Simple and efficient method for enantioselective determination of omeprazole in human plasma

Theoretical investigations of free energy of binding and chiral recognition studies of (R)- and (S)-Noradrenaline towards β-cyclodextrin

Noradrenaline (NA), one of the important excitatory catecholamine neurotransmitters, is used as a medication for Parkinson's Disease (PD). The β-cyclodextrin (β-CD) is one of the most effective drug carrier & also used in chiral separation. So, in this theoretical investigation, the R/S-Noradrenaline (R/S-NA) forms binding & chiral recognition mechanisms and energies with β-CD were explored. Using the AutoDock, R/S forms were first docked into the cavity of β-CD giving host-guest complexes with the free energy of binding for S-NA (-4.81 kcal/mol) larger than R-NA (-4.53 kcal/mol). The host-guest inclusion 1:1 complexes between R/S-NA and β-CD have been also modeled and optimized with ONIOM2 (B3LYP/6-31g++DP: PM6) method by using the Gaussian software. Further, frequency calculations were carried out to obtain the free energies. In comparison to the R-NA (-54.59 kcal/mol), it was observed that the S-NA (-56.48 kcal/mol) with β-CD is more stable. Furthermore, the H-bond results from molecular dynamics simulation revealed that S-NA/β-CD was more stable than R-NA/β-CD. In addition, the thermodynamic properties, vibrational analysis (IR), HOMO-LUMO band gap energy, inter molecular hydrogen bond interactions, and conformational analysis were investigated for both the R/S forms to support & compare the stability of the inclusion complex. These inclusion & high stability of S-NA/β-CD and in turn its theoretical chiral recognition behavior observed agreeing well with the reported NMR experimental data have implications in drug delivery and chiral separation research.

Determination and Pharmacokinetics of Omeprazole Enantiomers in Human Plasma and Oral Fluid Utilizing Microextraction by Packed Sorbent and Liquid Chromatography-Tandem Mass Spectrometry

In the present work, the determination of omeprazole (OME) enantiomers in oral fluid and plasma samples was carried out utilizing microextraction by packed sorbent (MEPS) and liquid chromatography-tandem mass spectrometry. A chiral column with cellulose-SB phase was used for the first time for enantiomeric separation of OME with an isocratic elution system using 0.2% ammonium hydroxide in hexane-ethanol mixture (70 : 30, v/v) as the mobile phase. OME enantiomers were determined utilizing a triple quadrupole tandem mass spectrometer in positive ion mode (ESI+) monitoring mass transitions: m/z 346.3 ⟶ 198.0 for OME and m/z 369.98 ⟶ 252.0 for internal standard. The limits of detection and quantification of the present method for both enantiomers were 0.1 and 0.4 ng/mL, respectively. The method validation provided good accuracy and precision. The matrix effect factor was less than 5%, and no interfering peaks were observed. The interday precision values ranged from 2.2 to 7.5 (%RSD), and the accuracy of determinations varied from −9.9% to 8.3%. In addition, the pharmacokinetics (PK) of omeprazole enantiomers in healthy subjects after a single oral dose was investigated. (S)-Enantiomers showed higher levels than (R)-enantiomers throughout 24 h. It was found that the mean maximum concentrations of (R)- and (S)-omeprazole in plasma samples were about two times higher than in oral fluid.

Simultaneous determination of omeprazole and their main metabolites in human urine samples by capillary electrophoresis using electrospray ionization-mass spectrometry detection

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.

CYP2C19 pharmacogenetics in advanced cancer: compromised function independent of genotype

CYP2C19 is a drug-metabolising enzyme involved in the metabolism of a number of chemotherapeutic agents including cyclophosphamide. Variants of the CYP2C19 gene result in a loss of function polymorphism, which affects approximately 3% of the Caucasian population. These individuals are poor metabolisers (PM) of a wide range of medications including omeprazole (OMP). In healthy subjects PM can be identified through homozygous variant genotype. However, a discordance between CYP2C19 genotype and phenotype has been reported previously in a small study of cancer patients. To investigate whether CYP2C19 activity was decreased in patients with advanced cancer, CYP2C19 genotype was determined in 33 advanced cancer patients using PCR-RFLP analysis for the two important allelic variants (*2,681G>A and *3,636G>A) and the activity of the enzyme was evaluated using the CYP2C19 probe drug OMP. The activity of the drug-metabolising enzyme CYP2C19 was severely compromised in advanced cancer patients, resulting in a PM status in 37% of the patients who had normal genotype. This is significantly (P<0.0005) higher than that would be predicted from the genotypic status of these patients. There was no evidence of a correlation between compromised CYP2C19 activity and any of the proinflammatory cytokines or acute phase response proteins studied. However, there was preliminary evidence of an association between PM status and low body mass (P=0.03). There is increasing interest in using pharmacogenetics to 'individualise medicine', however, the results of this study indicate that in a cancer population genotyping for CYP2C19 would significantly underestimate the number of phenotypic PM of drugs, such as cyclophosphamide, which may be metabolised by this enzyme.

Enantioselective quantification of omeprazole and its main metabolites in human serum by chiral HPLC–atmospheric pressure photoionization tandem mass spectrometry

Omeprazole is a proton pump inhibitor drug in widespread use for the reduction of gastric acid production. It is also proposed as a test substance for the phenotyping of cytochrome CYP3A4 and CYP2C19 enzyme activities. For this purpose, it is necessary to quantify, additionally to omeprazole, the two main metabolites 5-hydroxyomeprazole and omeprazole-sulfon in human plasma. Since omeprazole is a racemic mixture of two enantiomers and its enzymatic decomposition depends in part on its chiral configuration, full information about its metabolic breakdown can only be gained by enantioselective quantification of the drug and its metabolites. We introduce a new LC-MS/MS method that is capable to simultaneously quantify omeprazole and its two main metabolites enantioselectively in human serum. The method features solid-phase extraction, normal phase chiral HPLC separation and atmospheric pressure photoionization tandem mass spectrometry. As internal standards serve stable isotope labeled omeprazole and 5-hydroxyomeprazole. The calibration functions are linear in the range of 5-750 ng/ml for the omeprazole enantiomers and omeprazole-sulfon, and 2.5-375 ng/ml for the 5-hydroxyomeprazole enantiomers, respectively. Intra- and inter-day relative standard deviations are <7% for omeprazole and 5-hydroxyomeprazole enantiomers, and <9% for omeprazole-sulfon, respectively.

Analytical methodologies for the determination of omeprazole: An overview

Omeprazole, a gastric acid pump inhibitor, dose-dependently controls gastric acid secretion; the drug has greater antisecretory activity than histamine H(2)-receptor antagonists. Omeprazole has been determined in formulations and biological fluids by a variety of methods such as spectrophotometry, high-performance liquid chromatography with ultraviolet detection and liquid chromatography coupled with tandem mass spectrometry. The overview includes the most relevant analytical methodologies used in its determination since the origin still today.

Determination of omeprazole in human plasma by liquid chromatography–electrospray quadrupole linear ion trap mass spectrometry

An analytical method for the determination of omeprazole in human plasma has been developed based on liquid chromatography mass spectrometry. The analyte and internal standard sildenafil are extracted from plasma by liquid-liquid extraction using diethyl ether:dichloromethane (60:40, v/v) and separated by reversed phase high-performance liquid chromatography (HPLC) using acetonitrile:methanol:10 mM ammonium acetate (37.5:37.5:25, v/v/v) as mobile phase. Detection is carried out by multiple reaction monitoring on a Q TRAP LC/MS/MS system (Q TRAP). The method has a chromatographic run time of 3.5 min and is linear within the range 0.50-800 ng/mL. Intra- and inter-day precision expressed as relative standard deviation ranged from 0.4 to 8.5% and from 1.2 to 6.8%, respectively. Assay expressed as relative error was <5.7%. The method has been applied in a bioequivalence study of two capsule formulations of omeprazole.

Chiral separation of omeprazole and several related benzimidazoles using supercritical fluid chromatography

A study of the enantiomeric separation of omeprazole and several related benzimidazoles, using supercritical fluid chromatography (SFC), on the amylose based column Chiralpak AD is presented in this work. The effect of the organic modifier as well as temperature on the retention and enantioresolution was investigated. Alcohol-type modifiers provided the best results, allowing the enantiomeric separation of all the compounds studied with resolutions that were in most cases higher than 2, and analysis times lower than 10 minutes. An investigation of the temperature effect revealed that the isoelution temperature was below the working temperature range in only two cases, and hence it was better to work at the highest temperature permitted.