Biomedical subjects

Stefan Udrescu

Publications and source records attributed to Stefan Udrescu.

3 recordsLinked to original sources

PubMed2007

High-throughput liquid-chromatography method with fluorescence detection for reciprocal determination of furosemide or norfloxacin in human plasma.

A simple, high-throughput, highly selective and sensitive HPLC-FLD method for isolation and determination of furosemide and/or norfloxacin in human plasma samples following a simple organic solvent deproteinization step with acetonitrile as sample 'clean-up' procedure is reported. One of the two drug substances plays the internal standard role for the determination of the other. Separation of analyte and internal standard was achieved in less than 5.3 min (injection to injection) on a Chromolith Performance RP-18e column, using an aqueous component containing 0.015 mol/L sodium heptane-sulfonate and 0.2% triethylamine brought to pH = 2.5 with H(3)PO(4). The composition of the mobile phase was: acetonitrile-methanol-aqueous component = 70:15:15 (v/v/v) and the flow-rate was set up to 3 mL/min. The chromatographic method applied to the determination of furosemide relies on fluorescent detection parameters of 235 nm for the excitation wavelength, and 402 nm for the emission wavelength. In case of norfloxacin, the excitation wavelength is set up to 268 nm and the emission wavelength is set up to 445 nm. The overall method leads to quantitation limits of about 27 ng/mL for furosemide, and 19.5 ng/mL for norfloxacin, using an injection volume of 250 microL. The method was applied to the bioequivalence study of two furosemide-containing formulations.

Chromatography, High Pressure Liquid↗

PubMed2006

Achiral-chiral LC/LC-FLD coupling for determination of carvedilol in plasma samples for bioequivalence purposes.

Bioequivalence data for two pharmaceutical formulations (solid oral dosage forms) containing carvedilol is presented for both racemic and enantiomers of the active substance. This was achieved by on-line coupling of two liquid chromatographic separations followed by fluorescence detection. The first LC dimension was used for a fast separation of racemic carvedilol from propranolol (IS) and the endogenous matrix, by means of a reversed phase mechanism. The peak of racemic carvedilol was on-line transferred to the second enantioselective LC dimension, based on a reversed phase separation on cellulose tris(3,5-dimethyl-phenylcarbamate) stationary phase. Both stages were monitored over a single run by means of a fluorescence detector operated at an excitation wavelength of 285 nm and an emission wavelength of 355 nm. Automated shortcutting of the racemic carvedilol peak to the chiral column and simultaneous detection over the two LC dimensions have been obtained by using an experimental set-up based on two six-port rotative switching valves. Linearity was demonstrated on the interval 2-150 ng/mL for racemic carvedilol and on 1-75 ng/mL intervals for enantiomers. LLOQ fits between 0.7 and 1.4 ng/mL. Recoveries of the target compounds are 87+/-4 and 81+/-4% for the IS. Precision ranged from 0.6 to 2.5% and the mean accuracy obtained on quality control samples (measured as % bias) over the whole study falls between -0.8 and 6.3%.

Adolescent↗

PubMed2006

Fast RPLC-UV method on short sub-two microns particles packed column for the assay of tenoxicam in plasma samples.

An extraction-less sample preparation technique followed by a RPLC-UV method on sub-two microns particles packed short column were used for the assay of tenoxicam in plasma samples. Protein precipitation was made by means of trichloroacetic acid addition. Supernatant was injected to the chromatographic column without any further pH adjustment. The mobile phase consisted in a mixture of acetonitrile and aqueous 0.1% phosphoric acid, at 2 mL/min flow rate and gradient elution. The Zorbax SB-C18 column (50 mm length, 4.6 mm internal diameter and 1.8 microm particle size) was thermostated at 60 degrees C. The mobile phase gradient composition program allowed separation of tenoxicam and piroxicam (internal standard), column clean-up and re-equilibration within 4 min. UV detection was achieved at 368+/-10 nm. The method is characterized by a low limit of quantitation of 25 ng/mL for tenoxicam, with a linearity interval up to 5500 ng/mL. The use of a low volume detection cell and detector high frequency data acquisition rate produced high precision and accuracy through a whole bioequivalence study of tenoxicam in two commercially available tablet formulations, after a single oral administration dose. Full method validation is presented. The high throughput characteristic of the proposed method allowed full validation and bioanalytical study completion within a 96 h period.

Anti-Inflammatory Agents, Non-Steroidal↗