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Bucharest, Romania

Silvestro L.,3S Pharmacological Consultation and Research GmbH | Gheorghe M.,Pharma Serv Intl SRL | Gheorghe M.,University of Bucharest | Iordachescu A.,Pharma Serv Intl SRL | And 4 more authors.
Analytical and Bioanalytical Chemistry | Year: 2011

A new sensitive and fast quantitative analytical method for the simultaneous determination of clopidogrel, its main metabolite clopidogrel carboxylic acid, and the newly described acyl glucuronide metabolite, in human plasma samples, is presented. The analytical procedures (plasma storage, handling, and extract storage in the autosampler) were optimized in order to avoid back-conversion; a known drawback in measurements of clopidogrel. Clopidogrel acyl glucuronide was confirmed as a major source of back-conversion to the parent drug in the presence of methanol, and thorough stability experiments were carried out to find the most appropriate conditions for an accurate analysis of clopidogrel and the two metabolites. The method was validated by assessing selectivity, sensitivity, linearity, accuracy, and precision for all three analytes, in accordance to Food and Drug Administration guidelines. Spiked quality controls in plasma as well as incurred samples were used to verify back-conversion in the selected conditions, with results meeting European Medicines Agency acceptance criteria (concentrations within 80-120% of the first reading). The method was then applied to a pharmacokinetic study, and for the first time, a pharmacokinetic curve of clopidogrel acyl glucuronide in human plasma is presented. The concentrations ranged up to 1,048.684 ng/mL, with a mean of 470.268 ng/mL, while clopidogrel had a mean C max of 1.348 ng/mL; these orders of magnitude show how much the back-conversion of this metabolite may influence clopidogrel quantification if it is not properly controlled. © 2011 Springer-Verlag. Source


Iordachescu A.,Pharma Serv Intl SRL | Iordachescu A.,University of Bucharest | Silvestro L.,3S Pharmacological Consultation and Research GmbH | Tudoroniu A.,Pharma Serv Intl SRL | And 2 more authors.
Chromatographia | Year: 2012

This paper presents a new analytical method with adequate sensitivity, precision, accuracy, and specificity to quantitatively determine (-)-donepezil and (+)-donepezil in plasma, at concentrations that can be expected in real samples of pharmacokinetic studies. This method combines a HPLC separation on cellulose tris (3,5-dimethylphenyl carbamate) coated on 5-lm silica-gel column known as CHIRALCEL OD-RH eluted with mobile phase consisting of acetonitrile and ammonium bicarbonate and MS-MS detection. Under the HPLC conditions used (-)-donepezil and (+)-donepezil, as well as the enantiomers of the internal standard d 7-donepezil, eluted at 5 and 6.25 min, respectively. The curve fittings were optimal for the entire calibration range (0.05-25.0 ng mL -1) with correlation coefficients (r) = 0.999 for (-)-donepezil and (r) = 0.999 for (+)-donepezil (linear regression model with 1/x 2 weighing). The assay method showed a good specificity for donepezil enantiomers, and it could be successfully applied to pharmacokinetic studies. © Springer-Verlag 2012. Source


Silvestro L.,3S Pharmacological Consultation and Research GmbH | Savu S.R.,3S Pharmacological Consultation and Research GmbH | Savu S.N.,Pharma Serv Intl SRL | Tudoroniu A.,Pharma Serv Intl SRL | Tarcomnicu I.,Pharma Serv Intl SRL
Biomedical Chromatography | Year: 2012

A new method for the fast simultaneous quantification of fluticasone propionate and salmeterol from plasma samples by liquid chromatography-tandem mass spectrometry, with adequate sensitivity for pharmacokinetic applications, was developed and validated. The chromatographic separation and mass-spectrometric parameters were optimized for the retention and detection of the two compounds, despite quite different structures and properties. Two columns connected in series were used, cation-exchange (Zorbax 300-SCX, 5cm×2.1mm, 5μm) and octadecyl (Discovery HSC 18, 10cm×2.1mm, 5μm). The mass-spectrometric interface was operated in negative electrospray ionization mode; high sensitivity and lesser matrix effects were obtained, permitting smaller consumption of plasma. The sample preparation was based on supported liquid-liquid extraction in 96-well format plates that provided clean samples with a simplified procedure that was suitable for automation. The method was validated according to regulatory guidelines, by assessing lower limits of quantification, selectivity, linearity, accuracy, precision, extraction recoveries and matrix effects. A comparison with two other methods for the separate determination of fluticasone propionate and salmeterol in plasma samples, previously developed by our group, is presented. The statistical evaluation of the results obtained with the three methods on a set of unknown samples from treated patients demonstrated good correlation (R 2 0.987 for fluticasone propionate and 0.967 for salmeterol). © 2011 John Wiley & Sons, Ltd. Source


Silvestro L.,3S Pharmacological Consultation and Research GmbH | Tarcomnicu I.,Pharma Serv Intl SRL | Dulea C.,Pharma Serv Intl SRL | Attili N.R.B.N.,Pharma Serv Intl SRL | And 3 more authors.
Analytical and Bioanalytical Chemistry | Year: 2013

Diosmin is a flavonoid often administered in the treatment of chronic venous insufficiency, hemorrhoids, and related affections. Diosmin is rapidly hydrolized in the intestine to its aglicone, diosmetin, which is further metabolized to conjugates. In this study, the development and validations of three new methods for the determination of diosmetin, free and after enzymatic deconjugation, and of its potential glucuronide metabolites, diosmetin-3-O-glucuronide, diosmetin-7-O-glucuronide, and diosmetin-3,7-O- glucuronide from human plasma and urine are presented. First, the quantification of diosmetin, free and after deconjugation, was carried out by high-performance liquid chromatography coupled with tandem mass spectrometry, on an Ascentis RP-Amide column (150 × 2.1 mm, 5 μm), in reversed-phase conditions, after enzymatic digestion. Then glucuronide metabolites from plasma were separated by micro-liquid chromatography coupled with tandem mass spectrometry on a HALO C18 (50 × 0.3 mm, 2.7 μm, 90 Å) column, after solid-phase extraction. Finally, glucuronides from urine were measured using a Discovery HSF5 (100 × 2.1 mm, 5 μm) column, after simple dilution with mobile phase. The methods were validated by assessing linearity, accuracy, precision, low limit of quantification, selectivity, extraction recovery, stability, and matrix effects; results in agreement with regulatory (Food and Drug Administration and European Medicines Agency) guidelines acceptance criteria were obtained in all cases. The methods were applied to a pharmacokinetic study with diosmin (450 mg orally administered tablets). The mean C max of diosmetin in plasma was 6,049.3 ± 5,548.6 pg/mL. A very good correlation between measured diosmetin and glucuronide metabolites concentrations was obtained. Diosmetin-3-O-glucuronide was identified as a major circulating metabolite of diosmetin in plasma and in urine, and this finding was confirmed by supplementary experiments with differential ion-mobility mass spectrometry. © 2013 The Author(s). Source


Lupsor S.,Ovidius University | Tarcomnicu I.,Pharma Serv Intl SRL | Aonofriesei F.,Ovidius University | Iovu M.,Carol Davila University of Medicine and Pharmacy
Revista de Chimie | Year: 2011

In order to study their antimicrobial activity, series of 1-hydroxymethylazoles were synthesised by condensation reaction ofazoles (pyrazole, imidazole, 3, 5-dimethylpyrazole, 2-methylimidazole and benzimidazole) with paraformaldehyde. The reactions were carried out under microwave irradiation conditions using tetrahydrofurane (THF) or dimethyl sulfoxide (DMSO) as solvents. Obtaining hemiaminals ofazoles using the microwaves assisted procedure has noticeable advantages compared to classical methods: yield increase, substantial reduction of reaction time, solvents consumption and waste minimization. All obtained hemiaminals were characterized by melting points, absorption spectra (FT-IR, 1H-NMR and mass spectra (MS) while the purity was established by HPLC. Source

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