Modelling the pharmacokinetics of tramadol: On the difference between CYP2D6 extensive and poor metabolizers (original) (raw)
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Parent-Metabolite pharmacokinetic models for tramadol-tests of assumptions and predictions
Allometric principles were used to discern cross-species differences in (±)-tramadol disposition and formation of its primary analgesic metabolite, (±)-O-desmethyl-tramadol (M1). Species differences in formation of M1 may help predict the analgesic effectiveness of tramadol. Tramadol was administered intravenously by a zero-order (constant infusion) process or rapid bolus dose and racemic concentrations of tramadol and M1 measured. Data were pooled to define differences between species (human, rat, cat, dog, goat, donkey and horse). A two-compartment linear disposition model with first-order elimination was used to describe tramadol and M1 disposition. Slow metabolizers were detected in 6% of the population and tramadol clearance to M1 was 16.2% that of extensive metabolizers. Tramadol clearance to M1 was slower and tramadol clearance by other pathways was faster in rats, dogs, and horses compared to humans. There are substantial differences between species in the pharmacokinetics of tramadol and its M1 metabolite, which are not explained by differences in body weight. The hypothesis that volumes of distribution are similar across species was shown not to be true. M1 exposure in the goat, donkey and cat was comparable to humans, which indicates it is likely to be an effective analgesic at typically used doses in these species but not in dogs or horses.
Enantioselective pharmacokinetics of tramadol in CYP2D6 extensive and poor metabolizers
European Journal of Clinical Pharmacology, 2006
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≤0.0015), (−)-tramadol (P≤0.0062), (+)-M1 (P≤0.0198) and (−)-M1 (P≤0.0370), and significant differences in C max of (+)-M1 (P<0.0001) and (−)-M1 (P≤0.0010). In Phase A and C, significant differences in t max were seen for (+)-M1 (P≤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 dif-ferences 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.
Physiology-Based IVIVE Predictions of Tramadol from in Vitro Metabolism Data
Pharmaceutical Research, 2014
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 (CLint H ) 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 modelpredicted 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 systemspecific physiological information to come up with reliable PK predictions in adults.
Pharmacological Research, 2007
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 100 mg 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.
Impact of CYP2D6 Genetic Polymorphism on Tramadol Pharmacokinetics and Pharmacodynamics
Background and objective: Tramadol is metabolized by the highly polymorphic enzyme cytochrome P450 Abstract (CYP)2D6. Patients with different CYP2D6 genotypes may respond differently to tramadol in terms of pain relief and adverse events. In this study, we compare the pharmacokinetics and effects of tramadol in Malaysian patients with different genotypes to establish the pharmacokinetic-pharmacodynamic relationship of tramadol. Study design and setting: All patients received an intravenous dose of tramadol 100mg as their first postoperative analgesic. Blood was sampled at 0 minutes and subsequently at 15 and 30 minutes, 1, 2, 4, 8, 16, 20, and 24 hours for serum tramadol and analyzed by high-performance liquid chromatography (HPLC). Patients were genotyped for CYP2D6*1, *3, *4, *5, *9, *10, and *17 alleles and duplication of the gene by means of an allele-specific PCR. Pain was measured using the Visual Analog Scales, and adverse effects were recorded. Results: About half of the patients had the wild-type allele (CYP2D6*1), with the 'Asian' CYP2D6*10 allele accounting for most of the rest (40%). None of the genotypes predicted poor metabolism. Twenty-seven percent of the patients were intermediate metabolizers (IM) and 2.9% were ultra-rapid (UM) metabolizers; the remaining 70% were extensive metabolizers (EM). The mean total clearance (CL) predicted by the model was lower (19 L/ hour) and the half-life longer (5.9 hours) than those reported in Western populations. This may due to the high frequency of the CYP2D6*10 allele amongst Malaysian patients. The UM and EM groups had 2.6-and 1.3-times faster CL, respectively, than the IM. CL was 16, 18, 23, and 42 L/hour while mean half-lives were 7.1, 6.8, 5.6, and 3.8 hours among the IM, EM1, EM2, and UM groups, respectively. However, the analgesic effects of tramadol were not measured adequately among the postoperative patients to establish its full therapeutic effects. There were significant differences in the adverse-effect profiles amongst the various genotype groups, with the IM group experiencing more adverse effects than the EM, and the EM having more adverse effects than the UM. Conclusion: CYP2D6 activity may play an important role in determining the pharmacokinetics of tramadol and in predicting its adverse effects. If these results can be confirmed in a larger population, genotyping may be an important tool in determining the dose of tramadol.
European Journal of Pharmaceutical Sciences, 2016
Tramadol hydrochloride is a centrally acting analgesic used for the treatment of moderate-to-severe pain. It has three main metabolites: O-desmethyltramadol (M1), N-desmethyltramadol (M2), and N,O-didesmethyltramadol (M5). Because of the frequent use of tramadol by patients and drug abusers, the ability to determine the parent drug and its metabolites in plasma and cerebrospinal fluid is of great importance. In the present study, a pharmacokinetic approach was applied using two groups of five male Wistar rats administered a 20 mg/kg dose of tramadol via intravenous (i.v.) or intraperitoneal (i.p.) routes. Plasma and CSF samples were collected at 5-360 min following tramadol administration. Our results demonstrate that the plasma values of C max (C 0 in i.v. group) and area under the curve (AUC) 0-t for tramadol were 23,314.40 ± 6944.85 vs. 3187.39 ± 760.25 ng/mL (C max) and 871.15 ± 165.98 vs. 414.04 ± 149.25 μg•min/mL in the i.v. and i.p. groups, respectively (p b 0.05). However, there were no significant differences between i.v. and i.p. plasma values for tramadol metabolites (p N 0.05). Tramadol rapidly penetrated the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSFB) (5.00 ± 0.00 vs. 10.00 ± 5.77 min in i.v. and i.p. groups, respectively). Tramadol and its metabolites (M1 and M2) were present to a lesser extent in the cerebrospinal fluid (CSF) than in the plasma. M5 hardly penetrated the CSF, owing to its high polarity. There was no significant difference between the AUC 0-t of tramadol in plasma (414.04 ± 149.25 μg•min/mL) and CSF (221.81 ± 83.02 μg•min/mL) in the i.p. group. In addition, the amounts of metabolites (M1 and M2) in the CSF showed no significant differences following both routes of administration. There were also no significant differences among the K p,uu,CSF(0-360) (0.51 ± 0.12 vs. 0.63 ± 0.04) and K p,uu,CSF(0-∞) (0.61 ± 0.10 vs. 0.62 ± 0.02) for i.v. and i.p. pathways, respectively (p N 0.05). Drug targeting efficiency (DTE) values of tramadol after i.p. injection were more than unity for all scheduled time points. Considering the main analgesic effect of M1, it is hypothesized that both routes of administration may produce the same amount of analgesia.
Comparative bioequivalence studies of tramadol hydrochloride sustained-release 200 mg tablets
2010
Background: Tramadol hydrochloride is available as 50 mg immediate-release (IR) and 100 mg, 200 mg, and 300 mg sustained-release (SR) tablets. The recommended dose of tramadol is 50-100 mg IR tablets every 4-6 hours. The tramadol SR 200 mg tablet is a better therapeutic option, with a reduced frequency of dosing, and improved patient compliance and quality of life. The present study evaluated the bioequivalence of a generic tramadol SR 200 mg tablet. Methods: A comparative in vitro dissolution study was performed on the test and reference products, followed by two separate single-dose bioequivalence studies under fasting and fed conditions and one multiple-dose bioequivalence study under fasting conditions. These bioequivalence studies were conducted in healthy human subjects using an open-label, randomized, two-treatment, two-period, two-sequence, crossover design. The oral administration of the test and reference products was done on day 1 for both the single-dose studies and on days 1-5 for the multiple-dose study in each study period as per the randomization code. Serial blood samples were collected at predefined time points in all the studies. Analysis of plasma concentrations of tramadol and O-desmethyltramadol (the M 1 metabolite) was done by a validated liquid chromatography-mass spectrometry analytical method. The standard acceptance criterion of bioequivalence was applied on log-transformed pharmacokinetic parameters for tramadol and its M 1 metabolite. Results: The ratios for geometric least-square means and 90% confidence intervals were within the acceptance range of 80%-125% for log-transformed primary pharmacokinetic parameters for tramadol and its M 1 metabolite in all the three studies. Conclusion: The test product is bioequivalent to the reference product in terms of rate and extent of absorption, as evident from the single-dose and multiple-dose studies. Both the treatments were well tolerated.
A disposition kinetic study of tramadol in rat perfused liver
Biopharmaceutics & Drug Disposition, 2008
A recirculated perfusion system was used to investigate the metabolism of tramadol, an analgesic agent, in the isolated perfused rat liver. Tramadol was added to the perfusion medium at a concentration of 300 ng/ml, and the perfusate samples were collected for 180 min. The concentration of tramadol and its three main metabolites O-desmethyltramadol (M1) and N-desmethyltramadol (M2) and N,O-didesmethyltramadol (M5) were determined in perfusate samples by a rapid HPLC method. All through the study, the phase I metabolism of tramadol led to the formation of M1 metabolite from early sampling points while M5 metabolite was detectable after 50 min in 6 out of 10 perfused livers and the M2 metabolite was not detectable in any experiment. The kinetic parameters of tramadol and two detectable metabolites (M1 and M5) were then calculated in perfusate samples. The tramadol concentration decreased from 297.8 to 159.6 ng/ml, with a mean half-life of 232.4 min and a hepatic clearance of 0.73 ml/min. After 180 min, the mean concentration of M1 reached 59.5 ng/ml, resulting in a metabolic ratio of 16%, while the formation of M5 metabolite continued to a mean concentration of 14.6 ng/ml resulting in a metabolic ratio of 2% using AUC(0−180min). Copyright © 2008 John Wiley & Sons, Ltd.
Pharmaceutics
Cytochrome P450 2D6 (CYP2D6) gene polymorphisms influence the exposure to tramadol (T) and its pharmacologically active metabolite, O-demethyl tramadol (O-dT). Tramadol has been considered as a candidate probe drug for CYP2D6 phenotyping. The objective of the CYTRAM study was to investigate the value of plasma O-dT/T ratio for CYP2D6 phenotyping. European adult patients who received IV tramadol after surgery were included. CYP2D6 genotyping was performed and subjects were classified as extensive (EM), intermediate (IM), poor (PM), or ultra-rapid (UM) CYP2D6 metabolizers. Plasma concentrations of tramadol and O-dT were determined at 24 h and 48 h. The relationship between O-dT/T ratio and CYP2D6 phenotype was examined in both a learning and a validation group. Genotype data were obtained in 301 patients, including 23 PM (8%), 117 IM (39%), 154 EM (51%), and 7 UM (2%). Tramadol trough concentrations at 24 h were available in 297 patients. Mean value of O-dT/T ratio was significantly l...