Pharmacokinetic profile of injectable tramadol in the koala (Phascolarctos cinereus) and prediction of its analgesic efficacy

Tramadol is used as an analgesic in humans and some animal species. When tramadol is administered to most species it undergoes metabolism to its main metabolites M1 or O-desmethyltramadol, and M2 or N-desmethyltramadol, and many other metabolites. This study describes the pharmacokinetic profile of tramadol when a single subcutaneous bolus of 2 mg/kg was initially administered to two koalas. Based on the results of these two koalas, subsequently 4 mg/kg as a single subcutaneous injection, was administered to an additional four koalas. M1 is recognised as an active metabolite and has greater analgesic activity than tramadol, while M2 is considered inactive. A liquid chromatography assay to quantify tramadol, M1 and M2 in koala plasma was developed and validated. Liquid chromatography-mass spectrometry confirmed that M1 had been identified. Additionally, the metabolite didesmethyltramadol was identified in chromatograms of two of the male koalas. When 4 mg/kg tramadol was administered, the median half-life of tramadol and M1 were 2.89 h and 24.69 h, respectively. The M1 plasma concentration remained well above the minimally effective M1 plasma concentration in humans (approximately 36 ng/mL) over 12 hours. The M1 plasma concentration, when tramadol was administered at 2 mg/kg, did not exceed 36 ng/mL at any time-point. When tramadol was administered at 2 mg/kg and 4 mg/kg the area under the curve M1: tramadol ratios were 0.33 and 0.50, respectively. Tramadol and M1 binding to plasma protein were determined using thawed, frozen koala plasma and the mean binding was 20% and 75%, respectively. It is concluded that when tramadol is administered at 4 mg/kg as a subcutaneous injection to the koala, it is predicted to have some analgesic activity.

The Effect of Food on Tramadol and Celecoxib Bioavailability Following Oral Administration of Co-Crystal of Tramadol-Celecoxib (CTC): A Randomised, Open-Label, Single-Dose, Crossover Study in Healthy Volunteers

BACKGROUND AND OBJECTIVE

Co-Crystal of Tramadol-Celecoxib (CTC), in development for the treatment of moderate to severe acute pain, is a first-in-class co-crystal containing a 1:1 molecular ratio of two active pharmaceutical ingredients; rac-tramadol·HCl and celecoxib. This randomised, open-label, crossover study compared the bioavailability of both components after CTC administration under fed and fasting conditions.

METHODS

Healthy adults received single doses of 200 mg CTC under both fed and fasting conditions (separated by a 7-day washout). Each dose of CTC was administered orally as two 100 mg tablets, each containing 44 mg tramadol·HCl and 56 mg celecoxib. In the fed condition, a high-fat, high-calorie meal [in line with recommendations by the US Food and Drug Administration (FDA)] was served 30 min before CTC administration. Tramadol, O-desmethyltramadol and celecoxib plasma concentrations were measured pre- and post-dose up to 48 h. Pharmacokinetic parameters were calculated using non-compartmental analysis. Safety was also assessed.

RESULTS

Thirty-six subjects (18 female/18 male) received one or both doses of CTC; 33 provided evaluable pharmacokinetic data under fed and fasting conditions. For tramadol and O-desmethyltramadol, fed-to-fasting ratios of geometric least-squares means and corresponding 90% confidence interval (CI) values for maximum plasma concentration (Cmax) and extrapolated area under the plasma concentration-time curve to infinity (AUC∞) were within the pre-defined range for comparative bioavailability (80-125%). For celecoxib, Cmax and AUC∞ fed-to-fasting ratios (90% CIs) were outside this range, at 130.91% (116.98-146.49) and 129.34% (121.78-137.38), respectively. The safety profile of CTC was similar in fed and fasting conditions.

CONCLUSIONS

As reported for standard-formulation celecoxib, food increased the bioavailability of celecoxib from single-dose CTC. Food had no effect on tramadol or O-desmethyltramadol bioavailability.

CLINICAL TRIAL REGISTRATION NUMBER

152052 (registered with the Therapeutic Products Directorate of Health Canada).

Correlation between plasma concentrations of tramadol and its metabolites and the incidence of seizure in tramadol-intoxicated patients

BACKGROUND

Seizure is one of the important symptoms of tramadol poisoning, but its causes are still unknown. The aim of this study is to find a relationship between tramadol and the concentrations of its metabolites versus the incidence of seizures following the consumption of high doses of tramadol.

METHODS

For this purpose, the blood samples of 120 tramadol-intoxicated patients were collected. The patients were divided in two groups (seizure and non-seizure). The concentrations of tramadol and its metabolites (M1, M2 and M5) were measured by using a high-performance liquid chromatography method. The relationship between tramadol and the levels of its metabolites and seizure incidences was also investigated.

RESULTS

In 72% of the patients, seizures occurred in the first 3 h after the ingestion of tramadol. The seizure incidences were significantly correlated with the patients' gender, concentrations of tramadol, M1 and M2 and the history of previous seizures (p<0.001). The average concentration of M2 was significantly higher in males (p=0.003). A previous history of the use of sedative-hypnotics and the co-ingestion of benzodiazepines and other opioids were shown to significantly decrease the rate of seizure. The rate of seizure was directly related to the concentrations of tramadol and its metabolites. Higher M2 concentration in males can be considered a reason for increased incidences of seizures in males. The plasma concentration of M1 affected the onset of seizure.

CONCLUSIONS

Therefore, it can be concluded that differences in the levels of the metabolites can affect the threshold of seizure in tramadol-intoxicated patients.

Simultaneous quantitation of meperidine, normeperidine, tramadol, propoxyphene and norpropoxyphene in human plasma using solid-phase extraction and gas chromatography/mass spectrometry: Method validation and application to cardiovascular safety of therapeutic doses

RATIONALE

Several opioid analgesics have been related to the prolongation of cardiac repolarization, a condition which can be fatal. In order to establish a correct estimation of the risk/benefit balance of therapeutic doses of meperidine, normeperidine, tramadol, propoxyphene and norpropoxyphene, it was necessary to develop an analytical method to determinate plasma concentrations of these opioids.

METHODS

Here we describe a method which incorporates strong alkaline treatment to obtain norpropoxyphene amide followed by a one-elution step solid-phase extraction, and without further derivatization. Separation and quantification were achieved by gas chromatography/electron ionization mass spectrometry (GC/EI-MS) in selected-ion monitoring mode. Quantification was performed with 500 μL of plasma by the addition of deuterated analogues as internal standards.

RESULTS

The proposed method has been validated in the linearity range of 25-1000 ng/mL for all the analytes, with correlation coefficients higher than 0.990. The lower limit of quantification was 25 ng/mL. The intra- and inter-day precision, calculated in terms of relative standard deviation, were 2.0-12.0% and 6.0-15.0%, respectively. The accuracy, in terms of relative error, was within a ± 10% interval. The absolute recovery and extraction efficiency ranged from 81.0 to 111.0% and 81.0 to 105.0%, respectively.

CONCLUSIONS

A GC/MS method for the rapid and simultaneous determination of meperidine, normeperidine, tramadol, propoxyphene and norpropoxyphene in human plasma was developed, optimized and validated. This procedure was shown to be sensitive and specific using small specimen amounts, suitable for application in routine analysis for forensic purposes and therapeutic monitoring. To our knowledge, this is the first full validation of the simultaneous determination of these opioids and their metabolites in plasma samples.

Preliminary pharmacokinetics of tramadol hydrochloride after administration via different routes in male and female B6 mice

OBJECTIVE

1) To determine the pharmacokinetics of tramadol hydrochloride and its active metabolite, O-desmethyltramadol (M1), after administration through different routes in female and male C57Bl/6 mice; 2) to evaluate the stability of tramadol solutions; and 3) to identify a suitable dose regimen for prospective clinical analgesia in B6 mice.

STUDY DESIGN

Prospective, randomized, blinded, parallel design.

ANIMALS

A total of 18 male and 18 female C57Bl/6 mice (20-30 g).

METHODS

Mice were administered 25 mg kg^-1 tramadol as a bolus [intravenously (IV), intraperitoneally (IP), subcutaneously (SQ), orally per gavage (OS_gavage)] over 25 hours [orally in drinking water (OS_water) or Syrspend SF (OS_Syrsp)]. Venous blood was sampled at six predetermined time points over 4 to 31 hours, depending on administration route, to determine tramadol and M1 plasma concentrations (liquid chromatography and tandem mass spectrometry detection). Pharmacokinetic parameters were described using a noncompartmental model. The stability of tramadol in water (acidified and untreated) and Syrspend SF (0.20 mg mL^-1) at ambient conditions for 1 week was evaluated.

RESULTS

After all administration routes, C_max was >100 ng mL^-1 for tramadol and >40 ng mL^-1 for M1 (reported analgesic ranges in man) followed by short half-lives (2-6 hours). The mean tramadol plasma concentration after self-administration remained >100 ng mL^-1 throughout consumption time. M1 was found in the OS_Syrs group only at 7 hours, whereas it was detectable in OS_water throughout administration. Tramadol had low oral bioavailability (26%). Short-lasting side effects were observed only after IV administration. Water and Syrspend SF solutions were stable for 1 week.

CONCLUSIONS AND CLINICAL RELEVANCE

1) At the dose administered, high plasma concentrations of tramadol and M1 were obtained, with half-life depending on the administration route. 2) Plasma levels were stable over self-consumption time. 3) Solutions were stable for 1 week at ambient conditions.

Refractory Cardiogenic Shock During Tramadol Poisoning: A Case Report

Tramadol is a weak opioid analgesic indicated for the treatment of moderate to severe pain. Tramadol intoxication can be lethal, and this drug is frequently involved in voluntary overdose. Classically, tramadol intoxication is associated with neurological and respiratory side effects. In contrast, cardiac effects are poorly documented in the literature. We report a case of severe tramadol intoxication, with plasma concentration 20 times the toxic threshold, complicated by refractory cardiogenic shock, successfully treated by extra corporeal life support (ECLS) with a favorable cardiac outcome and ECLS weaning at day 10. Seizure, clonus, and nonreactive mydriasis were present during 4 days, and complete awakening was delayed to day 15. Poisoning caused by high doses of tramadol can lead to refractory cardiogenic shock, and ECLS can be considered as effective rescue therapy in this context.

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.

Simultaneous Determination of Tramadol and its Metabolite in Human Plasma by GC/MS

A simple and sensitive GC/MS method for the determination of tramadol and its metabolite (O-desmethyltramadol) in human plasma was developed and validated. Medazepam was used as an internal standard. The calibration curves were linear (r=0.999) over tramadol and O-desmethyltramadol concentrations ranging from 10 to 200 ng/mL and 7.5 to 300 ng/mL, respectively. The method had an accuracy of >95% and intra- and interday precision (RSD%) of ≤4.83% and ≤4.68% for tramadol and O-desmethyltramadol, respectively. The extraction recoveries were 97.6±1.21% and 96.3±1.66% for tramadol and O-desmethyltramadol, respectively. The LOQ using 0.5 mL human plasma was 10 ng/mL for tramadol and 7.5 ng/mL for O-desmethyltramadol. Stability studies showed that tramadol and O-desmethyltramadol were stable in human plasma after 8 h incubation at room temperature or after 1 week storage at -20°C with three freeze-thaw cycles. Also, this method was successfully applied to six patients who had been given an intravenous formulation of 100 mg tramadol with Cmax results of 2018.1±687.8 and 96.1±22.7 ng/mL for tramadol and O-desmethyltramadol, respectively.

Biopharmaceutical evaluation of new slow release tablets obtained by hot tableting of coated pellets with tramadol hydrochloride

This study was aimed at a biopharmaceutical evaluation of a new oral dosage form of tramadol hydrochloride (TH)--slow release tablets obtained by hot tableting of coated pellets, 100 mg (TP), compared to the conventional slow release tablets, Tramal Retard, 100 mg (TR). Both TP and TR formulations showed a similar release profile of TH (f2 was 71) in in vitro release studies. The in vivo study was a two-treatment, two-period, two-sequence, single-oral dose 100 mg, crossover design using rabbit model with the phases separated by a washout period of 14 days. It was shown that the amount of TH absorbed into the systemic circulation is similar for TP and TR (the 90% confidence intervals for the AUC(0-1), AUC(0-infinity) and ratios were 85-122 and 92-107%, respectively). However, after administration of slow release tablets obtained by hot tableting of coated pellets, a prolonged absorption and elimination processes and a smoother and more extended plasma profile of TH were observed. It can be assumed that the use of a new oral dosage form of TH in patients affects the extension of analgesia after single administration of the drug, with its gradual absorption into the systemic circulation.

Physiology-based IVIVE predictions of tramadol from in vitro metabolism data

PURPOSE

To predict the tramadol in vivo pharmacokinetics in adults by using in vitro metabolism data and an in vitro-in vivo extrapolation (IVIVE)-linked physiologically-based pharmacokinetic (PBPK) modeling and simulation approach (Simcyp®).

METHODS

Tramadol metabolism data was gathered using metabolite formation in human liver microsomes (HLM) and recombinant enzyme systems (rCYP). Hepatic intrinsic clearance (CLintH) was (i) estimated from HLM corrected for specific CYP450 contributions from a chemical inhibition assay (model 1); (ii) obtained in rCYP and corrected for specific CYP450 contributions by study-specific intersystem extrapolation factor (ISEF) values (model 2); and (iii) scaled back from in vivo observed clearance values (model 3). The model-predicted clearances of these three models were evaluated against observed clearance values in terms of relative difference of their geometric means, the fold difference of their coefficients of variation, and relative CYP2D6 contribution.

RESULTS

Model 1 underpredicted, while model 2 overpredicted the total tramadol clearance by -27 and +22%, respectively. The CYP2D6 contribution was underestimated in both models 1 and 2. Also, the variability on the clearance of those models was slightly underpredicted. Additionally, blood-to-plasma ratio and hepatic uptake factor were identified as most influential factors in the prediction of the hepatic clearance using a sensitivity analysis.

CONCLUSION

IVIVE-PBPK proved to be a useful tool in combining tramadol's low turnover in vitro metabolism data with system-specific physiological information to come up with reliable PK predictions in adults.

In vitro - in vivo evaluation of a new oral dosage form of tramadol hydrochloride--controlled-release capsules filled with coated pellets

The aim of this study was an in vitro - in vivo evaluation of a new oral dosage form of tramadol hydrochloride (TH), controlled-release capsules filled with coated pellets, 100 mg (TC), compared to the sustained release tablets, Tramal Retard, 100 mg (TR). In vitro release study of both formulations showed a similar release profile of TH over 8 h (f2 was 52). In vivo study (single oral, 100 mg dose administration in 8 rabbits) showed that the amount of TH absorbed into the systemic circulation after TC and TR administration was also similar (90% CI for AUC(0-t) and AUC(0-infinity) were 90-124% and 97-109%, respectively). However, a comparison of AUC(0-t) of pharmacokinetics of TC and TR indicates significantly prolonged absorption and elimination processes of TH when the drug is given in controlled-release capsules filled with coated pellets. It was manifested by longer: mean absorption time (p = 0.0016), mean residence time (p = 0.0268), absorption half-life (p = 0.0016), elimination half-life (p = 0.0493) and lower: absorption rate constant (p = 0.0016), elimination rate constant (p = 0.0148) and total body clearance Cl/F (p = 0.0076). It may be concluded that the new TH formulation could be expected to have a more prolonged analgesic activity than commercial sustained release tablets.

Effect of the cytochrome P450 2D6*10 genotype on the pharmacokinetics of tramadol in post-operative patients

The cytochrome P450 2D6 (CYP2D6) is the most highly polymorphic isoenzyme of the cytochrome P-450-system, which affects the metabolism of one-fourth of all prescription drugs. Tramadol, a narcotic-like pain reliever used to treat moderate to severe pain, is primarily metabolized by CYP2D6. The CYP2D6*10 allele is the most common allele in the Chinese population. Therefore, we investigated the effects of CYP2D6*10 on tramadol pharmacokinetics in 45 post-operative patients who had undergone gastrointestinal tract surgery. Tramadol was administered to the patients after the operation, and the plasma concentrations of tramadol and O-desmethyltramadol were subsequently evaluated at 12 time points. Pharmacokinetic analyses were performed using non-compartmental methods. The area under the curve (AUC), plasma clearance (CL), elimination half-life (T1/2), mean residence time (MRT), peak concentration, and peak time of tramadol and O-desmethyltramadol were calculated. CYP2D6*10 was genotyped by polymerase chain reaction-restriction fragment length polymorphism. The frequency of CYP2D6*10 alleles was 51% in the 45 patients. The patients were divided into three groups according to their CYP2D6*10 genotype: wild-type, heterozygous, and homozygous mutant. Pharmacokinetic parameters were compared among the three groups. The analyses showed that T1/2, MRT, and AUC of tramadol were larger, and CL was lower in homozygous mutant patients compared to the wild-type group (P< 0.05). These results show that the CYP2D6*10 genetic polymorphism has a significant impact on the pharmacokinetics of tramadol in Chinese post-operative patients.

Postmortem redistribution of tramadol and O-desmethyltramadol

Tramadol is a widely used analgesic opioid for moderate-to-severe pain due to its efficacy and safety. Although tramadol induces less adverse effects compared with other opioids, an increased number of documented cases of dependence, abuse, intentional overdose or intoxication have been described. In fatal intoxication, the interpretation of the probable cause of death often relies on the measurement of the tramadol concentration in blood. However, postmortem redistribution (PMR) may affect the results and therefore bias the autopsy report. In the present study, the postmortem cardiac and femoral blood samples from 15 cases of fatal tramadol intoxication were obtained to assess the PMR of tramadol and its main active metabolite, O-desmethyltramadol (M1). Toxicological analysis was performed by the gas chromatography-electron impact-mass spectrometry (GC-EI-MS) method, previously developed and validated for the quantification of both analytes. The cardiac-to-femoral blood ratios of 1.40 and 1.28 were obtained for tramadol and M1, respectively. Results were compared with those in the literature and it was possible to conclude that femoral blood should be considered for quantitative interpretations in fatal cases of tramadol intoxication.

Optimization of solvent bar microextraction combined with gas chromatography mass spectrometry for preconcentration and determination of tramadol in biological samples

A simple, rapid and sensitive analytical method for preconcentration and determination of tramadol in different biological samples have been developed using solvent bar microextraction (SBME) combined with gas chromatography-mass spectrometry (GC-MS). The target drugs were extracted from 12 ml of aqueous sample with pH 12.0 (source phase; SP) into an organic extracting solvent (n-nonanol) located inside the pores and lumen of a polypropylene hollow fiber (receiving phase; RP). In order to obtain high extraction efficiency, the effect of different variables on the extraction efficiency was studied using an experimental design. The variables of interest were the type of organic phase, pH of the source phases, ionic strength, volume of the source phase, stirring rate, extraction time and temperature. The experimental parameters of SBME were optimized using a Box-Behnken design (BBD) after a Plackett-Burman screening design. The detection limits were 0.02 μg L(-1) with 4.5% RSD (n=5, c=10 μg L(-1)) for tramadol. Finally, the applicability of the proposed method was evaluated by extraction and determination of the drugs in different biological samples. The results indicated that SBME method has excellent clean-up and high-preconcentration factor and can be served as a simple and sensitive method for monitoring of tramadol in the biological samples.

Near-fatal tramadol cardiotoxicity in a CYP2D6 ultrarapid metabolizer

BACKGROUND

Tramadol is a synthetic, centrally acting analgesic for the treatment of moderate to severe pain. The marketed tramadol is a racemic mixture containing 50% (+)tramadol and 50% (-)tramadol and is mainly metabolized to O-desmethyltramadol (M1) by the cytochrome P450 CYP2D6. Tramadol is generally considered to be devoid of any serious adverse effects of traditional opioid receptor agonists, such as respiratory depression and drug dependence.

CASE REPORT

A 22-year-old Caucasian female patient was admitted to our ICU in refractory cardiac arrest requiring extracorporeal membrane oxygenation. This aggressive support allowed resolution of multi-organ dysfunction syndrome. Repeated blood analyses using liquid chromatography-tandem mass spectrometry confirmed high concentrations of both tramadol and its main metabolite O-desmethyltramadol. Genotyping of CYP2D6 revealed the patient to be heterozygous for a duplicated wild-type allele, predictive of a CYP2D6 ultrarapid metabolizer (UM) phenotype, confirmed by calculation of the tramadol/M1 (MR1) metabolic ratio at all time points.

DISCUSSION

We here report a case of near-fatal isolated tramadol cardiotoxicity. Because of the inhibition of norepinephrine reuptake, excessive blood epinephrine levels in this CYP2D6R UM patient following excessive tramadol ingestion could explain the observed strong myocardial stunning. This patient admitted intermittent tramadol consumption to gain a "high" sensation. In patients with excessive morphinomimetic effects, levels of tramadol and its main metabolite M1could be measured, ideally combined with CYP2D6 genotyping, to identify individuals at risk of tramadol-related cardiotoxicity. Tramadol treatment could be optimized in these at-risk individuals, consequently improving patient outcome and safety.

[Distribution of tramadol in acute poisoned rats]

OBJECTIVE

To develop a rapid and accurate gas chromatography method and investigate the distribution of tramadol in acute poisoned rats for information of samples selection and results evaluation in forensic identification.

METHODS

After an oral administration of tramadol at 1140 mg/kg (5 x LD50), concentrations of tramadol in rats' biological fluids and tissues were determined by gas chromatography.

RESULTS

The limit of detection of tramadol in blood and urine was 0.1 microg/mL and the limit of detection in liver was 0.1 microg/g. The intra-day precision and inter-day precision were within 3.1% and 5.5% respectively, and the recovery of tramadol in blood was more than 98%. The average levels of tramadol displayed in descending order of heart blood, liver, peripheral blood, urine, vitreous humor, kidney, lung, spleen, heart, brain respectively.

CONCLUSION

The established method could meet the requirements for toxicological analysis, and the results of the study suggest that blood, urine, liver, lung and kidney are suitable samples for forensic toxicological analysis in tramadol poisoning cases.

Evaluation of tramadol and its main metabolites in horse plasma by high-performance liquid chromatography/fluorescence and liquid chromatography/electrospray ionization tandem mass spectrometry techniques

Tramadol is a centrally acting analgesic drug that has been used clinically for the last two decades to treat pain in humans. The clinical response of tramadol is strictly correlated to its metabolism, because of the different analgesic activity of its metabolites. O-Desmethyltramadol (M1), its major active metabolite, is 200 times more potent at the micro-receptor than the parent drug. In recent years tramadol has been widely introduced in veterinary medicine but its use has been questioned in some species. The aim of the present study was to develop a new sensible method to detect the whole metabolic profile of the drug in horses, through plasma analyses by high-performance liquid chromatography (HPLC) coupled with fluorimetric (FL) and photodiode array electrospray ionization mass spectrometric (PDA-ESI-MS) detection, after its sustained release by oral administration (5 mg/kg). In HPLC/FL experiments the comparison of the horse plasma chromatogram profile with that of a standard mixture suggested the identification of the major peaks as tramadol and its metabolites M1 and N,O-desmethyltramadol (M5). LC/PDA-ESI-MS/MS analysis confirmed the results obtained by HPLC/FL and also provided the identification of two more metabolites, N-desmethyltramadol (M2), and N,N-didesmethyltramadol (M3). Another metabolite, M6, was also detected and identified. The present findings demonstrate the usefulness and the advantage of LC/ESI-MS/MS techniques in a search for tramadol metabolites in horse plasma samples.

Pharmacokinetics of intravenous tramadol in dogs

The purpose of this study was to determine the pharmacokinetics of tramadol and the active metabolite mono-O-desmethyltramadol (M1) in 6 healthy male mixed breed dogs following intravenous injection of tramadol at 3 different dose levels. Verification of the metabolism to the active metabolite M1, to which most of the analgesic activity of this agent is attributed to, was a primary goal. Quantification of the parent compound and the M1 metabolite was performed using gas chromatography. Pharmacodynamic evaluations were performed at the time of patient sampling and included assessment of sedation, and evaluation for depression of heart and respiratory rates. This study confirmed that while these dogs were able to produce the active M1 metabolite following intravenous administration of tramadol, the M1 concentrations were lower than previously reported in research beagles. Adverse effects were minimal, with mild dose-related sedation in all dogs and nausea in 1 dog. Analgesia was not documented with the method of assessment used in this study. Tramadol may be useful in canine patients, but additional studies in the canine population are required to more accurately determine the effective clinical use of the drug in dogs and quantification of M1 concentrations in a wider population of patients.

[Importance of the formulation for a chronopharmacologically optimised way of pain therapy. Results of a comparative bioavailability study of tramadol extended-release capsules after single-dose evening versus morning administration]

Objective of this study was to investigate the rate and extent of tramadol bioavailability following evening versus morning administration.

METHODS

The study was performed following an open, randomised, cross-over study-design. 18 male and female volunteers were enrolled into the study and treated with 200 mg tramadol extended-release capsules (T-long), which were to be taken either in the morning or in the evening.

RESULTS

Plasma concentration versus time profiles obtained after morning and evening administration were almost superimposable for both, tramadol and its active metabolite. Maximum exposure of tramadol and O-desmethyltramadol (geometric means of c(max)-values) as well as extent of exposure (geometric means of AUC(0-48)-values) were comparable after morning and eveningadministration.

CONCLUSIONS

Time-point of administration does not have any relevant impact on the rate and extent of absorption in the investigated dosage form. Thus, time-point of administration may be adjusted to the patient's need in a chronopharmacologically optimised way for pain therapy.

Fatal unintentional intoxications with tramadol during 1995–2005

Tramadol is an extensively used centrally acting analgesic and is considered a safe drug devoid of many serious adverse effects of traditional opioids. However, recently, toxicity and an abuse potential of tramadol have been reported. This study examined fatal unintentional tramadol intoxications among Swedish forensic autopsy cases between 1995 and 2005. All fatal intoxications were selected, in which toxic concentrations of tramadol (>1 microg/g femoral blood) had been detected, and where the forensic pathologist considered the intoxication unintentional and the fatal outcome at least partly explained by tramadol. Toxicology analyses, police reports, autopsy protocols and medical records were scrutinized. A total of 17 cases (eleven men and six women) of fatal unintentional tramadol intoxications were identified. For these cases the median age was 44 years (range 18-78 years) and the median tramadol concentration was 2.0 microg/g (range 1.1-12.0 microg/g). Other pharmaceutical substances, illicit drugs or ethanol were detected in addition to tramadol in all of these cases. In fact, intoxication with multiple drugs was considered the cause of death in 10 (59%) cases. However, in seven cases tramadol was the only substance present in toxic concentrations. A history of substance abuse was identified in 14 (82%) subjects and a present tramadol abuse in 8 (47%). These results suggest that fatal intoxications with tramadol may occur unintentionally and that subjects with a history of substance abuse may be at certain risk. Precaution is therefore warranted when prescribing tramadol in such patients.

Fatal intoxication due to tramadol alone: case report and review of the literature

Poisoning may also lead to both coma and multiple organ failure, also in youngsters without a known major medical history. As not all toxic agents are routinely screened when a poisoning is suspected, it is useful to consider less frequently encountered poisons in certain cases. We describe the occurrence of asystole and multiple organ failure which occurred in a young man after a suspected tramadol overdose. The tramadol concentration on admission in the ICU was indeed 8 microg/ml (mg/l), far above the therapeutic range. Subsequently, the patient developed severe acute liver failure, finally leading to death. Post-mortem toxicology did not reveal any other poison responsible for this unfavourable course as only very high serum and tissue tramadol and desmethyltramadol concentrations were found. Only a few fatal poisonings attributable to tramadol alone, as observed in our case, have been reported. An overview of these cases is presented.

Improved liquid chromatographic method for the simultaneous determination of tramadol and its three main metabolites in human plasma, urine and saliva

Tramadol, an analgesic agent, and its main metabolites O-desmethyltramadol (M1), N-desmethyltramadol (M2) and O,N-didesmethyltramadol (M5) were determined simultaneously in human plasma, saliva and urine by a rapid and specific HPLC method. The sample preparation was a simple, one-step, extraction with ethyl acetate. Chromatographic separation was achieved with a Chromolith Performance RP-18e 100 mm x 4.6 mm column, using a mixture of methanol:water (19:81, v/v) adjusted to pH 2.5 by phosphoric acid, in an isocratic mode at flow rate of 2 ml/min. Fluorescence detection (lambda(ex) 200 nm/lambda(em) 301 nm) was used. The calibration curves were linear (r(2)>0.996) in the concentration ranges in plasma, saliva and urine. The lower limit of quantification was 2.5 ng/ml for all compounds. The within- and between-day precisions in the measurement of QC samples at four tested concentrations were acceptable in all analyzed body fluids The developed procedure was applied to assess the pharmacokinetics of tramadol and its main metabolites following administration of 100mg single oral dose of tramadol to healthy volunteers.

Quantification of Drugs in Plasma Without Primary Reference Standards by Liquid Chromatography-Chemiluminescence Nitrogen Detection: Application to Tramadol Metabolite Ratios

Lack of availability of reference standards for drug metabolites, newly released drugs, and illicit drugs hinders the analysis of these substances in biologic samples. To counter this problem, an approach is presented here for quantitative drug analysis in plasma without primary reference standards by liquid chromatography-chemiluminescence nitrogen detection (LC-CLND). To demonstrate the feasibility of the method, metabolic ratios of the opioid drug tramadol were determined in the setting of a pharmacogenetic study. Four volunteers were given a single 100-mg oral dose of tramadol, and a blood sample was collected from each subject 1 hour later. Tramadol, O-desmethyltramadol, and nortramadol were determined in plasma by LC-CLND without reference standards and by a gas chromatography-mass spectrometry reference method. In contrast to previous CLND studies lacking an extraction step, a liquid-liquid extraction system was created for 5-mL plasma samples using n-butyl chloride-isopropyl alcohol (98 + 2) at pH 10. Extraction recovery estimation was based on model compounds chosen according to their similar physicochemical characteristics (retention time, pKa, logD). Instrument calibration was performed with a single secondary standard (caffeine) using the equimolar response of the detector to nitrogen. The mean differences between the results of the LC-CLND and gas chromatography-mass spectrometry methods for tramadol, O-desmethyltramadol, and nortramadol were 8%, 32%, and 19%, respectively. The sensitivity of LC-CLND was sufficient for therapeutic concentrations of tramadol and metabolites. A good correlation was obtained between genotype, expressed by the number of functional genes, and the plasma metabolite ratios. This experiment suggests that a recovery-corrected LC-CLND analysis produces sufficiently accurate results to be useful in a clinical context, particularly in instances in which reference standards are not readily accessible.

Stereospecific high-performance liquid chromatographic analysis of tramadol and its O-demethylated (M1) and N,O-demethylated (M5) metabolites in human plasma

A stereospecific method for simultaneous quantitation of the enantiomers of tramadol (T) and its active metabolites O-demethyl tramadol (M1) and O-demethyl-N-demethyl tramadol (M5) in human plasma is reported. After the addition of penbutolol (IS), plasma (0.5 ml) samples were extracted into methyl tert-butyl ether, followed by back extraction into an acidic solution. The separation was achieved using a Chiralpak AD column with a mobile phase of hexanes:ethanol:diethylamine (94:6:0.2) and a flow rate of 1 ml/min. The fluorescence of analytes was then detected at excitation and emission wavelengths of 275 and 300 nm, respectively. All the six enantiomeric peaks of interest plus three unknown metabolite peaks and IS peak (a total of 10 peaks) eluted within 23 min, free from endogenous interference. The assay was validated in the plasma concentration range of 2.5-250 ng/ml, with a lower limit of quantitation of 2.5 ng/ml, for all the six analytes. The extraction efficiency (n=5) was close to 100% for both T and M1 enantiomers and 85% for M5 and IS enantiomers. The application of the assay was demonstrated by simultaneous measurement of plasma concentrations of T, M1, and M5 enantiomers in a healthy volunteer after the administration of 50 mg oral doses of racemic T.

Concentrations of tramadol and O-desmethyltramadol enantiomers in different CYP2D6 genotypes

The influence of CYP2D6 genotype and CYP2D6 inhibitors on enantiomeric plasma levels of tramadol and O-desmethyltramadol as well as response to tramadol was investigated. One hundred and seventy-four patients received one hundred intravenous tramadol 3 mg/kg for postoperative analgesia. Blood samples drawn 30, 90, and 180 min after administration were analyzed for plasma concentrations of the enantiomers (+)-, (-)tramadol and (+)-, (-)O-desmethyltramadol by liquid chromatography-tandem mass spectrometry. Different CYP2D6 genotypes displaying zero (poor metabolizer (PM)), one (heterozygous individual (HZ)/intermediate metabolizer (IM)), two extensive metabolizer (EM), and three (ultra rapid metabolizer (UM)) active genes were compared. Concentrations of O-desmethyltramadol differed in the four genotype groups. Median (1/3 quartile) area under the concentration-time curves for (+)O-desmethyltramadol were 0 (0/11.4), 38.6 (15.9/75.3), 66.5 (17.1/118.4), and 149.7 (35.4/235.4) ng x h/ml for PMs, HZ/IMs, EMs, and UMs (P<0.001). Comedication with CYP2D6 inhibitors decreased (+) O-desmethyltramadol concentrations (P<0.01). In PMs, non-response rates to tramadol treatment increased fourfold compared with the other genotypes (P<0.001). In conclusion, CYP2D6 genotype determined concentrations of O-desmethyltramadol enantiomers and influenced efficacy of tramadol treatment.

Pharmacokinetics of tramadol enantiomers and their respective phase I metabolites in relation to CYP2D6 phenotype

OBJECTIVE

Our objective was to evaluate the effect of CYP2D6 phenotype in the enantioselective metabolism of tramadol in Spanish healthy human volunteers.

METHODS

A single oral 100mg dose of racemic tramadol was administered to five subjects who were poor metabolizers (PMs) and 19 subjects who were extensive metabolizers (EMs), whose phenotypes were determined by the use of the racemic tramadol metabolic rate. The pharmacokinetic parameters were estimated from plasma concentrations of the enantiomers of tramadol and their main phase I metabolites, O-desmethyltramadol (M1) and N-desmethyltramadol (M2). Epinephrine plasma concentrations were also determinated.

RESULTS

The plasma concentrations of both tramadol enantiomers were consistently higher in PMs than in EMs of CYP2D6, with 1.98- and 1.74-fold differences in the mean area under the plasma concentration-time curves (AUC), respectively. The values for oral clearance of (+)- and (--)-tramadol were 1.91- and 1.71-fold greater in PMs, which were related to differences in both O-desmethylation and N-desmethylation in the two CYP2D6 metabolizer phenotypes. The mean AUC values of (+)-M1 and (--)-M1 were 4.33- and 0.89-fold greater in EMs, and it was related to similar differences in the formation rate constant. On the other hand, the differences were 7.40- and 8.69-fold greater in PMs for M2 enantiomers due to the involvement of CYP2D6 in their subsequent biotransformation. The time course of epinephrine systemic concentrations was completely different between both groups of metabolizers. In EMs plasma concentrations of epinephrine increased after tramadol administration whereas in PMs no effect was observed.

CONCLUSIONS

The polymorphic CYP2D6 appears to be a major enzyme involved in the metabolism of tramadol enantiomers. The N-desmethylation pathway was indirectly affected by CYP2D6 phenotypic differences. Epinephrine showed a good correlation with the pharmacokinetics of the opioid component of tramadol, (+)-M1 and was found to be useful for its pharmacodynamic profiling.

Pharmacokinetic model and simulations of dose conversion from immediate- to extended-release tramadol

OBJECTIVE

Extended-release tramadol (tramadol ER) is a once-daily formulation of tramadol approved in the United States for moderate to moderately severe chronic pain in adults. This modeling and simulation analysis was conducted to support dosing recommendations for switching patients receiving immediate-release tramadol (tramadol IR) to tramadol ER.

RESEARCH DESIGN AND METHODS

Monte Carlo simulations based on steady-state data from three Phase 1 studies predicted minimum plasma concentration (C(min)), maximum plasma concentration (C(max)), and area under the plasma-concentration-versus-time curve (AUC).

MAIN OUTCOME MEASURES

Pharmacokinetic parameters were compared between 100-mg daily increments of tramadol ER every 24 h (Q24H) and corresponding 25-mg increments of tramadol IR every 6 h (Q6H), such as tramadol ER 200 mg Q24H versus tramadol IR 200, 225, 250, and 275 mg daily.

RESULTS

Tramadol ER and IR were predicted to provide similar exposure (AUC) at a total daily dose of 100, 200, or 300 mg. Estimated exposure was comparable between tramadol IR 125-, 225-, and 325-mg and tramadol ER 100-, 200-, and 300-mg, respectively. Estimated exposure was 30-41% lower with tramadol ER 100 mg versus tramadol IR 150 and 175 mg daily, 15-26% lower with tramadol ER 200 mg versus tramadol IR 250 and 275 mg daily, and 8-19% lower with tramadol ER 300 mg versus tramadol IR 350 and 375 mg daily.

CONCLUSIONS

This pharmacokinetic analysis supports switching patients from a total daily dose of tramadol IR 200 or 300 mg directly to tramadol ER 200 and 300 mg once daily, respectively. Patients who take other doses of tramadol IR may switch to the next lower 100-mg increment of tramadol ER (e.g., from tramadol IR 225, 250, or 275 mg daily in divided doses to tramadol ER 200 mg once daily). Confirmation of these findings would require clinical studies comparing the systemic exposure of tramadol upon switching from the IR to the ER formulation.

Pharmacokinetics and dose proportionality of three Tramadol Contramid® OAD tablet strengths

A three-way crossover study in 27 human volunteers was conducted to characterize the pharmacokinetics and to assess the dose proportionality of 100 mg, 200 mg and 300 mg strengths of a novel once-a-day tramadol controlled-release tablet (Tramadol Contramid OAD) following single-dose administration. Serial blood samples were collected at predefined timepoints over a 48 h period and racemic tramadol and O-desmethyltramadol concentrations in plasma were determined using a validated LC-MS/MS method. Pharmacokinetic parameters were derived using noncompartmental methods. Following dose normalization and logarithmic transformation of concentration-dependent parameters, the results were compared using analysis of variance (ANOVA). The residual variability thereby obtained was used to construct 90% classical confidence intervals. The two one-sided tests procedure was used for all pairwise comparisons. Dose proportionality was concluded since the 90% CI for the ratio of geometric means was included in the acceptance range of 0.80-1.25 for all comparisons.

Peritoneal microdialysis in freely moving rodents: An alternative to blood sampling for pharmacokinetic studies in the rat and the mouse

By performing microdialysis in the peritoneal cavity, we studied the pharmacokinetics of Tramadol in awake, freely moving small laboratory animals. The systemic exposure to Tramadol was determined using both microdialysis sampling and collection of whole blood following a single intravenous injection (10 mg/kg) or a single oral dose (100 mg/kg) of Tramadol HCl. The sampling frequency of the dialysate was 10 min (mouse study) or 20 min (rat study). In rats and in mice, intraperitoneal microdialysis sampling gets reliable pharmacokinetic results without taking blood. The concentration-time curves obtained from peritoneal microdialysis were parallel to the concentration-time curves obtained from classical blood sampling. Accordingly, dose independent pharmacokinetic parameters were similar. A scaling factor, however, has to be introduced (e.g. peritoneal versus plasma AUC ratio) in order to obtain comparable pharmacokinetic results also with dose-dependent parameters. As there was no blood loss during the experiment, peritoneal microdialysis allowed the investigation of complete concentration-time curve profiles. Thus, the number of animals could be kept to a minimum. In conclusion, in vivo peritoneal microdialysis is a unique tool to obtain a complete set of free drug concentrations to determine reliable pharmacokinetic parameters from awake, freely moving rodents. Therefore, we suppose that the technique will have relevance for pharmacokinetic studies in future.

Postmortem Urine Immunoassay Showing False-Positive Phencyclidine Reactivity in a Case of Fatal Tramadol Overdose

This is a report of postmortem false-positive reactivity using an enzyme-multiplied urine phencyclidine (PCP) immunoassay (EMIT II+) due to a single-agent fatal tramadol overdose. An autopsy of a 42-year-old male who died alone at home revealed no identifiable lethal anatomic abnormalities, thus leading to toxicologic analysis. Femoral blood was obtained for drug testing by high-performance liquid chromatography (HPLC) and showed a tramadol level of 14.0 mg/L, 2 orders of magnitude greater than the therapeutic range (0.1 to 0.3 mg/L). Urine was also obtained and EMIT II+ immunoassay revealed positivity for PCP at 88 mAU/min. However, confirmatory testing by HPLC failed to identify PCP in either the urine or serum. To verify the suspicion that this was a false-positive PCP result, stock solutions of tramadol and its major metabolite (O-desmethyltramadol) at concentrations of 100 mg/L in 10% methanol/H2O were compared with a blank solution (10% methanol/H2O) for EMIT II+ PCP reactivity and demonstrated reactivities of 44 mAU/min and 27 mAU/min, respectively. While these individual results were below the cutoff reactivity for a positive EMIT II+ PCP result (ca. 85 mAU/min), they were much more reactive than the blank calibrator (set at 0 mAU/min). Therefore, we conclude that the immunoreactivity of tramadol and its metabolites in aggregate is responsible for the PCP immunoassay interference and false-positive result.

[Determination of tramadol hydrochloride in serum samples by disk solid phase extraction and gas chromatography-mass spectrometry in selected ion monitoring]

OBJECTIVE

Disk solid phase extraction (SPE) was assessed for tramadol hydrochloride from serum.

METHODS

The SPE was performed with SPEC C18AR/MP3 Disk SPE cartridge, offering hydrophobic C18 and strong cation ionic exchange interactions for the analytes, before being added into extraction column, 1 mL serum was diluted by 2 mL 0.1 mol/L phosphate buffer solution (pH 6) and the eluent was ethyl acetate containing 2% ammonia. Then SKF525 was added as internal standard into samples, which would be extracted simultaneously with analyte,quantitatively, determined by GC/MS/SIM.

RESULTS

The extraction recovery of tramadol hydrochloride was 98.9%, 92.5% and 84.8% for serum samples with corresponding amounts of standard addition of 0.1 microg/mL, 0.2 microg/mL and 0.5 microg/mL. And RSD measured 5 times was 3.2%, 8.7% and 10.9% respectively. The linear range varied from 0.1 microg/mL to 4 microg/mL. The multinomial regression correlation coefficient (r2) equaled 0.9939, and the detection limit was 21 ng/mL. After the same extraction column was continuously used for 5 times, there was no jam, pollution and decline of recovery and RSD.

CONCLUSION

This method is suitable for forensic toxicological analysis.

Enantiomeric Determination of Tramadol and O-Desmethyltramadol by Liquid Chromatography-Mass Spectrometry and Application to Postoperative Patients Receiving Tramadol

A liquid chromatographic-mass spectrometric assay with atmospheric pressure chemical ionization is presented for quantification (selected-ion mode) of tramadol (T) and O-desmethyltramadol (ODT) in blood plasma after liquid-liquid extraction. The enantiomeric separation was achieved on a Chiralpak AD column containing amylose tris-(3,5-dimethylphenylcarbamate) as chiral selector. The validation data were within acceptable limits. The assay was successfully applied to authentic plasma samples allowing confirmation of diagnosis of overdose or intoxication as well as monitoring of patients' compliance. In postoperative patients receiving T, mean therapeutic plasma concentrations were determined as follows: 422.8 and 440.8 ng/mL for (+)-T and (-)-T, respectively, and 23.7 and 40.7 ng/mL for (+)-ODT and (-)-ODT, respectively. Quantitative results demonstrated a great interindividual variability in postoperative plasma analgesic drug concentrations and, therefore, a wide therapeutic concentration range. The 7.7% of the samples that revealed negative results for ODT are likely explained by genetic polymorphisms resulting in absent enzyme activity of CYP2D6.

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.

Enhanced method performances for conventional and chiral CE-ESI/MS analyses in plasma

Due to its high efficiency, selectivity, and sensitivity, CE-ESI/MS has evolved as an efficient technique for the drugs and metabolites analysis in biological matrices. However, a sample preparation is mandatory prior to CE-ESI/MS analysis. To achieve fast and simplified sample preparation of plasma samples, protein precipitation (PP) and liquid-liquid extraction (LLE) were used with two injection techniques: hydrodynamic (HD) and electrokinetic (EK) injection. CE-ESI/MS analyses of pharmaceutical compounds and amphetamine derivatives were developed. Detection limits of 1 ppm were reached with PP and HD injection whereas 1 ppb was detected when samples were prepared with LLE and injected by EK. Same experiments were performed for stereoselective determinations in partial-filling mode and detection limits achieved were equivalent to conventional analysis (0.5 ppb per enantiomer). When complex matrices are analyzed, MS signal suppression or enhancement effects are generally not reproducible and could compromise results with ESI. Therefore, matrix effect was investigated in CE-ESI/MS with a commercially available coaxial sheath-liquid ESI interface used as postcapillary infusion system to determine MS signal alterations. Matrix effects were differentially evidenced according to the selected sample preparation. With PP, signal suppression was observed out of the analyses migration window, while for LLE no relevant matrix effect occurred in all experiments.

Miotic action of tramadol is determined by CYP2D6 genotype

Polymorphic CYP2D6 is the enzyme that activates the opioid analgesic tramadol by O-demethylation to its active metabolite O-demethyltramadol (M1). Our objective was to determine the opioid effects measured by pupillary response to tramadol of CYP2D6 genotyped volunteers in relation to the disposition of tramadol and M1 in plasma. Tramadol displayed phenotypic pharmacokinetics and it was possible to identify poor metabolizers (PM) with >99% confidence from the metabolic ratio (MR) in a single blood sample taken between 2.5 and 24 h post-dose. Homozygous extensive metabolizers (EM) differed from PM subjects by an almost threefold greater (P=0.0014) maximal pupillary constriction (Emax). Significant correlations between the AUC and Cmax values of M1 versus pupillary constriction were found. The corresponding correlations of pharmacokinetic parameters for tramadol itself were weaker and negative. The strongest correlations were for the single-point metabolic ratios at all sampling intervals versus the effects, with rs ranging from 0.85 to 0.89 (p<0.01). It is concluded that the concept of dual opioid/non-opioid action of the drug, though considerably stronger in EMs, is valid for both EM and PM subjects. This is the theoretical basis for the frequent use and satisfactory efficacy of tramadol in clinical practice when given to genetically non-selected population.

The analgesic effect of tramadol after intravenous injection in healthy volunteers in relation to CYP2D6

Tramadol analgesia results from a monoaminergic effect by tramadol itself and an opioid effect of its metabolite (+)-M1 formed by O-demethylation of tramadol by CYP2D6. In this study we sought to determine the impact of (+)-M1 on the analgesic effect of tramadol evaluated by experimental pain models. The effect of an IV injection of 100 mg tramadol on experimental pain was studied 15-90 min after dosing in volunteers, 10 extensive metabolizers with CYP2D6 and 10 poor metabolizers without CYP2D6 in 2 placebo-controlled trials. The pain tests included detection and tolerance threshold to single electrical sural nerve stimulation, pain summation threshold to repetitive electrical sural nerve stimulation (temporal summation), and the cold pressor test. In extensive metabolizers, tramadol reduced discomfort experienced during the cold pressor test (P = 0.002). In poor metabolizers, the pain tolerance thresholds to sural nerve stimulation were increased (P = 0.04). (+)-M1 could be detected in the serum samples from all extensive metabolizers except one, but (+)-M1 was below the limit of determination in all poor metabolizers. The opioid effect of (+)-M1 appears to contribute to the analgesic effect of tramadol, but the monoaminergic effect of tramadol itself seems to create an analgesic effect.

Comparative bioavailability between two tramadol once-daily oral formulations

The aim of this study was to compare the pharmacokinetic profile and oral bioavailability of Tramadol Contramid once-daily (o.d.) 200 mg tablets (Labopharm, Canada) with that of Zytram 200 mg tablets (Zambon, Spain), following single-dose administration in 26 healthy volunteers. The study had an open, randomized, crossover design with a 7-day wash-out. Data from 24 subjects were used for the pharmacokinetic (PK) analysis. Racemic tramadol and racemic O-demethyltramadol (M1) were assayed in plasma using a liquid chromatography/tandem mass spectrometry method. Primary PK parameters estimated were AUC(0-t), AUC(0-infinity), C(max), C(24 h), and T(max). Results were compared using an ANOVA, and the residual variability thereby obtained was used to construct the classical 90% confidence intervals. The parametric Schuirmann's test was also performed. T(max) was analyzed by a nonparametric approach. For both racemic tramadol and racemic O-demethyltramadol, the ANOVA showed a statistically significant formulation effect. Significantly higher values were obtained for Tramadol Contramid o.d. for all PK parameters, except for T(1/2). For Tramadol Contramid o.d., mean tramadol plasma levels were maintained at a plateau level above 200 ng/ml from 4 to 16 h after dose, while for the reference formulation, that level was sustained from 4 to only 6 h. Consistent results for both formulations were obtained for the metabolite. At the end of the dosing interval, plasma tramadol and O-demethyltramadol concentrations were 39% and 49% higher, respectively, for Tramadol Contramid o.d. than those for Zytram (p < 0.0001). Tramadol Contramid o.d. could be considered suprabioavailable to Zytram o.d.

Stereoselective pharmacokinetic analysis of tramadol and its main phase I metabolites in healthy subjects after intravenous and oral administration of racemic tramadol

The kinetics of tramadol enantiomers are stereoselective when doses of the racemic drug are given orally. To document whether the route of administration determines the stereoselective kinetics of tramadol enantiomers, healthy volunteers received 100 mg oral or intravenous doses of racemic tramadol, and serial blood samples were obtained to assay tramadol enantiomers and their main phase I metabolites, O-demethyltramadol and N-demethyltramadol. To assess accurately the involvement of their metabolites in the pharmacokinetics of tramadol, it is essential to determine the rate and extent of the formation of the enantiomers of these metabolites. A simultaneous pharmacokinetic model describing the plasma concentration-curves of the generated metabolites and the parent compounds after intravenous and oral drug administration is developed and presented. Tramadol and O-demethyltramadol were the major compounds detected in plasma after intravenous administration. Nevertheless, the N-demethylation of tramadol showed a significant increase when the oral route was used. After both oral and intravenous doses, the kinetics of the tramadol enantiomers were stereoselective. The AUC for (R )-(+)-tramadol was greater than the AUC for (S)-(-)-tramadol. The formation of N-demethyltramadol also was enantioselective after oral administration of racemic tramadol, with a greater AUC for (R)-(+)-N-demethyltramadol than for (S)-(-)-N-demethyltramadol. In the opposite form, (S)-(-)-O-demethyltramadol was formed faster than (R)-(+)-O-demethyltramadol. The metabolism of tramadol was also route-dependent with a different enantiomeric ratio for tramadol and its main phase I metabolites after intravenous and oral administration. The disposition of N-demethyltramadol was concentration-dependent.

O-demethylation of tramadol in the first months of life

OBJECTIVE

Assess in vivo O-demethylation activity in the first months of life.

METHODS

Time-concentration profiles of tramadol (M) and O-demethyl tramadol (M1) in plasma and urine were simultaneously collected in the first 24 h of continuous intravenous tramadol administration in neonates and young infants. M and M1 were determined by high performance liquid chromatography. Correlations between perinatal characteristics [postnatal age (PNA), postmenstrual age (PMA)] and the contribution of metabolites (M, M1) to overall tramadol elimination and to the plasma and urine log M/M1 were calculated.

RESULTS

Plasma samples were available in 20/29 and complete 24-h urine collections were available in 25/29 neonates (25-53 weeks PMA). Mean plasma log M/M1 value (>4 h, n=86) was 0.8 (SD 0.4). A significant correlation between plasma log M/M1 and PMA (r=-0.73, P<0.0001) and PNA (r=-0.58, P<0.005) was observed. In a multiple regression model, only PMA remained an independent variable. Mean urine log M/M1 was 0.94 (SD 0.7). Significant correlations of the urine log M/M1 ratio with PMA (r=-0.73, P<0.0001) and PNA (r=-0.56, P=0.0035) were observed. In a multiple regression model with the urine log M/M1 ratio as dependent variable, only PMA remained an independent variable. The maturational half-life of the log M/M1 ratio in early neonatal life in the age range evaluated is about 12-16 weeks without plateau.

CONCLUSIONS

O-demethylation activity was already observed in early neonatal life. A significant correlation with PMA was documented, but PMA can only partially explain the observed variability in O-demethylation activity. Polymorphism therefore likely already contributes to the interindividual variability observed in neonates.

Development and validation of a rapid HPLC method for simultaneous determination of tramadol, and its two main metabolites in human plasma

Tramadol, an analgesic agent, and its two main metabolites O-desmethyltramadol (M1) and N-desmethyltramadol (M2) were determined simultaneously in human plasma by a rapid and specific HPLC method. The sample preparation was a simple extraction with ethyl acetate. Chromatographic separation was achieved with a Chromolith Performance RP-18e 50 mm x 4.6 mm column, using a mixture of methanol:water (13:87, v/v) adjusted to pH 2.5 by phosphoric acid, in an isocratic mode at flow rate of 2 ml/min. Fluorescence detection (lambda(ex)=200 nm/lambda(em)=301 nm) was used. The calibration curves were linear (r(2)>0.997) in the concentration range of 2.5-500 ng/ml, 1.25-500 ng/ml and 5-500 ng/ml for tramadol, M1 and M2, respectively. The lower limit of quantification was 2.5 ng/ml for tramadol, 1.25 ng/ml for M1 and 5 ng/ml for M2. The within- and between-day precisions in the measurement of QC samples at four tested concentrations were in the range of 2.5-9.7%, 2.5-9.9% and 5.9-11.3% for tramadol, M1 and M2, respectively. The developed procedure was applied to assess the pharmacokinetics of tramadol and its two main metabolites following administration of 100mg single oral dose of tramadol to healthy volunteers.

Improved HPLC method for the simultaneous determination of tramadol and O-desmethyltramadol in human plasma

This paper describes an HPLC method for the determination of tramadol and its major active metabolite, O-desmethyltramadol (ODT), in human plasma. Sample preparation involved liquid-liquid extraction with diethyl ether-dichloromethane-butanol (5:3:2, v/v/v) and back extraction with sulphuric acid. Tramadol, ODT and the internal standard, sotalol, were separated by reversed phase HPLC using 35% acetonitrile and an aqueous solution containing 20 mM sodium phosphate buffer, 30 mM sodium dodecyl sulphate and 15 mM tetraethylammonium bromide pH 3.9. Detection was by fluorescence with excitation and emission wavelengths of 275 and 300 nm, respectively. The method was linear for tramadol (3-768 ng/ml) and ODT (1.5-384 ng/ml) with mean recoveries of 87.2% and 89.8%, respectively. Intra- and inter-day precisions were 10.34% and 8.43% for tramadol and 9.43% and 8.75% for ODT at the respective limits of quantitation (3 and 1.5 ng/ml). Accuracy for tramadol ranged from 96.2% to 105.3%. The method was applied to a pharmacokinetic study of tramadol in human volunteers.

Postmortem Distribution of Tramadol, Amitriptyline, and Their Metabolites in a Suicidal Overdose

A case report involving a 34-year-old white male who was found dead at home by his roommate is presented. At the time of his death, he was being treated with tramadol/acetaminophen, metaxalone, oxycodone, and amitriptyline. The decedent's mother stated that he had been taking increasing amounts of pain medication in order to sleep at night. There were no significant findings at autopsy; however, toxicology results supported a cause and manner of death resulting from suicidal mixed tramadol and amitriptyline toxicity. This case reports the tissue and fluid distribution of tramadol, amitriptyline, and their metabolites in an acutely fatal ingestion in an effort to document concentrations of these analytes in 12 matrices with respect to one another to assist toxicologists in difficult interpretations.

Rapid determination of tramadol in human plasma by headspace solid-phase microextraction and capillary gas chromatography-mass spectrometry

A simple, rapid and sensitive method for determination of tramadol in plasma samples was developed using headspace solid-phase microextraction (HS-SPME) and gas chromatography with mass spectrometry (GC-MS). The optimum conditions for the SPME procedure were: headspace extraction on a 65-microm polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber; 0.5 mL of plasma modified with 0.5 mL of sodium hydroxide (0.1 M); extraction temperature of 100 degrees C, with stirring at 2000 rpm for 30 min. The calibration curve showed linearity in the range of 1-400 ng mL(-1) with regression coefficient corresponding to 0.9986 and coefficient of the variation of the points of the calibration curve lower than 10%. The detection limit for tramadol in plasma was 0.2 ng mL(-1). The proposed method was successfully applied to determination of tramadol in human plasma samples from 10 healthy volunteers after a single oral administration.

The effects of tramadol on static and dynamic pupillometry in healthy subjects--the relationship between pharmacodynamics, pharmacokinetics and CYP2D6 metaboliser status

OBJECTIVES

The main objective of the present study was to provide information on whether static and dynamic pupillometry can be used for pharmacodynamic profiling, particularly when investigating opioid-like drugs, such as tramadol.

METHODS

Healthy subjects (n = 26) participated in this randomised, double-blind, placebo-controlled, crossover Phase 1 study. Of these, 20 extensive metabolisers (EMs) with respect to polymorphic isoenzyme cytochrome P450 2D6 (CYP2D6) received up to 150 mg of tramadol-HCl and placebo. The 6 poor metabolisers (PMs) with respect to CYP2D6 received 100 mg tramadol-HCl and placebo.

RESULTS

In EMs, serum concentrations of the enantiomers of tramadol and of O-demethylated metabolite (M1) increased with increasing doses. Comparing the 100-mg dose between EMs and PMs, the latter exhibited higher serum concentrations of both enantiomers of tramadol. Serum concentrations of (+)-M1 remained below the lower limit of quantification, and that of (-)-M1 were lower than those in EMs. In EMs, doses from 100 mg tramadol-HCl on induced a significant (P<0.05) miosis as compared with placebo. The maximum mean differences from placebo after dosing with 50, 100 and 150 mg tramadol-HCL were -0.5, -0.8 and -1.1 mm, respectively, indicating a dose-dependent character of the changes. Dynamic pupillometry revealed significant (P<0.05) effects for the amplitude, latency and duration of reaction. The amplitude and velocity of constriction were decreased only at the highest dose; whereas, the changes of the amplitude reached statistical significance (P<0.05). Both the latency and reaction duration behaved in a dose-dependent manner. For the latency, significant changes compared with placebo (P<0.05) were found at the 150-mg dose level, while the reaction duration was already significantly (P<0.05) decreased from the 100-mg dose on. The velocity of redilatation did not respond at all. In PMs, no effect on the initial pupil diameter was found. Although the statistical analysis failed to demonstrate any significant change from placebo for the dynamic pupillometry, the effect-time profiles of EMs and PMs were comparable. For both metaboliser groups, a decrease of amplitude, velocity of constriction and reaction duration as well as an increase of latency was observed. In principle, the direction and magnitude of changes were comparable between EMs and PMs. Most important was the finding that the time course of effects was completely different between both groups of metabolisers. In EMs, effects slowly reached a maximum between 4 h and 10 h after dosing and diminished until 24 h; whereas, in PMs, both maximum effects and the return to baseline occurred much earlier, at approximately 3 h and 8 h, respectively.

CONCLUSIONS

The EMs and PMs of CYP2D6 treated with tramadol behaved differently in static and dynamic pupillometry. The reason for this could largely be explained with the aid of the metaboliser status and the pharmacokinetic properties of tramadol. In EMs, the pupillometric response was mainly driven by the (+)-M1, which comprises the mu action component of tramadol; whereas, in PMs, the non-mu component appears to play an important role. Thus, pupillometry was found to be useful in pharmacodynamic profiling and provides a good correlation with the pharmacokinetics.

Paroxetine, a cytochrome P450 2D6 inhibitor, diminishes the stereoselective -demethylation and reduces the hypoalgesic effect of tramadol

OBJECTIVE

Tramadol hydrochloride (INN, tramadol) exerts its antinociceptive action through a monoaminergic effect mediated by the parent compound and an opioid effect mediated mainly by the O-demethylated metabolite (+)-M1. O-demethylation is catalyzed by cytochrome P450 (CYP) 2D6. Paroxetine is a very potent inhibitor of CYP2D6. The objective of this study was to investigate the influence of paroxetine pretreatment on the biotransformation and the hypoalgesic effect of tramadol.

METHODS

With and without paroxetine pretreatment (20 mg daily for 3 consecutive days), the formation of M1 and the analgesic effect of 150 mg of tramadol were studied in 16 healthy extensive metabolizers of sparteine in a randomized, double-blind, placebo-controlled, 4-way crossover study by use of experimental pain models.

RESULTS

With paroxetine pretreatment, the area under the plasma concentration-time curve (AUC) of (+)- and (-)-tramadol was increased (37% [P = .001] and 32% [P = .002], respectively), and the corresponding AUCs of(+)- and (-)-M1 were decreased (67% [P = .0004] and 40% [P = .0008], respectively). (+)-M1 and (-)-M1 could be determined in all subjects throughout the study period regardless of paroxetine pretreatment. The sums of differences between postmedication and premedication values of pain measures differed between the placebo/tramadol and the placebo/placebo combination, with median values as follows: pressure pain tolerance threshold, 390 kPa (95% confidence interval [CI], 211 to 637 kPa) versus -84 kPa (95% CI, - 492 to -32 kPa) (P = .001); single sural nerve stimulation pain tolerance threshold, 25.8 mA (95% CI, 15.3 to 29.8 mA) versus 9.0 mA (95% CI, 1.5 to 14.8 mA) (P = .005); pain summation threshold, 10.7 mA (95% CI, 5.2 to 17.6 mA) versus 5.0 mA (95% CI, 2.8 to 11.2 mA) (P = .066); cold pressor pain, -4.2 cm x s (95% CI, -6.8 to -1.9 cm x s) versus -0.4 cm x s (-1.4 to 1.4 cm x s) (P = .002); and discomfort, -4.7 cm (95% CI, -10.6 to -2.8 cm) versus 0.5 cm (-0.1 to 1.4 cm) (P = .002). The sums of differences of the paroxetine/tramadol combination also differed from placebo/tramadol for some of the measures, with median values as follows: cold pressor pain, -2.2 cm x s (95% CI, -3.7 to -0.4 cm x s) (P = .036, compared with placebo/tramadol); and discomfort, -2.0 cm (95% CI, -5.6 to -1.2 cm) (P = .056). For the other measures, the hypoalgesic effect was retained on the paroxetine/tramadol combination, with median values as follows: pressure pain tolerance threshold, 389 kPa (95% CI, 141 to 715 kPa) (P = .278, compared with placebo/tramadol); single sural nerve stimulation pain tolerance threshold, 12.5 mA (95% CI, 6.2 to 28.3 mA) (P = .278); and pain summation threshold, 8.2 mA (95% CI, 4.4 to 14.6 mA) (P = .179). Paroxetine in combination with placebo showed no analgesic effect.

CONCLUSIONS

It is concluded that paroxetine at a dosage of 20 mg once daily for 3 consecutive days significantly inhibits the metabolism of tramadol to its active metabolite M1 and reduces but does not abolish the hypoalgesic effect of tramadol in human experimental pain models, particularly in opioid-sensitive tests.

Investigation of the pharmacokinetics and determination of tramadol in rabbit plasma by a high-performance liquid chromatography–diode array detector method using liquid–liquid extraction

An HPLC system using a new, simple and rapid liquid-liquid extraction and high-performance liquid chromatography-diode array detector method (HPLC-DAD) detection was validated to determine tramadol concentration in rabbit plasma. The method described was applied to a pharmacokinetic study of intravenous tramadol injections in rabbits. The extraction with ethylacetate yielded good response. The recovery of tramadol from plasma averaged 90.40%. Serial plasma samples were obtained prior to, during and after completion of the infusion for determination of tramadol concentrations. Tramadol concentrations were measured using reverse-phase high-performance liquid chromatography and pharmacokinetic application with intravenous tramadol in rabbits revealed that tramadol followed one-compartment open model. Maximum plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC) for tramadol were 14.3 microg mL(-1) and 42.2 microg h mL(-1), respectively. The method developed was successfully applied to a simple, rapid, specific, sensitive and accurate HPLC method for investigation of the pharmacokinetics of tramadol in rabbit plasma.

Tramadol concentrations in blood and in cerebrospinal fluid in a neonate

Based on blood and cerebrospinal fluid samples collected in a full-term neonate, the penetration of tramadol in the central nervous system is described. Following intravenous administration of tramadol, a lag time of about 4 h was observed until full blood-brain equilibration was achieved. This pharmacokinetic observation is in line with a recent pharmacodynamic evaluation of the central opioid effects of tramadol in adults.