Tissue distribution and metabolism in rat of an ethynesulphonamide with filaricidal activity.

1. The tissue distribution and metabolism of a new filaricidal agent P903 (N-[(2-phenylethynyl)sulfonyl]morpholine) were studied in rat. 2. After s.c. administration of 14C and 13C P903, the Tmax in the blood was observed on day 2. Elimination was slow and > 95% was bound to protein. Radioactivity was distributed in the whole organism but particularly in erythrocytes and the lymphatic channel. Four days later, > 60% of the radioactivity was excreted in urine and faeces at equal amounts and 15% remained at the injection point. 3. In all biological fluids tested no P903 was found but only its metabolites. 4. One principal metabolite, the N-[(2-phenyloxo-2-ethane) sulphonyl] morpholine or oxosulphonamide was identified in blood, urine and faeces as compared with the reference compound by GC/MS and NMR. This latter molecule was detected following hydrolysis by hydrochloric acid but not with beta glucuronidase/sulphatase. 5. Unconjugated and conjugated oxosulphonamide represented > 85% of the radioactivity at all times tested in blood but only 38 and 35% respectively of urinary and faecal radioactivity on day 1 after the administration of the labelled drug. 6. Thus, P903 is rapidly converted to a reactive metabolite, probably an oxirene, which is then conjugated with endogenous components to form conjugated oxosulphonamide and an unknown metabolite. The role of this reactive metabolite in antifilarial activity seems to be very important in understanding the mechanism of action of P903.

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.

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.

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.

Disposition and metabolism of O6-alkylguanine-DNA alkyltransferase inhibitor in nude mice bearing human melanoma.

Tumor resistances to chloroethylnitrosourea (CENU) are mainly due to O6-alkylguanine-DNA alkyltransferase (AGT). Our laboratory has synthesized a new water-soluble AGT inhibitor. O6-benzyl-N-acetylguanosine (BNAG). We have shown that this compound is able to deplete AGT activity on M4Beu human melanoma cells and to enhance the antitumor power of CENU N'-[2-chloroethyl]-N-[2-(methylsulfonyl)ethyl]-N'-nitrosourea (cystemustine) towards the M4Beu melanoma grafted on nude mice. With a view to determining the best combination BNAG/CENUs conditions, we have studied the distribution and metabolism of BNAG in nude mice bearing M4Beu human melanoma. BNAG, labelled with carbon-14 on the benzyl group, was administered by single i.v. dose of 40 mg/kg. Blood analysis showed that the main radioactive compound was unchanged molecule, and only a small part was found as hippuric acid resulting from the metabolic cleavage of the benzyl group. BNAG and hippuric acid were mainly eliminated in the urine. Unchanged BNAG blood kinetics showed three phases: blood epuration (t1/2 (1) = 13 min), reabsorption and elimination (t1/2 (2) = 1.7 hr). This kinetic profile is probably due to an enterohepatic cycle. BNAG is distributed in several tissues (kidney, liver, skin, duodenum, colon, tumor) but not in the central nervous system, suggesting a poor blood-brain crossing. Because an important part of the administered dose is not metabolized, high unchanged BNAG level remains in most tissues, including M4Beu tumor, and AGT depletion can occur several hours after dosing.

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.

Identification of several human urinary metabolites of 6-benzoyl benzoxazolinone by gas chromatography/mass spectrometry.

The biotransformation of 6-benzoyl benzoxazolinone (6-BB), a non-narcotic peripheral analgesic, was studied in eight healthy volunteers after oral administration of a single dose of 1 g. Urinary metabolites were extracted either with ethyl acetate at different pH values or by percolating at pH 5 through Amberlite XAD 2 ion-exchange resin. Eluates were concentrated under vacuum, purified by thin-layer chromatography and analysed by gas chromatography/mass spectrometry or direct insertion probe mass spectrometry. Metabolites were identified with reference to the mass spectra of various synthesized compounds assumed to be metabolites of 6-BB, as N-methylated or monohydroxylated compounds. Another metabolic pathway was cleavage of the benzoxazolinone heterocycle giving 2-amino-5-benzoyl phenol after hydrolysis and decarboxylation. N-methyl, N-acetyl and hydroxylated metabolites having an amino-5-benzoyl phenol structure were also found.

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.

Chronopharmacokinetic and bioequivalence studies of two formulations of trimipramine after oral administration in man.

The bioavailability of two oral formulations of trimipramine, tablets and solution, was performed in twelve healthy volunteers, in a cross-over study. Each formulation was administered in the morning after a fasted period, and in the evening after a meal, in order to evaluate the role of both administration time and food consumption on the plasma kinetic parameters, under usual therapeutic conditions. A high interindividual variability of data was found. First, the extent of bioavailability was identical for the two formulations but the rate of bioavailability seemed to be different, with the p.o. solution, being more rapidly absorbed (tmax = 1.50 h). The effect of administration time was more obvious for the solution as shown by a lower quantitative absorption as well as a delay in time to reach the maximal concentration. Regardless of formulation and administration time, the t1/2 beta was about 10 hours and the mean MRT value was 11 hours.

Pharmacokinetics of metapramine and its demethylated metabolites in plasma and brain of mice.

Previous studies on pharmacokinetic parameters of tricyclic antidepressants (TCAs) in rodents have shown different results from those obtained for the same drugs in man. The kinetics of metapramine (META) and its major demethylated metabolites (METs) were studied in the SWISS CD 1 mouse after acute administration in order to establish the pharmacokinetic parameters in plasma and brain. The plasma half-life (T1/2) was very short (87 min) compared with the half-life (7 h) in man. The metabolism of META was intensive as was the transfer of META and its metabolites into the brain. The kinetic profiles of the substances were quite similar both in plasma and in brain, namely a bicompartment open model. META was rapidly absorbed (Tmax = 10 min) into and quickly eliminated (T 1/2 = 40 min) from the brain. These parameters were used to schedule sampling (blood and brain) at the appropriate time after acute administration of increased doses. The administered doses were significantly correlated to firstly the plasma or brain levels of META, secondly the plasma levels of the main monodemethylated metabolite (MET I), and thirdly the plasma or brain levels of META + METs. Finally, the evolution of plasma and brain levels of the substances was studied after repeated injections (i.e. every 40 min) and confirmed the high affinity of META and its metabolites for the brain regions.

Disposition and metabolism of letosteine in rats.

The metabolism and disposition of letosteine, labeled either with 14C or 35S, has been investigated in Sprague-Dawley rats. In separate experiments, rats received 20 mg/kg, iv or orally, [14C]letosteine or [35S]letosteine. Radioactivity was rapidly excreted, mainly in urine, after iv and oral administration. Recovery of radioactivity from 0-72-hr excreta averaged 95% after both routes of [14C]letosteine administration, whereas only 50% was recovered when [35S]letosteine was administered. 14CO2 accounted for about 7.3% (iv) and 5.1% (po) of the dose of [14C]letosteine. Comparison of the iv and oral areas under the plasma 14C radioactivity concentration-time curves suggested that oral absorption of letosteine was complete. Analysis of the radioactivity content of urine showed that letosteine undergoes rapid and extensive metabolism. Several metabolites were identified by TLC, HPLC, and MS. The findings are consistent with a splitting of the ester group of letosteine and subsequent cleavage of the thiazolidinyl ring, yielding cysteine, hypotaurine, taurine, and inorganic sulfate. The metabolite derived from the side chain was identified in the urine as 3-(hydroxycarbonylmethylthio)propanoic acid. It undergoes further oxidation into sulfoxide and sulfone derivatives, which are also present in the urine.

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).

Main excretion metabolites of 7-methoxy-2-nitronaphtho[2,1-b]furan (R 7000) in rats.

Major metabolites, isolated from rat bile and urine after administration of a single dose of 7-methoxy-2-nitronaphtho[2,1-b]furan (R 7000; MNNF) labelled with 14C on the furan ring and on the methoxy group, were identified by comparison of their chromatographic behaviour and mass spectra with synthetic authentic reference compounds. Analysis of metabolites indicated three metabolic pathways for this compound in vivo, namely, demethylation of the methoxy group, hydroxylation of the aromatic ring and cleavage of the furan ring, followed by the reduction of the nitro group to amine.

Kinetics of metapramine and its demethylated metabolites after single and chronic oral administration in man.

The kinetics of metapramine and two of its demethylated metabolites were determined in six normal subjects after oral administration of a single 150 mg dose on day 1 and 3 X 50 mg dose on day 2-6. This study has shown that three demethylated metabolites are found in plasma beside metapramine. The monodemethylated metabolite I appeared to be the predominant one and the mean area under the plasma concentration curve (AUCo24) was 49% of the metapramine value. Its half-life was shorter (5.92 h) than that of metapramine (8.29 h). The kinetic profiles of metapramine and its major metabolites I and II were similar and data over 24 h could be fitted by a tri-exponential equation even though entero-hepatic cycles were observed. A high interindividual variability of data was found for both metapramine and its metabolites. There were no significant differences between men and women. The minimal plasma level (Cmin) seemed in agreement with the half-life of the drug.