Enantioselective high-performance liquid chromatographic assay for determination of the enantiomers of a new anti-ulcer agent, E3810, in beagle dog plasma and rat plasma

Development and validation of dissolution testings in acidic media for rabeprazole sodium delayed-release capsules

Rabeprazole sodium (RAB) dissolved in acidic media is accompanied by its degradation in the course of dissolution testing. To develop and establish the accumulative release profiles of ACIPHEX^® Sprinkle (RAB) delayed-release capsules (ACIPHEX^® Sprinkle) in acidic media using USP apparatus 2 (paddle apparatus) as a dissolution tester, the issues of determination of accumulative release amount of RAB in these acidic media and interference of hydroxypropylmethyl cellulose phthalate were solved by adding appropriate hydrochloric acid (HCl) into dissolution samples coupled with centrifugation so as to remove the interference and form a solution of degradation products of RAB, which is of a considerably stable ultraviolet (UV) absorbance at the wavelength of 298 nm within 2.0 h. Therefore, the accumulative release amount of RAB in dissolution samples at each sample time points could be determined by UV-spectrophotometry, and the accumulative release profiles of ACIPHEX^® Sprinkle in the media of pH 1.0, pH 6.0, and pH 6.8 could be established. The method was validated per as the ICH Q2 (R1) guidelines and demonstrated to be adequate for quality control of ACIPHEX^® Sprinkle and the accumulative release profiles can be used as a tool to guide the formulation development and quality control of a generic drug for ACIPHEX^® Sprinkle.

Development and validation of a dissolution test for rabeprazole sodium in coated tablets

The aim of this work is to develop and validate a dissolution test for rabeprazole sodium coated tablets using a reverse-phase liquid chromatographic method. After test sink conditions, dissolution medium and stability of the drug, the best conditions were: paddle at 75 rotations per minute (rpm) stirring speed, HCl 0.1 M and borate buffer pH 9.0 as dissolution medium for acidic and basic steps, respectively, volume of 900 ml for both. The quantitation method was also adapted and validated. Less than 10% of the label amount was released in the acid step, while more than 95% was achieved over 30 min in the basic one. The dissolution profile for tablets was considered satisfactory. The dissolution test developed was adequate for its purpose and could be applied for quality control of rabeprazole tablets, since there is no official monograph.

Determination of rabeprazole enantiomers and their metabolites by high-performance liquid chromatography with solid-phase extraction

Here, we describe the development of a rapid, simple and sensitive high-performance liquid chromatography (HPLC) method for the simultaneous quantitative determination of rabeprazole enantiomers (1a,b) and their metabolites, rabeprazole-thioether (2) and rabeprazole sulfone (3), in human plasma. Analytes and the internal standard (omeprazole-thioether) were separated using a mobile phase of 0.5 M NaClO4-acetonitrile (6:4, v/v) over a Chiral CD-Ph column. Analysis required only 100 microl of plasma and involved solid-phase extraction with an Oasis HLB cartridge, which gave high recovery (>91.8%) with good selectivity for all analytes. The lower limit of quantification was 5 ng/ml for analytes 1a, 1b and 3 and 10 ng/ml for 2. Linearity of this assay was determined to lie between 5 and 1000 ng/ml for 1a, 1b and 3 and 10 and 1000 ng/ml for 2 (r2>0.982 of the regression line). Inter- and intra-day coefficients of variation were less than 7.8% and accuracies were within 8.4% over the linear range for all analytes. Our results indicate that this method is applicable to the simultaneous monitoring of plasma levels of rabeprazole enantiomers and associated metabolites in human plasma.

Liquid chromatographic/mass spectrometric assay of rabprazole in dog plasma for a pharmacokinetic study

In order to evaluate the pharmacokinetic (PK) profile of rabeprazole (RA) sterile powder for injection, a rapid, sensitive and specific assay for quantitative determination of RA in dog plasma was developed and validated. After a liquid-liquid extraction procedure, samples were analyzed by liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) using omepazole as the internal standard (IS). The analyte and IS was chromatographed on a ZORBAX Extend-C(18) analytical column (50 x 2 mm i.d, 5 microm, Agilent Technologies, USA). The assay was linear in the range 1-2000 ng/mL. The lower limit of quantification of RA was 1 ng/mL. The recovery of RA was greater than 70%. The within- and between-batch accuracy was 102.7-107.4% and 103.5-105.7%, respectively. The plasma samples for the PK study were collected at defined time points during and after an intravenous injection (1 mg/kg) to beagle dogs and analyzed by LC-ESI-MS method. The PK parameters, such as half-life, volume of distribution, total clearance and elimination rate constant, were determined. The PK profile of RA gave insights into the application in the clinics.

Pharmacokinetic Differences between Pantoprazole Enantiomers in Rats

PURPOSE

The purpose of this study was to quantitatively clarify the contribution of the absorption, protein binding, and metabolism of cytochrome P450 enzymes to the enantioselective pharmacokinetics of pantoprazole enantiomers in rats.

METHODS

The enantioselective pharmacokinetics of pantoprazole enantiomers was estimated by an oral administration of racemic pantoprazole to rats. The pharmacokinetic differences between pantoprazole enantiomers were evaluated by the experiments of the in situ perfusion into rat small intestine, the protein binding, and the in vitro metabolism in rat liver microsomes of pantoprazole enantiomers.

RESULTS

The mean area under the curve value of S-pantoprazole was 1.5 times greater than that of R-pantoprazole after administration of racemic pantoprazole to rats (20 mg/kg, p.o.). There were significant differences in k(e) (p < 0.05), t1/2 (p < 0.01), and mean residence time (p < 0.01) values between the two enantiomers. In the in situ absorption study, the absorption rate constants were of no significant differences between the two enantiomers. The mean unbound fraction of R-pantoprazole was slightly greater than that of S-pantoprazole. The intrinsic clearance (CLint) of the formation of the 5'-O-demethyl metabolite from S-pantoprazole was 4-fold lower than that from R-pantoprazole. However, the CLint value for the sulfone and 6-hydroxy metabolites from S-pantoprazole was higher than that from R-pantoprazole. The sum of the CLint of the formation of all three metabolites was 3.06 and 4.82 mL/min/mg protein for S- and R-pantoprazole, respectively.

CONCLUSIONS

This study suggests that the enantioselective pharmacokinetics of pantoprazole enantiomers in rats is probably ascribable to their enantioselective metabolism, which is contributed by all the three metabolic pathways, including sulfoxide oxidation, 4'-O-demethylation, and 6-hydroxylation.

Bioequivalence evaluation of two rabeprazole enteric coated formulations in healthy Chinese volunteers

A bioequivalence study of two rabeprazole enteric-coated formulations was carried out in 20 healthy Chinese volunteers according to a single dose, two-sequence, crossover randomized design. The two formulations were administered in two treatment days, separated by a washout period of 7 days. Blood samples were collected at specified time intervals over 10 hours post-dosing. Plasma samples were separated and assayed for rabeprazole using a selective and sensitive HPLC method with UV detection. The pharmacokinetic parameters AUC(0-T), AUCmax, Cmax, tmax, t(1/2) and MRT were determined from plasma concentration-time profile of both formulations. ANOVA and two one-sided t test procedures showed no significant difference in log-transformed Cmax, AUC(0-T) AUC(0-infinity) while the 90% confidence interval (CI) of the ratio of the geometric means of their values were also used to assess bioequivalence between the two formulations. The results of this study indicated that the two rabeprazole formulations can be considered to be bioequivalent.

High-performance liquid chromatography method for the quantification of rabeprazole in human plasma using solid-phase extraction

A simple, sensitive and selective HPLC method with UV detection (284 nm) was developed and validated for quantitation of rabeprazole in human plasma, the newest addition to the group of proton-pump inhibitors. Following solid-phase extraction using Waters Oasistrade mark SPE cartridges, the analyte and internal standard (Pantoprazole) were separated using an isocratic mobile phase of 5 mM ammonium acetate buffer (pH adjusted to 7.4 with sodium hydroxide solution)/acetonitrile/methanol (45/20/35, v/v) on reverse phase Waters symmetry C(18) column. The lower limit of quantitation was 20 ng/mL, with a relative standard deviation of less than 8%. A linear range of 20-1000 ng/mL was established. This HPLC method was validated with between- and within-batch precision of 2.4-7.2% and 2.2-7.3%, respectively. The between- and within-batch bias was -1.7 to 2.6% and -2.6 to 2.1%, respectively. Frequently coadministered drugs did not interfere with the described methodology. Stability of rabeprazole in plasma was excellent, with no evidence of degradation during sample processing (autosampler) and 3 months storage in a freezer. This validated method is sensitive, simple and repeatable enough to be used in pharmacokinetic studies.

Development of a liquid chromatography/tandem mass spectrometry assay for the quantification of rabeprazole in human plasma

A simple and sensitive liquid chromatography/tandem mass spectrometry method, employing electrospray ionization, has been developed and validated to quantify rabeprazole in human plasma using omeprazole as the internal standard. The method was validated to demonstrate the specificity, lower limit of quantification, accuracy, and precision of measurements. Selected reaction monitoring was specific for rabeprazole and omeprazole (the internal standard, IS); no endogenous materials interfered with the analysis of rabeprazole and IS from blank plasma. The assay was linear over the concentration range 0.2-200 ng/mL using a 2 microL aliquot of plasma. The correlation coefficients for the calibration curves ranged from 0.9988-0.9994. The intra- and inter-day precision, calculated from quality control samples, were less than 6.65%. A mixture of methanol and water (50:50) was used as the isocratic mobile phase, with 0.1% of formic acid in water, that did not affect the stability of rabeprazole or IS. A simple sample preparation method of protein precipitation with methanol was chosen. The method was employed in a pharmacokinetic study after oral administration of 20 mg rabeprazole to 24 healthy volunteers.

Reversed-phase liquid chromatographic separation of enantiomers on polysaccharide type chiral stationary phases

The direct chiral separation by chiral stationary phases (CSPs) is one of the most important techniques to analyze enantiomeric purity as well as to get enantiomerically pure material quickly. Among various types of CSPs, polysaccharide type CSPs are well known by their versatility and durability. They are not only effective under normal-phase conditions, but also under reversed-phase conditions. In order to get a good separation under the reversed-phase conditions, it is the key to choose an appropriate mobile phase. For example, a simple mixture of water/acetonitrile or water/methanol are sufficient for a neutral analyte, while it is necessary to use an acidic solution instead of water for an acidic analyte and a solution of a chaotropic salt (or a basic solution) for a basic analyte, respectively. The paper also presents lists of more than 350 separation examples that include 22 validated methods for drug analyses from serum, plasma, or urine samples on polysaccharide type CSPs under reversed-phase conditions.

Stereoselective chiral inversion of pantoprazole enantiomers after separate doses to rats

(+/-)-Pantoprazole ((+/-)-PAN), (+/-)-5-(difluoromethoxy)-2-[[3.4-dimethoxy-2-pyridinyl)methyl]sul finyl]- 1H-benzimidazole) is a chiral sulfoxide that is used clinically as a racemic mixture. The disposition kinetics of (+)-PAN and (-)-PAN given separately has been studied in rats. Serum levels of (+)- and (-)-PAN and its metabolites, pantoprazole sulfone (PAN-SO2), pantoprazole sulfide (PAN-S), 4'-O-demethyl pantoprazole sulfone (DMPAN-SO2), and 4'-O-demethyl pantoprazole sulfide (DMPAN-S) were measured by HPLC. Following single intravenous or oral administration, both enantiomers were rapidly absorbed and metabolized, resulting in similar serum concentrations, suggesting that the two enantiomers have approximately the same disposition kinetics. The major metabolite of both (+)- and (-)-PAN was PAN-SO2, while DMPAN-SO2 was also detected as a minor metabolite. Serum levels of PAN-S and DMPAN-S could not be quantified after intravenous or oral administration of either enantiomer. Significant chiral inversion occurred after intravenous and oral administration of (+)-PAN. The AUCs of (-)-PAN after intravenous and oral dosing of (+)-PAN were 36.3 and 28.1%, respectively of those of total [(+) + (-)] PAN. In contrast, the serum levels of (+)-PAN were below quantitation limits after intravenous or oral administration of (-)-PAN. Therefore, chiral inversion was observed only after administration of (+)-PAN, supporting the hypothesis that stereoselective inversion from (+)-PAN to (-)-PAN occurs in rats.

Chiral resolution of pantoprazole sodium and related sulfoxides by complex formation with bovine serum albumin in capillary electrophoresis

The separation of enantiomers of pantoprazole sodium, omeprazole and lansoprazole by capillary zone electrophoresis using bovine serum albumin (BSA) as the chiral selector is described. Baseline separation of the three structurally related drugs was obtained after optimization of the most important experimental parameters. For this purpose, influences such as BSA concentration, pH and concentration of 1-propanol as organic modifier on the separation were investigated. Increasing concentrations of BSA improved the chiral resolution but lowered the sensitivity of the detection system. Discrimination of the enantiomers was observed only in a narrow pH range of 7-8. An optimum of pH 7.4 was a good compromise in terms of enantio-resolution and peak shape. 1-Propanol when added to the buffer system, improved the peak shape of the analytes and the resolution. The optimized method has been validated for pantoprazole sodium and is useful for routine analysis.

Plasma direct injection high-performance liquid chromatographic method for simultaneously determining E3810 enantiomers and their metabolites by using flavoprotein-conjugated column

A high-performance liquid chromatographic method using the column-switching technique was developed for the simultaneous determination of E3810 and its metabolites (M1-M4). An avidin column was used for in-line pretreatment to exclude plasma proteins, allowing direct injection of a large volume of plasma. A flavoprotein-conjugated chiral stationary phase in a gradient elution mode then gave baseline separation of E3810 and the four metabolites. The enantiomers of E3810 and M3 were also separated. The method is simple, rapid, accurate, and precise. Since no extraction procedure is employed, which might involve different recoveries of different metabolites, no internal standard is necessary. The method was applied to analyze E3810 and its metabolites in plasma after intravenous injection of the drug in beagle dogs.