Search PubMed⌕ Search

Biomedical subjects

H Fabre

Publications and source records attributed to H Fabre.

At least 37 records · Page 2Linked to original sources
PubMed1985

Overlapping ionization constants for cefotaxime.

The attribution of three ionization constants (2.1, 3.4, and 10.9) for cefotaxime has been made, based on potentiometric titration and UV absorption data simultaneously. Two overlapping constants were found (2.1 and 3.4) and attributed to the carboxyl group in the 4 position and to the aminothiazole nucleus, respectively.

Cefotaxime↗
PubMed1984

Degradation kinetics in aqueous solution of cefotaxime sodium, a third-generation cephalosporin.

The degradation kinetics of a 3- acetoxymethylcephalosporin , cefotaxime sodium salt, in aqueous solution investigated by HPLC under different conditions (pH, ionic strength, temperature) and using different buffers. The scheme of degradation involves a cleavage of the beta-lactam nucleus and the deacetylation of the side chain. In highly acidic medium, the deacetylated derivative is easily converted to the lactone. The degradation rate constants were calculated at three pH values (1.9, 4.0, and 9.0) by measuring the residual cephalosporin and the main decomposition products. The degradation pathway is both supported by the results of a primary salt effect and by the agreement between the theoretical pH-rate profile and the experimental values. In the pH range from 3.0 to 7.0, the main process is a slow water-catalyzed or spontaneous cleavage of the beta-lactam nucleus with intramolecular participation of the side chain amido fraction in the 7-position. In alkaline or strongly acidic medium, the hydrolysis is a base- or acid-catalyzed reaction. Of the buffer systems investigated, carbonate buffer (pH 8.5) and borate buffers (pH 9.5 and 10.0) are found to increase the degradation rates, while acetate buffer decreases the degradation rates. The apparent activation energies determined at different pH values are compatible with a solvolysis mechanism and similar to those previously given in the literature for other cephalosporins. Cefotaxime in aqueous solution is slightly less stable than the main cephalosporin derivatives, despite its high resistance to the beta-lactamases and its remarkable biological activity.

Buffers↗
PubMed1984

Stability-indicating assay for phenylbutazone: high-performance liquid chromatographic determination of hydrazobenzene and azobenzene in degraded aqueous phenylbutazone solutions.

A high-performance liquid chromatographic method was developed for the simultaneous determination of azobenzene, hydrazobenzene, and four other decomposition products in phenylbutazone injectable formulations. Separation was achieved on a C18 column, with 0.1 M Tris-citrate buffer (pH 5.25) and acetonitrile (52:48), at a flow rate of 2 mL/min and a detection wavelength of 237 nm. Diphenylamine was used as an internal standard. The limit of quantitation is 0.5% (with respect to phenylbutazone) of each degraded product. The detectability is 2.4 X 10(-3) micrograms for azobenzene and 1.5 X 10(-3) micrograms for hydrazobenzene. The limit of quantitation may be lowered to 0.1% (with respect to phenylbutazone) for azobenzene and hydrazobenzene in the presence of the two major decomposition products, which have been determined in commercially available injectable formulations. A higher sensitivity was obtained for azobenzene using the mobile phase 0.1 M Tris-citrate buffer (pH = 5.25) and acetonitrile (40:60) with detection at 314 nm. Under these conditions, 0.025% (with respect to phenylbutazone) of azobenzene is quantitated.

Azo Compounds↗
PubMed1984

Autoxidation and hydrolysis kinetics of the sodium salt of phenylbutazone in aqueous solution.

The present investigation offers experimental results concerning the degradation kinetics of the sodium salt of phenylbutazone based on a reliable HPLC procedure. The method allows the simultaneous determination of the parent compound and its main decomposition products. The degradation kinetics at 37 degrees C were compared at pH 7.9 and 10.0 and under oxygen and nitrogen atmospheres. Parallel tests were carried out in the dark and under photolytic conditions for the aforementioned conditions. The influence of traces of iron and a chelating agent of iron on the degradation was studied. At pH 7.9 and pH 10.0 the main degradation products are 3-hydroxy-2-oxohexanoic acid 1,2-diphenylhydrazide and 3-carboxy-2-oxohexanoic acid 1,2-diphenylhydrazide. Azobenzene is formed only at pH 10.0. At pH 7.9, in the dark, the degradation proceeds with a lag phase. In contrast, no lag phase is observed under photolytic conditions. The process of autoxidation and hydrolysis is catalyzed by traces of iron both in the dark and under irradiation conditions. An unexpected increase in the degradation is observed in the presence of iron(III) and EDTA in aerobic conditions and under irradiation.

Anaerobiosis↗
PubMed1982

Quality control of phenylbutazone II: Analysis of phenylbutazone and its decomposition products in drugs by high-pressure liquid chromatography.

A rapid, sensitive, accurate, and reproducible procedure for the simultaneous separation and determination of phenylbutazone and three major degradation products is proposed using reversed-phase high-pressure liquid chromatography and UV detection. The method is approximately 20 times more sensitive than TLC and allows an accurate determination of degradation products without decomposition during the analysis.

Chromatography, High Pressure Liquid↗
PubMed1982

A stability-indicating assay for cefotaxime utilizing thin-layer chromatography with fluorescence detection.

A t.l.c. method on silicagel plate with a fluorescence indicator has been carried out to increase the native fluorescence of cefotaxime and four of its degradation products. A simultaneous improved fluorimetric quantitation of the compounds in situ is proposed using a chromatogram spectrophotometer. The detectability (0.20 microgram) shows that the procedure is twenty times more sensitive than high-pressure liquid chromatography with u.v. detection; it allows the determination of traces level (1%) degradation products.

Cefotaxime↗
PubMed1981

Quality control of phenylbutazone I: Analysis of phenylbutazone and decomposition products in drugs by TLC.

A modified TLC procedure for the analysis of phenylbutazone and its degradates on silica plates is reported. This method avoids phenylbutazone degradation in situ by chelating the iron of the silica plate, which allows rapid characterization with a fluorescence indicator. A selective and sensitive assay of phenylbutazone (0.025 microgram), using a chromatographic spectrophotometer, was performed on silica plates without a fluorescence indicator. Quantitative analysis of an injectable solution is outlined.

Chromatography, Thin Layer↗
PubMedDate not supplied

Individual degradation rate constants for cefotaxime, deacetylation profile.

The individual degradation rate constants for cefotaxime in aqueous solution were calculated within a pH range of 1.6-10.0 at 37 degrees C from high performance liquid chromatography data. This allowed the general degradation profile of cefotaxime to be decomposed into a degradation profile attributed to the opening of the beta-lactam nucleus and a degradation profile attributed to the deacetylation. From the calculations of the individual rate constants, the activity of degraded cefotaxime solutions could be predicted. In the pH range of injectable solutions of cefotaxime 5-7, roughly equivalent amounts of inactive beta-lactam cleavage products and deacetylated compound which has a different spectrum of antibacterial activity are formed.

Anti-Bacterial Agents↗