism represents the most prevalent mechanism for drug clearance. Many drugs are converted to metabolites that can retain the intrinsic affinity of the parent drug for the pharmacological target. Drug metabolism redox reactions such as heteroatom dealkylations, hydroxylations, heteroatom oxygenations, reductions, and dehydrogenations can yield active metabolites, and in rare cases even conjugation reactions can yield an active metabolite. To understand the contribution of an active metabolite to efficacy relative to the contribution of the parent drug, the target affinity, functional activity, plasma protein binding, membrane permeability, and pharmacokinetics of the active metabolite and parent drug must be known. Underlying pharmacokinetic principles and clearance concepts are used to describe the dispositional behavior of metabolites in vivo. A method to rapidly identify active metabolites in drug research is described. Finally, over 100 examples of drugs with active metabolites are discussed with regard to the importance of the metabolite(s) in efficacy and safety.

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.

Mechanistic and functional differentiation of tapentadol and tramadol

INTRODUCTION

Many opioid analgesics share common structural elements; however, minor differences in structure can result in major differences in pharmacological activity, pharmacokinetic profile, and clinical efficacy and tolerability.

AREAS COVERED

This review compares and contrasts the chemistry, pharmacodynamics, pharmacokinetics, and CNS 'functional activity' of tapentadol and tramadol, responsible for their individual clinical utilities.

EXPERT OPINION

The distinct properties of tapentadol and tramadol generate different CNS functional activities, making each drug the prototype of different classes of opioid/nonopioid analgesics. Tramadol's analgesia derives from relatively weak µ-opioid receptor (MOR) agonism, plus norepinephrine and serotonin reuptake inhibition, provided collectively by the enantiomers of the parent drug and a metabolite that is a stronger MOR agonist, but has lower CNS penetration. Tapentadol's MOR agonist activity is several-fold greater than tramadol's, with prominent norepinephrine reuptake inhibition and minimal serotonin effect. Accordingly, tramadol is well-suited for pain conditions for which a strong opioid component is not needed-and it has the benefit of a low abuse potential; whereas tapentadol, a schedule-II controlled substance, is well-suited for pain conditions requiring a strong opioid component-and it has the benefit of greater gastrointestinal tolerability compared to classical strong opioids. Both drugs offer distinct and complementary clinical options.

Fixed-dose combinations for emerging treatment of pain

INTRODUCTION

Pain is a large and growing medical need that is not currently being fully met, primarily due to the shortcomings of existing analgesics (insufficient efficacy or limiting side-effects). Better outcomes might be achieved using a combination of analgesics. The ratio of the combinations matters and should therefore be evaluated using rigorous quantitative and well-documented analysis.

AREAS COVERED

Advances have been made in understanding the normal physiology of pain processing, including the pathways and neurotransmitters involved. Insight has also been gained about physiological processes that can lead to different 'types' of pain and the transition from acute to chronic pain conditions. This 'multimechanistic' nature of most pains is better matched using a 'multimechanistic' rather than 'monomechanistic' analgesic approach. Such an approach - and the experimental design and data analysis to assess optimal combinations - is described and discussed.

EXPERT OPINION

There are sound pharmacologic, as well as practical, reasons for using combinations of drugs to treat pain. Compared with single agents, they offer a potential better match to the underlying pain physiology and thus greater efficacy or reduced side effects. The optimal efficacy and side-effect ratio must be determined in a scientifically rigorous manner.

Extended-release formulations of tramadol in the treatment of chronic pain

INTRODUCTION

Tramadol is a centrally acting analgesic available throughout the world. Its dual opioid and non-opioid mechanisms of action, favorable efficacy and safety clinical profiles and non-controlled regulatory status in most markets contribute to its widespread use. A drawback of the immediate-release formulation of tramadol (four-times-a-day dosing) might be addressed by an extended-release formulation. Extended-release formulations also can offer advantages in the management of chronic pain: convenience, reduced pill burden (possibly leading to improved compliance) and the attenuation of peaks and troughs in serum concentration (possibly leading to reduced adverse effects).

AREAS COVERED

The authors review tramadol's mechanisms of action and the clinical literature regarding the use of tramadol extended-release formulations for the management of conditions involving chronic pain, such as neuropathic pain syndromes, osteoarthritis and cancer pain.

EXPERT OPINION

Based on the literature cited, extended-release formulations of tramadol seem to offer a rational and important addition to the analgesic armamentarium. As is true for all such options, the benefits and risks must be assessed for each patient.

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.

Epileptic seizure following IV tramadol in a patient with mental retardation and cerebellar ataxia

OBJECTIVE

To present a case of an epileptic seizure related to intravenous (IV) tramadol for pain control following a total abdominal hysterectomy operation on a patient with mental retardation and cerebellar ataxia.

BACKGROUND

Tramadol is an analgesic with a dual mechanism of action and has several side effects, one of which is epileptic seizure.

CASE REPORT

A 42-year-old female with mental retardation and cerebellar ataxia presented with an epileptic seizure after administration of IV tramadol for postoperative pain. Magnetic resonance imaging scans were normal, but laboratory tests showed hypocalcemia. Next, calcium replacement was administered. Postoperative pain treatment with tramadol was discontinued because tramadol was felt to be a possible cause of the seizure observed in this patient. In order to treat the epileptic seizure, IV phenytoin sodium infusion was started. On the second postoperative day, calcium levels were found to be normal, and the IV antiepileptic medication was changed to an oral form. The patient had no subsequent seizures during the clinical follow-up. She was discharged on the fourth postoperative day without any other complications.

CONCLUSION

Even in recommended doses, IV tramadol may cause epileptic seizures on predisposed patients.

Personalized therapy in pain management: where do we stand?

Genomic variations influencing response to pharmacotherapy of pain are currently under investigation. Drug-metabolizing enzymes represent a major target of ongoing research in order to identify associations between an individual’s drug response and genetic profile. Polymorphisms of the cytochrome P450 enzymes (CYP2D6) influence metabolism of codeine, tramadol, hydrocodone, oxycodone and tricyclic antidepressants. Blood concentrations of some NSAIDs depend on CYP2C9 and/or CYP2C8 activity. Genomic variants of these genes associate well with NSAIDs’ side effect profile. Other candidate genes, such as those encoding (opioid) receptors, transporters and other molecules important for pharmacotherapy in pain management, are discussed; however, study results are often equivocal. Besides genetic variants, further variables, for example, age, disease, comorbidity, concomitant medication, organ function as well as patients’ compliance, may have an impact on pharmacotherapy and need to be addressed when pain therapists prescribe medication. Although pharmacogenetics as a diagnostic tool has the potential to improve patient therapy, well-designed studies are needed to demonstrate superiority to conventional dosing regimes.

Dose-independent occurrence of seizure with tramadol

INTRODUCTION

Tramadol, as a centrally-acting, opioid-like analgesic with serotonin reuptake inhibition property, is one of the most prescribed analgesics in the world. We assessed the incidence of seizure, as it is one of the most important adverse effects.

METHODS

In a cross-sectional study, 215 cases of tramadol users or abusers who were admitted to Loghman-Hakim Hospital Poisoning Center (LHHPC) in Tehran during a 5-month period, from April 2007 to September 2007, were assessed to evaluate the occurrence of seizure. Patients with positive history of co-ingestion of other drugs, addiction, convulsive disorders, renal diseases, or head trauma with abnormal electroencephalography (EEG) or computerized tomography (CT) scan of the brain were excluded, thus 132 patients were included in the study. For patients who had seizure, CT scan of the brain and EEG were performed, and frequency and type of seizure were identified. Mean tramadol dose was compared between patients with and without seizure.

RESULTS

Among the patients, 97 (73.5%) were male. Seizure occurred in 61 patients (46.2%) within 24 hours after tramadol ingestion. The majority of patients who had seizure were male (male, 83.6% vs. female, 16.4%). Mean tramadol dose was lower among females than males (males, 2413 mg vs. females, 1706 mg), but the difference was not statistically significant. Of 35 patients with documented seizure type, all showed generalized tonic-clonic seizure and 12 patients had abnormal EEG (35.3%). No statistically significant difference was observed in mean tramadol intake between patients with or without seizure. Analysis of patients with seizure, according to tramadol intake, indicated that most patients used tramadol in the dose range of 500-1000 mg followed in occurrence by 1500-2000 mg, then 100-500 mg, 2500-3000 mg, and 3500-4000 mg.

CONCLUSIONS

Mean tramadol intake does not differ between patients with and without seizure, and the most common dose range in those with seizure is 500-1000 mg. We thus conclude that the incidence of seizure with tramadol is not dose dependent.

CYP2D6 polymorphism in relation to tramadol metabolism: a study of faroese patients

Several studies have demonstrated the impact of CYP2D6 polymorphism on the pharmacokinetics of tramadol. However, the relationship between the O-demethylation of tramadol and O-desmethyltramadol (M1) and CYP2D6 activity has not previously been investigated with tramadol in multimedicated outpatients under steady-state conditions. Hence, the aim of this study was to determine if the well documented pharmacokinetics of tramadol regarding CYP2D6 could be verified in a study including 88 multimedicated Faroese patients, treated with tramadol at steady-state conditions. Further, the study aimed to investigate whether the previously observed frequency of CYP2D6 poor metabolizers (PMs) in the Faroese, which was shown to be double that of other Europeans, was evident in a patient group medicated with a CYP2D6 substrate. The patients were CYP2D6-phenotyped by the intake of sparteine, followed by urine collection over 12 hours. Sparteine and its metabolites were assayed by gas chromatography. Genotype analyses for the CYP2D6 3, 4, 6, and 9 alleles were performed by polymerase chain reaction and Taqman technology. Plasma and urinary concentrations of (+/-)-tramadol and (+/-)-M1 were determined by high-performance liquid chromatography. With use of CYP2D6 phenotyping, 10 patients (11.5% [95% confidence interval (CI), 5.7-20.1%]) were classified as CYP2D6 PMs, and 8 (9.3% [95% CI, 4.1-17.3%]) of these were genotyped as CYP2D6 PMs. The PM frequency was not statistically significantly higher than that in other European populations (7%-10%). The concentrations of (+)-M1 when corrected for dose (nM/mg) and the (+)-M1/(+)-tramadol ratio were approximately 14-fold higher in the extensive metabolizers (EMs) than in the PMs. In conclusion, the impact of the CYP2D6 polymorphism on the pharmacokinetics of tramadol was clearly demonstrated in a group of multimedicated patients treated with tramadol under steady-state conditions. Further, the frequency of PMs was not higher than that in other European populations, as previously shown in different Faroese groups, possibly because of discontinued tramadol treatment in Faroese patients who were PMs.

Inhibitory effects of opioids on compound action potentials in frog sciatic nerves and their chemical structures

An opioid tramadol more effectively inhibits compound action potentials (CAPs) than its metabolite mono-O-demethyl-tramadol (M1). To address further this issue, we examined the effects of opioids (morphine, codeine, ethylmorphine and dihydrocodeine) and cocaine on CAPs by applying the air-gap method to the frog sciatic nerve. All of the opioids at concentrations less than 10 mM reduced the peak amplitude of the CAP in a reversible and dose-dependent manner. The sequence of the CAP peak amplitude reductions was ethylmorphine>codeine>dihydrocodeine> or = morphine; the effective concentration for half-maximal inhibition (IC(50)) of ethylmorphine was 4.6 mM. All of the CAP inhibitions by opioids were resistant to a non-specific opioid-receptor antagonist naloxone. The CAP peak amplitude reductions produced by morphine, codeine and ethylmorphine were related to their chemical structures in such that this extent enhanced with an increase in the number of -CH(2) in a benzene ring, as seen in the inhibitory actions of tramadol and M1. Cocaine reduced CAP peak amplitudes with an IC(50) value of 0.80 mM. It is concluded that opioids reduce CAP peak amplitudes in a manner being independent of opioid-receptor activation and with an efficacy being much less than that of cocaine. It is suggested that the substituted groups of -OH bound to the benzene ring of morphine, codeine and ethylmorphine as well as of tramadol and M1, the structures of which are quite different from those of the opioids, may play an important role in producing nerve conduction block.

Unexceptional seizure potential of tramadol or its enantiomers or metabolites in mice

Tramadol is one of the most widely used centrally acting analgesics worldwide. Because of its multimodal analgesic mechanism (opioid plus nonopioid), the adverse effects profile of tramadol, similar to its analgesic profile, can be atypical compared with single-mechanism opioid analgesics. The comparison is often favorable (e.g., less respiratory depression or abuse), but it is sometimes cited as unfavorable in regard to seizure potential. As part of a broader study of this analgesic, we compared seizure induction in mice produced by administration of tramadol, the enantiomers and metabolites [M1 (O-desmethyl tramadol), M2 (N-desmethyl tramadol), M3 (N,N-didesmethyl tramadol), M4 (O,N,N-tridesmethyl tramadol), and M5 (O,N-didesmethyl tramadol)] of tramadol, and opioid and nonopioid reference compounds. We found that tramadol, its enantiomers, and M1 to M5 metabolites were of intermediate potency in this endpoint (on either a milligram per kilogram or millimole per kilogram basis). The SD50 (estimated dose required to induce seizures in 50% of test group) of tramadol to antinociceptive ED50 ratio was almost identical to that of codeine. The enantiomers of tramadol were about equipotent to tramadol on this endpoint. The M1 to M5 metabolites (and M1 enantiomers) of tramadol were less potent than tramadol. The relative potency of tramadol to opioids was not altered by quinidine (an inhibitor of CYP4502D6), noxious stimulus (48 degrees C hot-plate), multiple dosing, or in reserpinized mice. Tramadol seizures were increased by naloxone, principally at high tramadol doses and due to an effect on the (-)enantiomer that overcame the opposite effect on the (+)enantiomer. No synergistic effect on seizure induction was observed between concomitant tramadol and codeine or morphine.

Effects of the CYP2D6 gene duplication on the pharmacokinetics and pharmacodynamics of tramadol

The analgesic drug tramadol is bioactivated by CYP2D6 to the opioid receptor agonist O-desmethyltramadol. Case reports indicated that carriers of the CYP2D6 gene duplication may be at high risk for opioid adverse events. However, the effects of the CYP2D6 duplication on kinetics and dynamics of tramadol have not been systematically studied. Pharmacokinetics and effects were monitored after a single dose of 100 mg racemic tramadol in 11 carriers of a CYP2D6 gene duplication allele (ultrarapid metabolizer [UM]) and compared with 11 carriers of 2 active CYP2D6 genes (extensive metabolizer [EM]). Pharmacodynamics was measured by cold pressure test, pupillometry, and standardized adverse event recording. The maximum plasma concentrations of the active metabolite (+)R,R-O-desmethyltramadol were significantly higher in the UM group compared with the EM group (P = 0.005; t test) with a mean difference of 14 ng/mL (95% confidence limit of difference, 2-26 ng/mL). Median (+)R,R-tramadol area under the curve was 786 and 587 mug.h.L in EMs and UMs, and the corresponding median (+)R,R-O-desmethyltramadol area under the curve was 416 and 448 mug.h.L (P = 0.005, t test). There was an increased pain threshold and pain tolerance and a stronger miosis after tramadol in UMs compared with EMs. Almost 50% of the UM group experienced nausea compared with only 9% of the EM group. In conclusion, pharmacokinetic differences between EMs and UMs were smaller than expected; nevertheless, UMs were more sensitive to tramadol than EMs. Therefore, tramadol may frequently cause adverse effects in southern European and Northern African populations with a high proportion of UMs.

Modest opioid withdrawal suppression efficacy of oral tramadol in humans

RATIONALE

Tramadol is in an unscheduled atypical analgesic with low rates of diversion and abuse and mixed pharmacologic actions, including modest opioid agonist activity.

OBJECTIVES

The purpose of the current study was to characterize the opioid withdrawal suppression efficacy of oral tramadol.

MATERIALS AND METHODS

Residential, opioid-dependent adults (n = 10) were maintained on morphine (15 mg subcutaneously, quad in diem) for approximately 6 weeks. Spontaneous opioid withdrawal was produced by substituting placebo for scheduled morphine doses 17.5 h before experimental sessions that occurred twice weekly. The acute effects of placebo, tramadol (50, 100, 200, and 400 mg orally), naloxone (0.1 and 0.2 mg intramuscularly [IM]), and morphine (15 and 30 mg IM) were tested under double-blind, double-dummy, randomized conditions. Outcomes included observer- and subject-rated measures, physiologic indices, and psychomotor/cognitive task performance.

RESULTS

Naloxone and morphine produced prototypic opioid antagonist and agonist effects, respectively. Tramadol 50 and 100 mg produced effects most similar to placebo. Tramadol 200 and 400 mg initially produced significant dose-related increases in ratings of "bad effects" and "feel sick," followed by evidence of opioid withdrawal suppression. Tramadol did not produce significant increases on measures of positive drug effects nor any clinically significant physiologic changes.

CONCLUSIONS

Tramadol 200 and 400 mg show evidence of opioid withdrawal suppression without significant observer- and subject-rated opioid agonist effects. The profile of action did not suggest a high risk for tramadol abuse in opioid dependent individuals. Tramadol may be a useful medication for treating opioid withdrawal.

The addition of tramadol to morphine via patient-controlled analgesia does not lead to better post-operative pain relief after total knee arthroplasty

BACKGROUND

Tramadol is used as an analgesic in post-operative pain treatment. Intravenous tramadol is often combined with morphine to achieve better pain relief and less side-effects after orthopaedic surgery. However, the available evidence is insufficient to support this combination. For this reason, we conducted the present non-commercial, randomized, double-blind clinical trial.

METHOD

Sixty-three patients with osteoarthritis of the knee, selected for primary total knee arthroplasty (TKA), were randomized to receive saline or tramadol 100 mg/ml intravenously every 6 h during the first post-operative day (total, 400 mg/24 h). All patients had access to morphine via a patient-controlled analgesia (PCA) pump.

RESULTS

Neither during the 6 h after the first dose nor during the first post-operative day could we detect any statistically significant difference with regard to pain intensity, sedation and nausea between patients treated with tramadol and the placebo group. However, the withdrawal rate caused by insufficient pain relief was greater in the tramadol group (7/31) than in the saline group (2/32). This difference did not reach statistical significance. In the group of patients who remained in the study for 24 h ('per protocol'), those randomized to receive tramadol had a significantly (P < 0.05) lower morphine consumption (20 mg or 31%) than the placebo group.

CONCLUSION

Our study does not support the combination of tramadol and morphine via PCA for post-operative pain relief after primary TKA. In addition, our study indicates that morphine via PCA as the sole means of post-operative analgesia does not provide sufficient pain relief after TKA. Thus, other means of post-operative analgesia should be used following TKA.

Enantioselective pharmacokinetics of tramadol in CYP2D6 extensive and poor metabolizers

OBJECTIVE

To describe in detail the intravenous, single oral and multiple oral dose enantioselective pharmacokinetics of tramadol in CYP2D6 extensive metabolizers (EMs) and poor metabolizers (PMs).

METHODS

Eight EMs and eight PMs conducted three phases as an open-label cross-over trial with different formulations; 150 mg single oral tramadol hydrochloride, 50 mg single oral tramadol hydrochloride every 8 h for 48 h (steady state), 100 mg intravenous tramadol hydrochloride. Urine and plasma concentrations of (+/-)-tramadol and (+/-)-M1 were determined for 48 h after administration.

RESULTS

In all three phases, there were significant differences between EMs and PMs in AUC and t(1/2) of (+)-tramadol (P< or =0.0015), (-)-tramadol (P< or =0.0062), (+)-M1 (P< or =0.0198) and (-)-M1 (P< or =0.0370), and significant differences in C(max) of (+)-M1 (P<0.0001) and (-)-M1 (P< or =0.0010). In Phase A and C, significant differences in t(max) were seen for (+)-M1 (P< or =0.0200). There were no statistical differences between the absolute bioavailability of tramadol in EMs and PMs. The urinary recoveries of (+)-tramadol, (-)-tramadol, (+)-M1 and (-)-M1 were statistically significantly different in EMs and PMs (P<0.05). Median antimodes of the urinary metabolic ratios of (+)-tramadol / (+)-M1 and (-)-M1 were 5.0 and 1.5, respectively, hereby clearly separating EMs and PMs in all three phases.

CONCLUSION

The impact of CYP2D6 phenotype on tramadol pharmacokinetics was similar after single oral, multiple oral and intravenous administration displaying significant pharmacokinetic differences between EMs and PMs of (+)-tramadol, (-)-tramadol, -(+)-M1 and (-)-M1. The O-demethylation of tramadol was catalysed stereospecific by CYP2D6 in the way that very little (+)-M1 was produced in PMs.

Opioid metabolites

The metabolism of opioids closely relates to their chemical structure. Opioids are subject to O-dealkylation, N-dealkylation, ketoreduction, or deacetylation leading to phase-I metabolites. By glucuronidation or sulfatation, phase-II metabolites are formed. Some metabolites of opioids have an activity themselves and contribute to the effects of the parent compound. This can go as far that the main clinical activity is exerted through active metabolites while the parent compounds are only weak agonist at mu-opioid receptors, as in the case of codeine and tilidine. The clinical effects of tramadol also involve an important contribution of its active metabolite. With morphine, the active metabolite morphine-6-glucuronide exerts important clinical opioid effects when it accumulates in the plasma of patients with renal failure. However, after short-term administration of morphine, its contribution to the central nervous effects of morphine is probably poor. Morphine-6-glucuronide has recently been identified to exert important peripheral opioid effects. By this, it may play an important role in the clinical effects of morphine. Several other opioids, such as meperidine and perhaps also morphine and hydromorphone, produce metabolites with neuroexcitatory effects. In sum, the evidence suggests that the metabolites of several opioids account for an important part of the clinical effects that must be considered in clinical practice.

Actions of tilidine and nortilidine on cloned opioid receptors

Tilidine, alone or combined with naloxone to prevent drug abuse, is used as an oral opioid analgesic. Although the analgesic action of tilidine and its active metabolite nortilidine is reversed by naloxone and therefore believed to involve the activation of the Mu opioid (MOP, OP3, mu) receptor, this has never been studied in recombinant systems. We have measured the selectivity of tilidine and nortilidine for human opioid and opioid-like receptors stably expressed in CHO-K1 cells, using the inhibition of the forskolin (FK)-induced accumulation of cAMP as endpoint. In cells expressing the MOP receptor, tilidine and nortilidine inhibited cAMP accumulation with IC50 of 11 microM and 110 nM, respectively. The agonist effects of nortilidine and [D-Ala2-MePhe4-Gly5-ol]enkephalin (DAMGO) on the MOP receptor were reversed by naloxone with very similar IC50 (1.2 versus 1.8 nM). At concentrations up to 100 microM, tilidine and nortilidine had no agonist effect on the DOP, KOP and NOP receptors. In conclusion, this study on cloned human receptors demonstrates that nortilidine is a selective agonist of the MOP receptor.

Opioid peptide receptor studies. 17. Attenuation of chronic morphine effects after antisense oligodeoxynucleotide knock-down of RGS9 protein in cells expressing the cloned Mu opioid receptor

RGS proteins are a recently described class of regulators that influence G-protein-mediated signaling pathways. We have shown previously that chronic morphine results in functional uncoupling of the mu opioid receptor from its G protein in CHO cells expressing cloned human mu opioid receptors. In the present study, we examined the effects of morphine treatment (1 microM, 20 h) on DAMGO-stimulated high-affinity [35S]GTP-gamma-S binding and DAMGO-mediated inhibition of forskolin-stimulated cAMP accumulation in HN9.10 cells stably expressing the cloned rat mu opioid receptor, in the absence and presence of the RGS9 protein knock-down condition (confirmed by Western blot analysis). RGS9 protein expression was reduced by blocking its mRNA with an antisense oligodeoxynucleotide (AS-114). Binding surface analysis resolved two [35S]GTP-gamma-S binding sites (high affinity and low affinity sites). In sense-treated control cells, DAMGO-stimulated [35S]GTP-gamma-S binding by increasing the B(max) of the high-affinity site. In sense-treated morphine-treated cells, DAMGO-stimulated [35S]GTP-gamma-S binding by decreasing the high-affinity Kd without changing the B(max). AS-114 significantly inhibited chronic morphine-induced upregulation of adenylate cyclase activity and partially reversed chronic morphine effects as measured by DAMGO-stimulated [35S]GTP-gamma-S binding. Morphine treatment increased the EC50 (6.2-fold) for DAMGO-mediated inhibition of forskolin-stimulated cAMP activity in control cells but not in cells treated with AS-114 to knock-down RGS9. These results provide additional evidence for involvement of RGS9 protein in modulating opioid signaling, which may contribute to the development of morphine tolerance and dependence.

Genetic Predictors of the Clinical Response to Opioid Analgesics

This review uses a candidate gene approach to identify possible pharmacogenetic modulators of opioid therapy, and discusses these modulators together with demonstrated genetic causes for the variability in clinical effects of opioids. Genetically caused inactivity of cytochrome P450 (CYP) 2D6 renders codeine ineffective (lack of morphine formation), slightly decreases the efficacy of tramadol (lack of formation of the active O-desmethyl-tramadol) and slightly decreases the clearance of methadone. MDR1 mutations often demonstrate pharmacogenetic consequences, and since opioids are among the P-glycoprotein substrates, opioid pharmacology may be affected by MDR1 mutations. The single nucleotide polymorphism A118G of the mu opioid receptor gene has been associated with decreased potency of morphine and morphine-6-glucuronide, and with decreased analgesic effects and higher alfentanil dose demands in carriers of the mutated G118 allele. Genetic causes may also trigger or modify drug interactions, which in turn can alter the clinical response to opioid therapy. For example, by inhibiting CYP2D6, paroxetine increases the steady-state plasma concentrations of (R)-methadone in extensive but not in poor metabolisers of debrisoquine/sparteine. So far, the clinical consequences of the pharmacogenetics of opioids are limited to codeine, which should not be administered to poor metabolisers of debrisoquine/sparteine. Genetically precipitated drug interactions might render a standard opioid dose toxic and should, therefore, be taken into consideration. Mutations affecting opioid receptors and pain perception/processing are of interest for the study of opioid actions, but with modern practice of on-demand administration of opioids their utility may be limited to explaining why some patients need higher opioid doses; however, the adverse effects profile may be modified by these mutations. Nonetheless, at a limited level, pharmacogenetics can be expected to facilitate individualised opioid therapy.

Effects of tramadol on synovial fluid concentrations of substance P and interleukin-6 in patients with knee osteoarthritis: comparison with paracetamol

Both the analgesic drugs tramadol and paracetamol are widely used for the symptomatic therapy of osteoarthritis (OA). The aim of this double-blind, randomised study in patients with knee OA was to compare their effects on synovial fluid concentrations of interleukin (IL)-6 and substance P (SP). Moreover, we evaluated plasma and synovial fluid concentrations of tramadol and its active metabolite (O-desmethyl-tramadol, M1) after oral treatment with this drug. Twenty patients were enrolled. A group of 10 patients received tramadol (50 mg three times a day), and another group of 10 patients were treated with paracetamol (500 mg three times a day) for 7 days. Both drugs significantly reduced the intensity of joint pain. The synovial fluid concentrations of SP were significantly reduced only by the treatment with tramadol. In this group of patients, IL-6 synovial fluid concentrations were slightly, but not significantly, decreased. Paracetamol did not significantly change the synovial fluid concentrations of SP and IL-6. After oral administration, a considerable amount of tramadol was measurable in synovial fluid. Both in plasma and synovial fluid the concentrations of M1 were markedly lower than those of tramadol, with a T/M1 ratio of 14.7+/-4.6 and 9.3+/-3.9, respectively. These data demonstrate that the activity of tramadol may involve the modulation of inflammatory mediators. Moreover, they indicate that after oral treatment with tramadol, both the parent drug and its active metabolite can penetrate into synovial fluid.

An independent assessment of MEDWatch reporting for abuse/dependence and withdrawal from Ultram (tramadol hydrochloride)

OBJECTIVE

Assess the validity of medical products reporting program (MEDWatch) reports of abuse/dependence and withdrawal associated with Ultram (tramadol).

METHODS

Reports of possible abuse/dependence or withdrawal associated with Ultram during 13 quarters following launch were spontaneously reported to the manufacturer Ortho-McNeil Pharmaceutical (OMP) and also solicited from 255 NIDA grantees and addiction treatment professionals by an Independent Steering Committee (ISC). Reports were classified by the ISC using DSM-IV criteria, by the Drug Safety and Surveillance (DSS) units of Robert Wood Johnson Pharmaceutical Research Institute (PRI) using World Health Organization Adverse Reaction Terms (WHOART) terms, and reported to the food and drug administration (FDA) via MEDWatch. Rates of abuse/dependence and withdrawal per 100000 persons exposed were calculated separately for classifications made by the PRI and the ISC, and confidence intervals calculated to determine the degree to which they agreed.

RESULTS

For 681 reports submitted to PRI, confidence intervals of ISC ratings contained PRI ratings 12 of 13 times for abuse/dependence, and 12 of 13 times for withdrawal. For 242 reports submitted to the ISC, confidence intervals of ISC ratings contained PRI ratings 10 of 13 times for abuse/dependence, and 12 of 13 times for withdrawal. Proactive surveillance increased the total number of cases of abuse/dependence but not withdrawal. Many cases of withdrawal without signs or symptoms of abuse/dependence were identified.

CONCLUSIONS

There was good/excellent concordance between MEDWatch and ISC classifications. Proactive surveillance increased cases of abuse/dependence but not withdrawal. Withdrawal with no signs or symptoms of dependence was common. More use of proactive surveillance is likely to improve assessments of public health risks associated with adverse events.

Actions of tramadol on micturition in awake, freely moving rats

1 (+/-)-Tramadol, a widely used analgesic, is a racemate stimulating opioid receptors and inhibiting reuptake of noradrenaline and serotonin, that is, pharmacological principles previously shown to influence rat micturition. 2 We studied both (+/-)-tramadol and its enantiomers in conscious Sprague-Dawley rats undergoing continuous cystometry. The effects of these agents were compared to those of morphine ( micro -opioid receptor agonist) and tested after pretreatment with naloxone ( micro -opioid receptor antagonist). Cystometries were evaluated before and after intravenous (i.v.), intraperitoneal (i.p.) and intrathecal (i.t.) drug administrations. 3 The most conspicuous effects of i.v. (+/-)-tramadol (0.1-10 mg kg(-1)) was an increase in threshold pressure and an increase in micturition volume. 4 These effects were mimicked by (+)-tramadol (0.1-5 mg kg(-1) i.v.), whereas (-)-tramadol (5 mg kg(-1) i.v.) did not influence threshold pressure and micturition volume. 5 The effects of (+/-)-tramadol 5 mg kg(-1) on micturition volume were blocked by pretreatment with naloxone 0.3 mg kg(-1). Morphine (0.3-10 mg kg(-1) i.p.) increased threshold pressure but did not significantly increase micturition volume in doses not resulting in overflow incontinence. 6 (+/-)-Tramadol 10 mg kg(-1) increased urine production, an effect blocked by desmopressin 25 ng kg(-1). 7 (+/-)-Tramadol effectively inhibits micturition in conscious rats by stimulating micro -opioid receptors. A synergy between opioid receptor stimulation and monoamine reuptake inhibition may contribute to the micturition effects.

Pharmacokinetic/pharmacodynamic modeling of the antinociceptive effects of (+)-tramadol in the rat: role of cytochrome P450 2D activity

In this study the role of cytochrome P450 2D (CYP2D) in the pharmacokinetic/pharmacodynamic relationship of (+)-tramadol [(+)-T] has been explored in rats. Male Wistar rats were infused with (+)-T in the absence of and during pretreatment with a reversible CYP2D inhibitor quinine (Q), determining plasma concentrations of Q, (+)-T, and (+)-O-demethyltramadol [(+)-M1], and measuring antinociception. Pharmacokinetics of (+)-M1, but not (+)-T, was affected by Q pretreatment: early after the start of (+)-T infusion, levels of (+)-M1 were significantly lower (P < 0.05). However, at later times during Q infusion those levels increased continuously, exceeding the values found in animals that did not receive the inhibitor. These results suggest that CYP2D is involved in the formation and elimination of (+)-M1. In fact, results from another experiment where (+)-M1 was given in the presence and in absence of Q showed that (+)-M1 elimination clearance (CL(ME0)) was significantly lower (P < 0.05) in animals receiving Q. Inhibition of both (+)-M1 formation clearance (CL(M10)) and CL(ME0) were modeled by an inhibitory E(MAX) model, and the estimates (relative standard error) of the maximum degree of inhibition (E(MAX)) and IC(50), plasma concentration of Q eliciting half of E(MAX) for CL(M10) and CL(ME0), were 0.94 (0.04), 97 (0.51) ng/ml, and 48 (0.42) ng/ml, respectively. The modeling of the time course of antinociception showed that the contribution of (+)-T was negligible and (+)-M1 was responsible for the observed effects, which depend linearly on (+)-M1 effect site concentrations. Therefore, the CYP2D activity is a major determinant of the antinociception elicited after (+)-T administration.