Investigation of Bemethyl Biotransformation Pathways by Combination of LC-MS/HRMS and In Silico Methods

Bemethyl is an actoprotector, an antihypoxant, and a moderate psychostimulant. Even though the therapeutic effectiveness of bemethyl is well documented, there is a gap in knowledge regarding its metabolic products and their quantitative and qualitative characteristics. Since 2018, bemethyl is included to the Monitoring Program of the World Anti-Doping Agency, which highlights the challenge of identifying its urinary metabolites. The objective of the study was to investigate the biotransformation pathways of bemethyl using a combination of liquid chromatography-high-resolution mass spectrometry and in silico studies. Metabolites were analyzed in a 24 h rat urine collected after oral administration of bemethyl at a single dose of 330 mg/kg. The urine samples were prepared for analysis by a procedure developed in the present work and analyzed by high performance liquid chromatography–tandem mass spectrometry. For the first time, nine metabolites of bemethyl with six molecular formulas were identified in rat urine. The most abundant metabolite was a benzimidazole–acetylcysteine conjugate; this biotransformation pathway is associated with the detoxification of xenobiotics. The BioTransformer and GLORY computational tools were used to predict bemethyl metabolites in silico. The molecular docking of bemethyl and its derivatives to the binding site of glutathione S-transferase has revealed the mechanism of bemethyl conjugation with glutathione. The findings will help to understand the pharmacokinetics and pharmacodynamics of actoprotectors and to improve antihypoxant and adaptogenic therapy.

Multiresidue analysis of pesticides in urine of healthy adult companion dogs

The objective of this study was to determine the background exposures to pesticides as detected in urine from 21 healthy companion dogs in Northern Colorado. A panel of 301 pesticides was used to screen urine samples collected from dogs using an established ultraperformance liquid chromatography-mass spectrometry (UPLC-MS/MS) platform. Canine food intakes were controlled for one month on diets that were also screened for pesticide contents. Fifteen distinct pesticides were detected in urine. The most frequently detected compounds in canine urine samples collected over a 1 month period were atrazine, fuberidazole, imidacloprid, terbumeton, and clopyralid. Fuberidazole was the only pesticide detected in both the diets and urine. Companion dogs develop many similar chronic diseases as humans and represent a relevant model for biomonitoring combinations of environmental pesticide exposures, as well as for evaluating the potential relationships between environmental exposures and disease risk.

[Pharmacokinetics of afobazole metabolite (M-11) in rats]

Pharmacokinetics of compound M-11 (main metabolite of afobazole) after administration via different routes was studied in rats. After oral and intravenous administration, M-11 exhibited weakly pronounced bioconversion with the formation of a few metabolites that could be detected in plasma samples for about 3 hours. The absolute bioavailability of M-11 after oral administration was 68.3%. It was found that M-11 was completely absorbed from gastrointestinal tract of rats and characterized by "the first pass effect", after which approximately 70% of administered dose entered the circulation. The parent substance was determined neither in urine nor in feces.

[Afobazole metabolism in rats]

Metabolism of afobazole in rats has been studied using mass-spectrometry and HPLC, which revealed 17 products of afobazole biotransformation along with the parent compound. The structures of six afobazole metabolites were established and confirmed by comparison of HPLC retention times with the synthetic reference compounds and HPLC/mass spectrometry. Other metabolites were characterized by the masses of molecular ions. A significant fraction of the drug dose is biotransformed with the formation of hydroxylated benzimidazole moiety and oxidated morpholine.

[Pharmacokinetics of afobazole in rats]

Afobazole pharmacokinetics was studied after the administration via different ways in rats. After oral administration, afobazole is subject to intensive biotransformation with the formation of several metabolites (M-6, M-7, and M-11). The drug and its metabolites were detected in the blood plasma for 3 h and characterized by a high elimination rate after both oral and intravenous administration. Afobazole and its main metabolite (M-11) had a medium rate of permeability into brain (the target organ): the tissue availability was 0.584 for afobazole and 0.793 for M-11. The absolute bioavailability of afobazole upon oral administration was 43.6% for. Afobazole was completely absorbed from the gastrointestinal tract of rats and characterized by the first-pass effect, after which more than 40% of administered dose entered the circulation. The parent compound was determined in extremely low amounts in urine and feces: its content in 24-h urine on the average did not exceed 0.07% of the administered dose; in 24-h feces, it did not exceed 0.05 % after intravenous administration and 0.01% after oral administration).

Sequential-injection determination of traces of disodium phenyl dibenzimidazole tetrasulphonate in urine from users of sunscreens by on-line solid-phase extraction coupled with a fluorimetric detector

A sensitive and selective method to determine disodium phenyl dibenzimidazole tetrasulphonate (PDT) in the urine of sunscreen users, which is suitable for studies on body accumulation/excretion is proposed. On-line solid-phase extraction allows the analyte to be retained and subsequentely eluted, using a strong anion exchange (SAX) microcolumn. Standard addition calibration was carried out with only one standard. The wavelengths of excitation and emission were 330 and 454 nm, respectively. The method allows PDT to be determined in both, spiked and unspiked human urine samples, without any pre-treatment. Results obtained for spiked urine samples (40-200 ng ml(-1)) showed the accuracy of the method. The mean relative standard deviations (R.S.D.) of the results was 7%. Five volunteers applied a sunscreen lotion containing 5% PDT and their urinary excretion was controlled from the moment of application until the excreted amounts were no longer detectable. The sensitivity of the proposed method is in the order of 1900 ml microg(-1) and the detection limit (3S(y/x)/b) is in the order of 5 ng of PDT, which means 10 ng ml(-1) for a 500 microl injected volume, and this is suitable for the PDT levels found in the urine.

Novel polymer monolith microextraction using a poly(methacrylic acid-ethylene glycol dimethacrylate) monolith and its application to simultaneous analysis of several angiotensin II receptor antagonists in human urine by capillary zone electrophoresis

Novel polymer monolith microextraction (PMME) using a poly(methacrylic acid-ethylene glycol dimethacrylate) (poly(MAA-EGDMA)) monolith in conjunction with capillary zone electrophoresis (CZE) was developed for the determination of several angiotensin II receptor antagonists (ARA-IIs) in human urine. The extraction device consisted of a regular plastic syringe (1 mL), a poly(MAA-EGDMA) monolithic capillary (2 cm x 530 microm I.D.) and a plastic pinhead connecting the former two components seamlessly. The extraction was achieved by driving the sample solution through the monolithic capillary tube using a syringe infusion pump, and for the desorption step, an aliquot of organic solvent was injected via the monolithic capillary and collected into a vial for subsequent analysis by CZE. The best separation was realized at 25 kV using a buffer that consisted of 50% acetonitrile and 50% buffer solution (v/v) containing 10 mM disodium hydrogenphosphate (adjusted to pH 2.3 with 1M hydrochloric acid). The method was successfully applied to the determination of telmisartan (T), irbesartan (I) and losartan (L) in urine samples with candesartan (C) as internal standard, yielding the detection limit of 15-20 ng/mL. Close correlation coefficients (R>0.999) and excellent method reproducibility were obtained for all the analytes over a linear range of 0.08-3 microg/mL.

Metabolism of pantoprazole involving conjugation with glutathione in rats

We have investigated the metabolism of pantoprazole and have provided an explanation for the formation mechanism of its metabolites. Metabolites found in the urine of rats after oral administration of pantoprazole sodium (25 mg kg(-1)) were analysed by liquid chromatography/ion trap mass spectrometry (LC/MS(n)). The N -acetylcysteine derivatives of benzimidazole (M1) and pyridine (M2), four pyridine-related metabolites (M3-M6), and three benzimidazole-related metabolites (M7-M9) were found, none of which had been reported previously. Five of the metabolites (M1, M2, M3, M7, and M8) were isolated from the urine of rats after oral administration of pantoprazole sodium by semipreparative HPLC. Structures of these metabolites were identified by a combination analysis of LC/MS(n) and (1)H NMR spectra. Structures of the remaining four metabolites (M4, M5, M6, and M9) were tentatively assigned through LC/MS(n). The metabolites M2, M3, M4, M5 and M6 and the other metabolites (M1, M7, M8, and M9) reflected the fate of the pyridine moiety and the benzimidazole moiety, respectively. The proposed formation route of M3-M6 was via initial reduction to mercaptopyridine followed by S-methylation, O-demethylation, and S-oxidation to the corresponding sulfoxide or sulfone. Meanwhile, M8 and M9 were formed via initial reduction to the 5-difluoromethoxy-1H benzoimidazole-2-thiol (M7) followed by hydroxylation and S-methylation. The metabolism of pantoprazole included an attack by glutathione on the benzimidazole-2-carbon and pyridine-7'-carbon. It is an important metabolic pathway of pantoprazole in rats.

Experimental design approach for the optimisation of a HPLC-fluorimetric method for the quantitation of the angiotensin II receptor antagonist telmisartan in urine

A high performance liquid chromatographic method with fluorimetric detection has been developed for the quantitation of the angiotensin II receptor antagonist (ARA II) 4-((2-n-propyl-4-methyl-6-(1-methylbenzimidazol-2-yl)-benzimidazol-1-yl)methyl)biphenyl-2-carboxylic acid (telmisartan) in urine, using a Novapak C18 column 3.9 x 150 mm, 4 microm. The mobile phase consisted of a mixture acetonitrile-phosphate buffer (pH 6.0, 5 mM) (45:55, v/v) pumped at a flow rate of 0.5 ml min(-1). Effluent was monitored at excitation and emission wavelengths of 305 and 365 nm, respectively. Separation was carried out at room temperature. Chromatographic variables were optimised by means of experimental design. A clean-up step was used for urine samples consisting of a solid-phase extraction procedure with C8 cartridges and methanol as eluent. This method proved to be accurate (RE from -12 to 6%), precise (intra- and inter-day coefficients of variation (CV) were lower than 8%) and sensitive enough (limit of quantitation (LOQ), ca. 1 microg l(-1)) to be applied to the determination of the active drug in urine samples obtained from hypertensive patients. Concentration levels of telmisartan at different time intervals (from 0 up to 36 h after oral intake) were monitored.

Absorption, metabolism, and excretion of intravenously and orally administered [14C]telmisartan in healthy volunteers

The study was conducted in healthy male volunteers to evaluate the absorption, metabolic pattern, and mode of elimination of telmisartan, a nonpeptide angiotensin II receptor antagonist. [14C]telmisartan was administered orally in solution as a single 40 mg dose to 5 subjects. A further 5 subjects received short-term intravenous infusion of [14C]telmisartan 40 mg. Measurement of total 14C radioactivity in plasma showed that about 50% was absorbed following oral administration, with maximum plasma concentration observed after 0.5 to 1 hour. Absolute bioavailability was 43%. On average, 84% of total radioactivity in plasma reflected the parent compound. The remainder of total radioactivity could be ascribed to the glucuronide conjugate of telmisartan, which represented the only metabolite in man. About 99.5% of telmisartan was bound to plasma protein, mainly to albumin and alpha-1-acid glycoprotein. Telmisartan was reversibly distributed into erythrocytes. More than 90% of administered dose was excreted within 120 hours, and the excretion balance was complete 144 hours after dosing. Radioactivity was almost exclusively (> 98%) excreted via the feces; urinary excretion accounted for < 1% of the dose, irrespective of the route of administration. In the small fraction excreted into urine, the glucuronide conjugate of telmisartan was predominant. Although some telmisartan glucuronide was detected in plasma, only unchanged drug was identified in the feces. No changes in vital signs, electrocardiogram, or clinical laboratory tests were detected following telmisartan administration, and adverse events, predominantly unrelated to treatment and of mild intensity, were infrequent. One subject fainted and, on another occasion, reported faintness; these events were probably due to the antihypertensive action of the intravenous study medication.

Determination of candesartan cilexetil, candesartan and a metabolite in human plasma and urine by liquid chromatography and fluorometric detection

Liquid chromatographic methods are described for the determination of a new effective anti-hypertensive drug candesartan (CV-11974), its prodrug candesartan cilexetil (TCV-116) and a metabolite, CV-15959 in human plasma and urine. The assays comprise liquid-liquid extraction and separation on a phenyl column with fluorometric detection. The methods give absolute recoveries of 70, 83 and 78% for candesartan cilexetil, candesartan and CV-15959, respectively, and the limit of quantification is 5, 1 and 3 nM of plasma (RSD < 20%), respectively. The methods were applied to plasma and urine samples from biopharmaceutical and clinical studies in man.

Semi-automated solid-phase extraction procedure for the high-performance liquid chromatographic determination of alinastine in biological fluids

A solid-phase extraction (SPE) method for sample clean-up followed by a reversed-phase HPLC procedure for the assay of alinastina (pINN) in biological fluids is reported. The effects of the sample pH, composition of the washing and elution solvents and the nature of the SPE cartridge on recovery were evaluated. The selectivity of SPE was examined using spiked rat urine and plasma samples and the CH and PH cartridges gave rise to the cleanest extracts. The recoveries obtained in spiked rat urine and plasma samples were 91.2+/-2.7 and 99.9+/-2.8%, respectively. The proposed SPE method coupled off-line with a reserved-phase HPLC system with fluorimetric detection was applied to the quantitation of alinastine in real rat urine samples. The analytical method was also applied and validated for the determination of alinastine in dog plasma. The recovery from spiked dog plasma samples using the PH cartridge was around 65%. The within-day and between-day precisions were 7 and 12%, respectively. The detection and quantitation limits in dog plasma were 0.024 and 0.078 microg/ml, respectively.

High-performance liquid chromatographic assay for a new fasciolicide agent, alphaBIOF10, in biological fluids

This paper describes a high-performance liquid chromatographic method with ultraviolet absorbance detection at 304 nm for the determination of 6-chloro-5-(1-naphthyloxy)-2-methylthio benzimidazole (alphaBIOF10) -- a new fasciolicide agent -- and its sulphoxide (SOalphaBIOF10), in plasma and urine. It requires 2 ml of biological fluid, an extraction using Sep-Pak cartridges, and methanol for drug elution. Analysis is performed on a microBondapak C18 (10 microm) column, using methanol-acetonitrile-water (40:30:30, v/v) as the mobile phase. Results showed that the assay is sensitive: 7.2 ng/ml for alphaBIOF10 and SOalphaBIOF10 in plasma and 3.6 ng/ml for both compounds in urine. The response was linear between 0.195 and 12.5 microg/ml. Maximum intra-day coefficient of variation was 5.3%. Recovery obtained was 97.8% for both alphaBIOF10 and SOalphaBIOF10. In urine, recovery was 99.6% and 93.1% for alphaBIOF10 and SOalphaBIOF10 respectively. The method was used to perform a preliminary pharmacokinetic study in two sheep and was found to be satisfactory.

Quantitative gas chromatographic analysis of [1-(4-piperidinyl)-1,3-dihydro-2H-benzimidazole-2-one], the basic metabolite of bezitramide (Burgodin), in human urine

A gas chromatographic procedure with nitrogen-phosphorus detection was developed for the quantitative determination of 1-(4-piperidinyl)-1,3-dihydro-2H-benzimidazole-2-one, the basic metabolite of the narcotic analgesic bezitramide (Burgodin), in urine. Gas chromatography with mass spectrometric detection was used for confirmation. An internal standard with great structural resemblance to the basic metabolite was synthesized in our laboratory. For the isolation of the compound from urine, a liquid-liquid extraction with chloroform/isopropanol was performed. The extract was derivatized with pentafluorobenzoylchloride immediately before chromatographic analysis. The calibration curve was linear over a broad concentration range (10 to 1000 ng/mL). The quantitation limit was 10 ng/mL, and at a 250-ng/mL concentration, coefficients of variation of 2.8 and 3.4% were obtained for within-day and between-day precision, respectively. The selectivity and accuracy of the method were satisfactory. Out of 150 urine samples, mainly from persons suspected of using bezitramide or from known drug abusers, 22 samples revealed basic metabolite concentrations that ranged from 17.0 to 1695.5 ng/mL. The described method allows the quantitation of the basic metabolite of bezitramide with high sensitivity, selectivity, and precision. It can also be used to determine bezitramide abuse and to establish bezitramide overdoses.

Pharmacokinetics and tolerance of pantoprazole, a proton pump inhibitor after single and multiple oral doses in healthy Japanese volunteers

The pharmacokinetics and tolerance of pantoprazole were investigated after single (20, 40, 80, and 120 mg) and multiple (80 mg once a day for 7 days) oral administration as enteric-coated tablet formulation to healthy male Japanese volunteers. Pantoprazole was well tolerated with no serious adverse events at all doses. Pantoprazole was rapidly absorbed in the fasted state. The mean maximum concentration in serum (Cmax) ranged from 1.77-9.25 micrograms/ml for the 20-120 mg dose and the mean time to reach Cmax (tmax) ranged from 1.92-2.42 h. The half-life (t1/2) ranged from 0.74-1.16 h. A good linear correlation was found between the administered doses (20-120 mg) and the resulting area under the concentration-time curve (AUC) and Cmax with the correlation coefficients of 0.9088 and 0.9263, respectively. Within 24 h, pantoprazole was excreted into urine as the unchanged drug to a negligible extent. In the multiple dose study, 2 apparent poor metabolizers (PMs) of pantoprazole were observed. The means of Cmax, AUC and t1/2 for these 2 PMs were 1.6, 6.7, and 6.8 times higher than those of the extensive metabolizers (EMs). The pharmacokinetic parameters such as Cmax, AUC, and t1/2 after the 7th oral dose were not significantly different from those after the 1st dose both in the PMs and the EMs, which indicated that there was virtually no drug accumulation.

Monitoring of exposure to benomyl in nursery workers

We compared urinary levels of the metabolite methyl-5-hydroxy-2-benzimidazole carbamate (5-HBC) among nursery workers exposed to the fungicide benomyl (specifically Benlate 50 DF [DuPont, Wilmington, DE]) and workers not exposed to benomyl. Environmental exposures were quantitated from gloves, body patches, and air samples collected with area and personal monitors. The median concentration of 5-HBC in the urine of benomyl-exposed workers was 23.8 mumol of 5-HBC per mole of creatinine. No 5-HBC was detected in the reference group. Industrial hygiene results and biological monitoring findings indicate that use of Benlate 50 DF in the ornamental industry can lead to absorption of the active ingredient, benomyl. Weighing, mixing, and application activities involved the highest exposures. Dermal contact appeared to be the primary route of exposure.

Quantitative gas chromatographic analysis of 3-cyano-3,3-diphenylpropionic acid, the acidic metabolite of bezitramide (Burgodin), in urine

A sensitive gas chromatographic procedure with nitrogen-phosphorus detection was developed for the quantitative determination of 3-cyano-3,3-diphenylpropionic acid, the acidic metabolite of the narcotic analgesic bezitramide (Burgodin). Gas chromatography with mass spectrometric detection was used for confirmation. An internal standard, 5-cyano-5,5-diphenylvaleric acid, was synthesized and purified in our laboratory. The compound was extracted from 5 mL of hydrolyzed urine with n-hexane-ethyl acetate (85:15, v/v). Derivatization of the extract with an ethereal diazomethane solution was performed immediately before chromatographic analysis. Under the described conditions, the quantitation limit for 3-cyano-3, 3-diphenylpropionic acid in urine was 10 ng/mL. The extraction recovery was 82%. The calibration graph was linear over the concentration range from 10 to 500 ng/mL; at a 100-ng/mL concentration, within-day and day-to-day percent coefficients of variation of 1.9 and 3.7%, respectively, were obtained. Urine samples from 16 persons suspected of using bezitramide were analyzed, and they revealed metabolite concentrations that ranged from 10.5 to 88 ng/mL.

Quantitation of a new potent angiotensin II receptor antagonist, TCV-116, and its metabolites in human serum and urine

A sensitive high-performance liquid chromatographic (HPLC) method is described for the determination of a new potent antihypertensive agent, TCV-116, and its two metabolites (M-I and M-II) in human serum or urine. After pre-treatment of the specimens, the analytes were determined using a column switching technique, except for the metabolites in urine which were determined by gradient elution mode HPLC. The quantitation limits for TCV-116, M-I and M-II were all 0.5 ng/ml in serum, and 0.5, 10 and 110 ng/ml in urine, respectively. The methods were applied to clinical trials of TCV-116.

Development and validation of column-switching high-performance liquid chromatographic methods for the determination of a potent AII receptor antagonist, TCV-116, and its metabolites in human serum and urine

Column-switching HPLC methods have been developed and validated for the determination of a new antihypertensive prodrug, TCV-116 (I), and its metabolites, CV-11974 (II) and CV-15959 (III), in human serum and urine. Initial sample cleanup was achieved by extracting the analytes into an organic solvent. After chromatographing on an ODS column with a mobile phase consisting of acetonitrile and an acidic phosphate buffer, the zone of the analyte's retention was heart-cut onto a second ODS column with a mobile phase of acetonitrile and a phosphate buffer at a higher pH. Complete separation of the analytes and the endogenous peaks was accomplished by the two-dimensional chromatography. Good precision and linearity of the calibration standards, as well as the inter-day and intra-day precision and accuracy of quality control samples, were achieved. The limit of quantitation (LOQ), using 0.5 ml of serum, was 2 ng/ml for I, 0.8 ng/ml for II, and 0.5 ng/ml for III. The LOQ for urine sample was 10 ng/ml for II and III. Stability of the analytes during storage, extraction, and chromatography processes was established. The results illustrate the versatile application of column switching to method development of multiple analytes in various biological matrices. The methods have been successfully used for the analyses of I and its metabolites in thousands of clinical samples to provide pharmacokinetic data.

High-performance liquid chromatographic analysis of mibefradil in dog plasma and urine

The objective of the study was to develop a sensitive and specific assay for studying the pharmacokinetics of a novel calcium antagonist, a benzimidazolyl-substituted tetraline derivative, mibefradil (I) in the dog. The assay involves liquid-liquid extraction of a biological sample, reversed-phase HPLC separation and fluorescence detection (lambda ex = 270 nm and lambda em = 300 nm) of sample components. Each sample was eluted with a mobile phase pumping at a flow-rate of 2 ml/min. The mobile phase composition was a mixture of acetonitrile and aqueous solution (38:62, v/v). The aqueous solution contains 0.0393 M KH2PO4 and 0.0082 M Na-pentanesulphonic acid. The retention times were 10.7 min for I, and 12.2 min for internal standard Ro 40-6792. Calibration curves with concentrations of I ranging from 10 to 500 ng/ml were linear (r2 > 0.99). The detection limit for I was 0.5 ng/ml when 0.5 ml of plasma or urine was used. Intra- and inter-day accuracy and precision were within 10%. The assay was successfully applied to the pharmacokinetic studies of I in dogs.

A simple method for the determination of YM060 in plasma and urine by high performance liquid chromatography

We developed a simple method for the determination of YM060, a new 5-HT3 receptor antagonist, in plasma and urine. The method has good accuracy and precision, and sufficient sensitivity to allow use in pharmacokinetic studies of YM060 in humans and laboratory animals.

Determination of methyl 5-hydroxy-2-benzimidazole carbamate in urine by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic (HPLC) assay for methyl 5-hydroxy-2-benzimidazole carbamate (5-HBC) in urine was developed in order to assess the exposure of workers to the pesticide carbendazim. 5-HBC is measured in urine after hydrolysis, sample clean-up through a strong cation-exchange (SCX) column and extraction with ethyl acetate. HPLC with electrochemical detection provides selective and sensitive determination of 5-HBC with a detection limit of 5 micrograms/l. A C18 reversed-phase column was used with 0.06 M ammonium acetate solution (pH 8)-methanol (73:27) as mobile phase. The method was validated with respect to hydrolysis of urine samples, analytical recovery of spiked 5-HBC, stability of 5-HBC conjugates, limit of detection, background and precision. The overall analytical recovery from urine was better than 60%. 5-HBC, excreted in urine as a conjugate, was stable for at least one year when stored at -20 degrees C. A background of ca. 5 micrograms/l was detected in urine from some non-occupationally exposed persons. Between-day coefficients of variation as calculated from the results of the stability test were 7, 4 and 4% for concentrations of 61, 244 and 295 micrograms/l 5-HBC, respectively (n = 16).

Determination of luxabendazole in biological fluids by high-performance liquid chromatography

Luxabendazole, a new benzimidazole, is a highly potent broad-spectrum anthelmintic. A high-performance liquid chromatographic method has been developed for its determination in serum and urine samples. In order to optimize the clean-up of samples we compared two procedures: C18 Sep-Pak cartridges and ultrafiltration through a cellulose membrane with a 30,000 relative molecular mass cut-off. In order to obtain the most suitable mobile phase, we studied the influence of pH and acetonitrile content on the capacity factor (k'). Chromatographic separation and quantification were performed on a reversed-phase column packed with 5-microns Nucleosil C18. The mobile phase was acetonitrile-0.05 M phosphate buffer (pH 7.0), (40:60, v/v). The column effluent was monitored by ultraviolet-visible spectrophotometry at 290 nm. The method shows good recovery, precision and accuracy. The lower limit of detection for luxabendazole is 15 ng/ml in serum samples and 25 ng/ml in urine samples.

Direct injection/h.p.l.c. methods for the analysis of drugs in biological samples

1. Direct injection h.p.l.c. methods for zaprinast, and pantoprazole and its sulphone metabolite were developed. 2. Optimal recovery of pantoprazole and its sulphone metabolite was effected by the absence of transfer losses and the effective adjustment of sample pH on-line. 3. Acetonitrile reduced the recovery of pantoprazole and its sulphone metabolite at acetonitrile concentrations greater than 5% in serum. 4. Direct injection h.p.l.c. methods minimize sample handling losses, reduce human contact with biological samples and are sufficiently accurate and reproducible to be used to support pharmacodynamic and toxicokinetic studies.

Reversed-phase ion-pair high-performance liquid chromatographic determination of triclabendazole metabolites in serum and urine

An ion-pair high-performance liquid chromatographic method was developed for measuring the concentrations of triclabendazole metabolites (sulphoxide and sulphone) in plasma and urine samples. The diluted biological fluids are ultrafiltered before chromatography through a 30,000 relative molecular mass cut-off filter and then injected into a C18 column. They are then isocratically eluted with a mobile phase consisting of 0.05 M phosphate buffer (pH 7.0)-acetonitrile (55:45, v/v) with addition of 1.0 mmol/l sodium decanesulphonate and monitored by ultraviolet-visible spectrophotometry at 312 nm. Recoveries over the range 0.01-9.0 micrograms/ml for triclabendazole sulphoxide and sulphone are, respectively, 91.7% and 91.6% in serum and 90.3% and 90.2% in urine. For both metabolites, the limit of detection is 10 ng/ml in both urine and serum.

The effect of co-administration of parbendazole on the disposition of oxfendazole in sheep

The effect of intraruminal administration of parbendazole (PBZ) on the flow rate of bile and the pharmacokinetic behaviour of oxfendazole (OFZ) was examined in sheep. PBZ given at 18, 9 and 4.5 mg/kg resulted in a dose-related reduction in bile flow rate which was also inversely related to changing concentration of PBZ and its metabolites in plasma. Co-administration of 4.5 mg PBZ/kg with 5.0 mg [14C]-OFZ/kg resulted in increased concentrations of fenbendazole (FBZ), OFZ and fenbendazole sulphone (FBZ-SO2) in plasma, although total 14C levels remained unchanged compared with that observed when OFZ alone was administered. The presence of PBZ also reduced biliary secretion of 14C by 22% and altered the relative proportions of OFZ metabolites in bile during the 72-h experimental period. The ratio of 4'-hydroxy-OFZ (OH-OFZ) to 4'-hydroxy-FBZ (OH-FBZ) changed from 7:1 in the absence of PBZ to approximately 1:1 in the presence of PBZ. There was no change in urinary or faecal 14C excretion. The PBZ-induced effects were temporary since the pharmacokinetic behaviour of OFZ given alone two weeks before was similar to that given two weeks after PBZ co-administration. It is suggested that the presence of PBZ temporarily slowed hepatic metabolism and biliary secretion of OFZ metabolites but concomitantly increased extra-biliary transfer of OFZ and/or its metabolites from plasma into the gastrointestinal tract. Elevated exposure of parasites in the gut wall to plasma-derived drug, coupled with higher concentrations of anthelmintically active OH-FBZ secreted in bile, could contribute to the previously reported increased efficacy of OFZ when co-administered with PBZ.

Rapid analysis for metabolites of 11C-labelled drugs: fate of [11C]-S-4-(tert.-butylamino-2-hydroxypropoxy)-benzimidazol-2-one in the dog

Positron emission tomography (PET) requires the use of compounds labelled with short-lived, positron-emitting isotopes (e.g., t1/2 of 11C approximately 120 min). As the concentration of unbound, non-metabolised drug is required as the input function for modeling, this presents particular problems for the study of the kinetics and metabolism of such compounds. We have now developed a rapid extraction procedure, followed by high-performance liquid chromatography using a short analytical column coupled to an on-line gamma-detector to determine the metabolism and kinetics of a non-selective beta-adrenergic antagonist of high affinity, S-4-(tert.-butylamino-2-hydroxypropoxy)benzimidazol-2-one. This antagonist is potentially well suited to the non-invasive localisation of beta-receptors in vivo. The ligand was rapidly taken up into the beta-receptor pool or excreted in urine, with less than 5% of the drug converted to metabolites. Plasma protein binding was only 16%. No significant metabolism of the ligand was observed in the anaesthetised dog, and, therefore, no correction for blood metabolite concentration is required for kinetic analysis of the 11C-labelled ligand during PET studies in this species. The analytical method reported here should be widely applicable: quantification of metabolites enables accurate estimation of the input function and is critical to the interpretation of PET data.

[Triclabendazole (Fasinex) residue in milk: determination and excretion kinetics]

The determination of triclabendazole (Fasinex) in milk is described. The excretion of triclabendazole and its two main metabolites was measured under field conditions in twenty-five cows. Triclabendazole was administered to cows in a dosage of approximately 12 mg kg-1. The maximum concentration of the main metabolites of triclabendazole (triclabendzole sulphone) measured in milk was 1.415 mg/l. Metabolites could be detected in milk during a ten-day-period. Only 1.5% (maximum) of the triclabendazole administered was eliminated as triclabendazole sulphone by way of milk.

[Identification of the metabolites of an antiallergic agent, 1-(2-ethoxyethyl)-2-(hexahydro-4-methyl-1H-1,4-diazepine-1-yl)-1H- benzimidazole difumarate (KG-2413), in rats]

The urinary and biliary metabolites of a new antiallergic agent, 1-(2-ethoxyethyl)-2-(hexahydro-4-methyl-1H-1,4-diazepine-1-yl)-1H-b enzimidazole difumarate (KG-2413) in rats were identified by using a 14C-labelled drug and instrumental analyses, e.g., high performance liquid chromatography, gas chromatography (GC), 1H nuclear magnetic resonance, mass spectrometry (MS) and GC/MS. A slight amount of KG-2413 free base was detected only in the unconjugated fraction of urine. The main pathways of biotransformation of KG-2413 in rats were: (a) aromatic hydroxylation in the benzimidazole ring, (b) N-oxidation and N-demethylation in the 1,4-diazepine ring, (c) alpha-carbon oxidation (lactam formation) in the 1,4-diazepine ring (d) O-deethylation in the N-ethoxyethyl side chain. Regioselectivity was observed for aromatic hydroxylation, as only two of the four possible monohydroxylated metabolites could be detected. Furthermore, N-oxidation and lactam formation reactions were found to be regiospecific, that is, the former took place only at the position of 4-N atom and the latter at 5-C atom, respectively.

Identification of the main urinary metabolites of omeprazole after an oral dose to rats and dogs

The structures of seven urinary metabolites of omeprazole following high oral doses to rats and dogs were determined unambiguously by combining different analytical and spectroscopic techniques including derivatization and stable isotopes. Omeprazole was metabolized by aromatic hydroxylation at position 6 in the benzimidazole ring followed by glucuronidation. There was also oxidative O-dealkylation of both methoxy groups, and aliphatic hydroxylation of a pyridine methyl group followed by oxidation to the corresponding carboxylic acid. Due to the experimental design, implying no pH control of collected samples, all metabolites were isolated as sulfides. They were formed in both species with quantitative variations in the metabolic pattern. As far as identified metabolites are concerned, aromatic hydroxylation and subsequent glucuronide formation were the major biotransformation routes in the dog. In the rat, aliphatic hydroxylation and the formation of the carboxylic acid represented the major metabolic pathways. The identified metabolites corresponded approximately to 50% (rat) and 70% (dog) of the amount excreted in the 0-24-hr urine (about 12% of the given dose in both species).

Comparative metabolic disposition of oral doses of omeprazole in the dog, rat, and mouse

The metabolic disposition of [14C]omeprazole was studied in dogs, rats, and mice after the administration of pharmacologically active, single oral doses of drug in buffer solutions (pH 9). Averages of 38% (dogs), 43% (rats), and 55% (mice) of the radiolabeled doses were excreted in the urine in 72 hr. Most of the remaining dose was recovered in the feces. Omeprazole was extensively metabolized in all species studied and the metabolites were eliminated rapidly. No unchanged drug could be detected in the urine samples (less than 0.1% of dose). In each species at least 10 metabolites were detected in urine (pH 9) by gradient elution reverse phase HPLC. Based on liquid chromatographic retention data, the metabolic patterns were very complex and exhibited some quantitative differences between species. Bile was collected from rats and from chronic bile-fistulated dogs. Biliary excretion was a major route of elimination of omeprazole metabolites, and four polar metabolites were detected in the rat bile. The stability of omeprazole metabolites at varying pH values is discussed with reference to reductive metabolism of the parent compound.

Clinical pharmacokinetics of H1-receptor antagonists (the antihistamines)

This article reviews clinical pharmacokinetic data on the H1-receptor antagonists, commonly referred to as the antihistamines. Despite their widespread use over an extended period, relatively little pharmacokinetic data are available for many of these drugs. A number of H1-receptor antagonists have been assayed mainly using radioimmunoassay methods. These have also generally measured metabolites to greater or lesser extents. Thus, the interpretation of such data is complex. After oral administration of H1-receptor antagonists as syrup or tablet formulations, peak plasma concentrations are usually observed after 2 to 3 hours. Bioavailability has not been extensively studied, but is about 0.34 for chlorpheniramine, 0.40 to 0.60 for diphenhydramine, and about 0.25 for promethazine. Most of these drugs are metabolised in the liver, this being very extensive in some instances (e.g. cyproheptadine and terfenadine). Total body clearance in adults is generally in the range of 5 to 12 ml/min/kg (for astemizole, brompheniramine, chlorpheniramine, diphenhydramine, hydroxyzine, promethazine and triprolidine), while their elimination half-lives range from about 3 hours to about 18 days [cinnarizine about 3 hours; diphenhydramine about 4 hours; promethazine 10 to 14 hours; chlorpheniramine 14 to 25 hours; hydroxyzine about 20 hours; brompheniramine about 25 hours; astemizole and its active metabolites about 7 to 20 days (after long term administration); flunarizine about 18 to 20 days]. They also have relatively large apparent volumes of distribution in excess of 4 L/kg. In children, the elimination half-lives of chlorpheniramine and hydroxyzine are shorter than in adults. In patients with alcohol-related liver disease, the elimination half-life of diphenhydramine was increased from 9 to 15 hours, while in patients with chronic renal disease that of chlorpheniramine was very greatly prolonged. Little, if any, published information is available on the pharmacokinetics of these drugs in neonates, pregnancy or during lactation. The relatively long half-lives of a number of the older H1-receptor antagonists such as brompheniramine, chlorpheniramine and hydroxyzine suggest that they can be administered to adults once daily.

Determination of omeprazole and metabolites in plasma and urine by liquid chromatography

Omeprazole, a substituted benzimidazole and a new gastric acid inhibitor, has been determined in plasma and urine, together with three of its metabolites--the sulphide, the sulphone and the hydroxy compound. The methods comprise extraction from the biological materials with methylene chloride, followed either by direct injection of the extract onto a normal-phase liquid chromatography column or evaporation, dissolution and injection onto a reversed-phase system. The compounds were detected using ultraviolet spectrometry. The absolute recoveries obtained were mostly above 95%. The minimum determinable concentration for omeprazole was 20 nmol/l in plasma (relative standard deviation 10-15%) and 50 nmol/l in urine. The metabolites could also be determined at the same levels.

Plasma levels, biotransformation and excretion of oxatomide (R 35 443) in rats, dogs and man

Plasma levels, biotransformation and excretion of oxatomide were studied after single oral doses of 14C-oxatomide in male rats, dogs and humans. Oxatomide was very well absorbed, and almost completely metabolized in the three species. Excretion of the metabolites was very rapid and complete within a few days; the 14C label was excreted more in the faeces (54-62%) than in the urine (27-40%). Major metabolic pathways of oxatomide were oxidative N-dealkylations at the piperazine nitrogens and at the benzimidazolone nitrogen in rats and man, and also aromatic hydroxylation at the benzimidazolone moiety in man. The main urinary metabolite in the three species was 2,3-dihydro-2-oxo-1H-benzimidazole-1-propanoic acid, resulting from the oxidative N-dealkylation at the 1-piperazine nitrogen.

Simultaneous high-performance liquid chromatographic analysis of omeprazole and its sulphone and sulphide metabolites in human plasma and urine

Omeprazole, a substituted benzimidazole which suppresses gastric acid secretion, and its sulphone and sulphide metabolites were simultaneously measured in human plasma and urine using a selective, reversed-phase, high-performance liquid chromatographic method with a sensitivity of 5 ng/ml for omeprazole, 30 ng/ml for omeprazole sulphone, and 50 ng/ml for omeprazole sulphide. The coefficients of variation for within-day assays were 4.4, 7.5, and 17.5%, respectively. In a pilot pharmacokinetic study, 40 mg of omeprazole (encapsulated enteric-coated granules) were administered to two healthy volunteers. Peak plasma concentrations for omeprazole of 240 and 520 ng/ml, and for omeprazole sulphone of 320 and 400 ng/ml, were reached between 3 and 4 h post-dose. Omeprazole concentrations fell rapidly with apparent half-lives of about 40 min, and concentrations of both omeprazole and the sulphone metabolite were below the minimal detectable level by 6-8 h. Omeprazole sulphide could not be detected in this study.

[Pharmacokinetics and urinary metabolism of albendazole in man]

Albendazole, a new broad spectrum benzimidazole anthelmintic, has been administered in 10 male volunteers. Administration was randomized using 100 mg tablets, 200 mg tablets and a 2% suspension. Blood samples were obtained 0.5; 1; 1.5; 2; 2.5; 3; 3.5; 4; 5; 6; 8; 12; 24; 72 h after treatment. Albendazole sulfoxide, one of the mains albendazole blood metabolites, was assayed by HPLC and the blood half life was calculated as 8 1/2 h. The three different pharmaceutical formulations were considered bioequivalent. Urines were collected, and using T. L. C. Technics, main metabolites were identified and characterized. Hydrolysis of the carbamate function and oxidation of the sulfur atom, the alkyle chain and the aromatic ring were the main biotransformations observed.

Metabolic formation of N- and O-glucuronides of 3-(p-chlorophenyl)thiazolo[3,2-a]benzimidazole-2-acetic acid. Rearrangement of the 1-o-acyl glucuronide

Excretion of 3-(p-chlorophenyl)thiazolo[3,2-a]benzimidazole-2-acetic acid (I) and its metabolites was studied in rats, beagle dogs, and rhesus monkeys given 20-mg/kg doses of 14C-labeled drug. The urine of rhesus monkeys contained two metabolites in addition to unchanged drug. Both metabolites were hydrolyzed to I by beta-glucuronidase and the hydrolysis was inhibited by 1,4-saccharolactone, indicating that they were glucuronides of I. One of the metabolites (III) was not hydrolyzed by dilute alkali. Its NMR spectrum indicated that the site of conjugation was one of the nitrogen atoms, i.e., it was a quaternary N-glucuronide. The FAB mass spectrum was in conformity with this assignment. This metabolite was not present in the urine of dogs or rats given labeled drug. The other metabolite (II) was excreted in the urine of all three species as well as in the bile of the rat. It was readily hydrolyzed by dilute alkali (pH 11 for 0.5 hr at 37 degrees C), indicating that this metabolite was an acyl glucuronide. The metabolite was stable at pH 4.5 but it was readily converted to three isomers at 37 degrees C within 1 hr at pH 6.5 and above. The mass spectra of the derivatized isomers and metabolite were similar. The isomers were hydrolyzed to I by dilute alkali but not by beta-glucuronidase. They exhibited reducing properties (whereas metabolite II did not), suggesting that they were formed by acyl migration of the aglycone to the second, third, and fourth carbon atoms of the glucuronic acid moiety. Acyl migration probably plays a role in the disposition of I as well as other drugs that form labile glucuronides.

Biotransformation of methyl 5-cyclopropylcarbonyl-2-benzimidazolecarbamate (ciclobendazole) in rats and dogs

A major metabolite of ciclobendazole (methyl 5-cyclopropylcarbonyl-2-benzimidazolecarbamate) excreted in the urine, bile, and feces of rats was methyl 5-cyclopropylcarbonyl-6-hydroxy-benzimidazolecarbamate, established by comparison of the proton magnetic resonance and mass spectra with that of the authentic compound. This compound represented 8.2% and 7.1% of the dose, respectively, in extracts of 24-hr urine and 48-hr feces samples of rats, but was only a minor metabolite in dog urine (1% of the dose). The unchanged drug was only detected in dog feces, the major route of excretion of radioactivity in the dog. 5-Cyclopropylcarbonyl-2-amino-benzimidazole was present in rat urine (2.5% of the dose). A major metabolite in dog bile was probably 5-cyclopropylcarbinol-2-aminobenzimidazole, formed by loss of the methoxycarbonyl group and reduction of the carbonyl function in the 5-position.

Determination of the metabolites of bezitramide in urine. II. The basic metabolite

A high-performance liquid chromatographic method for the determination of low levels (less than 1 microgram/ml) of the basic metabolite of bezitramide, 1-(4-piperidinyl)-1,3-dihydro-2H-benzimidazol-2-one, in human urine is described. Special attention is given to the separation from the basic metabolite of droperidol, a drug frequently co-administered with bezitramide.

Determination of the metabolites of bezitramide in urine. I. Acidic metabolite

Two methylation methods are compared in relation to the determination of low levels (less than microgram/ml) of the acidic metabolite of bezitramide in human urine. It was necessary to use alkali flame ionisation detector, which specifically detects nitrogen-containing compounds. Several difficulties associated with the use of this detector are described.

Antiviral activity of a bis-benzimidazole against experimental rhinovirus infections in chimpanzees

The marked antiviral activity of (S,S-1,2-bis(5-methoxy-2-benzimidazolyl)-1,2-ethanediol (Abbott 36683) against rhinoviruses in tissue culture warranted investigation of its antiviral activity in vivo. Antiviral levels in mouse sera were attained with an oral dose as small as 10 mg/kg and detectable antiviral levels of drug were also found in lung, liver, kidney, intestinal contents, and urine of mice given a single 300 mg/kg oral dose. Antiviral serum levels were also obtained when monkeys were given a single oral dose of Abbott 36683. Six chimpanzees were infected with 100 median tissue culture infective dose units (TCID(50)) of rhinovirus 30. Three of the animals were treated with Abbott 36683, 100 mg/kg daily for 4 consecutive days. Virus shedding occurred in the infected controls but could not be demonstrated in the treated animals from postinfection days 1 to 8. Two of the treated animals did, however, shed virus on day 9. The compound was retested in chimpanzees at dosage levels of 15 and 50 mg/kg daily for 4 days. Each animal was challenged with 100 TCID(50) of rhinovirus 49. Partial protection was obtained. In a third trial, a single 100 mg/kg dose of the compound was administered to chimpanzees infected with rhinovirus 44. Virus was isolated from all throat smears taken from treated animals, indicating that at the lowest drug level no protection occurred.