Simultaneous determination of antidementia drugs in human plasma: Procedure transfer from HPLC–MS to UPLC–MS/MS

Detecting the therapeutic drugs in blood samples through PDMS-printed paper spray mass spectrometry

In this paper, paper microfluidic channel fabricated by directly screen-printing of polydimethylsiloxane (PDMS) is proposed for paper spray mass spectrometry analysis of therapeutic drugs in the blood samples. Compared with traditional paper spray, PDMS-printed paper spray (PP-PS) allows fluid to flow to the tip of paper with less sample loss which significantly improved the signal intensity of target compounds in blood samples. As paper can reduce the matrix effect, PP-PS also has a greater advantage than electro-spray Ionization (ESI) when directly analyzing complex biological sample in terms of the detection efficiency. Linearity and limits of detection (LOD) were evaluated for five psychotropic drugs: olanzapine, quetiapine, 9-hydroxyrisperidone, clozapine, risperidone. As a result, PP-PS improved the signal intensity of the psychotropic drugs at a concentration of 250 ng/ml in blood samples by a factor of 2-5 times and lowered the relative standard deviation (RSD) by a factor of 2-5.6 times compared with traditional paper spray. And PP-PS also improved signal intensity by a factor of 9-33 times compared with ESI. Quantitative experiments of PP-PS mass spectrometry indicated that the linear range was 5-500 ng/ml and the LOD were improved by a factor of 5-71 times for all these drugs compared with traditional paper spray. In addition, PP-PS was applied to the home-made miniaturized mass spectrometer and the precursor ions of all five psychotropic drugs (250 ng/ml) in the mass spectrometry results were obtained as well. These could prove that PP-PS has the potential to analyze complex biological samples in application on the miniaturized mass spectrometer which can be used outside the laboratory.

Ultrasensitive SERS aptasensor using Au@Ag bimetallic nanorod SERS tags for the selective detection of amantadine in foods

Herein, a novel surface enhanced Raman spectroscopy (SERS) aptasensor was developed for amantadine (AMD) detection, based on magnetite nanoparticles coated with polyethylenimine, silver nanoclusters and aptamers (Fe3O4@PEI@AgNC-apt) as the capture probe and complementary DNA-modified gold nanorods (AuNRs@4-MPBA@Ag-c-DNA containing 4-mercaptophenylboric acid molecules) as the reporter probe. In the presence of AMD, the AMD and the reporter probe competed for the aptamer on the surface of the capture probe, resulting in the reporter probe detaching from the capture probe leading to a decrease in intensity of the SERS signal at 1067 cm-1 for 4-MPBA. Under optimal conditions, a good linear relationship was established between the SERS intensity at 1067 cm-1 and the logarithm of the AMD concentration over the range 10-6-102 mg L-1, with a LOD of 0.50 × 10-6 mg L-1. The AMD levels in spiked samples were evaluated using the SERS aptasensor, with good recoveries ranging from 90.57% to 113.49% being obtained.

Development and Validation of a Simple UV-HPLC Method to Quantify the Memantine Drug Used in Alzheimer's Treatment

Memantine, a non-competitive NMDA receptor antagonist, is used to treat Alzheimer's disease. Therefore, loading memantine in nanoparticles (NPs) could be an essential tool to improve the treatment effectiveness while reducing drug toxicity. Even though some approaches have been described to quantify memantine, none reported optimized methods using high-performance liquid chromatography resorting to ultraviolet detection (UV-HPLC) to determine encapsulation in NPs. The present research developed a HPLC method using pre-column derivatization for quantitatively analyzing memantine hydrochloride in NPs. Memantine was derivatized using 9-fluorenylmethyl chloroformate (FMOC). The developed method was fully validated regarding suitability, specificity, linearity, sensitivity, precision, accuracy, and robustness according to the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use guidelines. The retention time of memantine was 11.393 ± 0.003 min, with a mean recovery of 92.9 ± 3.7%. The new chromatographic method was validated and found to respond linearly over 5-140 μg/mL, with a high coefficient of determination. Intraday precision lay between 3.6% and 4.6%, and interday precision between 4.2% and 9.3%. The stability of memantine was also tested at 4 °C and -20 °C, and no signs of decay were found for up to 6 months. The new method was properly validated and proved simple, sensitive, specific, accurate, and precise for determining memantine encapsulation efficiency in lipid NPs. Greenness was evaluated, presenting a final score of 0.45. In the future, this methodology could also be applied to quantify memantine in different nanoformulations.

Pharmacogenetic studies in Alzheimer disease

INTRODUCTION

Alzheimer disease (AD) is the most common cause of dementia and is considered one of the main causes of disability and dependence affecting quality of life in elderly people and their families. Current pharmacological treatment includes acetylcholinesterase inhibitors (donepezil, galantamine, rivastigmine) and memantine; however, only one-third of patients respond to treatment. Genetic factors have been shown to play a role in this inter-individual variability in drug response.

DEVELOPMENT

We review pharmacogenetic reports of AD-modifying drugs, the pharmacogenetic biomarkers included, and the phenotypes evaluated. We also discuss relevant methodological considerations for the design of pharmacogenetic studies into AD. A total of 33 pharmacogenetic reports were found; the majority of these focused on the variability in response to and metabolism of donepezil. Most of the patients included were from Caucasian populations, although some studies also include Korean, Indian, and Brazilian patients. CYP2D6 and APOE are the most frequently studied biomarkers. The associations proposed are controversial.

CONCLUSIONS

Potential pharmacogenetic biomarkers for AD have been identified; however, it is still necessary to conduct further research into other populations and to identify new biomarkers. This information could assist in predicting patient response to these drugs and contribute to better treatment decision-making in a context as complex as aging.

Ultrafast liquid chromatography-tandem mass spectrometry determination of donepezil in human plasma: application to a bioequivalence study

A liquid chromatography equipped with tandem mass spectrometric method using multi-stage flow rates was developed for the determination of donepezil in human plasma to support a randomized, crossover bioequivalence (BE) study in which healthy volunteers each received a single oral dose of the reference and test formulations of 10 mg donepezil hydrochloride. This integrated liquid chromatography with tandem mass spectrometry (LC-MS/MS) system with electrospray ionization and a deuterium-labeled internal standard (IS) were employed for the positive multiple-reaction-monitoring (MRM) analyses. The baseline separation using a high-resolution monolithic column under gradient and flexible flowrate conditions between donepezil and multiple interfering peaks from the extracted quality control, calibration standard and study plasma samples following simple protein precipitation extraction procedures was accomplished within 1.5 minutes. The ultrafast monolithic column performance in terms of chromatographic separation efficiency, peak asymmetry and resolution and retention time reproducibility was found to be sustainable. The linear dynamic range was detected over a concentration range of 0.2–50 ng/mL. The intra- and inter-day assay accuracy and precision were within 15% for the analyte in individual biological fluids. A positive correlation coefficient (r) greater than 0.995 for donepezil concentrations in study plasma samplers measured by the proposed and the other validated LC-MS/MS methods in support of a bioequivalence study was observed.

Diagnostic Fragment-Ion-Based for Rapid Identification of Chlorogenic Acids Derivatives in Inula cappa Using UHPLC-Q-Exactive Orbitrap Mass Spectrometry

Inula cappa (Buch.-Ham. ex D. Don) DC has been used in traditional Chinese medicine to treat malaria, dysentery, and hepatitis. Previous studies have shown that chlorogenic acid is the effective ingredient of plants in this family. And the research of the chlorogenic acid in Inula cappa will help to further improve the effective resource utilization rate of this plant. Therefore, it is necessary to establish an accurate method to characterize the chlorogenic acid components in Inula cappa. In this study, a simple, fast, and sensitive UHPLC-Q-Exactive Orbitrap mass spectrometry method was established, which can simultaneously analyze known and unknown ingredients in a short time (within 30 minutes) in Inula cappa. According to the diagnosis fragmentation ions, retention time, and bibliography, 68 chlorogenic acid derivatives were identified in Inula cappa. The results of this experiment lay the foundation for the active substances and quality control of Inula cappa and provide a theoretical basis for whether Inula cappa can be an alternative to the endangered wild medicinal materials of the same family.

LC-MS bioanalysis of targeted nasal galantamine bound chitosan nanoparticles in rats' brain homogenate and plasma

Validated LC-MS method for the direct quantitative analysis of galantamine (acetylcholinesterase inhibitor) was developed in rat cerebrospinal fluid and brain homogenate besides rat plasma, utilizing structurally close nalbuphine as an internal standard. After a simple protein precipitation step, samples are separated on 2-μm C18 column kept at 40 °C, using isocratic flow of 80% methanol in pH 9.5 ammonium formate buffer, and retention times were about 1.8 and 2.9 min for galantamine and nalbuphine, respectively. Mass detection with electrospray ionization (ESI) and positive polarity was able to detect 0.2 ng mL^-1 galantamine using single ion monitoring mode (SIM) at m/z 288 for galantamine and m/z 358 for nalbuphine. The method showed linearity within the range of 0.5 - 300 ng mL^-1. The proposed method was validated according to FDA guidelines. Trueness and precision showed acceptable values at all quality control levels, and recoveries were within 85.6 - 114.3% in all matrices at all runs and with relative standard deviations within 0.2 - 12.4%. The method was used to study in vivo brain uptake and pharmacokinetics of galantamine from brain homogenate and plasma samples following the administration of nasal galantamine-bound chitosan nanoparticles compared to oral and nasal galantamine solutions, in scopolamine-induced Alzheimer's disease rat model.

Review of Chromatographic Methods Coupled with Modern Detection Techniques Applied in the Therapeutic Drugs Monitoring (TDM)

Therapeutic drug monitoring (TDM) is a tool used to integrate pharmacokinetic and pharmacodynamics knowledge to optimize and personalize various drug therapies. The optimization of drug dosing may improve treatment outcomes, reduce toxicity, and reduce the risk of developing drug resistance. To adequately implement TDM, accurate and precise analytical procedures are required. In clinical practice, blood is the most commonly used matrix for TDM; however, less invasive samples, such as dried blood spots or non-invasive saliva samples, are increasingly being used. The choice of sample preparation method, type of column packing, mobile phase composition, and detection method is important to ensure accurate drug measurement and to avoid interference from matrix effects and drug metabolites. Most of the reported procedures used liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) techniques due to its high selectivity and sensitivity. High-performance chromatography with ultraviolet detection (HPLC-UV) methods are also used when a simpler and more cost-effective methodology is desired for clinical monitoring. The application of high-performance chromatography with fluorescence detection (HPLC-FLD) with and without derivatization processes and high-performance chromatography with electrochemical detection (HPLC-ED) techniques for the analysis of various drugs in biological samples for TDM have been described less often. Before chromatographic analysis, samples were pretreated by various procedures-most often by protein precipitation, liquid-liquid extraction, and solid-phase extraction, rarely by microextraction by packed sorbent, dispersive liquid-liquid microextraction. The aim of this article is to review the recent literature (2010-2020) regarding the use of liquid chromatography with various detection techniques for TDM.

Simultaneous determination of donepezil, 6-O-desmethyl donepezil and spinosin in beagle dog plasma using liquid chromatography‒tandem mass spectrometry and its application to a drug-drug interaction study

Spinosin, which is traditionally used for sedation and sleep disorders, has recently shown potential effects in alleviating memory loss. As spinosin is the main bioactive component in a standardized dried 50% ethanol extract of the seeds of Zizyphus jujuba var. spinosa, a Phase IIb clinical trial is ongoing, in Korea for the combination of the above extract formulated in a tablet (DHP1401 tablet) with donepezil hydrochloride (Aricept® tablet) in patients with mild to moderate Alzheimer's disease. Therefore, to promote safety and efficacy evaluations, a reliable method for the simultaneous detection and analysis of the two drugs is needed. Toward this end, in this study, we established and validated a rapid and sensitive LC-MS/MS method for the simultaneous determination of donepezil, its pharmacologically active metabolite 6-O-desmethyl donepezil, and spinosin in beagle dog plasma (50 μL). After optimization of the system, we used methanol for simple protein precipitation. Chromatographic separation was performed using a Phenomenex Luna C₁₈ column (100 × 2.0 mm, 3 μm) with a mobile phase consisting of 0.1% formic acid in acetonitrile-0.1% formic acid in distilled water (2:8, v/v) at a flow rate of 0.65 mL/min. All analytes were detected and quantified in selected reaction monitoring mode. All calibration curves showed good linearity (r ≥ 0.9965) over the concentration range of 0.02-20, 0.02-10, and 0.5-250 ng/mL for donepezil, for 6-O-desmethyl donepezil, and spinosin, respectively. This validated method was then successfully applied to a pharmacokinetic study in beagle dogs with no evidence for potential drug-drug interactions between DHP1401 and donepezil hydrochloride. This information and optimized assay can be useful for the anticipated co-administration of these two drugs in clinical settings.

Rational design and implementation of a cucurbit[8]uril-based indicator-displacement assay for application in blood serum

In this study, we report the first supramolecular indicator displacement assay (IDA) based on cucurbit[n]uril (CBn) host and a [2.2]paracyclophane derivative as indicator that is operational in blood serum.

In this study, we report the first supramolecular indicator-displacement assay (IDA) based on cucurbit[n]uril (CBn) hosts that is operational in blood serum. Rational design principles for host–guest chemosensing in competitively binding media were derived through detailed mathematical simulations. It was shown that currently known CBn-based chemosensing ensembles are not suited for use in highly competitive matrices such as blood serum. Conversely, the simulations indicated that a combination of cucurbit[8]uril (CB8) and an ultra-high affinity dye would be a promising IDA reporter pair for the detection of Alzheimer's drug memantine in blood serum. Therefore, a novel class of [2.2]paracyclophane-derived indicator dyes for the host CB8 was developed that possesses one of the highest host–guest affinities (K_a > 10¹² M^–1 in water) known in supramolecular host–guest chemistry, and which provides a large Stokes shift (up to 200 nm). The novel IDA was then tested for the detection of memantine in blood serum in a physiologically relevant sub- to low micromolar concentration range.

Pharmacokinetic Drug-Drug Interaction and Responsible Mechanism between Memantine and Cimetidine

A sensitive and simple chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to evaluate memantine in rat plasma. Memantine and propranolol (internal standard) in rat plasma was extracted using a methanol precipitation method. The standard curve value was 0.2–1000 ng/mL and selectivity, linearity, inter-day and intra-day accuracy and precision were within acceptance criteria. Using this validated method, drug-drug interactions between memantine and cimetidine was measured following co-administration of memantine and cimetidine intravenously and orally. Plasma exposure of memantine was increased by 1.6- and 3.0-fold by co-medication with cimetidine intravenously and orally, respectively. It suggested that the drug interaction occurred during the gut absorption process, which was consistent with the results showing that the intestinal permeability of memantine in the presence of cimetidine was 3.2-fold greater than that of memantine alone. Inhibition of cimetidine on hepatic elimination of memantine rather than renal excretion was also attributed to the drug-drug interaction between memantine and cimetidine, which explained the decreased clearance of memantine by co-medication with cimetidine. In conclusion, the newly developed simple and sensitive LC-MS/MS analytical method was applied to investigate the pharmacokinetic drug-drug interactions of memantine. Plasma exposure of memantine by co-administration with cimetidine was increased because of its enhanced intestinal permeability and the decreased metabolic activity of memantine.

Pre-clinical pharmacokinetic-pharmacodynamic modelling and biodistribution studies of donepezil hydrochloride by a validated HPLC method

A simple, sensitive and robust HPLC-PDA assay was developed and validated for rapid determination of donepezil hydrochloride (DNP), a potent acetylcholinesterase inhibitor in rat plasma and tissues. All biological samples were prepared by the solid-phase extraction method using loratadine as an internal standard. Separation of the analytes was achieved on a Waters Nova-Pak C18 column (3.9 × 150 mm, 4 μm) using an isocratic mobile phase of acetonitrile and ammonium formate (pH 6.4; 0.01 M) (62 : 38% v/v) at a flow rate of 1 mL min-1. All validation parameter results were within the acceptable range described in the guidelines for bioanalytical method validation. The method showed linearity in the concentration range of 50-5000 ng mL-1 with LOD of 20 ng mL-1 and LLOQ of 50 ng mL-1. Moreover, the advantage of this method over previously published methods is the short analysis run time of 6 min in HPLC itself, alongside its application not only for plasma samples but also in tissues, with low LLOQ. The method was successfully applied for studying the compartmental pharmacokinetics, tissue distribution and pharmacodynamics. A two-compartmental micro model was statistically fitted for the assessment of pharmacokinetic parameters. The tissue distribution studies suggest that the kidneys, lungs and liver are the primarily responsible organs for metabolism and elimination of DNP. Pharmacodynamic studies were performed by measuring acetylcholinesterase inhibitory activity of DNP, which indicated that the pharmacokinetic and pharmacodynamic data are in correlation with each other.

Development and validation of a UPLC-MS method for the determination of galantamine in guinea pig plasma and its application to a pre-clinical bioavailability study of novel galantamine formulations

To evaluate the bioavailability and pharmacokinetic profiles of two novel galantamine formulations as medical countermeasure products, an ultra-performance liquid chromatography-single quadrupole mass spectrometry (UPLC-MS) method was developed and validated for quantifying galantamine in guinea pig plasma using solid-phase extraction with a mixed mode strong cation exchange reversed-phase cartridge. Chromatographic separation was achieved on a Waters Acquity UPLC BEH C18 column maintained at 40°C. The mobile phases were solution A, acetonitrile-water, 5:95 (v/v) and solution B, acetonitrile-water 90:10 (v/v), both containing 2 mM ammonium formate and 0.2% formic acid. The mobile phase was delivered utilizing a 3 min gradient program start with 95%A-5%B at a flow rate of 0.6 mL/min. The analyte and internal standard, galantamine-d3, were detected by selected ion monitoring mode on a Waters 3100 single quadrupole mass spectrometer with positive electrospray ionization. The method was validated according to the US Food and Drug Administration bioanalytical guidance. The method was selective and was linear over the analytical range of 2-2000 ng/mL. Accuracy and precision were acceptable with intra- and inter-day accuracies between 96.8 and 101% and precisions (RSD) <4.88%. The method was successfully implemented to measure galantamine plasma levels in a series of pre-clinical bioavailability studies for the evaluation of novel galantamine formulations.

An LC-MS/MS method for the simultaneous determination of lycorine and galanthamine in rat plasma and its application to pharmacokinetic study of Lycoris radiata extract in rats

A rapid, sensitive, and selective liquid chromatography-tandem mass spectrometry was developed for the simultaneous determination of lycorine and galanthamine, two major constituents in Lycoris radiata extract, in rat plasma. Liquid-liquid extraction with ethyl ether was carried out using diphenhydramine as the internal standard. The two bioactive alkaloids were separated on a Zorbax SB-C18 reserved-phase column (150 mm × 4.6 mm, i.d., 5 μm) by gradient elution using a mobile phase consisting of methanol with 0.1% formic acid (A) and water with 0.1% formic acid (B) at a flow rate of 0.6 mL/min. All analytes showed good linearity over a wide concentration range (r (2)>0.99) and the lower limit of quantification was 3.00 ng/mL for each analyte. The average extraction recovery of the analytes from rat plasma was more than 82.15%, and the intra-day and inter-day accuracy and precision of the assay were less than 12.6%. The validated method was successfully applied to monitoring the concentrations and pharmacokinetic studies of two Amaryllidaceous alkaloids in rat plasma after an oral administration of Lycoris radiata extract.

Rapid determination of memantine in human plasma by using nanoring carboxyl-functionalized paramagnetic molecularly imprinted polymer d-μ-SPE and UFLC-MS/MS

A novel, simple, and sensitive method based on the use of dispersive micro-solid-phase extraction (d-μ-SPE) procedure combined with ultra-fast liquid chromatography-tandem quadrupole mass spectrometry (UFLC-MS/MS) for the determination of memantine (ME) was developed and validated over the linearity range 0.05-10.0 µg/L with 100 μL of human plasma using memantine-D6 (ME-D6) as the internal standard. The novel nanoring carboxyl-functionalized paramagnetic molecularly imprinted polymer (NR-CF-Mag-MIP) was synthesized by ultrasound-assisted suspension polymerization, using ME as a template molecule, methacrylic acid as a functional monomer, and divinylbenzene as a cross-linking agent. The NR-CF-Mag-MIP was used as the d-μ-SPE sorbent to extract ME from human plasma samples. The obtained results demonstrated the higher extraction capacity of NR-CF-Mag-MIP with recoveries between 97.6 and 101%. The limits of quantification (LOQs) for ME was 0.015 µg/L. Validation results on linearity, specificity, accuracy, precision, and stability, as well as on application to the analysis of samples taken up to 480 h after oral administration of 20 mg (two 10 mg capsules) of ME in healthy volunteers demonstrated the applicability to bioequivalence studies.

A Stability-Indicating HPLC Method for the Determination of Memantine Hydrochloride in Dosage Forms through Derivatization with 1-Fluoro-2,4-dinitrobenzene

Memantine is chemically a tricyclic amine and is used for Parkinson’s disease and movement disorders. Although several HPLC methods with different derivatization reagents have been developed for the determination of memantine in biological fluids, there are some complications which limit the use of these methods in routine analysis of memantine in in vitro tests. We established a simple, sensitive, precise, and accurate HPLC method for the quantification of memantine in dosage forms. Pre-column derivatization of memantine was performed with 1-fluoro-2,4-dinitrobenzene and the reaction product was separated on a Nova-Pak C18 column. A mixture of acetonitrile and sodium dihydrogenphosphate (pH 2.5; 0.05 M) (70: 30, v/v) was used as the mobile phase. UV detection was performed at 360 nm. Forced degradation studies were performed on a powdered tablet sample of memantine hydro-chloride using acidic (0.1 M hydrochloric acid), basic (0.1 M sodium hydroxide), oxidative (10% hydrogen peroxide), thermal (105°C), photolytic, and humidity conditions. Good linearity (r²=0.999) was obtained over the range of 1–12 μg mL⁻¹ of memantine hydrochloride with acceptable within-day and between-day precision values in the range of 0.05–0.95%. The proposed method was used for the assay determination and dissolution rate study of memantine dosage forms with excellent specificity.

Highly sensitive LC-MS/MS method for determination of galantamine in rat plasma: application to pharmacokinetic studies in rats

A rapid and highly sensitive assay method has been developed and validated for the estimation of galantamine (GLM) in rat plasma using liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in the positive-ion mode. The assay procedure involves a simple liquid-liquid extraction of GLM and phenacetin (internal standard, IS) from rat plasma using acetonitrile. Chromatographic separation was achieved with 0.2% formic acid:acetonitrile (50:50, v/v) at a flow rate of 0.60 mL/min on an Atlantis dC18 column with a total run time 2.5 min. The MS/MS ion transitions monitored were 288.10 → 213.10 for GLM and 180.10 → 110.10 for IS. Method validation was performed as per United States Food and Drug Administration guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 0.12 ng/mL and linearity was observed from 0.12 to 525 ng/mL. The intra- and inter-day precision were in the ranges of 4.73-11.7 and 5.83-8.64%, respectively. This novel method has been applied to a pharmacokinetic study in rats.

Review of the validated HPLC and LC-MS/MS methods for determination of drugs used in clinical practice for Alzheimer's disease

Alzheimer's disease (AD) is a neurological disorder and is the most frequent type of dementia among elderly people. Donepezil, rivastigmine, galantamine, tacrine and memantine are the US Food and Drug Administration approved oral drugs used in the treatment of AD. Quantitation of these drugs in various biological matrices and monitoring them in long-term treatment is essential to titer the dose of these drugs and ensure patient compliance. This review provides a comprehensive account of various HPLC and LC-MS/MS assays, which have been successfully employed to measure the drug levels in various biological matrices arising from preclinical and clinical studies. In addition, this review collates various considerations such as internal standard selection, extraction schemes, matrix effect, selectivity evaluation and optimization of mass spectrometric conditions to enable the development of sound bioanalytical methods for quantitation of Alzheimer's drugs. Overall LC-MS/MS methods have proven to be the choice of bioanalytical method for the quantification of Alzheimer's drugs in both preclinical and clinical studies. In conclusion, important features of LC-MS/MS methodology for Alzheimer's drugs include shortened analysis time, increased throughput, selectivity and lower cost of analysis.

Buprenorphine and norbuprenorphine quantification in human plasma by simple protein precipitation and ultra-high performance liquid chromatography tandem mass spectrometry

A highly sensitive ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method was developed for the quantification of buprenorphine and its major metabolite norbuprenorphine in human plasma. In order to speed up the process and decrease costs, sample preparation was performed by simple protein precipitation with acetonitrile. To the best of our knowledge, this is the first application of this extraction technique for the quantification of buprenorphine in plasma. Matrix effects were strongly reduced and selectivity increased by using an efficient chromatographic separation on a sub-2 μm column (Acquity UPLC BEH C18 1.7 μm, 2.1×50 mm) in 5 min with a gradient of ammonium formate 20 mM pH 3.05 and acetonitrile as mobile phase at a flow rate of 0.4 ml/min. Detection was made using a tandem quadrupole mass spectrometer operating in positive electrospray ionization mode, using multiple reaction monitoring. The procedure was fully validated according to the latest Food and Drug Administration guidelines and the Société Française des Sciences et Techniques Pharmaceutiques. Very good results were obtained by using a stable isotope-labeled internal standard for each analyte, to compensate for the variability due to the extraction and ionization steps. The method was very sensitive with lower limits of quantification of 0.1 ng/ml for buprenorphine and 0.25 ng/ml for norbuprenorphine. The upper limit of quantification was 250 ng/ml for both drugs. Trueness (98.4-113.7%), repeatability (1.9-7.7%), intermediate precision (2.6-7.9%) and internal standard-normalized matrix effects (94-101%) were in accordance with international recommendations. The procedure was successfully used to quantify plasma samples from patients included in a clinical pharmacogenetic study and can be transferred for routine therapeutic drug monitoring in clinical laboratories without further development.