A simple and sensitive HPLC method for the analysis of rabeprazole in plasma is described using UV detection in the presence of lorazepam as the internal standard. Rabeprazole and lorazepam were extracted with ethyl ether and quantitated using a reverse-phase C(18) column. The method was specific as there were no interfering peaks in the human plasma eluting at the retention times of rabeprazole and lorazepam. The method was fully validated in human plasma for the concentration range of 20.0-1000.0 ng/ml. The correlation coefficients were greater than 0.999. Extraction recoveries were 72.3% for the drug and 79.1% for the internal standard. The method was simple, reliable, and accurate for the quantitation of rabeprazole in human plasma. The same plasma samples, which were collected in healthy male volunteers administered a 20 mg tablet of Pariet, were analyzed by HPLC and LC/MS/MS. As a result of that, there was no significant difference between pharmacokinetic parameters. The suitability of HPLC method for pharmacokinetic studies was verified by determining the relevant pharmacokinetic parameters.

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The purpose of the present study was to test a sustained release-tablet newly formulated with synthetic paraffin and compare its bioequivalence to that of the Imdur® Long-Acting tablet, based on the guidelines of the Korean Food and Drug Administration.Dissolution test was performed in 4 different dissolution media. A LC/MS/MS method of isosorbide 5-mononitrate in human plasma was validated. In vivo bioequivalence tests of the 2 isosorbide 5-mononitrate tablets were performed in both preprandial and postprandial states.A comparative dissolution test gave similar results for both tablets in all dissolution media tested: 40% dissolution in pH 1.2 at 2 h and 80% dissolution in pH 4.0, pH 6.8, or water at 10 h. In a bioequivalence study to compare 2 tablets, the mean total area under the curve (AUCt) and peak concentration (Cmax) in the fasted state were 8 476.0 ng · h/mL and 540.4 ng/mL, respectively, for the Imdur® Long Acting Tablet 60 mg, and 8 701.4 ng · h/mL and 564.2 ng/mL, respectively, for the test tablet. The mean AUCt and Cmax in the fed state were 8 793.5 ng · h/mL and 559.9 ng/mL, respectively, for the Imdur® Long-Acting tablet 60 mg, and 8 639.8 ng · h/mL and 617.9 ng/mL, respectively, for the test tablet. The 90% confidence intervals using log transformed data were within the acceptable range of 0.8 - 1.25.Based on these statistical analyses, we conclude that the test tablet is bioequivalent to the Imdur® Long-Acting tablet 60 mg in both the preprandial and postprandial states.

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