Characterization of metabolites of Celecoxib in rabbits by liquid chromatography/tandem mass spectrometry

Preclinical Pharmacokinetics and Metabolism of MAK683, a Clinical Stage Selective Oral Embryonic Ectoderm Development (EED) Inhibitor for Cancer Treatment

1. MAK683 (N-((5-fluoro-2,3-dihydrobenzofuran-4-yl)methyl)-8-(2-methylpyridin-3-yl)-[1,2,4]triazolo[4,3-c]pyrimidin-5-amine) is a potent and orally bioavailable EED inhibitor for the potential treatment in oncology. Pharmacokinetics (PK) in preclinical species are characterized by low to moderate plasma clearances, high oral exposure and moderate to high oral bioavailability at dose of 1-2 mg/kg.2. A species comparison of the metabolic pathways of MAK683 has been made using [¹⁴C]MAK683 incubations with liver microsomes and hepatocytes from rat, dog, cynomolgus monkey and human. Overall, the in vitro hepatic metabolism pathway of MAK683 in all five species was very complex. A total of 60 metabolites with 19 metabolites greater than 1.5% of the total integrated area in the radiochromatogram of at least one species were identified in five species (rat, mouse, dog, monkey and human).3. The primary in vitro hepatic oxidative metabolism pathway identified in human involved 2-hydroxylation of the dihydrofuran ring to form an alcohol (M28), which was in a chemical equilibrium favoring the formation of its aldehyde form. The aldehyde was then oxidized to the carboxylic acid metabolite (M26) or reduced to the O-hydroxyethylphenol (M29). N-dealkylation (M1), 3-hydroxylation of the dihydrofuran ring (M27), N-oxidation of the pyridine moiety (M53) and sulfate conjugation of M28 to form M19 were also important biotransformation pathways in human hepatocytes. The above major human hepatic metabolic pathways were also observed across the animal species (rat, mouse, dog and monkey) mostly providing precursors for the formation of other metabolites via further oxygenation, glucuronidation, and sulfation pathways.4. No human specific metabolites were observed. In addition, in-vivo biotransformation was also conducted in bile-duct cannulated (BDC) rat. The metabolism in BDC rat was similar to these observed the in vitro hepatocytes.

Pharmacokinetics, metabolism and excretion of celecoxib, a selective cyclooxygenase-2 inhibitor, in horses

Celecoxib, a nonsteroidal anti-inflammatory drug, is frequently used to treat arthritis in humans with minimal gastrointestinal side effect compared to traditional NSAIDs. The primary aim of this study was to determine the pharmacokinetic profile of celecoxib-a selective cyclooxygenase-2 (COX-2) inhibitor in horses. Six horses were administered a single oral dose of celecoxib at 2 mg/kg (body weight). After oral dosing, the drug reached a maximum concentration (mean ± SD) in blood of 1,088 ± 324 ng/ml in 4.58 hr. The elimination half-life was 13.60 ± 3.18 hr, and the area under the curve was 24,142 ± 1,096 ng hr ml^-1 . The metabolism of celecoxib in horses was via a single oxidative pathway in which the methyl group of celecoxib is oxidized to a hydroxymethyl metabolite and is further oxidized to form a carboxylic acid metabolite. Celecoxib is eliminated mainly through faeces as unchanged drug and as metabolites in urine. Therefore, instructions for a detection time following therapeutic dosing of celecoxib can be set by the racing practitioner and veterinarians to control illegal use in horse racing based on the results of this study.

Photochemical, thermal, biological and long-term degradation of celecoxib in river water. Degradation products and adsorption to sediment

Celecoxib is an anti-inflammatory drug with antibacterial activity whose fate in surface water is unknown. Thus, some assays have been conducted under forced biological, photochemical and thermal conditions, and non-forced conditions, to establish its persistence and degradation products in river water. The results suggest that celecoxib dissolved in river water is not biologically degraded while it is minimally altered after its exposure to sunlight or high temperature (70°C). Only the irradiation at 254nm promotes its complete degradation. Celecoxib is degraded about 3%, in 36 weeks, when water was kept at room temperature and the exposure to sunlight was partially limited as it happens inside a body of water. Residues were monitored by ultra-pressure liquid chromatography/quadrupole time-of-flight/mass spectrometry after solid-phase extraction; eleven degradation products were detected and the structures of nine of them were unequivocally proposed from the molecular formulae and fragmentation observed in high-resolution tandem mass spectra. The long-term transformation products under non-forced conditions were 4-[5-(4-methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]benzenesulfonic acid, 4-[1-(4-sulfoaminephenyl)-3-(trifluoromethyl)-1H-pyrazol-5-yl]benzoic acid and a hydroxylated derivative. The degradation over time in presence of sediment was monitored, being slightly higher, about 4%. The adsorption equilibrium constants of celecoxib and degradation products on river sediment were estimated.

Albumin Cys34 adducted by acrolein as a marker of oxidative stress in ischemia-reperfusion injury during hepatectomy

The aim of this study was to measure and identify the reactive carbonyl species (RCSs) released in the blood of humans subjected to hepatic resection. Pre-anesthesia malondialdehyde (MDA) plasma content (0.36 ± 0.11 nmol/mg protein) remained almost unchanged immediately after anaesthesia, before clamping and at the 10th min after ischemia, while markedly increased (to 0.59 ± 0.07 nmol/mg; p < 0.01, Tukey's post test) at the 10th min of reperfusion. A similar trend was observed for the protein carbonyls (PCs), whose pre-anesthesia levels (0.17 ± 0.13 nmol/mg) did not significantly change during ischemia, while increased more than fourfold at the 10th min of reperfusion (0.75 ± 0.17 nmol/mg; p < 0.01, Tukey's post test). RCSs were then identified as covalent adducts to the albumin Cys34, which we previously found as the most reactive protein nucleophilic site in plasma. By using a mass spectrometry (MS) approach based on precursor ion scanning, we found that acrolein (ACR) is the main RCS adducted to albumin Cys34. In basal conditions, the adducted albumin was 0.6 ± 0.4% of the native form but it increased by almost fourfold at the 10th min of reperfusion (2.3 ± 0.7%; p < 0.01, t-test analysis). Since RCSs are damaging molecules, we propose that RCSs, and ACR in particular, are new targets for novel molecular treatments aimed at reducing the ischemia/reperfusion damage by the use of RCS sequestering agents.

Quantitation of celecoxib and four of its metabolites in rat blood by UPLC-MS/MS clarifies their blood distribution patterns and provides more accurate pharmacokinetics profiles

A sensitive UPLC-MS/MS method was established and validated for the quantitation of celecoxib and its metabolites in rat blood. The analytes were extracted from rat blood samples by a salting-out liquid-liquid extraction method followed by the UPLC chromatography. The mass analysis of effluent was performed on an API 5500 Qtrap mass spectrometer via multiple reactions monitoring (MRM). The linear response ranges were 0.3-20000nM for celecoxib, and 1.2-20000nM, 0.3-20000nM, 2.0-2000nM, 1.5-6000nM for its metabolites carboxycelecoxib (M2), hydroxycelecoxib (M3), hydroxycelecoxib glucuronide (M1), and carboxycelecoxib glucuronide (M5), respectively. The inter-day and intra-day accuracies were within 85-115%, and the inter-day and intra-day precision were acceptable (<12%) for all analytes. Recoveries were above 70% and no obvious matrix effects were observed. The validated UPLC-MS/MS method was successfully applied to a pharmacokinetics study of oral celecoxib (20mg/kg) in Sprague-Dawley rats, and the rat blood concentrations (0-48h) of celecoxib and two of its metabolites M2 and M3 were successfully determined. Using the same method, we also showed preferential distributions of celecoxib, M2 and M3 in the blood cells as compared to the plasma. In conclusion, our results showed that our validated LC-MS/MS method can be successfully used for the pharmacokinetic studies of celecoxib and that the blood cells are a very important compartment for this drug such that profiles of celecoxib and its metabolites in whole blood will be more comprehensive and accurate representation of their profiles in vivo than the plasma.

Determination of Celecoxib in human plasma using liquid chromatography with high resolution time of flight-mass spectrometry

A sensitive method for the determination of Celecoxib (CXB) in human plasma samples was developed using liquid chromatography coupled to electrospray ionization and time of flight mass spectrometry (LC-ESI-TOF-MS). A full factorial design of experiments (FF-DOE) methodology was applied to optimize the ESI conditions for CXB determination and also to predict the effects of interactions of multiple parameters affecting ionization (i.e., capillary voltage, fragmentor voltage, electrolyte and electrolyte concentration). The optimum ionization voltages were 4500V and 220V for capillary and fragmentor, respectively. Even though the highest ESI efficiency was obtained without electrolytes, the addition of 1.0mM ammonium acetate was shown to be essential to buffer the matrix effect and ensure a consistent response. In contrast to previous studies, deuterated CXB was used as a recovery (surrogate) standard, which enabled the correction of CXB loss during sample preparation. The extraction recovery using solid phase extraction was 87-98%. The instrumental limit of detection of CXB (LOD), 0.33ng/mL, and matrix affected LOD, 0.55ng/mL, were similar and comparable to the previously reported LC-MS/MS LODs. This method was employed to determine CXB concentrations in human plasma samples. Upon administration of 400mg CXB to the healthy women, the concentrations found in the plasma were 440-3300ng/mL. The inter-day repeatability was less than 4% RSD.

Fragmentation of toxicologically relevant drugs in negative-ion liquid chromatography-tandem mass spectrometry

Negative-ion LC-MS analysis of drugs is applied far less frequently than positive-ion LC-MS. Data on the interpretation of negative-ion MS-MS spectra are even more scarce. Therefore, following the recent review on the class-specific fragmentation of toxicologically relevant compounds in positive-ion MS-MS, it was decided to perform a similar study in negative-ion MS-MS. To this end, a set of over 500 negative-ion MS-MS spectra was collected from three libraries applied in toxicological general unknown screening and systematic toxicological analysis. The compounds involved were classified by chemical and therapeutic class. The MS-MS spectra were manually interpreted and relevant interpretation data were searched for in the scientific literature. The emphasis in the discussion is on class-specific fragmentation, because discussing fragmentation of all individual compounds would take far too much space. Negative-ion MS-MS fragmentation is discussed for a wide variety of toxicologically relevant compounds, including dihydropyridine calcium channel blockers, diuretics, barbiturates, anti-inflammatory drugs, anti-diabetics, sulfonamide and betalactam antibiotics, and a number of classes of pesticides.

Chromatographic techniques in analysis of cyclooxygenase-2 inhibitors in drugs and biological samples

Non-steroidal anti-inflammatory drugs, as a therapeutic class, are among the most often used active pharmaceutical ingredients in heath care in the world. They are mostly available without prescription and often used for treatment of fever and pain. An extensive research of the literature published in analytical and pharmaceutical chemistry journals has been conducted and the chromatographic methods which were used for the purity, stability and pharmacokinetic studies of the cyclooxygenase-2 inhibitors, in formulations and biological materials have been reviewed. The methodology for the analysis of selected drugs is very well documented and many examples are available in the literature. The common use of chromatographic techniques with various detection attachments provide possibility for monitoring of drugs in therapy.

Inhibitory effect of dietary atorvastatin and celecoxib together with voluntary running wheel exercise on the progression of androgen-dependent LNCaP prostate tumors to androgen independence

We determined the inhibitory effect of dietary atorvastatin, dietary celecoxib and voluntary running wheel exercise (RW) alone or in combination on the formation and growth of androgen-independent LNCaP tumors in castrated SCID mice. Male SCID mice were injected subcutaneously with androgen-dependent prostate cancer LNCaP cells. When the tumors reached a moderate size, the mice were surgically castrated and treated with atorvastatin (0.02% in the diet), celecoxib (0.05% in the diet) or RW alone or in combination for 42 days. RW or celecoxib alone had a moderate inhibitory effect on the androgen-independent growth of LNCaP tumors, but atorvastatin alone had little or no effect on tumor growth. Combinations of atorvastatin and celecoxib had a stronger inhibitory effect on the formation and growth of androgen-independent LNCaP tumors than either drug alone. A combination of RW together with atorvastatin and celecoxib had the most potent inhibitory effect on the progression of LNCaP tumors to androgen independent growth. The serum concentration of atorvastatin after two weeks of oral administration of atorvastatin was 6.1 ng/ml. The serum concentration of celecoxib after treatment with dietary celecoxib for two weeks was 1090 ng/ml. The serum concentration of atorvastatin but not that of celecoxib was substantially reduced when the two drugs were given in combination. The drug concentrations observed in our animal studies are comparable or less than those commonly found in humans treated with atorvastatin or celecoxib. Our results indicate that administration of atorvastatin and celecoxib together with voluntary exercise may be an effective strategy for the prevention of prostate cancer progression from androgen dependence to androgen independence.

Analysis of the volatile compounds in Senecio scandens Buch-Ham by gas chromatography-tandem mass spectrometry based on diversified scan technologies

Static headspace gas chromatography-tandem mass spectrometry was used to identify volatile compounds from Senecio scandens Buch-Ham. The elemental composition of compounds was confirmed by exploiting the tandem mass spectra of isotopic peaks from the precursor ion. Some isomers were well distinguished by the diversified scan technologies of tandem mass spectrometry (MS/MS). The MS/MS included a product ion scan, a precursor ion scan and a neutral loss scan. The results showed that 46 volatile compounds were completely identified, and the great of majority compounds were α-pinene (11.93%), n-caproaldehyde (9.02%) and dehydrosabinene (6.22%). This qualitative method is convenient and accurate and can be considered as a complementary identification method for the qualitative analysis of volatile compounds in complex samples.

A sensitive and specific precursor ion scanning approach in liquid chromatography/electrospray ionization tandem mass spectrometry to detect methylprednisolone acetate and its metabolites in rat urine

A new, simple, sensitive and specific liquid chromatography/electrospray ionization tandem mass spectrometric (LC/ESI-MS/MS) method in precursor ion scanning (PIS) mode has been developed for the rapid detection of methylprednisolone acetate (MPA) and its metabolites in rat urine. A suitable product ion specific for methylprednisolone (MP) and MPA was selected after a fragmentation study on 20 (cortico)steroids at different collision energies (5-40 eV). Urine samples were simply treated with acetonitrile then dried in a SpeedVac system. The method was validated and compared with other PIS methods for detecting corticosteroids in human urine. It was more sensitive, with limit of detection (LOD) and lower limit of quantitation (LLOQ), respectively, of 5 and 10 ng mL(-1). The method was applied for the analysis of rat urine collected before and after (24, 48, 72 h) intra-articular (IA) injection of a marketed formulation of MPA (Depo-Medrol(R)). MS/MS acquisitions were taken at different collision energies for the precursor ions of interest, detected in PIS mode, to verify the MP-related structure. Six different metabolites were detected in rat urine, and their chemical structures were assigned with a computational study.

Biotransformation of celecoxib using microbial cultures

Microbial transformation studies can be used as models to simulate mammalian drug metabolism. In the present investigation, biotransformation of celecoxib was studied in microbial cultures. Bacterial, fungal, and yeast cultures were employed in the present study to elucidate the metabolism of celecoxib. The results indicate that a number of microorganisms metabolized celecoxib to various levels to yield eight metabolites, which were identified by high-performance liquid chromatography diode array detection and liquid chromatography tandem mass spectrometry analyses. HPLC analysis of biotransformed products indicated that majority of the metabolites are more polar than the substrate celecoxib. The major metabolite was found to be hydroxymethyl metabolite of celecoxib, while the remaining metabolites were produced by carboxylation, methylation, acetylation, or combination of these reactions. The methyl hydroxylation and further conversion to carboxylic acid was known to occur in metabolism by mammals. The results further support the use of microorganisms for simulating mammalian metabolism of drugs.

Tissue distribution of puerarin and its conjugated metabolites in rats assessed by liquid chromatography-tandem mass spectrometry

Puerarin (an isoflavone C-glucoside from kudzu root) has been the focus of several studies investigating its potential effects on health benefits. In this study, we determined single dose tissue distribution of puerarin and its metabolites in order to examine whether they undergo selective uptake by specific organs. Puerarin was administered orally (50 mg/kg) to rats and the concentration of puerarin in tissue compartments was determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Puerarin was widely distributed in rat tissues with highest concentrations in lungs (799+/-411.6 ng/g wet tissues). In addition, we examined the excretion of puerarin into the bile. LC-MS/MS analysis of bile samples collected after infusing puerarin directly into the portal vein indicated that puerarin was excreted into the bile predominantly in the form of unconjugated puerarin. This report identifying puerarin in several organs including kidney and pancreas may explain its beneficial effects in diabetes.

A tandem MS precursor-ion scan approach to identify variable covalent modification of albumin Cys34: a new tool for studying vascular carbonylation

We developed a liquid chromatography electrospray ionisation multi-stage mass spectrometry (LC-ESI-MS/MS) approach based on precursor-ion scanning and evaluated it to characterize the covalent modifications of Cys34 human serum albumin (HSA) caused by oxidative stress and reactive carbonyl species (RCS) adduction. HSA was isolated and digested enzymatically to generate a suitable-length peptide (LQQCPF) containing the modified tag residue. The resulting LQQCPF peptides were identified by LC-ESI-MS/MS in precursor-ion scan mode and further characterized in product-ion scan mode. The product ions for precursor-ion scanning were selected by studying the MS/MS fragmentation of a series of LQQCPF derivatives containing Cys34 modified with different alpha,beta-unsaturated aldehydes and di and ketoaldehydes. We used a Boolean logic to enhance the specificity of the method: this reconstitutes a virtual current trace (vCT) showing the peaks in the three precursor-ion scans, marked by the same parent ion. The method was first evaluated to identify and characterize the Cys34 covalent adducts of HSA incubated with 4-hydroxy-hexenal, 4-hydroxy-trans-2-nonenal (HNE) and acrolein (ACR). Then we studied the Cys34 modification of human plasma incubated with mildly oxidized low-density lipoproteins (LDL), and the method easily identified the LQQCPF adducts with HNE and ACR. In other experiments, plasma was oxidized by 2,2'-azobis(2-amidinopropane) HCl (AAPH) or by Fe2+/H2O2. In both conditions, the sulfinic derivative of LQQCPF was identified and characterized, indicating that the method is suitable not only for studying RCS-modified albumin, but also to check the oxidative state of Cys34 as a marker of oxidative damage.

Repeated glucuronidation at one hydroxyl group leads to structurally novel diglucuronides of steroid sex hormones

Androgens (androsterone, dihydrotestosterone and testosterone) and estrogens (estradiol, estriol and estrone) were incubated with liver microsomes from rats, dogs, monkeys and humans in the presence of uridine diphosphoglucuronic acid (UDPGA), and the glucuronides produced were structurally characterized by liquid chromatography-tandem mass spectrometry. After 2-h incubation with dog liver microsomes, all substrates tested were converted (approximately 2-10%) to structurally novel diglucuronides, where two glucuronosyl groups are bound to a single hydroxyl group in tandem. Two-dimensional nuclear magnetic resonance spectroscopy unambiguously elucidated the chemical structures of the 3-O-diglucuronide of estrone and the 17-O-diglucuronide of testosterone isolated from the incubation mixture. Monkey and human liver microsomes were also found to have the activity to form this type of diglucuronide, albeit more slowly than the dog liver microsomes, but rat liver microsomes produced no detectable diglucuronides. The rate of formation of estrone 3-O-diglucuronide from the corresponding monoglucuronide in dog liver microsomes followed classical Michaelis-Menten kinetics at substrate concentrations from 50 to 1000 microM, with a K(m) value of 127.1 microM and a V(max) value of 47.0 pmol/min/mg protein.

Simultaneous determination of celecoxib, meloxicam, and rofecoxib using capillary electrophoresis with surfactant and application in drug formulations

A simple and selective CE using surfactant with UV detection is described for the simultaneous determination of selective cyclooxygenase-2 inhibitors, celecoxib, meloxicam, and rofecoxib. The simultaneous analysis of celecoxib, meloxicam, and rofecoxib was performed in Tris buffer (10 mM; pH 11) with 60 mM sodium octane-sulfonate and 20% ACN as an anionic surfactant and organic modifier, respectively. Under this condition, good separation with high efficiency and the required short analysis time is achieved. The linear ranges of the method for the determination of celecoxib, meloxicam, and rofecoxib were over 5-100 microg/mL; the detection limits at 200 nm (S/N = 3; injection 3.45 kPa, 5 s) were 2, 1, and 1 microg/mL, respectively. The small amount of sample required and the expeditiousness of the procedure allow content uniformity to be determined in individual pharmaceutical products.

An overview of the recent developments in analytical methodologies for determination of COX-2 inhibitors in bulk drugs, pharmaceuticals and biological matrices

An extensive survey of the literature published in various analytical and pharmaceutical chemistry related journals has been conducted and the instrumental analytical methods which were developed and used for determination of COX-2 inhibitors in bulk drugs, formulations and biological fluids have been reviewed. This review covers the time period from 1995 to 2004 during which 138 analytical methods including all types of spectrophotometric and chromatographic techniques were reported. HPLC with UV detection was found to be the technique of choice for many workers and more than 100 methods were based on LC and UV. A critical analysis of the reported data has been carried out and the present state-of-art of the analytical techniques for determination of celecoxib, rofecoxib, etoricoxib, etodolac, nimesulide and meloxicam has been discussed.

Disposition and pharmacokinetics of L-N6-(1-iminoethyl)lysine-5-tetrazole-amide, a selective iNOS inhibitor, in rats

The metabolism, pharmacokinetics, tissue distribution, and excretion of L-N6-(1-iminoethyl)lysine-5-tetrazole-amide (L-NIL-TA), a selective inducible NO synthase (iNOS) inhibitor, were investigated in rats. [(14)C]L-NIL-TA is extensively metabolized after either oral or IV administration with a minor amount (<1%) excreted as the prodrug. L-NIL-TA is metabolized via a single hydrolysis pathway to form the active drug, L-N6-(1-iminoethyl)lysine (L-NIL). The oxidative deamination of 2-amino group of L-NIL forms a 2-keto metabolite (M5), which further loses carbon dioxide to yield a carboxylic acid metabolite (M6). Acetylation of L-NIL and M5 resulted in the formations of metabolites M7 and M4, respectively. Complete recovery of the radioactive dose was achieved after either oral (91.2% in urine and 4.66% in feces) and IV (99.3% in urine and 5.11% in feces) administration. L-NIL-TA-related material was extensively distributed to the tissues, with the highest concentration of radioactivity being found in muscle. Maximal concentration of radioactivity was reached between 0.5 and 1 h post-dose in the majority of tissues, with the exception of muscle and skin where the maximal concentrations were achieved at 8 h post-dose.

Prediction of MS/MS data. 1. A focus on pharmaceuticals containing carboxylic acids

Metabolite identification is a necessary step in developing safe and effective drugs. Metabolite analysis typically involves rapid identification of the chemical composition of the metabolite by automated HPLC-MS methods, followed by the laborious process of identifying the structure of the metabolite. Since MS is typically utilized to identify the metabolite, it is logical to utilize MS/MS to structurally characterize the sample. However, interpretation of MS/MS data may not provide sufficient information, as fragmentation pathways are not well understood or predictable. Therefore, other more time-consuming methods of analysis are often undertaken. If the dissociation rules for low-energy MS/MS experiments were clearly defined for all classes of compounds, more information would be obtained from MS/MS data, and metabolite identification would proceed more rapidly. We are currently developing methods to define these fragmentation rules. By screening approximately 100 carboxylic acids at a time and applying knowledge of physical-organic chemistry, predictive rules are under development that describe how compounds dissociate under low-energy collision-induced dissociation conditions. Studies of carboxylic acid dissociation demonstrate that this approach is practical and reliable. Dissociation rules were predicted with a 90% success rate, when tested on acid-containing pharmaceuticals. This predictive power cannot be matched by any commercially available software. This study, and others like it, will be used to develop algorithms that more rapidly identify drug metabolites and degradation products, based on MS/MS data. Such algorithms will benefit drug development for all types of pharmaceuticals.

Pharmacokinetics, metabolism and excretion of an inhibitor of inducible nitric oxide synthase, L-NIL-TA, in dog

1. The pharmacokinetics, metabolism and excretion of L-NIL-TA, an inducible nitric oxide synthase inhibitor, were investigated in dog. 2. The dose of [14C]L-NIL-TA was rapidly absorbed and distributed after oral and intravenous administration (5 mg kg-1), with Cmax of radioactivity of 6.45-7.07 microg equivalents g-1 occurring at 0.33-0.39-h after dosing. After oral and intravenous administration, radioactivity levels in plasma then declined with a half-life of 63.1 and 80.6-h, respectively. 3. Seven days after oral and intravenous administrations, 46.4 and 51.5% of the radioactive dose were recovered in urine, 4.59 and 2.75% were recovered in faeces, and 22.4 and 22.4% were recovered in expired air, respectively. The large percentages of radioactive dose recovered in urine and expired air indicate that [14C]L-NIL-TA was well absorbed in dogs and the radioactive dose was cleared mainly through renal elimination. The mean total recovery of radioactivity over 7 days was approximately 80%. 4. Biotransformation of L-NIL-TA occurred primarily by hydrolysis of the 5-aminotetrazole group to form the active drug L-N6-(1-iminoethyl)lysine (NIL or M3), which was further oxidized to the 2-keto acid (M5), the 2-hydroxyl acid (M1), an unidentified metabolite (M2) and carbon dioxide. The major excreted products in urine were M1 and M2, representing 22.2 and 21.2% of the dose, respectively.

Isolation, synthesis and characterization of impurities in Celecoxib a cox-2 inhibitor

During the impurity profile of Celecoxib, four polar impurities (impurity I, II, III and IV) and one non-polar impurity (impurity V) with respect to Celecoxib were detected by HPLC. LC-MS has been employed in this impurity profile study. The three polar impurities (I, II and III) were found to be process related while impurities (IV and V) turned out to be isomers. The impurities III, IV and V were isolated with the help of preparative HPLC. The structure of impurities III, IV (ortho-isomer) and V (regio-isomer) were confirmed as [5-(4-methylphenyl)-3-trifluoromethyl-1H-pyrazole], 4-[5-(2'-methyl phenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl] benzenesulfonamide, and 4-[4-(4'-methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]-benzenesulfonamide, respectively. The structures of impurities I, II, III and IV were confirmed by synthesis and structural characterization using spectral data. However, the impurity V was not synthesized.

Identification of phenolic compounds in artichoke waste by high-performance liquid chromatography-tandem mass spectrometry

A new fast and efficient method combining liquid chromatography coupled to ionspray mass spectrometry in tandem mode with negative ion detection is described for the qualitative analysis of artichoke waste. Forty-five phenolic compounds were identified on the basis of their mass spectra in full scan mode, mass spectra in different MS-MS modes, and retention times compared with those of available reference substances. The major compounds were found to be both caffeoylquinic and dicaffeoylquinic acids, luteolin glucuronide, luteolin galactoside, quercetin, and some quercetin glycosides.

Analysis of albendazole metabolites by electrospray LC-MS/MS as a probe to elucidate electro-oxidation mechanism of albendazole

The electrochemical oxidation of albendazole was accomplished by controlled potential electrolysis technique. The oxidation was carried out in different pH solutions and yields the same products obtained by in vivo and in vitro metabolism, i.e. albendazole sulfoxide and albendazole sulfone. The identification of albendazole oxidation products was carried out by LC-MS/MS.

Pharmacokinetics and metabolism of a COX-2 inhibitor, valdecoxib, in mice

The pharmacokinetics and metabolism of valdecoxib, a potent cyclooxygenase-2 selective inhibitor, were investigated in mice. Valdecoxib was extensively metabolized after a single 5 mg/kg oral administration of [(14)C]valdecoxib and elimination of unchanged drug was minor (less than 1%) in male and female mice. The total mean percentage of administered radioactive dose recovered was 99.8% in the male mice and 94.7% in the female mice. Sixteen metabolites were identified in mouse plasma, red blood cells, urine, and feces. The main phase I metabolic pathway of valdecoxib in mice involved the oxidation of the 5-methyl group to form the active hydroxymethyl metabolite M1. M1 was further oxidized to the carboxylic acid metabolite M4, which underwent opening of the isoxazole ring to form M6 and M13. Phase II metabolism included glucuronide, glucoside, and methyl sulfone conjugations. M1 was also conjugated with glucuronic acid and glucose to yield M-G and M1-glucose, respectively. Three novel methylsulfone conjugates M20, M21, and M21-G were detected in blood or urine. Valdecoxib and M1 were the major radioactive components in plasma and red blood cells. The plasma area under the curve from zero to infinity (AUC(0-infinity)) values for valdecoxib and M1 were 3.58 and 0.850 microg. h/ml in males and 2.08 and 1.63 microg. h/ml in females, respectively. The RBC AUC(0-infinity) values for valdecoxib and M1 were 12.1 and 22.6 microg. h/g in males and 6.42 and 35.2 microg. h/g in females, respectively.

Quantification of nimesulide in human plasma by high-performance liquid chromatography/tandem mass spectrometry. Application to bioequivalence studies

A method based on liquid chromatography with negative ion electrospray ionization and tandem mass spectrometry is described for the determination of nimesulide in human plasma. Liquid-liquid extraction using a mixture of diethyl ether and dichloromethane was employed and celecoxib was used as an internal standard. The chromatographic run time was 4.5 min and the weighted (1/x) calibration curve was linear in the range 10.0-2000 ng x ml(-1). The limit of quantification was 10 ng x ml(-1), the intra-batch precision was 6.3, 2.1 and 2.1% and the intra-batch accuracy was 3.2, 0.3 and 0.1% for 30, 300 and 1200 ng x ml(-1) respectively. The inter-batch precision was 2.3, 2.8 and 2.7% and the accuracy was 3.3, 0.3 and 0.1% for 30, 300 and 1200 ng x ml(-1) respectively. This method was employed in a bioequivalence study of one nimesulide drop formulation (nimesulide 50 mg x ml(-1) drop, Medley S/A Indústria Farmacêutica, Brazil) against one standard nimesulide drop formulation (Nisulid, 50 mg x ml(-1) drop, Astra Médica, Brazil). Twenty-four healthy volunteers (both sexes) took part in the study and received a single oral dose of nimesulide (100 mg, equivalent to 2 ml of either formulation) in an open, randomized, two-period crossover way, with a 2-week washout interval between periods. The 90% confidence interval (CI) for geometric mean ratios between nimesulide and Nisulid were 93.1-109.6% for C(max), 87.7-99.8% for AUC(last) and 88.1-99.7% for AUC(0-infinity). Since the 90% CI for the above-mentioned parameters were included in the 80-125% interval proposed by the US Food and Drug Administration, the two formulations were considered bioequivalent in terms of both rate and extent of absorption.