Search PubMed⌕ Search

Biomedical subjects

R Boulieu

Publications and source records attributed to R Boulieu.

At least 37 records · Page 2Linked to original sources
PubMed1998

Simultaneous determination of 6-thioguanine and methyl 6-mercaptopurine nucleotides of azathioprine in red blood cells by HPLC.

6-thioguanine (6-TGN) and methyl 6-mercaptopurine nucleotides (Me6-MPNs) are the two major metabolites found in erythrocytes after administration of azathioprine. In an attempt to understand the role of these metabolites in the pharmacologic and toxic activity of thiopurines, we have developed a HPLC method for the simultaneous determination of 6-TGNs and Me6-MPNs in erythrocytes. A simple and rapid treatment procedure based on deproteinization by perchloric acid with dithiothreitol is described. The nucleotides were hydrolyzed to their own bases by heating the sample for 45 min at 100 degrees C. During acid hydrolysis Me6-MP was converted into a compound analyzed on a Purospher RP18-e column with 0.02 mol/L dihydrogenophosphate buffer-methanol as eluents. With this procedure, mean recoveries of 73.1% and 84.0% for 6-TGN and Me6-MPN derivatives, respectively, were found.

Azathioprine↗
PubMed1998

HPLC determination of ketamine, norketamine, and dehydronorketamine in plasma with a high-purity reversed-phase sorbent.

We developed an isocratic, selective, and very sensitive HPLC method for the determination of ketamine and its two main metabolites in plasma. The compounds were extracted from plasma by a liquid-liquid extraction with a dichloromethane:ethyl acetate mixture followed by an acidic back-extraction. Separation was achieved on a new stationary phase, Purospher RP-18 endcapped, with a mobile phase containing acetonitrile:0.03 mol/L phosphate buffer (23:77 by vol) adjusted to pH 7.2. Because of the high column efficiency and the significant improvement of peak symmetry, the quantification limit could be down to 5 micrograms/L for ketamine and norketamine (NK). The intraday and interday CVs ranged from 1.7% to 5.8% and 3.1% to 10.2% for all compounds respectively. The method is sensitive enough for monitoring ketamine, NK, and dehydroketamine in plasma during pharmacokinetic studies after an intravenous bolus of a low dose of ketamine.

Acetates↗
PubMed1998

Identification of 6-methylmercaptopurine derivative formed during acid hydrolysis of thiopurine nucleotides in erythrocytes, using liquid chromatography-mass spectrometry, infrared spectroscopy, and nuclear magnetic resonance assay.

6-Thioguanine and 6-methylmercaptopurine (Me6-MP) nucleotides are the two major thiopurine metabolites of azathioprine found in erythrocytes. During the acid hydrolysis required for the conversion of thiopurine nucleotides into their free bases, Me6-MP was converted into a compound that could be analyzed on a Purospher RP18-e column with dihydrogen phosphate-methanol buffer as eluent. The pH of the acid extract strongly influenced the conversion of Me6-MP into its derivative. The Me6-MP derivative was identified using liquid chromatography-mass spectrometry and infrared and nuclear magnetic resonance spectrometric methods. During the acid hydrolysis of thiopurine nucleotides in erythrocytes, Me6-MP undergoes degradation, leading to 4-amino-5-(methylthio)carbonyl imidazole.

Azathioprine↗
PubMed1997

Determination of acyclovir in human plasma by high-performance liquid chromatography.

A selective and sensitive isocratic high-performance liquid chromatographic method for the analysis of acyclovir in human plasma was described. Acid deproteinisation was used as sample treatment. Mean analytical recoveries were higher than 94% at low and high concentrations. The quantification limit was 0.1 mg/l for a plasma volume of 500 microl and precision study exhibits coefficients of variation lower than 5%. The method is suitable for therapeutic monitoring of acyclovir concentrations in organ-transplant recipients.

Acyclovir↗
PubMed1997

Dynamics of MLAEP changes in midazolam-induced sedation.

This study aimed at assessing the effects of midazolam (MDZ) sedation on auditory brainstem (BAEP) and middle latency (MLAEP) evoked potentials in intensive care conditions. Ten ventilated comatose patients were receiving an intravenous MDZ bolus dose (0.2 mg/kg) followed by a 2 h continuous infusion (0.1 mg/kg/h). MLAEPs and BAEPs elicited by clicks (90 dB HL + masking) were simultaneously and continuously monitored during the first 6 h and for 30 min the next morning. We found no effect of MDZ sedation on BAEPs. Only MLAEP components were modified. However, none of the patients presented any total abolition of the MLAEPs. Bolus injection led to very early alteration of cortical responses, beginning after 5 min and lasting almost 1 h (maximum Pa latency increase, 3.1 ms; maximum Pa-Nb amplitude decrease, 46%). During continuous infusion, MLAEPs remained slightly, although significantly, altered (Pa latency, +1.3 ms; Pa-Nb amplitude, 27%). The Nb wave seemed to be modified earlier and to return to normality later than the Pa wave. These findings incite a careful interpretation of MLAEP tracings acquired during the first hour following MDZ bolus injection. If possible, MDZ should be administered as continuous infusion for reliable interpretation of evoked potential changes in intensive care unit, or during surgery.

Adult↗
PubMed1997

Pharmacokinetics of acyclovir in patients undergoing continuous venovenous hemodialysis.

The pharmacokinetics of acyclovir in three patients undergoing continuous venovenous hemodialysis was investigated. Acyclovir was administered as an intravenous infusion over 1 hour at a dose of 5 mg/kg daily in one patient and 10 mg/kg every 48 hours in two patients. Samples from the arterial and venous blood lines and from ultrafiltrate were collected to calculate pharmacokinetic parameters, sieving coefficient and clearance of ultrafiltration. Plasma concentrations of acyclovir were assessed by high-performance liquid chromatography. Peak plasma concentrations were 9.3 mg/l for the patient receiving 5 mg/kg daily, 29.6 mg/l and 20.7 mg/l for the two patients with 10 mg/kg every 48 hours. The elimination half-life ranged from 8.8 to 11.2 hours and was approximately half those found in patients with renal impairment. The clearance by ultrafiltration was from 17.4 to 22.3 ml/minute and reached nearly 35% of the total clearance. The sieving coefficient ranged from 0.92 to 0.98 with an average rate of removal over the dosing interval ranging from 6.7 to 13.0 mg/hour. These data should be taken into account to optimize drug therapy in patients on continuous hemodialysis. Until formal guidelines are defined, acyclovir dosage should be adjusted according to monitoring of plasma drug concentrations.

Acyclovir↗
PubMed1997

Intracellular thiopurine nucleotides and azathioprine myelotoxicity in organ transplant patients.

AIMS: Despite widespread use of azathioprine in organ transplant recipients, the mechanism of its myelotoxicity remains unclear. The aim of this study was to assess the importance of thiopurine metabolites on bone marrow toxicity. METHODS: We investigated the relationship between intracellular concentrations of 6-thioguanine (6-TGN), 6-mercaptopurine (6-MPN) and 6-thioxanthine (6 TXN) nucleotides and the absolute count of white or red cells in forty-seven lung or heart/lung transplant patients after oral administration of azathioprine. RESULTS: No significant correlation between red cell concentrations of 6-TGN or total thiopurine metabolites and white or red cell counts was found, with no difference between the sexes. Likewise, high 6-TGN levels were not related to bone marrow depletion. CONCLUSIONS: These results suggest that red blood cell 6-TGN alone do not predict the haematopoietic toxicity of azathioprine.

Adolescent↗
PubMed1997

Predictions of carbamazepine concentrations using a Bayesian program (PKS System, Abbott): a retrospective evaluation in an outpatient population.

This work evaluates the performance of a Bayesian program (PKS System, Abbott) for predicting carbamazepine concentrations in an outpatient population. The retrospective study involved 20 epileptic patients (12 adults and 8 children) receiving carbamazepine monotherapy orally. The program was used to predict measured serum levels after feedback of 0, 1 or 2 steady-state concentrations. A significant negative prediction bias was observed when no feedback concentration was used for estimation. However, the prediction bias (mean prediction error; m.e.) decreased as soon as one feedback concentration was used for estimation. Precision (mean absolute prediction error; m.a.e.) was significantly improved with one feedback concentration and was even better with two concentrations. Likewise, r.m.s.e. (root mean squared error; composite of bias and precision) regularly decreased when the number of feedback concentrations used was increased. Eleven percent of the estimates were unacceptable clinically (prediction error > 2 mg L-1) when 1 feedback concentration was used; less than 3% were unacceptable when two concentrations were used. Thus the performance of the Bayesian dosing program is acceptable when two feedback concentrations are known, and seems able to help the clinician adjust carbamazepine dosage in an outpatient population.

Administration, Oral↗
PubMed1996

Comparison of capillary electrophoretic and liquid chromatographic determination of hypoxanthine and xanthine for the diagnosis of xanthinuria.

A capillary electrophoretic (CE) method for the determination of hypoxanthine and xanthine in urine was developed to diagnose xanthinuria. The linearity was excellent up to 200 mumol l-1 for the two compounds and the limit of quantitation was 2 mumol l-1. A comparison o the results obtained using CE was made with those obtained by the high-performance liquid chromatographic (HPLC) technique described previously. With regard to specificity, sensitivity and reproducibility, the results are similar but CE is more rapid than HPLC.

Chromatography, High Pressure Liquid↗
PubMed1996

Sample preparation for the determination of purine nucleotide analogues in tissues.

A sample treatment procedure for the determination of thiopurine and ganciclovir nucleotides in human tissues was developed. Owing to the lack of suitable standards for most of the active nucleotide analogues, the procedure was based on two steps: (1) perchloric acid homogenization and deproteinization of the tissue specimen and (2) conversion of purine nucleotides into parent drug or free bases by enzymatic or acid hydrolysis. The parent drug or purine bases formed were then analyzed on a Hypersil ODS column using isocratic elution with dihydrogenphosphate buffer for ganciclovir nucleotides or the gradient elution mode with dihydrogenphosphate buffermethanol for thiopurine nucleotides. The sample treatment procedure was evaluated using guanosine triphosphate (GTP), 6-thioinosinic acid (6TIMP) and 6-thioguanosine monophosphate (6TGMP) as standards. Mean analytical recoveries determined by adding known concentrations of standards to the tissue specimen before sampling processing were higher than 97%. The sample preparation described is simple and represents a suitable method for the investigation of active nucleotide pool in tissues.

Antimetabolites↗
PubMed1996

Liquid-chromatographic study of purine metabolism abnormalities in purine nucleoside phosphorylase deficiency.

Using HPLC methods, we measured the concentrations of nucleosides and nucleotides for a patient with no purine nucleoside phosphorylase (PNP; EC 2.4.2.1) enzymatic activity. Concentrations of inosine and guanosine were abnormally high in urine and plasma, whereas guanosine diphosphate (GDP) and guanosine triphosphate (GTP) concentrations in erythrocytes were depleted. The unusual presence of deoxyribonucleosides (deoxyinosine and deoxyguanosine) and deoxyribonucleotides (dGDP and dGTP) was also notable. Thus, HPLC represents an accurate and useful tool for the study of purine metabolic disorders.

Chromatography, High Pressure Liquid↗
PubMed1995

Determination of midazolam and its unconjugated 1-hydroxy metabolite in human plasma by high-performance liquid chromatography.

A selective and sensitive high-performance liquid chromatographic method for the analysis of midazolam and its unconjugated 1-hydroxy metabolite in plasma samples was developed. The compounds were extracted from plasma by a liquid-liquid extraction procedure with diethyl ether. Mean analytical recoveries were 87% and 86% at a concentration of 300 ng/ml for midazolam and 1-hydroxymidazolam, respectively, and the quantification limit was 2 ng/ml for a plasma volume of 1 ml. The separation of midazolam, 1-hydroxymidazolam and flurazepam (internal standard) was achieved on a Spherisorb 5 CN column using methanol-2(r)propanol (75:25, v/v) containing 0.015% perchloric acid at a flow-rate of 1.5 ml/min. The method is sensitive enough for monitoring midazolam and also the unconjugated form of the active metabolite in plasma during pharmacokinetic studies.

Calibration↗
PubMed1995

Determination of thiopurine nucleotides in human lung tissue by high-performance liquid chromatography.

A method for the analysis of thiopurine nucleotides in human transbronchial lung biopsy was developed. The sample treatment procedure is based on perchloric acid homogenisation and deproteinisation with dithiothreitol and hydrolysis of thiopurine nucleotides into their free bases by heating of the acid extract. Then, the free bases were analyzed in the gradient elution mode on a Hypersil ODS, 3-microns column using dihydrogenphosphate buffer-methanol as eluent. Mean analytical recoveries for 6-thioguanosine monophosphate and 6-thioinosinic acid from lung tissue were 97.0 +/- 2.0 and 98.0 +/- 1.8% at a concentration of 3.0 nmol/ml and the minimum detectable amounts were 3.5 and 2 pmol, respectively. The procedure described is simple and represents a suitable method for the investigation of thiopurine nucleotides in tissues.

Chromatography, High Pressure Liquid↗
PubMed1994

High-performance liquid chromatographic determination of ganciclovir nucleotides in human myocardial tissue.

A method for the analysis of ganciclovir nucleotides in myocardial tissues was developed. The antiviral effect of ganciclovir is attributed to intracellular ganciclovir nucleotides. The procedure is based on perchloric acid deproteinization and enzymatic hydrolysis of the ganciclovir nucleotides to ganciclovir. Then, the parent drug was analyzed on a Hypersil ODS column using potassium dihydrogenphosphate buffer as mobile phase. The mean analytical recovery of ganciclovir from myocardial tissue was 101 +/- 2% and the detection limit was 2 pmol. The sample treatment procedure described is simple and presents a suitable analytical tool for the investigation of the ganciclovir nucleotides pool in tissues.

Alkaline Phosphatase↗