Simple and sensitive method for determination of metronidazole in human serum by high-performance liquid chromatography.

A simple and sensitive HPLC method for determination of metronidazole in human plasma has been developed. A step of freezing the protein precipitate allowed an efficient separation of aqueous and organic phases minimizing the noise level and improved therefore the limit of quantitation (10 ng ml(-1) using 1 ml of plasma sample). The separation of compounds was performed on a RP 18 column with acetonitrile-aqueous 0.01 M phosphate solution (15:85, v/v) as mobile phase. Detection was performed by UV absorbance at 318 nm. Metronidazole was well resolved from the plasma constituents and internal standard. An excellent linearity was observed between peak-height ratios plasma concentrations over a concentration range of 0.01 to 10 microg ml(-1). Within-day and between-day precision (expressed by relative standard deviation) and accuracy (mean error in per cent) did not exceed 4% between 1 and 10 microg ml(-1) and 8.3 and 7.2% respectively for the limit of quantitation. The method is suitable for bioavailability and pharmacokinetic studies in humans.

Comparative study of the biotransformation of bepridil analogs in isolated liver cells from one rat. Relationships between structure and in vitro liver toxicity.

The biotransformation of several analogs of the anti-calcium agent bepridil was studied comparatively in liver cells isolated from one rat. Three types of metabolites were identified by mass spectrometry, resulting from three phase I reactions: hydroxylation, N-debenzylation and pyrrolidine ring opening. The amount of each bepridil analog untransformed after 18 h of incubation depended on its liver toxicity rather than on its concentration in the culture medium. The proportion of phase I metabolites identified remained constant regardless of toxicity. The difference delta c (in %) between the initial concentration of the analog tested and the sum of the concentrations of untransformed material and of identified metabolites decreased with the increasing hepatocyte toxicity. The analogs tested were responsible for the liver toxicity. The presence of substituents in different positions on the N-phenyl moiety increased liver toxicity; ortho-substituted analogs were more toxic than para- or meta-substituted ones.

Gas chromatographic-mass spectrometric determination of isosorbide 5-mononitrate in human plasma.

A highly specific and precise method using gas chromatography-mass spectrometry was developed for the measurement of isosorbide 5-mononitrate in plasma using isomannide mononitrate as internal standard. With regard to the numerous analytical problems encountered when organic mononitrates were determined in plasma, such as thermal instability and adsorption, compounds were silylated before gas chromatography. In order to increase the specificity of the assay, two specific ions of the isosorbide 5-monitrate were simultaneously recorded. The accuracy of the assay was tested day to day with quality specimens spiked blind to the analyst.

Determination of oxeladin in human plasma by gas chromatography--mass spectrometry.

A capillary gas chromatographic method with mass-selective detection was developed for the determination of oxeladin in human plasma. Plasma samples (1 mL) were alkalinized and extracted using 5mL of hexane: isoamyl alcohol (99:1). The method was demonstrated to be sensitive (limit of quantitation at 1 ng/mL), linear between 1 and 150 mg/mL, accurate and precise enough (mean error and mean coefficient of variation at the limit of quantitation were 2.3 and 13.3%, respectively) to support pharmacokinetic evaluation of the drug at doses down to 30 mg.

Determination of phloroglucinol in human plasma by gas chromatography-mass spectrometry.

A specific and sensitive method has been developed for the determination of phloroglucinol in plasma; it involves an optimized procedure for blood sampling designed to minimize the in vitro oxidation of the molecule, and gas chromatography-mass spectrometry after silylation of the compound. The method allowed a reliable determination of phloroglucinol in plasma. The precision and accuracy of the assay, reported as coefficients of variation, were below 15%. Using a plasma sample of 0.25 ml, the limit of quantitation was 5 ng/ml with a precision of 17.4%, which is sensitive enough for pharmacokinetic studies. Stability studies under different conditions revealed that ascorbic acid limits the degradation of phloroglucinol in plasma during storage at freezer temperatures.

Measurement of trazodone in plasma and brain of rat by capillary gas chromatography with a nitrogen-selective detector.

A specific and highly sensitive method for the measurement of trazodone in plasma and brain of rat is presented. The compound and the internal standard were extracted from alkalinized samples with hexane and analysed by capillary gas chromatography with nitrogen-selective detection. The method was demonstrated to be accurate and precise. The limits of determination were 2 ng/ml for plasma and 24 ng/g for brain, which makes this procedure suitable for pharmacokinetic analysis.

Biotransformation study of para-substituted phenylpiperazines in beagle dogs by gas chromatography-mass spectrometry.

1. Beagle dogs were treated orally (10 mg/kg) with para-chloro-, para-fluoro- and para-methyl-phenylpiperazine derivatives, and urine was collected for 72 h after treatment. 2. Metabolites were extracted, converted into trimethylsilyl (TMS) derivatives and examined by g.l.c.-mass spectrometry. 3. The metabolites fall into two main groups, N-desphenylated metabolites, which result from N-desphenylation, and N-phenyl metabolites. 4. Two kinds of hydroxylated metabolites were found. Some lost the original para substituent (Cl, F or CH3); others retained it. 5. These results are consistent with the NIH shift reaction.

N-dephenylated and N-phenyl urinary metabolites of mociprazine (CERM 3517) in beagle dogs after oral administration. A mass spectrometric determination.

CERM 3517 (mociprazine), a new anti-emetic compound, was administered orally to six beagle dogs at 10 mg/kg b.i.d. for four days. Unconjugated urinary metabolites were identified by GC-MS analysis against synthesized reference compounds, after solvent extraction, purification by TLC and concentration. Twenty one metabolites were identified indicating the following biotransformations: N-dephenylation followed by reactions on the exposed secondary amine such as methylation acetylation; and parahydroxylation on the phenyl ring, and monohyrdoxylation on the cyclohexyl ring in different positions. The parahydroxylation on the phenyl ring was confirmed by NMR analysis. Some reactions on the secondary amine were unexpected, such as N-formylation. N-dephenylation and N-formylation were confirmed not to be artifacts. The role of the para-hydroxyl intermediate was proved to be essential for the N-dephenylation after intravenous administration of meta- and para-hydroxylated derivatives of CERM 3517 to five beagle dogs.

Kinetics of allopurinol and its metabolite oxypurinol after oral administration of allopurinol alone or associated with benzbromarone in man. Simultaneous assay of hypoxanthine and xanthine by gas chromatography-mass spectrometry.

Allopurinol, oxypurinol, hypoxanthine and xanthine were assayed simultaneously using a highly specific method combining gas chromatography and mass spectrometry. Two hypo-uricaemic prescriptions were compared: i) 300 mg of allopurinol (AL); and ii) 100 mg of allopurinol plus 20 mg of benzbromarone (AL + BZB). When administered acutely, their effects on blood uric acid levels were similar. Analysis of the pharmacokinetic parameters of allopurinol and its metabolite after each treatment showed dose-linearity for the metabolite but not for the drug itself. The area under the concentration time curve for allopurinol was 40.3 +/- 9.3 mumol l-1 h after AL, against 8.4 +/- 3.9 mumol-1 h after AL + BZB, while for oxypurinol it was 948.0 +/- 125.4 mumol l-1 h after AL and 285.2 +/- 77.9 mumol l-1 h after AL + BZB. The difference in dosage form may partly account for this difference, but the benzbromarone also seems to be involved. Its role on the blood uric acid lowering action of the drug association is complex. Although benzbromarone appreciably favors the elimination of oxypurinol, which should result in a weakening of its hypo-uricaemic action, this is offset by enhanced elimination of hypoxanthine and xanthine. Renal clearance of xanthine was significantly increased under AL + BZB (173.1 +/- 65.6 ml/min against 112.2 +/- 32.9 ml/min after AL). Similarly, blood xanthine levels were proportionately higher in the presence of benzbromarone. The action of the two agents may thus be synergistic and not antagonistic, a pharmacological justification for the therapeutic use of this drug association.

Plasma and blood assay of xanthine and hypoxanthine by gas chromatography-mass spectrometry: physiological variations in humans.

Plasma and blood xanthine and hypoxanthine levels were assayed using a sensitive and specific method involving gas chromatography-mass spectrometry, associated with an optimized sample preparation procedure. Physiological variation was studied in 224 subjects with no purine metabolism disorders. An age dependency for both compounds was found, comparable with that known for uric acid. The mean plasma levels for the 224 subjects were 0.65 +/- 0.24 microM for xanthine and 1.65 +/- 0.78 microM for hypoxanthine. Corresponding mean blood levels were 0.59 +/- 0.21 microM for xanthine and 1.72 +/- 0.74 microM for hypoxanthine. Plasma and blood levels were significantly different, by ca. 10%. Rapid in vitro release of hypoxanthine from erythrocytes and continuation of intraerythrocytal metabolism lead to overestimation exceeding 10% within half an hour after sample blood collection. Hence samples must be deproteinized promptly. Blood can therefore be conveniently used for oxypurine assay instead of plasma when prompt spinning of samples is difficult to manage, as is usually encountered in clinical practice.

Pharmacokinetics of cyclophosphamide administered alone or in combination with vindesin or cisplatin in 5 patients with bronchial adenocarcinoma.

The pharmacokinetics of cyclophosphamide (CPH) administered intravenously at doses between 200-400 mg alone or in combination with vindesin (VDS) or cisplatin (cisPt) were studied in 5 patients who had bronchial adenocarcinoma, with normal liver and kidney functions. The linearity and the reproducibility of CPH kinetics were confirmed and its pharmacokinetic parameters were found to be unaffected by simultaneous or sequential administration of either vindesin or cisplatin. Total clearance was 7.69 +/- 3.53 1.hr-1 for CPH administered alone and 6.76 +/- 1.63 1.hr-1 for CPH administered with vindesin. Biological half-life was 4.3 +/- 1.5 hr (CPH alone) and 5.1 +/- 2.2 hr (CPH + VDS).

Pharmacokinetic study of 3H-labelled PAF-acether II. Comparison with 3H-labelled lyso-PAF-acether after intravenous administration in the rabbit and protein binding.

The blood and plasma kinetics of intravenously administered 3H-labelled PAF-acether were determined in seven rabbits. PAF-acether was rapidly distributed and slowly eliminated. Individual variations were very small. The main route of metabolism involves deacetylation of the PAF-acether into lyso-PAF-acether, leading to an equilibrium between the two molecules (10%/90%). This equilibrium, observed within 30 minutes, was still the same after 6 hours suggesting in vivo reacetylation of lyso-PAF-acether into PAF-acether. However, this could not be verified. After intravenous administration of lyso-PAF-acether in two rabbits, PAF-acether could not be found in any blood sample. The pharmacokinetic behaviour of both PAF-acether and lyso-PAF-acether can be described by a three-compartment model.

[Assay of plasma xanthine and hypoxanthine by coupled gas chromatography-mass spectrometry and sampling problems]. / Dosage de la xanthine et de l'hypoxanthine plasmatiques par couplage chromatographie en phase gazeuse-spectrométrie de masse et problèmes d'échantillonnage.

The differential assay of xanthine and hypoxanthine in plasma, serum and erythrocytes was performed using a combination of GC and MS with chemical ionisation. The influence of sampling conditions was studied, in particular the latency period between the collection of the blood and the separation of the plasma and the cells, the nature of the anticoagulant used and the method of storage of the samples. Firstly, this study confirms that EDTA is the most appropriate anticoagulant. It also showed that an immediate deproteinisation is necessary after separation of the plasma and the cells, in order to prevent any "in vitro" modification of the oxypurines, in particular erythrocyte hypoxanthine.

Pharmacokinetic study of PAF-acether. Preliminary results after the intravenous administration of a 3H-labelled product to the rabbit.

3H-PAF-acether was rapidly distributed and deacetylated to 3H-lyso-PAF-acether after its intravenous administration to the rabbit. Within 30 min, an equilibrium was established between PAF-acether (10%) and lyso-PAF-acether (90%). A pharmacokinetic study and a preliminary metabolic evaluation were carried out in three rabbits, after the intravenous administration of 3H-labelled PAF-acether (40 Ci/mM, CEA, Saclay, France). This work required the development of a method for the separation of the unchanged product from its potential plasma metabolites, particularly from lysoPAF which appears to be the only early degradation product.

Mass fragmentographic determination of xanthine and hypoxanthine in biological fluids.

The method presented for the simultaneous determination of xanthine and hypoxanthine, uses mass-fragmentography in the electron impact (EI) mode, after the gas chromatographic separation of butylated derivatives. Butylation, rather than methylation, is used in order to avoid interference coming from exogenous caffeine, which is frequently encountered. [7,9-15N]Xanthine is used as the internal standard, and for each sample, a blank is obtained by xantine oxidase reaction. In the biological fluids studied the sensitivity was about 50 ng/ml.

[Pharmacokinetics and bioavailability of naftidrofuryl capsules in man]. / Etude de la pharmacocinétique du naftidrofuryl et de sa biodisponibilité sous forme de gélule chez l'homme.

We have studied the pharmacokinetics of a single dose of naftidrofuryl in man. Two phases of diffusion have been observed, 11,0 +/- 2,6 respectively 26,5 +/- 3,61. This indicates that the drug is not extensively bound to tissues but mainly distributed throughout the extracellular space. The bioavailability of its oral form, gelatin capsules, is good, if in the same person the area under the plasma curves after oral administration is compared to the one after intravenous injection.