Biomedical subjects

E Roets

Publications and source records attributed to E Roets.

At least 55 records · Page 3Linked to original sources

PubMed1998

Analysis of amikacin by liquid chromatography with pulsed electrochemical detection.

The analysis of amikacin by liquid chromatography using a column packed with poly(styrene-divinylbenzene) and pulsed electrochemical detection on a gold electrode is described. A two-step gradient was necessary to obtain a good separation together with a reasonable analysis time of 60 min. The mobile phases consisted of an aqueous solution of 1 g/l or 60 g/l sodium sulfate, 1.8 g/l sodium octanesulfonate and 50 ml/l 0.2 M phosphate buffer, pH 3.0. Sodium hydroxide was added postcolumn. The influence of the different chromatographic parameters on the separation was investigated. When a number of commercial samples of amikacin was analyzed using this method, ten different components were separated.

Amikacin↗

PubMed1998

Determination of netilmicin sulfate by liquid chromatography with pulsed electrochemical detection.

The determination of netilmicin sulfate by liquid chromatography using a column packed with poly (styrene-di-vinylbenzene) and pulsed electrochemical detection on a gold electrode is described. The mobile phase consisted of an aqueous solution containing 35 g 1-1 of sodium sulfate, 0.5 g 1-1 of sodium octanesulfonate, 10 ml 1-1 of tetrahydrofuran and 50 ml 1-1 of 0.2 M phosphate buffer (pH 3.0). The total analysis time was not more than 25 min. The effects of the different chromatographic parameters on this selection were also investigated. When a number of commercial samples of netilmicin sulfate was analyzed using this method, eight different components were separated, three of which were of unknown identities.

Chromatography, Liquid↗

PubMed1998

Interlaboratory study of the analysis of benzylpenicillin by liquid chromatography.

A liquid chromatography method for analysis of benzylpenicillin was examined in a collaborative study involving seven laboratories. The method comprised an isocratic part, which is used in the assay. The isocratic part corresponds to the assay method for benzylpenicillin used by a manufacturer. When the isocratic part is combined with gradient elution, the method is suitable for purity control. Five samples of benzylpenicillin (sodium and potassium salts) were analysed. The main component and the impurities were determined. An analysis of variance proved the absence of consistent laboratory bias. The laboratory-sample interaction was not significant. Estimates for the repeatability and reproducibility of the method, expressed as standard deviations (S.D.) of the result of the determination of benzylpenicillin, were calculated to be 0.71 and 0.80, respectively.

Analysis of Variance↗

PubMed1998

Analysis of cefadroxil by micellar electrokinetic capillary chromatography: development and validation.

A method is developed and validated for analysis of the antibiotic cefadroxil using micellar electrokinetic capillary chromatography. It permits cefadroxil to be completely separated from ten of its known related substances within 15 min (including the washing procedure). The separation is performed in an acetate buffer (50 mM, pH 5.25) containing sodium dodecyl sulfate (SDS; 110 mM). The fused-silica capillary was 44 cm long (36 cm effective length), 50 microm ID; the voltage, 18 kV; temperature, 15 degrees C; and the detection wavelength; 254 nm. The influence of the type of buffer, buffer pH and concentration, and of the SDS concentration was investigated. The robustness of the method was examined by means of a full-fraction factorial design. The parameters for validation such as linearity, precision, limit of detection and limit of quantitation are also reported.

Cefadroxil↗

PubMed1998

Study of the stability of erythromycin in a hydrophilic creme basis by liquid chromatography.

The stability of the macrolide antibiotic erythromycin, incorporated at a 2% m/m concentration in a hydrophilic creme basis containing 2% m/m of chlorocresol, was monitored over a period of 2 months using liquid chromatography as the analytical method. Extracts of the creme were analysed using wide-pore poly(styrene-divinylbenzene) PLRP-S 1000 A as the stationary phase and a mixture of 2-methyl-2-propanol-acetonitrile-potassium phosphate buffer (pH 11.0; 0.02 M)-water (165:30:50:755, v/v/v/v) as the mobile phase. The method showed good selectivity towards chlorocresol, erythromycin A, its related substances and degradation products. As the pH of the creme containing erythromycin was 8.6, alkaline degradation products were expected to be formed. The presence of pseudoerythromycin A enol ether was observed after storage of the creme for 1 week at a temperature of 25 degrees C. After 1 month the content of erythromycin was still more than 95%.

Anti-Bacterial Agents↗

PubMed1998

Neomycin: microbiological assay or liquid chromatography?

In a multicentre study involving six laboratories, a microbiological assay was performed on three neomycin samples containing respectively, 0.12, 2.1 and 11% (m/m) of neomycin C, as well on a pure neomycin C sample. The potency was determined according to the European Pharmacopoeia method but using a neomycin B base standard. The relative standard deviations between laboratories (RSD) on the potencies varied from 4.8 to 50%, depending on the sample examined. The RSD increased with the neomycin C content of the samples and the highest RSD values were observed for the pure neomycin C sample. The activity of neomycin C relative to neomycin B was found to be 62% by diffusion (RSD:41%) and 56% by turbidimetry (RSD: 50%). This confirmed that the presence of neomycin C in a neomycin sample influences the reproducibility of the microbiological assay. T estimate the influence of this effect on official standard, their composition was verified by liquid chromatography. The neomycin C base content of the standards varied between 0.4 and 5.8% (m/m). Based on the results obtained and on formerly published reports discussing problems encountered with microbiological assay of neomycin, it is proposed to introduce liquid chromatography in official monographs to replace microbiological assay.

Anti-Bacterial Agents↗

PubMed1998

Analysis of gentamicin by liquid chromatography with pulsed electrochemical detection.

The analysis of gentamicin by liquid chromatography using a column packed with poly(styrene-divinylbenzene) and pulsed electrochemical detection on a gold electrode is described. The mobile phase consists of an aqueous solution containing sodium sulfate, tetrahydrofuran, sodium 1-octanesulfonate and a phosphate buffer of pH 3.0. In contradistinction to methods previously published, this method not only allows a better separation of gentamicins C1, C1a, C2, C2a and C2b, but also the separation of several other, minor components, most of which were not identified. The effects of the different chromatographic parameters on the separation were also investigated. A number of commercial samples was analysed using this method, allowing sensitive detection of gentamicin without derivatization, and the results were compared with the results obtained with the European Pharmacopoeia method, prescribing pre-column derivatization.

Carbohydrate Sequence↗

PubMed1998

Evaluation of LC methods for the separation of phenoxymethylpenicillin and its related substances.

Five isocratic reversed-phase liquid chromatography (LC) methods have been examined for the separation of phenoxymethylpenicillin and its related substances. A method previously selected for the analysis of benzylpenicillin gave the best selectivity. The mobile phase of this method is composed of 0.5 M phosphate buffer (pH 3.5)-water-methanol (10:50:40), the amount of organic modifier was slightly adapted when it was used with different columns. Similar selectivity is obtained not only on different C18 materials but also on C8 packings. The selectivity on poly(styrenedivinylbenzene) is less good. As method performance test a resolution test with benzylpenicillin was used. The robustness of this method was examined by applying a full factorial design to test the influence of the content of organic modifier in the mobile phase, the pH of the mobile phase, the concentration of buffer in the mobile phase and the temperature of the column. The results show that the method is robust.

Chemistry Techniques, Analytical↗

PubMed1998

In vitro expression of adhesion receptors and diapedesis by polymorphonuclear neutrophils during experimentally induced Streptococcus uberis mastitis.

The expression of adhesion receptors and diapedesis by polymorphonuclear neutrophils (PMN) were studied before and during experimentally induced Streptococcus uberis mastitis. Both quarters of the left half of the udders of five midlactation cows were inoculated with a suspension containing approximately 500 CFU of S. uberis 0140J. Clinical signs of an inflammatory reaction and leukocyte influx were observed 24 h after challenge. The expression of CD11b/CD18 adhesion receptors, determined by flow cytometry, was upregulated 24 h after challenge. A confluent monolayer of bovine secretory mammary epithelial cells on collagen-coated inserts was used to study PMN diapedesis. Bovine C5a was used as the chemoattractant. An 80% decrease in PMN diapedesis was observed 24 h after challenge. The decrease in diapedesis continued for 3 weeks after challenge.

Animals↗

PubMed1998

Reduction of acyloxyacyl hydrolase activity in circulating neutrophils from cows after parturition.

Bovine neutrophils contain the enzyme acyloxyacyl hydrolase, which hydrolyzes the acyloxyacyl linkage of the two nonhydroxylated fatty acyl chains to two 3-hydroxy fatty acids in the highly conserved lipid A part of endotoxins with high specificity. This hydrolysis decreases the toxicity of lipid A, but the immunostimulatory capacity of endotoxins is largely maintained. In two trials, we studied the activity of acyloxyacyl hydrolase in neutrophils that had been isolated from the blood of 18 dairy cows around parturition. Between 10 and 26 d after parturition, the activity of acyloxyacyl hydrolase in neutrophils decreased approximately 20% below prepartum activity. At about 2 mo after parturition, acyloxyacyl hydrolase activity returned to prepartum values. Changes in acyloxyacyl hydrolase activity could not be attributed to changes in binding of lipopolysaccharides by the CD14 molecules on neutrophils or monocytes. We hypothesize that decreased acyloxyacyl hydrolase activity in neutrophils shortly after parturition is a factor that increases the susceptibility of dairy cows to coliform mastitis during early lactation.

Animals↗

PubMed1997

Increased surface expression of CD11b receptors on polymorphonuclear leukocytes is not sufficient to sustain phagocytosis during Escherichia coli mastitis in early postpartum dairy cows.

Phagocytosis, CD11a and CD11b adhesion receptor expression, O2-production and maturity of circulating polymorphonuclear leukocytes (PMN) were studied during acute coliform mastitis in early postpartum dairy cows to obtain a better insight in the role of neutrophils in the pathology of this disease. The mammary gland of twelve newly calved high-yielding dairy cows was experimentally infected with Escherichia coli. Variability in clinical signs of mastitis and inhibition of milk production among cows was very high. There was a significant negative correlation between the number of circulating neutrophils immediately before infection and severity of mastitis represented by the decrease in milk production of non-infected quarters two days after infection. Pre-infection phagocytosis of E. coli, CD11a and CD11b receptor expression, phorbol myristate acetate (PMA)-induced O2-production and maturity of neutrophils on a per cell basis were not related to severity of mastitis. However, significant correlations between severity of mastitis and the total number of phagocytic PMN and mature PMN in blood immediately before infection were found. PMN characteristics responded differently to mastitis depending on the severity of the disease. Neutrophil functions from cows classified as severe (S) and moderate (M) responders to infection of the mammary gland were compared. Surface expression of CD11a receptors on PMN was decreased in all cows 24 h after infection, and this decrease was long-continued in S responders. A biphasic upregulation of the number of CD11b receptors on PMN was observed with a more pronounced response in S cows. PMN phagocytosis was decreased 12 h after infection in S cows and 18 h after infection in S and M cows and was normalized 24 h post-infection. The decrease of phagocytosis coincided with the first peak of CD11b receptor expression. Phorbol myristate acetate (PMA)-induced production of O2-by PMN was decreased for three days after infection in S responders compared to only one day in M responders and was followed by an upregulation. These data demonstrate a complexity in alterations of PMN functions during mastitis and suggest the involvement of differences in systemic factors dependent on severity of mastitis.

Animals↗

PubMed1997

Analysis of kanamycin sulfate by liquid chromatography with pulsed electrochemical detection.

The analysis of kanamycin sulfate by liquid chromatography using a column packed with poly(styrene-divinylbenzene) and pulsed electrochemical detection on a gold electrode is described. A two-step gradient was necessary to obtain a good separation together with a reasonable analysis time of maximum 45 min. The mobile phases consisted of an aqueous solution of 20 g/l or 60 g/l sodium sulfate, 1.3 g/l sodium octanesulfonate and 50 ml/l 0.2 M phosphate buffer pH 3.0. Sodium hydroxide was added post-column. The influence of the different chromatographic parameters on the separation was investigated. A number of commercial samples were analyzed using this method. Besides the previously reported impurities, such as kanamycins B and C, two other impurities were separated, one of which is called kanamycin D. In total, eight components were separated.

Chromatography, Liquid↗

PubMed1997

Liquid chromatographic analysis of a formulation containing polymyxin, gramicidin and neomycin.

The development of a liquid chromatographic essay system for the stability study of a formulation containing polymyxin, gramicidin and neomycin is described. For the determination of each group of antibiotics, poly(styrenedivinylbenzene) is used as the stationary phase. The mobile phase for the determination of polymyxin consists of an aqueous solution containing 7 g l-1 of sodium sulfate, 50 ml l-1 of 1 M phosphoric acid and 160 ml l-1 of acetonitrile. UV detection is performed at 215 nm. An aqueous solution containing 70 g l-1 of sodium sulfate, 1.4 g l-1 of sodium octanesulfonate and 50 ml l-1 of 0.2 M phosphate buffer pH 3.0 is used as the mobile phase for the determination of neomycin. Since neomycin has no UV-absorbing chromophore, pulsed electrochemical detection is chosen to determine neomycin. For each method, the influence of the different chromatographic parameters on the separation, the selectivity towards the other active compounds and the excipients, the repeatability and the linearity were investigated. The stability of the formulation was examined at 0, 6 and 12 months.

Anti-Bacterial Agents↗

PubMed1997

Optimized methods for capillary electrophoresis of tetracyclines.

Optimized methods for the analysis of some tetracyclines by capillary electrophoresis are described. Different buffer systems were employed for the separation of tetracycline, oxytetracycline and demeclocycline from their respective major impurities, including the 2-acetyl-2-decarboxamido derivatives. The influence of buffer pH and buffer concentration was systematically investigated. Non-ionic surfactant Triton X-100 and methyl-beta-cyclodextrin were used to obtain improved selectivity in the case of oxytetracycline and demeclocycline. The results are compared with those of previously established liquid chromatography methods. Good correlations were obtained.

Buffers↗

PubMed1997

Bioavailability of different artemisinin tablet formulations in rabbit plasma--correlation with results obtained by an in vitro dissolution method.

The demonstration of a good overall correlation with in vivo data is the ultimate proof of qualification for any dissolution-rate test. For artemisinin, a very hydrophobic compound at a high content in oral solid dosage forms, all official dissolution apparatus were estimated unsuitable. A modified two phase partition-dissolution method was applied to solve this problem. This study reports on the bioavalability of three different formulations of artemisinin tablets in rabbit plasma. Artemisinin concentrations in plasma were determined by liquid chromatography. A linear correlation between results obtained by the partition-dissolution method described and the obtained in vivo data confirmed the validity of the dissolution method.

Animals↗

PubMed1997

Liquid chromatographic separation of hexopyranosylated cytosine nucleosides from their degradation products.

Development of a liquid chromatographic method which can separate each of a series of hexopyranosylated cytosine nucleosides from their degradation products formed at acid, neutral and basic pH is described. Both silica-based reverse-phase and polymer columns were examined. Influence of the mobile phase pH, ion-pairing agent, concentration of the buffer and type and concentration of organic modifier were systematically investigated. The concentration of the ion-pairing agent and the buffer were found to have a major effect on selectivity. Samples were finally analyzed on a poly(styrene-divinylbenzene), PLRP-S 100 A (8 microns) 250 x 4.6 mm I.D. column at 60 degrees C and with a mobile phase consisting of acetonitrile-sodium octanesulphonate (pH 2.5; 0.02 M)-potassium phosphate buffer (pH 2.5; 0.2 M)-water (X:25:50:25-X, v/v, where X is variable).

Antineoplastic Agents↗

PubMed1996

Determination of neomycin sulfate by liquid chromatography with pulsed electrochemical detection.

The determination of neomycin sulfate by liquid chromatography using a column packed with a poly(styrenedivinylbenzene) co-polymer and pulsed electrochemical detection on a gold electrode is described. The mobile phase consisted of an aqueous solution containing 70 g/l of sodium sulfate, 1.4 g/l of sodium 1-octanesulfonate and 50 ml/l of a 0.2 M phosphate buffer (pH 3.0). Sodium hydroxide was added post-column. The influence of the different chromatographic parameters on the separation was investigated. The method shows good linearity and repeatability and is stability indicating. A number of commercial samples was analyzed using this method and the results were compared with results obtained with the European Pharmacopoeia method and a previously described thin-layer chromatographic method.

Anti-Bacterial Agents↗

PubMed1996

The gelatinase inhibitory activity of tetracyclines and chemically modified tetracycline analogues as measured by a novel microtiter assay for inhibitors.

A quantitative nonisotopic solution assay for gelatinases and inhibitors was developed using biotinylated gelatin as enzyme substrate. In this assay, residual biotinylated substrate is sandwiched between avidin-coated plates and streptavidin-peroxidase and is quantified by the peroxidase reaction. This assay was useful for measuring gelatinase activities and defining the activities of gelatinase inhibitors. When 23 tetracycline analogues were compared, significant differences in gelatinase B inhibition were found between various compounds. 4-epioxytetracycline base, 4-epichlortetracycline, meclocyclinesulfosalicylate, and unmodified metacycline and minocycline proved to be the most potent gelatinase B (EC 3.4.24.35) inhibitors. The gelatinase B inhibitory activity of tetracyclines was clearly dissociated from their antimicrobial activity. The effect of high-molecular-weight inhibitors, such as monoclonal antibodies, was also demonstrable in the microtiter plate assay. In view of the pathophysiological function of gelatinases, the definition of gelatinase inhibitors with known efficacy, safety, and side effects is crucial for the treatment of diseases such as rheumatoid arthritis and multiple sclerosis. Particular tetracyclines fulfil these criteria and the described assay is useful for defining other gelatinase-inhibiting lead compounds.

Enzyme Inhibitors↗