1.Simultaneous determination of omeprazole and their main metabolites in human urine samples by capillary electrophoresis using electrospray ionization-mass spectrometry detection.
Nevado JJ1, Peñalvo GC1, Dorado RM1, Robledo VR2. J Pharm Biomed Anal. 2014 Apr;92:211-9. doi: 10.1016/j.jpba.2013.12.020. Epub 2014 Jan 17.
We report a novel method for the simultaneous determination of omeprazole and their main metabolites (omeprazole sulphide, omeprazole sulphone and 5-hydroxy omeprazole) in human urine samples. For this purpose, two new capillary electrophoresis (CE) methods were developed for the simultaneous determination of target compounds, using initially diode-array for optical detection and electrospray ionization-mass spectrometry (ESI-MS) for metabolites identification and identity confirmation. A new metabolite (5-hydroxysulphide omeprazole) was identified by electrospray ionization multi-stage mass spectrometry (ESI-MS2) fragment which was then used to support the proposed chemical structure. Pharmacokinetic results using CE method were compared with those obtained when a HPLC method was used. Equivalent pharmacokinetics profiles resulted when any analytical methods were carried out.
2.Validation of an automated liquid chromatographic method for omeprazole in human plasma using on-line solid-phase extraction.
García-Encina G1, Farrán R, Puig S, Martínez L. J Pharm Biomed Anal. 1999 Nov;21(2):371-82.
An automated system using on-line solid-phase extraction and HPLC with UV detection has been validated in order to determine omeprazole in human plasma. The extraction was carried out using C18 cartridges. After washing, omeprazole was eluted from the cartridge with mobile phase onto an Inertsil ODS-2 column. The developed method was selective and linear for drug concentrations ranging between 5 and 500 ng ml(-1). The recovery of omeprazole ranged from 88.1 to 101.5%, and the limit of quantitation (LOQ) was 5 ng ml(-1). The intraday accuracy ranged from 93.1 to 106.2% and the interday accuracy varied from 95.4 to 105.1%. For the LOQ, good values of precision (8.7 and 17.5% for intraday and interday, respectively) were also obtained. This automated system has been applied to determine omeprazole in human plasma samples from bioequivalence studies.
3.Pharmacokinetics of [14C]omeprazole in patients with impaired renal function.
Naesdal J, Andersson T, Bodemar G, Larsson R, Regårdh CG, Skånberg I, Walan A. Clin Pharmacol Ther. 1986 Sep;40(3):344-51.
Pharmacokinetics of [14C]omeprazole and its metabolites were studied after single intravenous and oral doses of 20 and 40 mg, respectively, to 12 patients with chronic renal insufficiency. Blood samples for determination of total radioactivity, omeprazole, OH-omeprazole, sulfone, and sulfide were taken for 24 hours. Urine was collected over 96 hours for determination of total radioactivity and during the first 24 hours for additional assay of omeprazole and metabolites. The mean systemic availability was 70%. The mean plasma t1/2 of omeprazole was 0.6 hours. Unchanged omeprazole was not measurable in urine. Derived pharmacokinetic constants of intact omeprazole were within the range of those reported in healthy individuals. The accumulated 24-hour excretion of radioactive metabolites was related significantly to creatinine clearance. The cumulative excretion of total radioactivity in urine over 96 hours in percent of given dose varied between 25% and 83%.
4.Development and preliminary application of a high-performance liquid chromatographic assay for omeprazole metabolism in human liver microsomes.
Kobayashi K1, Chiba K, Tani M, Kuroiwa Y, Ishizaki T. J Pharm Biomed Anal. 1994 Jun;12(6):839-44.
A high-performance liquid chromatography assay was developed to measure the enzymatic activities of the 5-hydroxylation and sulphoxidation of omeprazole, a proton pump inhibitor, in human liver microsomes. The preliminary study was also undertaken to assess the assay's applicability for the enzyme kinetic analysis of omeprazole metabolism by human liver microsomes. The recovery of 5-hydroxyomeprazole, omeprazole sulphone and phenacetin (internal standard) after the precipitation of microsomal protein by acetonitrile was nearly complete. The intra-assay relative standard deviations (n = 6) were 8.2 and 12.8% for quantitation of the 5-hydroxylation and sulphoxidation activities of omeprazole, respectively. Eadie-Hofstee plots for the formation of 5-hydroxyomeprazole and omeprazole sulphone gave a biphasic relationship for all the microsomal samples studied (n = 6). The respective mean (+/- SD) high- and low-affinity component kinetic parameters for the 5-hydroxylation and sulphoxidation of omeprazole estimated by a two-enzyme kinetic analysis were: Km1 = 6.