Simultaneous stereoselective analysis by capillary electrophoresis of tramadol enantiomers and their main phase I metabolites in urine

A handheld fluorescent lateral flow immunoassay platform for highly sensitive point-of-care detection of methamphetamine and tramadol

The escalating issue of drug abuse poses a significant threat to public health and societal stability worldwide. An on-site drug detection platform is vital for combating drug abuse and trafficking, as it eliminates the need for additional tools, extensive processes, or specialized training. Therefore, it is imperative to develop a fast, sensitive, non-invasive, and reliable multiplex drug testing platform. In this study, we have presented a silica core@dual quantum dot-shell nanocomposite (SI/DQD)-based fluorescent lateral flow immunoassay (LFIA) platform for the highly sensitive and simultaneous point-of-care (POC) detection of methamphetamine (MET) and tramadol (TR). A 3D-printed attachment was designed to integrate optical and electrical components, facilitating the miniaturization of the instrument and reducing both cost and complexity. The device's advanced hardware and effective fluorescence extraction algorithm with waveform reconstruction enable swift, automatic noise reduction and data analysis. SI/DQD nanocomposites were utilized as fluorescent nanotags in the LFIA strips due to their outstanding luminous efficiency and robustness. This LFIA platform achieves impressive detection limits (LODs) of 0.11 ng mL-1 for MET and 0.017 ng mL-1 for TR. The method has also successfully detected MET and TR in complex biological samples, demonstrating its practical application capabilities. The proposed fluorescent LFIA platform, based on SI/DQD technology, holds significant promise for the swift and accurate POC detection of these substances. Its affordability, compact size, and excellent analytical performance make it suitable for on-site drug testing, including at borders and roadside checks, and open up new possibilities for the design and implementation of drug testing methods.

Comprehensive overview of analytical and bioanalytical methodologies for the opioid analgesics - Tramadol and combinations

Synthetic opioids like Tramadol are used to treat mild to moderate pain. Its ability to relieve pain is about a tenth that of morphine. Furthermore, Tramadol shares similar effects on serotonin and norepinephrine to several antidepressants known as serotonin-norepinephrine reuptake inhibitors (SNRIs), such as venlafaxine and duloxetine. The present review paper discusses the recent developments in analytical methods for identifying drugs in pharmaceutical preparations and toxicological materials, such as blood, saliva, urine, and hair. In recent years, a wide variety of analytical instruments, including capillary electrophoresis, NMR, UV-visible spectroscopy, HPTLC, HPLC, LC-MS, GC, GC-MS, and electrochemical sensors, have been used for drug identification in pharmaceutical preparations and toxicological samples. The primary quantification techniques currently employed for its quantification in various matrices are highlighted in this research.

Simultaneous determination of tramadol and paracetamol in human plasma using LC-MS/MS and application in bioequivalence study of -fixed-dose combination

The study aimed to develop a sensitive and high-throughput liquid chromatography coupled with tandem mass spectrometry method to quantify concentrations of tramadol and paracetamol simultaneously in human plasma. Sample preparation involved single-step protein precipitation using methanol and two deuterated internal standards, tramadol D6 and paracetamol D4. Agilent Poroshell 120 EC-C18 (100 × 2.1 mm, 2.1 µm) analytical column was employed to achieve chromatographic separation. Detection was in positive ion multiple reaction monitoring mode. A tailing factor (Tf) of <1.2, separation factor (K prime) of >1.5 from the column dead time and signal-to-noise (S/N) ratio >10, were obtained for analytes and internal standards. The standard curve was linear over the concentration range of 2.5-500.00 ng/mL for tramadol and 0.025-20.00 μg/mL for paracetamol. A small injection volume of 1 µL, low flow rate of 440 µL/min and short analysis time of 3.5 min reduced the solvent consumption, analysis cost and system contamination. The results of method validation parameters fulfilled the acceptance criteria of bioanalytical guidelines. The method was successfully applied to a bioequivalence study of fixed-dose combination products of tramadol and paracetamol in Malaysian healthy subjects.

Physiologically-based Pharmacokinetic Modeling to Assess the Impact of CYP2D6-Mediated Drug-Drug Interactions on Tramadol and O-Desmethyltramadol Exposures via Allosteric and Competitive Inhibition

Tramadol is an opioid medication used to treat moderately severe pain. Cytochrome P450 (CYP) 2D6 inhibition could be important for tramadol, as it decreases the formation of its pharmacologically active metabolite, O‐desmethyltramadol, potentially resulting in increased opioid use and misuse. The objective of this study was to evaluate the impact of allosteric and competitive CYP2D6 inhibition on tramadol and O‐desmethyltramadol pharmacokinetics using quinidine and metoprolol as prototypical perpetrator drugs. A physiologically based pharmacokinetic model for tramadol and O‐desmethyltramadol was developed and verified in PK‐Sim version 8 and linked to respective models of quinidine and metoprolol to evaluate the impact of allosteric and competitive CYP2D6 inhibition on tramadol and O‐desmethyltramadol exposure. Our results show that there is a differentiated impact of CYP2D6 inhibitors on tramadol and O‐desmethyltramadol based on their mechanisms of inhibition. Following allosteric inhibition by a single dose of quinidine, the exposure of both tramadol (51% increase) and O‐desmethyltramadol (52% decrease) was predicted to be significantly altered after concomitant administration of a single dose of tramadol. Following multiple‐dose administration of tramadol and a single‐dose or multiple‐dose administration of quinidine, the inhibitory effect of quinidine was predicted to be long (≈42 hours) and to alter exposure of tramadol and O‐desmethyltramadol by up to 60%, suggesting that coadministration of quinidine and tramadol should be avoided clinically. In comparison, there is no predicted significant impact of metoprolol on tramadol and O‐desmethyltramadol exposure. In fact, tramadol is predicted to act as a CYP2D6 perpetrator and increase metoprolol exposure, which may necessitate the need for dose separation.

Determination of antiretroviral drugs for buyers' club in Switzerland using capillary electrophoresis methods

Human immunodeficiency virus-acquired immunodeficiency syndrome continues to be a major global public health issue, having claimed almost 33 million lives to date. Due to the high cost of antiretroviral treatment, access to these drugs remains difficult for vulnerable populations, such as migrants and people living in prisons, who often do not have health insurance. These factors lead to poorer health outcomes and higher transmission rates. The personal importation scheme for unapproved generics from foreign countries is one option to access affordable human immunodeficiency virus treatment. However, the risk of importing falsified medicine remains high, and the quality control of unapproved drugs is lacking. In this context, three CE methods for the analysis of nine antiviral drugs found in commercial pharmaceutical formulations were evaluated. The selected compounds were emtricitabine, tenofovir disoproxil, tenofovir alafenamide, rilpivirine, efavirenz, raltegravir, dolutegravir, abacavir, and lamivudine. The developed methods were successfully applied to determine the active pharmaceutical ingredients of commercial formulations and unapproved generics. The quality control of unapproved generics by CE is an attractive approach due to its good standard of quality, low cost, ecofriendliness, and ease of implementation.

Enantioselective pharmacokinetics of tramadol and its three main metabolites; impact of CYP2D6, CYP2B6, and CYP3A4 genotype

Tramadol is a complex drug, being metabolized by polymorphic enzymes and administered as a racemate with the (+)- and (-)-enantiomers of the parent compound and metabolites showing different pharmacological effects. The study aimed to simultaneously determine the enantiomer concentrations of tramadol, O-desmethyltramadol, N-desmethyltramadol, and N,O-didesmethyltramadol following a single dose, and elucidate if enantioselective pharmacokinetics is associated with the time following drug intake and if interindividual differences may be genetically explained. Nineteen healthy volunteers were orally administered either 50 or 100 mg tramadol, whereupon blood samples were drawn at 17 occasions. Enantiomer concentrations in whole blood were measured by LC-MS/MS and the CYP2D6,CYP2B6 and CYP3A4 genotype were determined, using the xTAG CYP2D6 Kit, pyrosequencing and real-time PCR, respectively. A positive correlation between the (+)/(-)-enantiomer ratio and time following drug administration was shown for all four enantiomer pairs. The largest increase in enantiomer ratio was observed for N-desmethyltramadol in CYP2D6 extensive and intermediate metabolizers, rising from about two to almost seven during 24 hours following drug intake. CYP2D6 poor metabolizers showed metabolic profiles markedly different from the ones of intermediate and extensive metabolizers, with large area under the concentration curves (AUCs) of the N-desmethyltramadol enantiomers and low corresponding values of the O-desmethyltramadol and N,O-didesmethyltramadol enantiomers, especially of the (+)-enantiomers. Homozygosity of CYP2B6 *5 and *6 indicated a reduced enzyme function, although further studies are required to confirm it. In conclusion, the increase in enantiomer ratios over time might possibly be used to distinguish a recent tramadol intake from a past one. It also implies that, even though (+)-O-desmethyltramadol is regarded the enantiomer most potent in causing adverse effects, one should not investigate the (+)/(-)-enantiomer ratio of O-desmethyltramadol in relation to side effects without consideration for the time that has passed since drug intake.

Computational contribution to the electrophoretic enantiomer separation mechanism and migration order using modified β-cyclodextrins

Capillary electrophoresis (CE) is an extremely effective technique in many kinds of separations, including separation of enantiomers. Some additional techniques may be necessary to determine the enantiomer migration order (EMO) and also the mechanism involved in chiral recognition. This paper reports the development and optimization of a CE method for enantioseparation of racemic mixture of both R- and S-stereoisomers of tramadol (TRM) with a computational contribution for the EMO determination and the responsible mechanisms for chiral distinction. Parameters such as composition and concentration of background electrolyte (BGE) and type and concentration of cyclodextrins (CD) were evaluated. For calculations, a sequential methodology was used, resorting to semiempirical Parametric Model 3 (PM3) followed by calculations accomplished using density functional theory. The best results were obtained with sulfated-β-CD (s-β-CD) and carboxymethyl-β-cyclodextrin (cm-β-CD) as chiral selector. Calculations show that the inclusion of TRM is not a probable process due to the shape of the TRM molecule and the size CDs cavities. Therefore, the chiral recognition process occurs by the formation of association complexes between modified β-CD and groups of TRM molecules. The structural analysis of the fragments of complexes at a pH of 10 and a thermodynamic analysis of the complexes' formation process allows determining the EMO. Comparing results obtained experimentally and computationally, it seems that the developed method is adequate for separation of TRM enantiomers and the computational methodology is also adequate to get a sense of the system at a molecular level.

Determination of tramadol by dispersive liquid-liquid microextraction combined with GC-MS

Dispersive liquid-liquid microextraction (DLLME) coupled with gas chromatography-mass spectrometry (GC-MS) has been developed for preconcentration and determination of tramadol, ((±)-cis-2-[(dimethylamino)methyl]-1-(3-methoxyphenyl)cyclohexanol-HCl), in aqueous and biological samples (urine, blood). DLLME is a simple, rapid and efficient method for determination of drugs in aqueous samples. Efficient factors on the DLLME process has defined and optimized for extraction of tramadol including type of extraction and disperser solvents and their volumes, pH of donor phase, time of extraction and ionic strength of donor phase. Based on the results of this study, under optimal conditions and by using 2-nitro phenol as internal standard, tramadol was determined by GC-MS, and the figures of merit of this work were evaluated. The enrichment factor, relative recovery and limit of detection were obtained 420, 99.2% and 0.08 µg L(-1), respectively. The linear range was between 0.26 and 220.00 µg L(-1) (R(2) = 0.9970). The relative standard deviation for 50.00 µg L(-1) of tramadol in aqueous samples by using 2-nitro phenol as IS was 3.6% (n = 7). Finally, the performance of DLLME was evaluated for analysis of tramadol in urine and blood.

Pharmacokinetics of tramadol after subcutaneous administration in a critically ill population and in a healthy cohort

Background

Tramadol is an atypical centrally acting analgesic agent available as both oral and parenteral preparations. For patients who are unable to take tramadol orally, the subcutaneous route of administration offers an easy alternative to intravenous or intramuscular routes. This study aimed to characterise the absorption pharmacokinetics of a single subcutaneous dose of tramadol in severely ill patients and in healthy subjects.

Methods/design

Blood samples (5 ml) taken at intervals from 2 minutes to 24 hours after a subcutaneous dose of tramadol (50 mg) in 15 patients (13 male, two female) and eight healthy male subjects were assayed using high performance liquid chromatography. Pharmacokinetic parameters were derived using a non-compartmental approach.

Results

There were no statistically significant differences between the two groups in the following parameters (mean ± SD): maximum venous concentration 0.44 ± 0.18 (patients) vs. 0.47 ± 0.13 (healthy volunteers) mcg/ml (p = 0.67); area under the plasma concentration-time curve 177 ± 109 (patients) vs. 175 ± 75 (healthy volunteers) mcg/ml*min (p = 0.96); time to maximum venous concentration 23.3 ± 2 (patients) vs. 20.6 ± 18.8 (healthy volunteers) minutes (p = 0.73) and mean residence time 463 ± 233 (patients) vs. 466 ± 224 (healthy volunteers) minutes (p = 0.97).

Conclusions

The similar time to maximum venous concentration and mean residence time suggest similar absorption rates between the two groups. These results indicate that the same dosing regimens for subcutaneous tramadol administration may therefore be used in both healthy subjects and severely ill patients.

Trial registration

ACTRN12611001018909

Advances in perioperative pain management: use of medications with dual analgesic mechanisms, tramadol & tapentadol

Recovery from ambulatory surgical procedures can be limited by postoperative pain. Inadequate analgesia may delay or prevent patient discharge and can result in readmission. More frequently, postoperative pain produces discomfort and interrupts sleep, contributing to postoperative fatigue. The development of effective analgesic regimens for the management of postoperative pain is a priority especially in patients with impaired cardiorespiratory, hepatic, or renal function. Tramadol and tapentadol hydrochloride are novel in that their analgesic actions occur at multiple sites. Both agents are reported to be mu-opioid receptor agonists and monoamine-reuptake inhibitors. In contrast to pure opioid agonists, both drugs are believed to have lower risks of respiratory depression, tolerance, and dependence. The Food and Drug Administration has approved both drugs for the treatment of moderate-to-severe acute pain in adults. This article provides an evidence-based account of the role of tramadol and tapentadol in modern clinical practice.

The pharmacokinetics, metabolism and urinary detection time of tramadol in camels

The pharmacokinetics of tramadol in camels (Camelus dromedarius) were studied following a single intravenous (IV) and a single intramuscular (IM) dose of 2.33 mg kg(-1) bodyweight. The drug's metabolism and urinary detection time were also investigated. Following both IV and IM administration, tramadol was extracted from plasma using an automated solid phase extraction method and the concentration measured by gas chromatography-mass spectrometry (GC/MS). The plasma drug concentrations after IV administration were best fitted by an open two-compartment model. However a three-compartment open model best fitted the IM data. The results (means+/-SEM) were as follows: after IV drug administration, the distribution half-life (t(1/2)(alpha)) was 0.22+/-0.05 h, the elimination half-life (t(1/2)(beta)) 1.33+/-0.18 h, the total body clearance (Cl(T)) 1.94+/-0.18 L h kg(-1), the volume of distribution at steady state (Vd(ss)) 2.58+/-0.44 L kg(-1), and the area under the concentration vs. time curve (AUC(0-infinity)) 1.25+/-0.13 mg h L(-1). Following IM administration, the maximal plasma tramadol concentration (C(max)) reached was 0.44+/-0.07 microg mL(-1) at time (T(max)) 0.57+/-0.11h; the absorption half-life (t(1/2 ka)) was 0.17+/-0.03 h, the (t(1/2)(beta)) was 3.24+/-0.55 h, the (AUC(0-infinity)) was 1.27+/-0.12 mg h L(-1), the (Vd(area)) was 8.94+/-1.41 L kg(-1), and the mean systemic bioavailability (F) was 101.62%. Three main tramadol metabolites were detected in urine. These were O-desmethyltramadol, N,O-desmethyltramadol and/or N-bis-desmethyltramadol, and hydroxy-tramadol. O-Desmethyltramadol was found to be the main metabolite. The urinary detection times for tramadol and O-desmethyltramadol were 24 and 48 h, respectively. The pharmacokinetics of tramadol in camels was characterised by a fast clearance, large volume of distribution and brief half-life, which resulted in a short detection time. O-Desmethyltramadol detection in positive cases would increase the reliability of reporting tramadol abuse.

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.

High sensitivity analysis of oxprenolol in urine by capillary electrophoresis with C18 packed on-line preconcentrator

High sensitivity analysis of oxprenolol in spiked human urine has been performed by capillary zone electrophoresis (CZE) in ammonium formate buffer pH 2.5 using an uncoated capillary with 1cm length C18 on-capillary preconcentrator at the inlet side. The preconcentrator was fabricated in laboratory using the packing method and not encapped C18 5 microm particles as stationary phase material. The packed path was retained into the capillary by sintered stationary phase frits. Before running the CZE analysis, the oxprenolol was eluted from the preconcentrator by injecting a short plug of acetonitrile/water mixtures. With respect to classical CZE, the use of on-line preconcentrator widely increased the method sensitivity allowing the detection of the drug at 0.5 ng/mL (injected concentration). The method showed a linear response in the range of 1-150 ng/mL oxprenolol standard compound. The intra-day repeatability (n = 11) R.S.D. values for migration time, peak area and normalized peak area were 0.72%, 3.96% and 3.66%, respectively, while inter-day repeatability (n = 5 days) R.S.D. values were 2.74%, 9.41% and 9.83%, respectively. The method was successfully applied to the analysis of oxprenolol in extracted urine spiked at 250 pg/mL (oxprenolol LOQ concentration in urine).

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.

Clinical pharmacology of tramadol

Tramadol, a centrally acting analgesic structurally related to codeine and morphine, consists of two enantiomers, both of which contribute to analgesic activity via different mechanisms. (+)-Tramadol and the metabolite (+)-O-desmethyl-tramadol (M1) are agonists of the mu opioid receptor. (+)-Tramadol inhibits serotonin reuptake and (-)-tramadol inhibits norepinephrine reuptake, enhancing inhibitory effects on pain transmission in the spinal cord. The complementary and synergistic actions of the two enantiomers improve the analgesic efficacy and tolerability profile of the racemate. Tramadol is available as drops, capsules and sustained-release formulations for oral use, suppositories for rectal use and solution for intramuscular, intravenous and subcutaneous injection. After oral administration, tramadol is rapidly and almost completely absorbed. Sustained-release tablets release the active ingredient over a period of 12 hours, reach peak concentrations after 4.9 hours and have a bioavailability of 87-95% compared with capsules. Tramadol is rapidly distributed in the body; plasma protein binding is about 20%. Tramadol is mainly metabolised by O- and N-demethylation and by conjugation reactions forming glucuronides and sulfates. Tramadol and its metabolites are mainly excreted via the kidneys. The mean elimination half-life is about 6 hours. The O-demethylation of tramadol to M1, the main analgesic effective metabolite, is catalysed by cytochrome P450 (CYP) 2D6, whereas N-demethylation to M2 is catalysed by CYP2B6 and CYP3A4. The wide variability in the pharmacokinetic properties of tramadol can partly be ascribed to CYP polymorphism. O- and N-demethylation of tramadol as well as renal elimination are stereoselective. Pharmacokinetic-pharmacodynamic characterisation of tramadol is difficult because of differences between tramadol concentrations in plasma and at the site of action, and because of pharmacodynamic interactions between the two enantiomers of tramadol and its active metabolites. The analgesic potency of tramadol is about 10% of that of morphine following parenteral administration. Tramadol provides postoperative pain relief comparable with that of pethidine, and the analgesic efficacy of tramadol can further be improved by combination with a non-opioid analgesic. Tramadol may prove particularly useful in patients with a risk of poor cardiopulmonary function, after surgery of the thorax or upper abdomen and when non-opioid analgesics are contraindicated. Tramadol is an effective and well tolerated agent to reduce pain resulting from trauma, renal or biliary colic and labour, and also for the management of chronic pain of malignant or nonmalignant origin, particularly neuropathic pain. Tramadol appears to produce less constipation and dependence than equianalgesic doses of strong opioids.

Migration behaviour and separation of tramadol metabolites and diastereomeric separation of tramadol glucuronides by capillary electrophoresis

Capillary electrophoresis with UV detection was used to separate tramadol (TR), a centrally acting analgesic, and its five phase I (M1, M2, M3, M4, M5) and three phase II metabolites (glucuronides of M1, M4 and M5). Several factors were evaluated in optimisation of the separation: pH and composition of the background electrolyte and the influence of a micellar modifier, sodium dodecyl sulfate. Baseline separation of TR and all the analytes was obtained with use of 65 mM tetraborate electrolyte solution at pH 10.65. The lowest concentrations of the analytes that could be detected were below 1 microM for the O-methylated, below 2 microM for the phenolic and ca. 7 microM for the glucuronide metabolites. The suitability of the method for screening of real samples was tested with an authentic urine sample collected after a single oral dose (50 mg) of TR. After purification and five-fold concentration of the sample (solid-phase extraction with Oasis MCX cartridges), the parent drug TR and its metabolites M1, M1G, M5 and M5G were easily detected, in comparison with standards, in an interference-free area of the electropherogram. Diastereomeric separation of TR glucuronides in in vitro samples was achieved with 10 mM ammonium acetate-100 mM formic acid electrolyte solution at pH 2.75 and with basic micellar 25 mM tetraborate-70 mM SDS electrolyte solution at pH 10.45. Both separations showed that glucuronidation in vitro produces glucuronide diastereomers in different amounts. The authentic TR urine sample was also analysed by micellar method, but unambiguous identification of the glucuronide diastereomers was not achieved owing to many interferences.

Synthesis of d1-N-ethyltramadol as an internal standard for the quantitative determination of tramadol in human plasma by gas chromatography–mass spectrometry

A gas chromatography-mass spectrometry (GC-MS) assay for the determination of tramadol in human plasma is presented. The synthesis of an N-ethyl analogue of the drug is described and its use as an internal standard for the quantitative measurement of tramadol in human plasma is described. The method involves extraction at plasma pH and analysis of the underivatized drug by gas chromatography-electron ionization mass spectrometry using m/z 58 and 73 for detection of tramadol and internal standard, respectively. The calibration curve was linear in the range of 5-640 ng/ml plasma (r=0.9999). The method was validated in the abovementioned calibration range. Data on solution stability, long- and short-term stability of tramadol in plasma samples, freeze-thaw-stability, as well as inter- and intra-day precision and accuracy have been evaluated and are presented. The application of the method to the pharmacokinetic profiling of the drug is demonstrated.

Simultaneous stereoselective analysis of tramadol and its primary phase I metabolites in plasma by liquid chromatography

This paper describes a bioanalytical method involving a simple liquid-liquid extraction for the simultaneous HPLC determination of the enantiomers of tramadol, the active metabolite O-desmethyltramadol (M1), and the other main metabolite N-desmethyltramadol (M2) in biological samples. Chromatography was performed at 5 degrees C on a Chiracel OD-R column containing cellulose tris(3,5-dimethylphenylcarbamate) as chiral selector, preceded by a achiral end-capped C8 column (LiChrospher 60-RP-selected B 5 microm, 250 mm x 4 mm). The mobile phase was a mixture of phosphate buffer containing sodium perchlorate (1 M) adjusted to pH 2.5-acetonitrile-N,N-dimethyloctylamine (74.8:25:0.2). The flow rate was 0.5 ml/min. Fluorescence detection (lambda(ex) 200 nm/lambda(em) 301 nm) was used. Fluconazol was selected as internal standard. The limit of quantitation of each enantiomer of tramadol and their metabolites was 0.5 ng/ml (sample size = 0.5 ml). The chiral conditions and the LC optimisation were investigated in order to select the most appropriate operating conditions. The method developed has also been validated. Mean recoveries above of 95% for each enantiomer were obtained. Calibration curves for tramadol enantiomers (range 1-500 ng/ml), M1 enantiomers (range 0.5-100 ng/ml), and M2 enantiomers (range 0.5-250 ng/ml) were linear with coefficients of correlation better than 0.996. Within-day variation determined on four different concentrations showed acceptable values. The relative standard deviation (R.S.D.) was determined to be less than 10%. This method was successfully used to investigate plasma concentration of enantiomers of tramadol, O-desmethyltramadol and N-desmethyltramadol in a pharmacokinetic study.

Kinetic spectrophotometric determination of tramadol hydrochloride in pharmaceutical formulation

Two simple and sensitive kinetic methods for the determination of tramadol hydrochloride are described. The first method is based upon a kinetic investigation of the oxidation reaction of the drug with alkaline potassium permanganate at room temperature for a fixed time at 20 min. The absorbance of the colored manganate ions was measured at 610 nm. The second method is based on the reaction of tramadol hydrochloride with 4-chloro-7-nitrobenzofurazan (NBD-Cl) in presence of 0.1 M sodium bicarbonate. The spectrophotometric measurements were recorded by measuring the absorbance at 467 nm, at fixed time at 25 min on thermostated water bath at 90+/-1 degrees C. All variables affecting the development of the colour have been investigated and the conditions were optimised. The absorbance concentration plots in both methods were rectilinear over the range 5-25 and 50-250 microg ml(-1), for the first and second methods, respectively. The two methods have been applied successfully to commercial capsule and ampoule dosage form. The results obtained are compared statistically with those given by the reference spectrophotometric method. The determination of tramadol hydrochloride by the fixed concentration and rate constant methods is feasible with the calibration equations obtained, but the fixed time method proves to be more applicable.

High-performance liquid chromatographic determination of tramadol and its O-desmethylated metabolite in blood plasma. Application to a bioequivalence study in humans

Simultaneous HPLC determination of the analgetic agent tramadol, its major pharmacodynamically active metabolite (O-desmethyltramadol) in human plasma is described. Simple methods for the preparation of the standard of the above-mentioned tramadol metabolite and N1,N1-dimethylsulfanilamide (used as the internal standard) are also presented. The analytical procedure involved a simple liquid-liquid extraction of the analytes from the plasma under the conditions described previously. HPLC analysis was performed on a 250x4 mm chromatographic column with LiChrospher 60 RP-selectB 5-microm (Merck) and consists of an analytical period where the mobile phase acetonitrile-0.01 M phosphate buffer, pH 2.8 (3:7, v/v) was used, and of a subsequent wash-out period where the plasmatic ballast compounds were eluted from the column using acetonitrile-ultra-high-quality water (8:2, v/v). The whole analysis, including the equilibration preceding the initial analytical conditions lasted 19 min. Fluorescence detection (lambda(ex) 202 nm/lambda(em) 296 nm for tramadol and its metabolite, lambda(ex) 264 nm/lambda(em) 344 nm for N1,N1-dimethylsulfanilamide) was used. The validated analytical method was applied to pharmacokinetic studies of tramadol in human volunteers.

Selected fundamental aspects of chiral electromigration techniques and their application to pharmaceutical and biomedical analysis

While capillary electrophoresis has been established as a major enantioseparation technique within the last decade, the potential of capillary electrochromatography is still studied extensively. This review summarizes recent applications of electromigration techniques with regard to the enantioseparation of chiral drugs. The first part discusses the general aspects of migration models and the enantiomer migration order. The application of capillary electrophoresis to chiral pharmaceutical analysis considers recent literature on: (1) chiral resolutions of non-racemic mixtures of enantiomers for the development of assays and the determination of the stereochemical purity of the drugs, (2) chiral separations of compounds in pharmaceutical formulations and products, and (3) enantioseparations of drugs in biological samples. A shorter section devoted to chiral electrochromatography discusses some fundamental aspects as well as the application to the chiral analysis of drugs including bioanalysis.

Direct chiral assay of tramadol and detection of the phase II metabolite O-demethyl tramadol glucuronide in human urine using capillary electrophoresis with laser-induced native fluorescence detection

A chiral separation using carboxymethyl-beta-cyclodextrin and methyl-beta-cyclodextrin for the direct assay of tramadol in human urine by capillary electrophoresis (CE) with laser-induced native fluorescence detection was developed. Furthermore, the phase II metabolite O-demethyl tramadol glucuronide was determined from the urine samples and the ratio of the diasteromers was determined. The chiral method was validated. Correlation coefficients were higher than 0.999. Within day variation showed accuracy in the range 96.1-105.8% with a RSD less than 6.00%. Day to day variation present an accuracy ranging from 100.2 to 103.5% with a RSD less than 5.4%. After oral administration of 150 mg tramadol hydrochloride to a healthy volunteer, the urinary excretion was monitored during 24 h. About 11.4% of the dose was excreted as 1S,2S-tramadol, 16.4% as 1R,2R-tramadol and 23.7% as O-demethyl tramadol glucuronide. The amount of 1S,2S O-demethyl tramadol glucuronide was more than three fold higher as IR,2R-O-demethyl tramadol glucuronide. The enantiomeric ratio of tramadol and the diastereomeric ratio of O-demethyl tramadol glucuronide was deviated from 1.0 showing that a stereoselective metabolism of tramadol occurs.

Advances ofcapillary electrophoresis in clinical and forensic analysis (1999-2000)

In this paper, capillary electrophoresis in clinical and forensic analysis is reviewed on the basis of the literature of 1999, 2000 and the first papers in 2001. An overview of progress relevant examples for each major field of application, namely (i) analysis of drug seizures, explosives residues, gunshot residues and inks, (ii) monitoring of drugs, endogenous small molecules and ions in biofluids and tissues, (iii) general screening for serum proteins and analysis of specific proteins (carbohydrate deficient transferrin, alpha1-antitrypsin, lipoproteins and hemoglobins) in biological fluids, and (iv) analysis of nucleic acids and oligonucleotides in biological samples, including oligonucleotide therapeutics, are presented.

Recent advances in pharmacokinetic applications of capillary electrophoresis

This article reviews recent capillary electrophoresis (CE)-based assays which were published for pharmacokinetic studies. Both the advantages and disadvantages of these CE-based assays are discussed based on their feasibility and the significance towards the better understanding of pharmacokinetics. In addition, as a future outlook, novel assays such as immunoaffinity CE and chip-based CE for analyzing drugs in biological fluids are summarized in view of their potential for pharmacokinetic applications.

Liquid-liquid extraction procedures for sample enrichment in capillary zone electrophoresis

This review article presents an overview of applications of liquid-liquid extraction (LLE) for analyte enrichment and clean-up of samples prior to capillary zone electrophoresis (CZE). The basic principles of LLE are discussed with special emphasis on analyte enrichment. In addition, attention is focused on the requirements for the final extract to be compatible with CZE. The paper discusses selected examples from the literature with special emphasis on detection limits in drug analysis and in environmental chemistry. Finally, the paper focus on alternative liquid-phase extraction concepts based on electroextraction, supported liquid membranes, and liquid-phase microextraction.

Enantiomeric determination of tramadol and its main metabolite O-desmethyltramadol in human plasma by liquid chromatography-tandem mass spectrometry

Pharmacokinetic studies require sensitive analytical methods to allow the determination of low concentrations of drugs and metabolites. When drugs present an asymmetric center, the enantiomeric determination of the compounds of interest should be performed. The method developed is based on on-line LC-MS-MS using atmospheric pressure chemical ionization as an interface determination of enantiomers of tramadol (T) and its active metabolite O-desmethyltramadol (ODT) in human plasma. This determination is preceded by an off-line solid-phase extraction (SPE) on disposable extraction cartridges (DECs), performed automatically by means of a sample processor equipped with a robotic arm (ASPEC system). The DEC filled with ethyl silica (50 mg) was first conditioned with methanol and water. The washing step was performed with water and the analytes were finally eluted by dispensing methanol. The collected eluate was then evaporated to dryness before being dissolved in the LC mobile phase and injected into the LC system. The enantiomeric separation of tramadol and ODT was achieved on a Chiralpak AD column containing amylose tris-(3,5-dimethylphenylcarbamate) as chiral selector. The mobile phase was isohexane-ethanol-diethylamine (97:3:0.1, v/v). The LC system was then coupled to a tandem mass spectrometry system with an APCI interface in the positive ion mode. The chromatographed analytes were detected in the selected reaction monitoring mode. The MS-MS ion transitions monitored were 264-->58 for tramadol, 250-->58 for ODT, and 278-->58 for ethyltramadol, used as internal standard. The method was validated. The recoveries were around 90% for both T and ODT. The method was found to be linear for each enantiomer of both compounds (r2>0.999). The mean RSD values for repeatability and intermediate precision were 3.5 and 6.4% for T enantiomers and 5.0 and 5.6% for ODT enantiomers, respectively. Moreover, the method was found to be selective towards other metabolites, N-desmethyltramadol and N,O-desmethyltramadol (NODT). The method developed was successfully used to investigate plasma concentration of enantiomers of T and ODT in a pharmacokinetic study.

Enantiomeric separation of dihydroxyphenylalanine (DOPA), methyldihydroxyphenylalanine (MDOPA) and hydrazinomethyldihydroxyphenylalanine (CDOPA) by using capillary electrophoresis with sulfobutyl ether-beta-cyclodextrin as a chiral selector

Capillary electrophoresis (CE) was successfully applied to the enantiomer resolution of racemic structurally related compounds, namely dihydroxyphenylalanine (DOPA), methyldihydroxyphenylalanine (MDOPA) and hydrazinomethyldihydroxyphenylalanine (CDOPA). The chiral resolution was performed in an untreated fused-silica capillary by using a phosphate buffer at pH 2.5 or 3.0 supplemented with sulfobutylated beta-cyclodextrin (SBE-CD). Resolution was strongly influenced by the concentration of the chiral selector added to the background electrolyte. In fact, 2-5 mM of SBE-CD enabled the resolution of DOPA and MDOPA enantiomers, while CDOPA optical isomers were resolved by using either 0.5 mM or 6-20 mM of SBE-CD. The latter separation conditions (reversed polarity mode) made it possible to obtain inversion of migration order.

Assay of tramadol in urine by capillary electrophoresis using laser-induced native fluorescence detection

Capillary electrophoresis (CE) with UV laser-induced native fluorescence detection was developed as a sensitive and selective assay for the direct determination of tramadol in human urine without extraction or preconcentration. The main problem in CE is the small inner diameter of the capillary which causes a low sensitivity with instruments equipped with a UV detector. Laser-induced native fluorescence with a frequency doubled argon ion laser at an excitation wavelength of 257 nm was used for the direct assay of tramadol in urine to enhance the limit of detection about 1,000-fold compared to UV absorption detection. The detection system consists of an imaging spectrograph and an intensified CCD camera, which views an illuminated 1.5 mm section of the capillary. This set-up is able to record the whole emission spectra of the analytes to achieve additionally wavelength-resolved electropherograms. In the concentration range of 20 ng/ml-5 microg/ml in human urine coefficients of correlation were better than 0.998. Within-day variation determined on four different concentrations showed accuracies ranging from 90.2 to 108.4%. The relative standard deviation (RSD) was determined to be less than 10%. Day-to-day variation presented accuracies ranging from 90.9 to 103.1% with an RSD less than 8%.

Tramadol--present and future

The atypical opioid, tramadol, has recently been introduced into Australia and New Zealand. Tramadol's efficacy in a wide range of acute and chronic pain states, its multi-formulation availability, and its low serious side-effect potential at high doses and in prolonged therapy, combine to bestow on it a user-friendly profile, for short- and long-term use in hospitals and communities. This paper reviews the following: its formulation and routes of administration; its unique enantiomeric biochemistry and metabolism; its triple mechanisms of action; its pharmacokinetics and pharmacodynamics; its analgesic efficacy compared with other opioids; the indications for its clinical use in a variety of acute and chronic (including cancer) painful states; its specific use in the elderly, in paediatric and in obstetric patients; its adverse event (including drug interaction) and safety profile; its advantages in terms of its relative lack of respiratory depression, major organ toxicity and histamine release, and dependence and abuse potential. The review looks at new uses for this drug and what can be expected in this area in the future.

Enantiospecific analysis by capillary electrophoresis: applications in drug metabolism and pharmacokinetics

Enantiospecific analysis has an important role in drug metabolism and pharmacokinetic investigations and its now no longer acceptable to determine total drug, or metabolite, concentrations following the administration of a racemate. Inspite of the fact that capillary electrophoresis (CE) has become an essential technique in pharmaceutical and enantiospecific analysis, the chromatographic methodologies remain the most commonly used approach for the determination of the enantiomeric composition of drugs in biological fluids. The application of CE to bioanalysis has been slow, which is in part associated with the complexity of biological matrices together with the relatively poor concentration limits of detection achievable. However, as a result of its versatility, high separation efficiency, minimal sample requirements, speed of analysis and low consumable expense CE is likely to play an increasingly significant role in the area. This review present an overview of enantiospecific CE in bioanalysis in which the approaches to enantiomeric resolution and the problems associated with biological matrices are briefly discussed. The application of enantiospecific CE to samples of biological origin is illustrated using examples where the methodology has either solved an analytical problem, or provided a useful alternative to the currently available chromatographic methods. Such improvements in methodology are associated with either the high separation efficiency and/or microanalytical capabilities of the technique. Enantiospecific CE will not replace the chromatographic methodologies but does provide the bioanalyst with a useful addition to his armamentarium.

Enantioselective determination by capillary electrophoresis with cyclodextrins as chiral selectors

This review surveys the separation of enantiomers by capillary electrophoresis using cyclodextrins as chiral selector. Cyclodextrins or their derivatives have been widely employed for the direct chiral resolution of a wide number of enantiomers, mainly of pharmaceutical interest, selected examples are reported in the tables. For method optimisation, several parameters influencing the enantioresolution, e.g., cyclodextrin type and concentration, buffer pH and composition, presence of organic solvents or complexing additives in the buffer were considered and discussed. Finally, selected applications to real samples such as pharmaceutical formulations, biological and medical samples are also discussed.

Enantiomer separation of drugs by capillary electromigration techniques

The review summarizes the most recent developments in the field of enantioseparation of chiral drugs using capillary electromigration techniques. The basic principles of enantioseparations in CE are discussed. Recent developments in sample introduction, separation and detection in capillary electrophoresis and capillary electrochromatography are summarized. The applications are arbitrarily divided into the following three groups: (a) racemates and artificial mixtures of enantiomers, (b) drug forms and (c) chiral drugs and their metabolites in biological fluids. Among the various techniques involved the relatively new developments such as CEC in aqueous and nonaqueous buffers, on-line CE-MS coupling, etc. are emphasized.

Enantioselective determination of drugs in body fluids by capillary electrophoresis

During the past decade, chiral capillary electrophoresis (CE) emerged as a promising, effective and economic approach for the enantioselective determination of drugs in body fluids, hair and microsomal preparations. This review discusses the principles and important aspects of CE-based chiral bioassays, provides a survey of the assays developed and presents an overview of the key achievements encountered. Applications discussed encompass the pharmacokinetics of drug enantiomers, the elucidation of the stereoselectivity of drug metabolism and bioanalysis of drug enantiomers of toxicological and forensic interest.

Simultaneous stereoselective analysis of tramadol and its main phase I metabolites by on-line capillary zone electrophoresis-electrospray ionization mass spectrometry

On-line combination of partial filling capillary electrophoresis and electrospray ionization mass spectrometry was demonstrated for the simultaneous enantioseparation of tramadol and its main phase I metabolites. The partial filling technique was efficient at avoiding MS contamination by the chiral selector. Different experimental factors were investigated, including the chiral selector nature and concentration, plug length as well as the separation temperature. The best enantioseparation of the investigated compounds was achieved with a coated polyvinyl alcohol capillary and a 40 mM ammonium acetate buffer, pH 4.0, adding sulfobutyl ether beta-cyclodextrin (2.5 mg/ml) as the chiral selector. The charged cyclodextrin not only allowed enantioseparation of tramadol and its metabolites, but also improved the selectivity of compounds with the same molecular mass. Finally, CE-electrospray ionisation-MS was successfully applied to the stereoselective analysis of tramadol and its main metabolites in plasma after a simple liquid-liquid extraction.