Discovery of a Novel Lidocaine Metabolite by Human Liver Microsome and Identification of Microbial Species Which Produces the Same Metabolite.

Preparation of drug metabolites at the milligram scale is essential for determining the structure and toxicity of drug metabolites. However, their preparation using recombinant proteins and human liver microsomes (HLM) is often difficult because of technical and ethical issues. Reproducing human drug metabolism in food-derived microorganisms may be useful for overcoming these challenges. In this study, we identified an unknown metabolite of the anaesthetic drug lidocaine, which is metabolised by HLM. By screening for lidocaine metabolic activity in five types of foods (blue cheese, shiitake mushroom, natto, yoghurt, and dry yeast), we found that bacteria isolated from natto reproduced the lidocaine metabolic reaction that occurs in HLM. A fraction containing the unknown lidocaine metabolite was prepared through mass cultivation of a Bacillus subtilis standard strain, ethyl acetate extraction, open column chromatography, and HPLC purification. We identified the unknown metabolite as 3-(2,6-dimethylphenyl)-1-ethyl-2-methyl-4-imidazolidinone using NMR. Our results showed that food-derived microorganisms can produce large amounts of human drug metabolites via large-scale cultivation. Additionally, food microorganisms that can reproduce drug metabolism in humans can be used to examine drug metabolites at a low cost and without ethical issues.

An isocratic RP-HPLC-UV method for simultaneous quantification of tizanidine and lidocaine: application to in vitro release studies of a subcutaneous implant.

Implantable devices have been widely investigated to improve the treatment of multiple diseases. Even with low drug loadings, these devices can achieve effective delivery and increase patient compliance by minimizing potential side effects, consequently enhancing the quality of life of the patients. Moreover, multi-drug products are emerging in the pharmaceutical field, capable of treating more than one ailment concurrently. Therefore, a simple analytical method is essential for detecting and quantifying different analytes used in formulation development and evaluation. Here, we present, for the first time, an isocratic method for tizanidine hydrochloride (TZ) and lidocaine (LD) loaded into a subcutaneous implant, utilizing reversed-phase high-performance liquid chromatography (RP-HPLC) coupled with a UV detector. These implants have the potential to treat muscular spasticity while providing pain relief for several days after implantation. Chromatographic separation of the two drugs was accomplished using a C18 column, with a mobile phase consisting of 0.1% TFA in water and MeOH in a 58 : 42 ratio, flowing at 0.7 ml min-1. The method exhibited specificity and robustness, providing accurate and precise results. It displayed linearity within the range of 0.79 to 100 µg ml-1, with an R2 value of 1 for the simultaneous analysis of TZ and LD. The developed method demonstrated selectivity, offering limits of detection and quantification of 0.16 and 0.49 µg ml-1 for TZ, and 0.30 and 0.93 µg ml-1 for LD, respectively. Furthermore, the solution containing both TZ and LD proved stable under various storage conditions. While this study applied the method to assess an implant device, it has broader applicability for analysing and quantifying the in vitro drug release of TZ and LD from diverse dosage forms in preclinical settings.

A simple, fast, and cost-effective smartphone-based digital imaging method for quantification of lidocaine hydrochloride in pharmaceutical formulations.

OBJECTIVE: A simple, highly specific, accurate and fast method by smartphone-based digital imaging was developed for estimating lidocaine hydrochloride in pharmaceutical formulations. MATERIAL AND METHODS: To obtain the images, a Galaxy A03 Core smartphone and an image acquisition device developed in the laboratory were used to control the incident factors in reproducibility of the measurements. The processing of the images was carried out with the Color Grab application. Finally, the absorbance values were calculated using the RGB intensity values of blank, standard, and sample solutions. The proposed method was compared with spectroscopic and chromatographic methods. RESULTS: The reaction between copper and lidocaine hydrochloride was characterized, showing better results in an equimolar ratio and maintaining the pH of the solution above 11.5. The use of the device for the capture of digital images allowed to control those sensitive parameters for reproducibility so that the analytical measurements showed adequate precision and accuracy. Validation of the main parameters of the method showed compliance with acceptance criteria. The application of the method for the analysis of injectable samples achieved reliable results, which were statistically similar to other reference instrumental methods. CONCLUSION: The proposed method presented figures of merit in relation to linearity, precision, selectivity, accuracy, and robustness; it was carried out by designing and manufacturing a device for capturing digital images on a smartphone, which were analyzed to obtain RGB intensity values. These data are finally used to calculate absorbance values of solutions. All these elements provide this work with innovative characteristics in the field of analysis for control of pharmaceutical formulations.

Qualitative LC-Q-TOF Analysis of Umbilical Cord Tissue via Data-Dependent Acquisition as an Indicator of In Utero Exposure to Toxic Adulterating Substances.

Toxic adulterants are drug or chemical agents used to add bulk volume to traditional drugs of abuse such as cocaine and heroin. These cutting agents include levamisole, metamizole, noxiptillin, phenacetin and xylazine as well as common legal drugs such as acetaminophen, caffeine, diphenhydramine, lidocaine, quinine, quetiapine and tramadol. Because they possess pharmacological activity they result in exposure of the user, but also in the case of pregnant women, the developing fetus, to potential drug toxicity. We describe the development, validation and implementation of a rapid (48 second sample-to-sample) test based on a qualitative data-dependent liquid chromatography-quadrupole time of flight mass spectrometry method for the analysis of toxic adulterating substances in umbilical cord tissue (UCT) samples. The method provides a means of studying potential in utero exposure to these agents. Library spectra comparison at three different collision energies was used in conjunction with retention time and accurate mass to identify these substances in UCT. Analytically based reporting limits were established to determine positivity rates of adulterants in UCT utilizing a standard addition approach. The method was applied to authentic cocaine and opioid positive UCT to screen for toxic adulterants. There were a total of 82 potential adulterant positives found in a 30-sample cohort of authentic UCT samples, with an average of 2.7 substances per case. Lidocaine was the predominant finding followed by caffeine, and diphenhydramine all of which could result from non-illicit drug exposure, however, there were positives for levamisole, phenacetin, noxiptillin and xylazine none of which are approved in the United States for human therapeutic use. This initial set of data established a preliminary positivity rate of potentially toxic adulterants in UCT samples positive for cocaine or opioid use.

Cutting agents in cocaine: A temporal study of the period 2015-2017 in the Northern Region of Colombia.

Cocaine is a naturally occurring psychostimulant drug available worldwide. Drug trafficking networks adulterate pure cocaine with cutting agents to increase their earnings. This study presents a descriptive statistical analysis of the cutting agents found in 2118 cocaine samples that were seized in the Northern Region of Colombia (in the period 2015-2017). The data used in this study was drawn from the GC-MS analytical reports of the National Institute of Legal Medicine and Forensic Sciences -Colombia, Northern Region. Results showed diverse cutting agents in seized cocaine samples, from which the most commonly used are caffeine, phenacetin, lidocaine, imidazole and levamisole. In addition, cocaine samples showed different mixtures of the above cutting agents, predominantly caffeine/phenacetin and caffeine/lidocaine/phenacetin mixtures.

Simultaneous analysis of oxytetracycline hydrochloride, lidocaine, and bromhexine hydrochloride in the presence of many interfering excipients.

A gradient elution high-performance liquid chromatographic method with a diode array detector is introduced for the first time for the simultaneous estimation of three drugs, namely, oxytetracycline hydrochloride (OXT), lidocaine (LDC), and bromhexine hydrochloride (BRH), in a veterinary formulation (OxyClear® solution) that contains many interfering additives. The method used a C-8 column. The chromatographic eluting solution included acidified water (0.1% trifluoroacetic acid in water) and acetonitrile at a 1-ml/min flow rate and 254 nm as a nominated detection wavelength. The chromatographic process was assessed in terms of linearity, precision, accuracy, LOD, and LOQ. OXT, LDC, and BRH were linear in the range of 1-60, 5-100, and 1-60 µg/ml, respectively. The three drugs were determined successfully without the interference of three excipients having UV absorbances. Furthermore, the purities of the peaks of the three drugs were confirmed by comparing the UV spectra of investigated peaks to the UV reference spectra in Clarke's Analysis of Drugs and Poisons. The greenness value of the method was 0.69 with a faint green-colored pictogram using the AGREE tool. These merits recommend the application of the planned method in QC laboratories for purity testing and concentration assays for the pure drugs and commercial formulations.

Voltammetry of local anesthetics: theoretical and practical aspects.

Local anesthetics (LAs) are widely used in anesthesiology, ophthalmology, and otolaryngology as well as for treatment of chronic and oncological pain. However, anesthetics can cause adverse effects up to lethal ones. In this work, we cited reviews on chromatographic and spectroscopic methods of local anesthetics determination published earlier, and the main purpose was to review the possibilities and advantages of voltammetric methods used for the LAs determination. The electrochemical behavior, mechanism of LAs transformation on the various working electrodes and analytical parameters of voltammetric methods used for their determination were reviewed in the work. Vast majority of these methods were developed for the most widely used anesthetics in medicine like benzocaine, lidocaine and procaine. Special attention was paid to possible mechanisms of electrochemical oxidation and in some cases reduction of LAs or their derivatives. Voltammetry is used for the determination of LAs in pharmaceutical formulations and in biological fluids. The analytical characteristics in terms of sensitivity, selectivity, reproducibility also were discussed in the article.

The Oral Administration of Lidocaine HCl Biodegradable Microspheres: Formulation and Optimization.

PURPOSE: Lidocaine (LID) is a local anesthetic that is administered either by injection and/or a topical/transdermal route. However, there is a current need to develop efficacious methods for the oral delivery of LID with optimized bioavailability. METHODS: We developed oral LID biodegradable microspheres that were loaded with alginate-chitosan with different mass ratios, and characterized these microspheres in vitro. We also developed, and utilized, a simple and sensitive HPLC-tandem mass spectrometry (LC-MS-MS) method for assaying LID microspheres. RESULTS: The mean particle size (MPS) of the LID microspheres ranged from 340.7 to 528.3 nm. As the concentration of alginate was reduced, there was a significant reduction in MPS. However, there was no significant change in drug entrapment efficiency (DEE), or drug yield, when the alginate concentration was either increased or decreased. DSC measurements demonstrated the successful loading of LID to the new formulations. After a slow initial release, less than 10% of the LID was released in vitro within 4 h at pH 1.2. In order to evaluate nephrotoxicity, we carried out MTT assays of LID in two types of cell line (LLC-PK1 and MDCK). LID significantly suppressed the cell toxicity of both cell lines at the concentrations tested (100, 200, and 400ng/µL). CONCLUSION: Experiments involving the oral delivery of LID formulations showed a significant reduction in particle size and an improvement in dissolution rate. The formulations of LID developed exhibit significantly less toxicity than LID alone.

HPLC-MS/MS measurement of lidocaine in rat skin and plasma. Application to study the release from medicated plaster.

A simple, sensitive HPLC-MS/MS method was developed and validated for the determination of lidocaine in skin and plasma of rats. The methods were established and validated assessing lower limit of quantitation (LLOQ), linearity, intra and inter-day precision and accuracy, selectivity, recovery and matrix effect. Chromatography was done on a Gemini column embedded with C18 stationary phase (50 mm × 2.0 mm, 5 µm particle size), using a gradient with mobile phases consisting of 0.1% HCOOH in bidistilled water and 0.1% HCOOH in acetonitrile. The mass spectrometer worked with electrospray ionization in positive ion mode and selected reaction monitoring, using target ions m/z 235.10 for lidocaine and m/z 245.10 for lidocaine-d10, used as internal standard. RESULTS: The linearity of the method was in the ranges of lidocaine concentrations 10.0-200.0 ng/mL for skin homogenate (accuracy 94.1-105.5%; R2 ≥ 0.998) and 0.025-2 ng/mL for plasma (accuracy 96.2-104.8%; R2 ≥ 0.996). The intra- and inter-day precision and accuracy determined on three quality control samples (20, 75 and 170 ng/mL for skin and 0.075, 0.4 and 1.5 ng/mL for plasma) were ≤4.2% and 103.8-108.2% for skin and ≤12.4% and 95.5-101.4% for plasma. The LLOQ was 10 ng/mL in skin homogenate and 0.025 ng/mL in plasma. The applicability of the method was demonstrated by measuring lidocaine in skin and plasma after exposure to medicated patches containing 5% lidocaine.

Iontophoretic delivery of lidocaine hydrochloride through ex-vivo human skin.

Background: Iontophoresis is one of the widely used noninvasive and painless transdermal drug delivery technique.Objective: Transdermal delivery of Lidocaine Hydrochloride using continuous and modulated iontophoresis were evaluated across human skin ex-vivo and further assessed for skin tolerance in-vivo in the Swiss albino mice.Methods: Continuous DC was modified into modulated DC by introducing ON-OFF time in continuous DC. Iontophoresis studies were conducted on human skin samples for 60 min.Results: Drug permeation of 2% lidocaine HCl was enhanced in current density-, duty cycle- and time-dependent manner across human skin. The lidocaine HCl concentration obtained with modulated DC and continuous DC iontophoresis were about three-fold and four-fold higher than passive group respectively for all current densities across human skin. Continuous DC iontophoresis was found to be more effective than modulated DC. However, no significant difference was observed in transport of lidocaine HCl between 75% and 100% (continuous) duty cycle at all current density. Further, in-vivo reversibility studies with mice confirmed that modulated iontophoresis was well tolerated by the tissue and the injury caused is transient and reversible.Conclusion: For clinical application, modulated DC iontophoresis with 75% duty cycle at 0.5 mA/cm2 current density would be recommended.

Stability-indicating HPLC method for acyclovir and lidocaine in topical formulations.

A simple, rapid and accurate stability-indicating HPLC assay was developed for the determination of acyclovir and lidocaine in topical formulations. Chromatographic separation of acyclovir and lidocaine was achieved using a reversed-phase C18 column and a gradient mobile phase (20 mm ammonium acetate pH 3.5 in water and acetonitrile). The degradation products of acyclovir and lidocaine in the samples were analyzed by ultra performance liquid chromatography-time of flight mass spectrometry. The HPLC method successfully resolved the analytes from the impurities and degradation products in the topical formulation. Furthermore, the method detected the analytes from the human skin leachables following the extraction of the analytes in the skin homogenate samples. The method showed linearity over wide ranges of 5-500 and 10-200 µg/ml for acyclovir and lidocaine in the topical product, respectively, with a correlation coefficient (r2 ) >0.9995. The relative standard deviations for precision, repeatability, and robustness of the method validation assays were <2%. The skin extraction efficiency for acyclovir and lidocaine was 92.8 ± 0.7% and 91.3 ± 3.2%, respectively, with no interference from the skin leachables. Thus, simultaneous quantification of acyclovir and lidocaine in the topical formulations was achieved.

Adulterants in crack cocaine in Brazil.

INTRODUCTION: Brazil is the world's biggest consumer of crack cocaine, and dependence is a major public health issue. This is the first study to investigate the prevalence of potentially harmful adulterants present in hair samples from Brazilian patients with crack cocaine dependence. METHOD: We evaluated adulterants in hair samples extracted by convenience from 100 patients admitted at the 48 hour-observation unit of Centro de Referência de Álcool, Tabaco e Outras Drogas (CRATOD), Brazil's largest center for addiction treatment. A cross-sectional analysis was performed with the data obtained. RESULTS: Adulterants were found in 97% of the analyzed hair samples. The most prevalent adulterant was lidocaine (92%), followed by phenacetin (69%) and levamisole (31%). CONCLUSION: Adulterants were widely prevalent in hair samples from crack users treated at CRATOD: at least one adulterant was present in virtually all the hair samples collected. This points to a need to monitor adverse effects in the clinical setting in order to provide this high-risk group of patients with prompt and effective care related to the acute and chronic complications associated with these adulterants.

Adulterants in crack cocaine in Brazil / Adulterantes no crack vendido na "Cracolândia"

Abstract Introduction Brazil is the world's biggest consumer of crack cocaine, and dependence is a major public health issue. This is the first study to investigate the prevalence of potentially harmful adulterants present in hair samples from Brazilian patients with crack cocaine dependence. Method We evaluated adulterants in hair samples extracted by convenience from 100 patients admitted at the 48 hour-observation unit of Centro de Referência de Álcool, Tabaco e Outras Drogas (CRATOD), Brazil's largest center for addiction treatment. A cross-sectional analysis was performed with the data obtained. Results Adulterants were found in 97% of the analyzed hair samples. The most prevalent adulterant was lidocaine (92%), followed by phenacetin (69%) and levamisole (31%). Conclusion Adulterants were widely prevalent in hair samples from crack users treated at CRATOD: at least one adulterant was present in virtually all the hair samples collected. This points to a need to monitor adverse effects in the clinical setting in order to provide this high-risk group of patients with prompt and effective care related to the acute and chronic complications associated with these adulterants.

Resumo Introdução O Brasil é o maior consumidor mundial de crack, e a dependência é um grande problema de saúde pública. Este é o primeiro estudo a investigar a prevalência de adulterantes potencialmente nocivos presentes em amostras de cabelo de pacientes brasileiros com dependência de crack. Métodos Foram avaliados adulterantes em amostras de cabelos extraídos por conveniência de 100 pacientes internados na unidade de observação de 48 horas do Centro de Referência de Álcool, Tabaco e Outras Drogas (CRATOD), o maior centro de tratamento de dependência do Brasil. Uma análise transversal foi realizada com os dados obtidos. Resultados Foram encontrados adulterantes em 97% das amostras de cabelo analisadas. O adulterante mais prevalente foi a lidocaína (92%), seguida da fenacetina (69%) e levamisol (31%). Conclusão Os adulterantes foram amplamente prevalentes em amostras de cabelo de usuários de crack tratados no CRATOD: pelo menos um adulterante estava presente em praticamente todas as amostras de cabelo coletadas. Isso aponta para a necessidade de monitorar os efeitos adversos no ambiente clínico, a fim de proporcionar a esse grupo de pacientes de alto risco cuidados imediatos e efetivos relacionados às complicações agudas e crônicas associadas a esses adulterantes.

Toxicological analysis of cocaine adulterants in blood samples.

Cocaine was the second most widely used drug in Europe in 2016, with 3.5 million consumers aged 15-64 years old. Adulterants are pharmacologically active substances developed for medical purposes, however, there is little knowledge about their influence in the human body when there is concomitant use with cocaine. The objective of this work was to validate a method that allows the identification, confirmation and quantification of cocaine adulterants in blood samples collected in vivo or post-mortem. The studied substances were atropine, phenacetin, hydroxyzine, ketamine, lidocaine and tetramisole. A retrospective study of the prevalence of these substances, as well as their relative concentrations, was made analysing 97 real blood samples previously tested positive for cocaine and/or its metabolites. The analytes of interest were extracted, using a simple method based on protein precipitation with frozen acetonitrile and further analysis by GC/MS. The method was fully validated in accordance with parameters and criteria implemented in the lab and SWGTOX recommendations (mean recovery: 94-115%; CV: 6.2-13%; BIAS: 2.7-7.8%). 31 samples were positive for adulterants: phenacetin (19%), tetramisole (15%), lidocaine (8%) and hydroxyzine (1%). Concentrations were higher in post-mortem samples for all compounds analysed. Lidocaine was more prevalent in samples collected in vivo whereas tetramisole was present almost exclusively in post-mortem samples. Phenacetin was evenly distributed between post-mortem and in vivo samples. The validated method allows rapid, precise, accurate and economic analysis of selected compounds and requires smaller sample aliquots which can be important in post-mortem cases. The information collected can be important in future studies of correlation between the presence of adulterants and cocaine toxicity.

A special case of medicine in disguise: Tattoo inks containing anaesthetics.

This paper describes a case of medicine in disguise: seized tattoo inks containing lidocaine and tetracaine at high concentration. Identification of anaesthetics was performed by LC MS Q-TOF with ESI+ source, by accurate mass measurement and by comparing the fragmentation patterns of molecular ions, at 30 V and 10 V of collision-offset voltage, with reference standards. Quantification was also performed by LC MS Q-TOF on the chromatographic peaks in the extracted ion chromatograms, by calibration curves obtained at different standard concentrations and by standard additions approach. The measurement uncertainty was estimated from validation data. The paper gives also chromatographic parameters, MS and MS/MS data and a quantitation method, with a full validation, of other six "caines". Thus the paper intends to provide a tool for identification and quantitation of the most common local anaesthetics that could be fraudulently added to tattoo inks. The results here reported show that the seized samples of inks represent a serious health risk owing to the high anaesthetic content - therapeutic-like dosage - found.

Theoretical Investigation of Design Space for Multi Layer Drug Eluting Bioresorbable Suture Threads.

BACKGROUND: The work presented here is focused on the development of a comprehensive theoretical model for the description of drug release from a double - layer bioresorbable suture thread and the therapeutic efficacy of the active compounds delivered in the surrounding tissue. METHODS: In particular, the system under investigation is composed of a core of slow-degrading polylactic- acid-co-ε-caprolactone (PLCL), where an antibiotic compound (Vancomycin) is loaded, surrounded by a shell of a fast-degrading polylactic-co-glycolic acid (PLGA) which contains an anesthetic drug (Lidocaine hydrochloride) for the post-surgical pain relief. RESULTS: This system is of potential interest for the combined effects provided by the different active molecules, but the different release and polymer degradation dynamics, as well as their mutual influence, do not allow an intuitive a priori evaluation of device behavior, which can be rationalized through mathematical modeling. The model takes into account the main involved phenomena (polymer degradation and diffusion of the drugs within the device and the tissue, where they are metabolized) and their synergic effects on the overall system behavior. CONCLUSION: Model results are discussed in order to quantify the impact of the main design parameters on device performances, thanks to the use of phase diagrams (which show drug effect in time and space) whose insights are summarized in order to determine a design space according to the specific needs.

[Rapid on-site screening of five prohibited ingredients in cosmetics using thermal desorption-corona discharge ionization coupled with ion mobility spectrometry].

A rapid on-site analytical method is developed for screening lidocaine and four other types of prohibited ingredients in cosmetics using thermal desorption-corona discharge ionization together with ion mobility spectrometry. Performing no pretreatment, we dropped or sprayed cosmetic samples onto a Nomex sampling swab. The sampler was placed into a compartment for thermal desorption and corona discharge ionization; then, ion mobility spectrometry analysis was performed. The limits of detection (LODs) for the five analytes ranged from 10 to 50 ng. The instrumental analysis time for a single run was less than 20 ms, and the total sample analysis period was within 1 min. The proposed method is simple, fast, and has low cost, and could be used as an analytical tool for rapid on-site screening of prohibited ingredients in cosmetics.

Estimation of day of death using micro-segmental hair analysis based on drug use history: a case of lidocaine use as a marker.

During investigations of unnatural death, the time of death is generally estimated using anatomical examinations. However, it can be difficult to accurately determine the day of death, because postmortem changes in the body tissues can be greatly affected by the circumstances of the location of the corpse. We recently developed a method to estimate the day of drug ingestion, using micro-segmental hair analysis based on internal temporal markers (ITMs). In this method, ITMs are ingested at a specific time interval before hair collection to mark timescales within individual hair strands. A single hair strand is segmented at 0.4-mm intervals, corresponding to average daily hair growth. The day of drug ingestion is eventually estimated by calculating the distances between segments containing the drug and ITMs in a hair strand. In the present study, the method was applied to estimate the day of death. A corpse was discovered with a documented medical history of lidocaine administration for surgery 57 days before the discovery. Micro-segmental analysis of a hair plucked from the corpse was performed using lidocaine as an ITM. Lidocaine was detected at specific regions in the hair strands. The day of death was estimated using the known surgery day, the distance from the hair root to the lidocaine peak in the hair strand, and the average hair growth rate. The novel estimation method using a hair enabled us to narrow the estimated time range of death up to the day of death, unlike the conventional anatomical examination. The micro-segmental hair analysis based on drug use history can be extremely helpful in determining the time of an unnatural death.

[A novel dispersive liquid-liquid microextraction method with high performance liquid chromatography for detection of 2,6-dimethylaniline in lidocaine hydrochloride injection].

A novel hexafluoroisopropanol (HFIP)-octanol supramolecular solvent (SUPRAS) based dispersive liquid-liquid microextraction (DLLME) method was developed for the determination of 2,6-dimethylaniline (2,6-DMA) in lidocaine hydrochloride injection coupled with high performance liquid chromatography-ultraviolet detection (HPLC-UV). n-Octanol was selected as extraction solvent while HFIP was served as dispersing agent, self-assembly inducer of n-octanol as well as density-regulating agent of n-octanol. The HFIP-octanol SUPRAS displays reverse micellar aggregate structures (2-6 µm) with hydrophilic inner cores and is located in the bottom phase of the system after phase separation, which not only facilitates the efficient extraction and enrichment of polar 2,6-DMA, but also simplifies the extraction process. Several parameters influencing the extraction efficiency of 2,6-DMA were investigated and optimized. Under optimum conditions (0.4%(v/v) n-octanol, 5% (v/v) HFIP, vortex for 3 s at 60 W, standing for 3 min, centrifugation for 3 min at 3000 r/min, sample solution pH 9), the novel DLLME-HPLC method shows good linearity for quantitative detection of 2,6-DMA in the range of 1-100 µg/L (R=0.9989). The limit of detection (LOD) was 0.33 µg/L. The enrichment factor (EF) reached about 63. Intra-day and inter-day precisions (n=3) were all below 2.5%. The recoveries were from 93.9% to 100.8%. The results demonstrate that the novel DLLME-HPLC method is suitable for the accurate quantitative determination of 2,6-DMA in lidocaine hydrochloride injection with advantages of simplicity, rapidness, high efficiency and environmental friendliness, and may own high potential in future prospects.

Reduced graphene oxide as an efficient sorbent in microextraction by packed sorbent: Determination of local anesthetics in human plasma and saliva samples utilizing liquid chromatography-tandem mass spectrometry.

Herein, reduced graphene oxide (RGO) has been utilized as an efficient sorbent in microextraction by packed sorbent (MEPS). The combination of MEPS and liquid chromatography-tandem mass spectrometry has been used to develop a method for the extraction and determination of three local anesthetics (i.e. lidocaine, prilocaine, and ropivacaine) in human plasma and saliva samples. The results showed that the utilization of RGO in MEPS could minimize the matrix effect so that no interfering peaks at the retention times of the analytes or internal standard was observed. The high extraction efficiency of this method was approved by mean recoveries of 97.26-106.83% and 95.21-105.83% for the studied analytes in plasma and saliva samples, respectively. Intra- and inter-day accuracies and precisions for all analytes were in good accordance with the international regulations. The accuracy values (as percentage deviation from the nominal value) of the quality control samples were between -2.1 to 13.9 for lidocaine, -4.2 to 11.0 for prilocaine and between -4.5 to -2.4 for ropivacaine in plasma samples while the values were ranged from -4.6 to 1.6 for lidocaine, from -4.2 to 15.5 for prilocaine and from -3.3 to -2.3 for ropivacaine in human saliva samples. Lower and upper limit of quantification (LLOQ, ULOQ) were set at 5 and 2000 nmol L-1 for all of the studied drugs. The correlation coefficients values were ≥0.995. The limit of detection values were obtained 4 nmol L-1 for lidocaine and prilocaine, and 2 nmol L-1 for ropivacaine.