Development and comparison of high-performance liquid chromatographic methods with tandem mass spectrometric and ultraviolet absorbance detection for the determination of cyclobenzaprine in human plasma and urine

Electrochemical Determination of Cyclobenzaprine Hydrochloride Muscle Relaxant Using Novel S-GCN/TiO2-Based Carbon Electrode

We have successfully prepared the titanium dioxide (TiO2) nanoparticles (NPs) and sulfur-incorporated graphitic carbon nitride (S-GCN)-modified carbon paste electrode (CPE). The CPEs modified with TiO2 NPs and S-GCN were employed for detecting and quantifying the skeletal muscle relaxant cyclobenzaprine hydrochloride (CBP) using cyclic voltammetry and square wave voltammetry (SWV) techniques. Optimal electrochemical conditions were indicated by the pH study results, with the highest peak current observed at a physiological pH of 7.4. The electrochemical process was determined to involve an equivalent number of protons (H+) and electrons (e-). The concentration variation of CBP (ranging from 0.06 to 10 × 10-7 mol L-1) was explored using SWV. The limits of detection and quantification were determined as 6.4 × 10-9 and 2.1 × 10-8 M, respectively. The proposed electrode configuration was applied to analyze real samples, including water, biomedical, and pharmaceutical specimens.

A novel nanozyme doped ZnO/r-GO-based sensor for highly sensitive electrochemical determination of muscle-relaxant drug: cyclobenzaprine HCl

A nanocomposite of Ce-doped ZnO/r-GO was synthesized using a conventional hydrothermal method. The synthesized nanocomposites were utilized for the purpose of sensitive and selective detection of cyclobenzaprine hydrochloride (CBP). The properties of the composite were extensively analyzed, including its morphology, structure, and electrochemical behavior. This study investigates the application of a modified glassy carbon electrode for the detection of CBP, a muscle relaxant used to treat musculoskeletal diseases that cause muscle spasms. The electrode is modified with Ce-doped ZnO/r-GO. Various detection methods, such as cyclic voltammetric and square wave techniques (SWV), were utilized. The composite material showed high effectiveness as an electron transfer mediator in the oxidation of CBP. The electrode showed a good response for SWV evaluations in CBP identification, with a minimum detection limit of 1.6 × 10-8 M and a wide linear range from 10 × 10-6 M to 0.6 × 10-7 M, under ideal conditions. The rate constant for charge transfer (ks) and the estimation of the electrochemical active surface area were obtained. A developed sensor exhibited desirable selectivity, long-lasting stability, and remarkable reproducibility. A sensor was used to analyze water, human serum, and urine samples, resulting in positive recovery results.

A Novel Method for Determination of Cyclobenzaprine in the Different Matrixes by UHPLC-DAD: Application to Real Human Plasma and Pharmaceutical Formulations

This study presents a novel and efficient method for determining of cyclobenzaprine (CBP) in human plasma and tablets using simple liquid-liquid microextraction and ultra-high performance liquid chromatography-diode-array detector. The developed method was optimized and validated for selectivity, linearity, precision, accuracy, limit of detection (LOD) and limit of quantification (LOQ). The chromatographic separation was achieved using a C18 column with a mobile phase consisting of a mixture of deionized water containing 0.1% TFA and methanol (30:70, v:v) at a flow rate of 1.0 mL/min. The extraction process provided high-efficiency recovery of CBP with a small plasma volume (%94.3). The method showed good linearity within the concentration range of 0.005-10 μg/mL, with a correlation coefficient of 0.999. The LOD and LOQ values were found to be 0.0013 and 0.005 μg/mL, respectively. The intra- and inter-day %RSD were <8%, and %RE were ranged from -0.50 to 0.01%. The proposed method was successfully applied to the analysis of CBP in real human plasma samples and tablets, indicating its applicability in clinical and pharmaceutical research. In conclusion, the simple, low cost, high sensitivity and rapid nature of this method make it an attractive option for the quantification of CBP in human plasma and pharmaceutical dosage forms.

Fabrication of an (α-Mn2O3:Co)-decorated CNT highly sensitive screen printed electrode for the optimization and electrochemical determination of cyclobenzaprine hydrochloride using response surface methodology

A new chemically optimized screen-printed electrode modified with a cobalt-doped α-Mn2O3 nanostructure on carbon nanotube paste (α-Mn2O3:Co@CNTs) has been constructed for the recognition of cyclobenzaprine hydrochloride. The prepared paste is based on the incorporation of oxide ion conductors, such as the α-Mn2O3 nanostructure with cobalt and ion pairs (tetraphenyl borate coupled with the drug), as electroactive species in the screen-printed electrode to increase the sensor surface area and decrease electrical resistance. The central composite design is a useful methodology for the estimation and modeling of the exact optimum parameters specifically designed for this process. This is a good way to graphically clarify the relationship between various experimental variables and the slope response. The proposed sensor, α-Mn2O3:Co@CNTs, possesses very good sensitivity and the ability to recognize the drug over the concentration range of 1 × 10-6 to 1 × 10-2 mol L-1 at 25 ± °C with a detection limit of 2.84 × 10-7 mol L-1. It exhibits a reproducible potential and stable linear response for six months at a Nernstian slope of 58.96 ± 0.76 mV per decade. The proposed electrode approach has been successfully applied in the direct determination of the drug in its pure and dosage forms.

Green analytical chromatographic assay method for quantitation of cyclobenzaprine in tablets, spiked human urine and in-vitro dissolution test

Cyclobenzaprine hydrochloride, a skeletal muscle relaxant has been determined using an ecofriendly micellar HPLC method in its pure form and tablets. The chromatographic determination was performed using C₈ monolithic column (100mm×4.6mm i.d., 5μm particle size) and micellar eluent which was composed of sodium dodecyl sulfate (0.15M), n-propanol (15%), 0.02M orthophosphoric acid (pH 4.5) and 0.3% triethylamine using UV detection of effluent was set at 225nm. The calibration plot showed good linearity over concentration range from 2-40μg/mL. The assay results were statistically validated for linearity, accuracy, precision and specificity according to ICH guidelines. Additionally, regarding USP guidelines, the uniformity of tablets content and in-vitro dissolution test of the tablets was tested using the proposed method. Simple and rapid applicability of the developed method allowed determination of the drug in its pure and tablet dosage forms. Moreover, the major advantage of micellar HPLC technique is to determine the drug in biological fluids without prior extraction steps. Depending on this, the estimation of cyclobenzaprine in spiked human urine was so simple without traditional tedious procedures. The proposed method offers the advantages of sensitivity and simplicity in addition to short analysis time which didn't exceed 6 minutes.

Five modified classical least squares based models for stability indicating analysis of cyclobenzaprine HCl with its major degradation products: A comparative study

Five modified multivariate calibration models based on classical least squares (CLS) in addition to traditional CLS model are developed and validated for assaying cyclobenzaprine HCl (CZ) with its major degradants; dibenzocycloheptatrienone (DZ) and anthraquinone (AQ), whether in its pure form or in pharmaceutical dosage form. The five models are net analyte processing CLS (NAP-CLS), orthogonal signal correction CLS (OSC-CLS), direct orthogonal signal correction CLS (DOSC-CLS) and hybrid linear analysis following the strategy of Xu and Schechter (HLA-XS) or Goicoechea et al. (HLA-GO). The five modified CLS models in addition to traditional CLS were subjected to a comparative study through manipulation of ultra-violet absorption data in the region of 220-350 nm. Three factor four level experimental design was adopted which results in 16 mixtures calibration set covering various concentrations of CZ, DZ and AQ. An extra validation set, composed of nine mixtures, was prepared for validation of the prediction power of the presented models. Experimental results showed high capability of the proposed modified CLS models for assaying CZ successfully without any interference from the co-existing degradation products (DZ and AQ). A statistical comparison between the results of CZ analysis in its dosage form by the six CLS based models and the reported HPLC method was carried out presenting no significant difference in regards to precision and accuracy. Significance of CLS based models is a consequent of their high quantitative and qualitative power for assaying multi-components mixtures.

Pharmacokinetics and bioequivalence evaluation of cyclobenzaprine tablets

The purpose of this study was to investigate cyclobenzaprine pharmacokinetics and to evaluate bioequivalence between two different tablet formulations containing the drug. An open, randomized, crossover, single-dose, two-period, and two-sequence design was employed. Tablets were administered to 23 healthy subjects after an overnight fasting and blood samples were collected up to 240 hours after drug administration. Plasma cyclobenzaprine was quantified by means of an LC-MS/MS method. Pharmacokinetic parameters related to absorption, distribution, and elimination were calculated. Cyclobenzaprine plasma profiles for the reference and test products were similar, as well as absorption pharmacokinetic parameters AUC (reference: 199.4 ng ∗ h/mL; test: 201.6 ng ∗ h/mL), Cmax (reference: 7.0 ng/mL; test: 7.2 ng/mL), and T(max) (reference: 4.5 h; test: 4.6 h). Bioequivalence was evaluated by means of 90% confidence intervals for the ratio of AUC (93%-111%) and C(max) (93%-112%) values for test and reference products, which were within the 80%-125% interval proposed by FDA. Cyclobenzaprine pharmacokinetics can be described by a multicompartment open model with an average rapid elimination half-life (t(1/2)β) of 3.1 hours and an average terminal elimination half-life (t(1/2)γ) of 31.9 hours.

A review of clinical diagnostic applications of liquid chromatography-tandem mass spectrometry

Liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) technology is emerging as a complementary method to traditional methodology used for clinical applications. Enhanced specificity and high-throughput capabilities are providing significant benefits to clinical diagnostic laboratories conducting routine analyses. This technology is expected to expand rapidly as scientists focus on more complicated challenges that can be solved efficiently by adding LC/MS/MS to their arsenal of techniques.

A decade of HPLC-MS/MS in the routine clinical laboratory--goals for further developments

During the past decade, tandem mass spectrometry hyphenated to liquid chromatography separation systems (HPLC-MS/MS) has developed to an important technology in clinical chemistry - not only for research purposes but also for routine use. At present, most important application fields are target analyses in therapeutic drug monitoring (TDM) and metabolic disorders diagnosis. The essential strengths of HPLC-MS/MS include potentially high analytical specificity, wide range of applicability to small and large molecules, capability of multi- and mega-parametric tests, and the opportunity to develop powerful assays with a high degree of flexibility within a short time frame. The technique has overcome important limitations of GC-MS and is characterized by short analytical runtimes, applicability to thermo labile, polar and large molecules, and straightforward sample preparation. However, implementation of HPLC-MS/MS assays still requires substantial expertise and know-how. At the present, its application is limited to a rather small number of clinical routine laboratories. Nonetheless, HPLC-MS/MS has the potential to be further developed to a commonly applied high-throughput technique in clinical chemistry, complementary to present standard techniques as photometry and ligand binding methods. This review intends to characterize working characteristics of present day HPLC-MS/MS instrumentations used in clinical routine laboratories. Limitations of currently available systems and applications will be critically discussed. Required instrument improvements supporting the successful spreading of HPLC-MS/MS in laboratory medicine within the next decade will be outlined.

Cyclobenzaprine pharmacokinetics, including the effects of age, gender, and hepatic insufficiency

The pharmacokinetics and bioavailability of cyclobenzaprine, a widely used muscle relaxant, were investigated in four clinical studies, and the effects of age, gender, and hepatic insufficiency were characterized. Cyclobenzaprine plasma clearance was 689 ml/min, and the bioavailability of a 5 mg oral dose was 0.55. Following oral doses of 2.5 to 10 mg tid in healthy young subjects, cyclobenzaprine pharmacokinetics were linear, and plasma concentrations generally increased proportional to dose. There was about a fourfold accumulation of the drug in plasma on multiple dosing, corresponding to an effective half-life of 18 hours. Steady-state plasma concentrations of cyclobenzaprine in elderly subjects were twice as high as in young subjects following oral doses of 5 mg tid. Steady-state plasma concentration also appeared to be up to twofold higher in subjects with mild hepatic insufficiency compared to healthy controls. The magnitude of any difference in steady-state plasma concentration between males and females appears to be small relative to intersubject variability. A reduction in dose or dosing frequency should be considered in the elderly and in patients with liver disease.

Determination of rofecoxib (MK-0966), a cyclooxygenase-2 inhibitor, in human plasma by high-performance liquid chromatography with tandem mass spectrometric detection

A method for the determination of 4-(4-methanesulfonylphenyl)-3-phenyl-5H-furan-2-one (Rofecoxib, Vioxx, MK-0966, I) a cyclooxygenase-2 inhibitor, in human plasma has been developed. The method is based on high-performance liquid chromatography (HPLC) with atmospheric pressure chemical ionization tandem mass spectrometric (APCI-MS-MS) detection in negative ionization mode using a heated nebulizer interface. Drug and internal standard (II) were isolated from basified plasma using liquid-liquid extraction. The organic extracts were dried, reconstituted in mobile phase and injected into the HPLC-MS-MS system. Compounds I and II were chromatographed on a narrow bore (100 mm x 3.0 mm) C18 analytical column, with mobile phase consisting of acetonitrile:water (1:1, v/v) at a flow-rate of 0.4 ml/min. The MS-MS detection was performed on a PE-Sciex API III Plus tandem mass spectrometer operated in selected reaction monitoring mode. The parent-->product ion combinations of m/z 313-->257 and 327-->271 were used to quantify I and II, respectively, after chromatographic separation of the analytes. The assay was validated in the concentration range of 0.1 to 100 ng/ml of plasma. The precision of the assay (expressed as coefficient of variation) was less than 10% at all concentrations within the standard curve range, with adequate assay accuracy. The effect of HPLC mobile phase components on the ionization efficiency and sensitivity of detection in the positive and negative ionization modes, and the detailed description of all necessary steps involved in the assay for I in plasma are presented.

Effect of the sample matrix on the determination of indinavir in human urine by HPLC with turbo ion spray tandem mass spectrometric detection

The HPLC/tandem mass spectrometric (LC/MS/MS) behavior of indinavir, an HIV protease inhibitor, in human urine is presented as an example of a case where endogenous matrix components were found to interfere with the ionization of the target analyte. The MS/MS system used for these experiments was equipped with a turbo ion spray LC interface. Results from two sample preparation procedures (direct dilution of urine vs urine extraction) and two chromatographic systems (low vs. high capacity factor (k')) for the analytes were compared. Additionally, the precision of the analysis that was achieved while using a stable isotope labeled internal standard is contrasted with the results obtained using an analog of indinavir as internal standard. The results obtained indicated that during development and validation of LC/MS/MS based assays the potential effect of co-eluting 'unseen' endogenous species should be evaluated to ensure that sample preparation and chromatography is adequate to overcome the matrix effect problems.

Development of high-performance liquid chromatography-tandem mass spectrometric methods for the determination of a new oxytocin receptor antagonist (L-368,899) extracted from human plasma and urine: a case of lack of specificity due to the presence of metabolites

The purpose of this work was to develop HPLC-MS-MS methods for the quantification of L-368,899 (1) in human plasma and urine and to evaluate the selectivity of these methods in post-dose samples in the presence of metabolites. Assays were based on double liquid-liquid extraction of the drug and internal standard (I.S., 2) from basified plasma, evaporation of the extracts to dryness, derivatization of the primary amino groups of 1 and 2 with trifluoroacetic anhydride (TFAA) to form trifluoroacetylated (TFA) analogs, and HPLC analysis using tandem mass spectrometer equipped with the heated nebulizer interface as a detector. The derivatization with TFAA was required to eliminate the carryover and adsorption problems encountered when underivatized molecules were chromatographed, and allowed quantitation at low concentration (0.5 ng/ml) in plasma and urine. Initially, assays in control human plasma and urine were validated in the concentration range of 0.5-75 ng/ml, using simplified chromatographic conditions with a 2-min run-time and no separation of the drug from I.S.. Quantitation was based on the high selectivity of detection and multiple reaction monitoring (MRM) using the precursor-->product ion combinations of m/z 651-->152 and m/z 665-->425 for the TFA-derivatized 1 and 2, respectively. However, when selected post-dose urine samples from a clinical study were analyzed using this assay, the area of the I.S. peak was 4 to 7 times larger than the area of I.S. peak in pre-dose urines, indicating the presence of metabolites giving rise to the m/z 665-->425 I.S. peak. A number of metabolites contributing to the I.S. ion pair were separated from 1 and 2 using a longer analytical column, a weaker mobile phase, and by extending the HPLC run-time to 12 min. Under these new conditions, the modified assays both in plasma and urine were validated in the concentration range of 0.5 to 75.0 ng/ml. These assays were selective in the post-dose urine samples in the presence of metabolites.

Liquid chromatography-mass spectrometry in forensic and clinical toxicology

This paper reviews liquid chromatographic-mass spectrometric (LC-MS) procedures for the identification and/or quantification of drugs of abuse, therapeutic drugs, poisons and/or their metabolites in biosamples (whole blood, plasma, serum, urine, cerebrospinal fluid, vitreous humor, liver or hair) of humans or animals (cattle, dog, horse, mouse, pig or rat). Papers published from 1995 to early 1997, which are relevant to clinical toxicology, forensic toxicology, doping control or drug metabolism and pharmacokinetics, were taken into consideration. They cover the following analytes: amphetamines, cocaine, lysergide (LSD), opiates, anabolics, antihypertensives, benzodiazepines, cardiac glycosides, corticosteroids, immunosuppressants, neuroleptics, non-steroidal anti-inflammatory drugs (NSAID), opioids, quaternary amines, xanthins, biogenic poisons such as aconitines, aflatoxins, amanitins and nicotine, and pesticides. LC-MS interface types, mass spectral detection modes, sample preparation procedures and chromatographic systems applied in the reviewed papers are discussed. Basic information about the biosample assayed, work-up, LC column, mobile phase, interface type, mass spectral detection mode, and validation data of each procedure is summarized in tables. Examples of typical LC-MS applications are presented.

Matrix effect in quantitative LC/MS/MS analyses of biological fluids: a method for determination of finasteride in human plasma at picogram per milliliter concentrations

Contrary to common perceptions, the reliability of quantitative assays for the determination of drugs in biological fluids using high-performance liquid chromatography with tandem mass spectrometric (LC/MS/MS) detection methods and the integrity of resulting pharmacokinetic data may not be absolute. Results may be adversely affected by lack of specificity and selectivity due to ion suppression caused by the sample matrix, interferences from metabolites, and "cross-talk" effects. In this paper, an example of the effect of the sample matrix on the determination of finasteride (I) in human plasma is presented. The ion suppression effect was studied by analyzing standards of I injected directly in mobile phase and comparing the response (peak areas) of I and an internal standard (II) with the peak areas of the same analytes spiked before extraction into five different plasma pools and standards spiked into the plasma extracts after extraction. The LC/MS/MS analyses were performed using a turbo ion spray interface (TISP) under chromatographic conditions, characterized by minimal (total run time of 2 min, capacity factors, k' of 1.50 and 1.75 for I and II, respectively) and high retention of the analytes (total run time 6 min, k' of 3.25 and 13.25 for I and II, respectively). The absolute peak areas for I and II in different plasmas were calculated, and the slopes and peak area ratios at all concentrations within the standard curve ranges were compared. When analyses were performed under conditions of minimal HPLC retention, the slope of the standard line for one set of plasma samples was substantially different (about 50% higher) from that from other plasma sources. The precision of the assay, expressed as coefficient of variation (CV, %) was also inadequate and varied from 15 to 30% at all concentrations within the standard curve range. When the same experiments were repeated using high HPLC retention, the slopes from different plasma sources were practically the same, and the CV was improved to 6-14%. By increasing k' and providing more chromatographic retention of analytes, the "unseen" interferences from plasma matrix were mostly separated from analytes, practically eliminating the ion suppression. In addition, by eliminating from plasma extracts a number of endogenous components through more selective extraction, the ion suppression was also minimized. The detailed data and the design of these experiments are presented. In addition, development of a highly sensitive assay for I in human plasma at low picogram per milliliter concentrations using LC/MS/MS with a heated nebulizer (HN) interface, instead of a TISP interface, is described. In this case, the effects of sample matrixes were not observed.

Matrix effect in quantitative LC/MS/MS analyses of biological fluids: a method for determination of finasteride in human plasma at picogram per milliliter concentrations

Contrary to common perceptions, the reliability of quantitative assays for the determination of drugs in biological fluids using high-performance liquid chromatography with tandem mass spectrometric (LC/MS/MS) detection methods and the integrity of resulting pharmacokinetic data may not be absolute. Results may be adversely affected by lack of specificity and selectivity due to ion suppression caused by the sample matrix, interferences from metabolites, and "cross-talk" effects. In this paper, an example of the effect of the sample matrix on the determination of finasteride (I) in human plasma is presented. The ion suppression effect was studied by analyzing standards of I injected directly in mobile phase and comparing the response (peak areas) of I and an internal standard (II) with the peak areas of the same analytes spiked before extraction into five different plasma pools and standards spiked into the plasma extracts after extraction. The LC/MS/MS analyses were performed using a turbo ion spray interface (TISP) under chromatographic conditions, characterized by minimal (total run time of 2 min, capacity factors, k' of 1.50 and 1.75 for I and II, respectively) and high retention of the analytes (total run time 6 min, k' of 3.25 and 13.25 for I and II, respectively). The absolute peak areas for I and II in different plasmas were calculated, and the slopes and peak area ratios at all concentrations within the standard curve ranges were compared. When analyses were performed under conditions of minimal HPLC retention, the slope of the standard line for one set of plasma samples was substantially different (about 50% higher) from that from other plasma sources. The precision of the assay, expressed as coefficient of variation (CV, %) was also inadequate and varied from 15 to 30% at all concentrations within the standard curve range. When the same experiments were repeated using high HPLC retention, the slopes from different plasma sources were practically the same, and the CV was improved to 6-14%. By increasing k' and providing more chromatographic retention of analytes, the "unseen" interferences from plasma matrix were mostly separated from analytes, practically eliminating the ion suppression. In addition, by eliminating from plasma extracts a number of endogenous components through more selective extraction, the ion suppression was also minimized. The detailed data and the design of these experiments are presented. In addition, development of a highly sensitive assay for I in human plasma at low picogram per milliliter concentrations using LC/MS/MS with a heated nebulizer (HN) interface, instead of a TISP interface, is described. In this case, the effects of sample matrixes were not observed.

Highly sensitive method for the determination of tamsulosin hydrochloride in human plasma dialysate, plasma and urine by high-performance liquid chromatography-electrospray tandem mass spectrometry

A highly sensitive method for the determination of tamsulosin hydrochloride, a structurally new type of sulphamoile derivative, in human plasma dialysate, plasma and urine has been developed by using liquid chromatography-electrospray tandem mass spectrometry (LC-MS-MS). Plasma dialysate, plasma and urine samples were extracted by brief liquid-phase extraction and analyzed using an HPLC system coupled to a mass spectrometer via an electrospray ionization interface. Selected reaction monitoring was used for the detection of tamsulosin and its internal standard. This method was validated in the concentration range 10-1000 pg/ml in plasma dialysate, 0.5-50 ng/ml in plasma, and 1-100 ng/ml in urine with sufficient specificity, accuracy and precision. The in vivo protein binding study demonstrated that the unbound tamsulosin in human plasma obtained by the equilibrium dialysis after 0.4-mg oral dosing was measurable. In addition, the percentage of unbound tamsulosin in an in vitro study (0.71-0.91%) obtained by using spiked 14C-labelled tamsulosin was slightly larger than that of the in vivo study (0.68-0.86%), indicating that the unbound concentration calculated by the product of the plasma concentration and the in vitro unbound fraction (fu) was unfavorably overestimated. These results suggest that the combination of LC-MS-MS and equilibrium dialysis method has enough sensitivity to determine the unbound concentration in clinical use and gives the concentration more exactly than the in vitro fu.

Determination of a substance P antagonist in human plasma and urine using high-performance liquid chromatography with ultraviolet absorbance and tandem mass spectrometric detection

A high-performance liquid chromatographic (HPLC) assay using ultraviolet (UV) detection was developed and compared with a HPLC method with tandem mass spectrometric (HPLC/MS-MS) detection for the determination of a substance P receptor antagonist 2(S)-((3,5-bis(trifluoromethyl)benzyl)-oxy)-3(S)-phenyl-4-((3-oxo-1,2,4- triazol-5-yl) methyl)morpholine (Fig. 1, Ia, L-742 694) in human plasma and urine. The drug was isolated from the biological matrix through liquid-liquid extraction. In the HPLC/UV method, the samples were initially injected onto a cyano Hypersil column, and the chromatographic region containing the peaks of interest was heart-cut onto an analytical C-18 Hypersil column via a column switching device. The analyte was quantified by monitoring absorbance at 205 nm. The limit of quantification for I extracted from 1 ml of plasma or urine was 2.5 ng ml-1, and the assays were validated in the concentration range 2.5-500 ng ml-1. The HPLC/MS-MS method were validated in the concentration range 0.2-500 ng ml-1. Both assays provided data with precision, measured as coefficient of variation, better than 10% at all points within the standard curve range and with adequate accuracy.

Determination of a novel growth hormone secretagogue (MK-677) in human plasma at picogram levels by liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry

A sensitive and specific method for the determination of N-[1(R)¿[1,2-dihydro-1-methylsulfonylspiro(3H-indole-3,4'-piper idin)-1'-yl]carbonyl¿-2-(phenylmethoxy)ethyl]-2-amino-2-meth ylpropanamide (MK-677, I), a growth hormone secretagogue, has been developed. The method is based on high-performance liquid chromatography (HPLC) with tandem mass spectrometric (MS-MS) detection. The analyte and internal standard (II) were isolated from the basified plasma using a liquid-liquid extraction with methyl-tert.-butyl ether (MTBE). The organic extract was evaporated to dryness, the residue was reconstituted in mobile phase and injected into the HPLC system. The MS-MS detection was performed on a PE Sciex API III Plus tandem mass spectrometer using a heated nebulizer interface. Multiple reaction monitoring of parent-->product ion combinations at m/z 529-->267 and 527-->267 was used to quantify I and II, respectively. The assay was validated in human plasma in the concentration range of 0.1 to 100 ng/ml, and the limit of quantification (LOQ) was 0.1 ng/ml. The precision of the assay, as expressed as coefficients of variation (C.V.,%) was less than 7% at all concentrations within the standard curve range, with adequate assay specificity and accuracy. The HPLC-MS-MS method provided sufficient sensitivity to completely map the pharmacokinetic time-course following a single 5-mg oral dose of I.

Low level determination of dorzolamide and its de-ethylated metabolite in human plasma by liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry

A sensitive and specific method for the determination of dorzolamide (I) and its de-ethylated metabolite (II) in human plasma has been developed utilizing high pressure liquid chromatography (HPLC) with tandem mass spectrometric (MS/MS) detection. The analytes and internal standard (III) were isolated from the deproteinized pH 8.0 buffered plasma, using a liquid-liquid extraction with a mixture of ethyl acetate, toluene, and isopropanol. The analytes were then back extracted into 0.085% phosphoric acid (200 microliters) and after washing the acidic extract with hexane, the organic layer was discarded and a fraction (50 microliters) of the acid extract was injected into the LC/MS/MS system. The MS/MS detection was performed on a PE Sciex API III tandem mass spectrometer using a heated nebulizer interface. Multiple reaction monitoring of the parent-->product ion combinations of m/z 325-->199, 297-->199, and 397-->306 were used to quantify I, II, and III, respectively. The assay was validated in the concentration ranges of 0.5-100 and 2.5-100 ng ml-1 of plasma for I and II, respectively. The precision of the assays, expressed as coefficients of variation (C.V.%), were less than 10% over the entire concentration range, with adequate assay specificity and accuracy. The LC/MS/MS method provided a 10-fold increase in the sensitivity of I over the previously reported HPLC/UV method [1].

Picogram determination of a novel dopamine D4 receptor antagonist in human plasma and urine by liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry

A sensitive and specific assay for the determination of 3-[[4-(4-chlorophenyl)piperazin-1-yl]methyl]-1H-pyrrolo[2,3-b]p yri dine (I, L-745,870), a potential antipsychotic agent, has been developed, utilizing high-performance liquid chromatography (HPLC) with tandem mass spectrometric (MS-MS) detection. The analyte and the internal standard (II, 3-[[4-(4-trifluoromethyl)piperazin-1-yl]methyl]-1H-pyrrolo[2,3-b] pyridine) were isolated from a basified biological matrix using liquid-liquid extraction with methyl-tert.-butyl ether. The organic extract was evaporated to dryness, the residue was reconstituted in a mobile phase and injected into the HPLC system. The chromatographic conditions used for the analysis were a Keystone Scientific C18 BDS 150 x 4.6 mm, 5 microns column with a mobile phase consisting of a 40:60 (v/v) mixture of acetonitrile and water containing 10 mM ammonium acetate and 0.1% formic acid pumped at a flow-rate of 1.2 ml/min, yielding retention times of 3.4 and 5.0 min for I and II, respectively. The MS-MS detection was performed on a PE Sciex API III Plus tandem mass spectrometer using a heated nebulizer interface. Multiple reaction monitoring using the parent-->product ion combinations of m/z 327-->131 and 361-->131 were utilized to quantitate I and II, respectively. The assays were validated in the concentration range of 0.1 to 100 and 0.5 to 500 ng/ml for plasma and urine, respectively. The precision of the assays, expressed as coefficients of variation were less than 10% over the entire concentration range, with adequate assay accuracy, sensitivity and specificity to determine the pharmacokinetics in human subjects following a single 1-mg dose.

Determination of an in vivo metabolite of a human immunodeficiency virus protease-inhibitor in human plasma by high-performance liquid chromatography with tandem mass spectrometry

A method for the determination of a metabolic of the human immunodeficiency virus protease inhibitor indinavir, in human plasma is described. Isolation of the analyte and the internal standard from plasma was achieved via liquid-liquid extraction with a mixture of isopropanol-chloroform (5:95, v/v). The analytes were chromatographed under reversed-phase conditions on a Waters Symmetry C, column. A Sciex API III+ tandem mass spectrometer equipped with a heated nebulizer was used as a detector and was operated in the positive ion mode. Multiple reaction monitoring using the precursor-->production combinations of m/z, 523.4-->273.4 and 512.4-->345.2 was used to quantify analyte and internal standard, respectively. The method was validated in the concentration range of 5-500 ng/ml plasma with adequate assay precision and accuracy. The assay was used to analyze samples collected during drug interaction studies of indinavir.

Simultaneous determination of unlabeled and deuterium-labeled indinavir in human plasma by high-performance liquid chromatography with tandem mass spectrometric detection

A method for the simultaneous determination of indinavir and its hexadeuterated analog (d6-indinavir) in human plasma is described. Isolation of the analytes and internal standard from plasma was achieved via liquid-liquid extraction with methyl-t-butyl ether. The analytes were chromatographed under reversed-phase conditions on a BDS-Hypersil C8 column. A Sciex API III+ tandem mass spectrometer equipped with a turbo ion-spray interface was used as the detector. Multiple reaction monitoring using the parent-->product ion combinations of m/z 614-->465, 620-->471 and 654-->505 were used to quantify indinavir, d6-indinavir, and internal standard, respectively. The method was validated, using 1-mL aliquots of plasma, in the concentration range in plasma of 1 to 200 ng/mL. Precision of the assay, as measured by the coefficient of variation, ranged from 0.9 to 4.3% and 0.9 to 6.2% for indinavir and d6-indinavir, respectively. Indinavir assay accuracy ranged from 95.8 to 105.0% of nominal, whereas the accuracy of the assay for d6-indinavir ranged from 97.4 to 104.0% of nominal. The assay was used to support a clinical study in which the stable isotope technique was used to determine the bioavailability of indinavir.

Quantitative determination of a nonpeptide antithrombotic in dog plasma by microbore high-performance liquid chromatography-tandem mass spectrometry utilizing pneumatically assisted electrospray ionization

A method has been developed and is described for the quantitative determination of a nonpeptide antithrombotic in dog plasma. The assay employs reversed phase microbore high-performance liquid chromatography in conjunction with tandem mass spectrometry utilizing pneumatically assisted electrospray ionization. The analyte and internal standard are isolated from the plasma matrix by solid-phase extraction. The mass spectrometer is operated in the positive ion multiple reaction monitoring mode and is set to detect the presence of a precursor-product ion pair for both the analyte and internal standard to generate product ion chromatograms for both species. The analyte is quantified by using weighted least-squares regression of the peak height ratio of drug:internal standard. The method provides linear response for plasma concentrations ranging from 5 ng/mL (25 pg on-column) to 2500 ng/mL. Statistical evaluation and examples of authentic sample assays are also presented.

Determination of a glycine/NMDA receptor antagonist in human plasma and urine using column-switching high-performance liquid chromatography with ultraviolet, fluorescence and tandem mass spectrometric detection

High-performance liquid chromatography (HPLC) assays using ultraviolet (UV) and fluorescence (FL) detection were developed and compared with a liquid chromatography/tandem mass spectrometry (LC/MS-MS) method for determination of the glycine receptor antagonist 7-chloro-4-hydroxy-3-(3-phenoxy)phenyl-2(1H)-quinolone (L-701, 324, I) in human plasma and urine. The drug and internal standard (II) were isolated from the biological matrix through liquid-liquid extraction. In the HPLC-UV and HPLC-FL methods, the samples were initially injected onto a Cyano BDS Hypersil column, and the chromatographic region containing the peaks of interest was heart-cut onto an analytical C-18 BDS Hypersil column via a column-switching device. The analyte was quantified by monitoring either absorbance at 226 nm or fluorescence at 385 nm following 230 nm excitation. The limit of quantitation for I extracted from 1 ml of plasma or urine was 5 ng ml-1, and the assays were validated in the concentrated range of 5-200 ng ml-1. The LC/MS-MS method also utilized a column-switching protocol and was validated in the concentration range of 1-200 ng ml-1. Both assays provided data with precision and accuracy within less than 10% for all points in the standard curve range.