Phenotype of CYP2C19 and CYP3A4 by determination of omeprazole and its two main metabolites in plasma using liquid chromatography with liquid-liquid extraction

We present a new simple and reliable HPLC method for measuring omeprazole and its two main metabolites in plasma. This can be used for studying CYP2C19 and CYP3A4 genetic polymorphisms using omeprazole as the probe drug. Omeprazole, hydroxyomeprazole and omeprazole sulfone were extracted from plasma samples with phosphate buffer and dichloromethane-ether (95:5). HPLC separation was achieved using an Ultrasphere ODS C(18) (Beckman) column. The mobile phase was acetonitrile-phosphate buffer (24:76, pH 8), containing nonylamine at 0.015%. Retention times were 9.5 min for omeprazole, 3.25 min for hydroxyomeprazole, 7.4 min for omeprazole sulfone and 6.27 min for internal standard (phenacetine). Detection (UV at 302 nm) of analytes was linear in the range from 96 to 864 ng/ml. This is useful for calculating metabolic index for CYP2C19 and CYP3A4 in adults and children. This method is stable, reproducible, improves resolution and has practical advantages such as low cost.     

Sensitive quantification of omeprazole and its metabolites in human plasma by liquid chromatography-mass spectrometry

A sensitive method was developed for the simultaneous determination of omeprazole and its major metabolites 5-hydroxyomeprazole and omeprazole sulfone in human plasma by HPLC-electrospray mass spectrometry. Following liquid-liquid extraction HPLC separation was achieved on a ProntoSil AQ, C18 column using a gradient with 10 mM ammonium acetate in water (pH 7.25) and acetonitrile. The mass spectrometer was operated in the selected ion monitoring mode using the respective MH(+) ions, m/z 346 for omeprazole, m/z 362 for 5-hydroxy-omeprazole and omeprazol-sulfone and m/z 300 for the internal standard (2-{[(3,5-dimethylpyridine-2-yl)methyl]thio}-1H-benzimidazole-5-yl)methanol. The limit of quantification (LOQ) achieved with this method was 5 ng/ml for 5-hydroxyomeprazole and 10 ng/ml for omeprazole and omeprazole-sulfone using 0.25 ml of plasma. Intra- and inter-assay variability was below 11% over the whole concentration range from 5 to 250 ng/ml for 5-hydroxyomeprazol and from 10 to 750 ng/ml for omeprazole and omeprazole-sulfone. The method was successfully applied to the determination of pharmacokinetic parameters of esomeprazole and the two major metabolites after a single dose and under steady state conditions.     

Analysis of omeprazole, midazolam and hydroxy-metabolites in plasma using liquid chromatography coupled to tandem mass spectrometry

A method has been developed and validated for the quantitation of midazolam, alphahydroxy-midazolam, omeprazole, and hydroxyomeprazole from one 250 microL sample of human plasma using high performance liquid chromatography coupled to tandem mass spectrometry. The method was validated for a daily working range of 0.400-100 ng/mL, with limits of detection between 2 and 15 pg/mL. The inter-assay variation was less than 15% for all analytes at four control concentrations and the samples were stable for three freeze-thaw cycles under the analysis conditions and 24 h in the post-preparative analysis matrix. This method was used to analyze samples in support of clinical studies probing the activity of the cytochrome P-450 enzyme system.     

Sensitive determination of omeprazole and its two main metabolites in human plasma by column-switching high-performance liquid chromatography: application to pharmacokinetic study in relation to CYP2C19 genotypes

A simple and sensitive column-switching high-performance liquid chromatographic method was developed for the simultaneous determination of omeprazole and its two main metabolites, 5-hydroxyomeprazole and omeprazole sulfone, in human plasma. Omeprazole, its two metabolites and lansoprazol as an internal standard were extracted from 1 ml of alkalinized plasma sample using diethyl ether-dichloromethane (45:55, v/v). The extract was injected into a column I (TSK-PW precolumn, 10 microm, 35 mm x 4.6 mm i.d.) for clean-up and column II (Inertsil ODS-80A column, 5 microm, 150 mm x 4.6mm i.d.) for separation. The mobile phase consisted of phosphate buffer-acetonitrile (92:8 v/v, pH 7.0) for clean-up and phosphate buffer-acetonitrile-methanol (65:30:5 v/v/v, pH 6.5) for separation, respectively. The peak was detected with an ultraviolet detector set at a wavelength of 302 nm, and total time for chromatographic separation was approximately 25 min. The validated concentration ranges of this method were 3-2000 ng/ml for omeprazole, 3-50 ng/ml for 5-hydroxyomeprazole and 3-1000 ng/ml for omeprazole sulfone. Mean recoveries were 84.3% for omeprazole, 64.3% for 5-hydroxyomeprazole and 86.1% for omeprazole sulfone. Intra- and inter-day coefficient variations were less than 5.1 and 6.6% for omeprazole, 4.6 and 5.0% for 5-hydroxyomeprazole and 4.6 and 4.9% for omeprazole sulfone at the different concentrations. The limits of quantification were 3 ng/ml for omeprazole and its metabolites. This method was suitable for use in pharmacokinetic studies in human volunteers, and provides a useful tool for measuring CYP2C19 activity.     

Determination of esomeprazole and its two main metabolites in human, rat and dog plasma by liquid chromatography with tandem mass spectrometry

A LC-MS/MS method was developed for quantitative determination of esomeprazole, and its two main metabolites 5-hydroxyesomeprazole and omeprazole sulphone in 25 microL human, rat or dog plasma. The analytes and their internal standards were extracted from plasma into methyl tert-butyl ether - dichloromethane (3:2, v/v). After evaporation and reconstitution of the organic extract the analytes were separated on a reversed-phase LC column and measured by atmospheric-pressure positive ionisation MS. The linearity range was 20-20,000 nmol/L for esomeprazole and omeprazole sulphone, and 20-4000 nmol/L for 5-hydroxyesomeprazole. The extraction recoveries ranged between 80 and 105%. The intra- and inter-day imprecision were less than 9.5% with accuracy between 97.7% and 100.1% for all analytes.     

Assay of omeprazole and omeprazole sulfone by semi-microcolumn liquid chromatography with mixed-function precolumn

A column-switching system based on semi-microcolumns was used for direct analysis of omeprazole and omeprazole sulfone in human plasma samples. Plasma samples were injected into a mixed-function (MF Ph-1) column (35 mm×4.6 mm I.D.) to remove proteins and other non-specific peak producing substances from the analyte-containing time zone. The analyte-containing fraction was thereafter transferred to a C-18 semi-microcolumn (250 mm×1.5 mm I.D.) after concentration at the C-18 intermediate column. The absorbance at 302 nm in a ultraviolet (UV) detector was recorded to measure the concentration. The detection limit for omeprazole and omeprazole sulfone in the present method was 10 ng/ml. Interbatch variation (coefficient of variation) of the QC samples spanned less than 10% and intra-batch variation less than 2%. The recovery ratios of omeprazole and omeprazole sulfone were over 98%. The current method can be used as a simpler procedure with similar sensitivity and reproducibility as previously reported methods.     

Chiral assay of omeprazole and metabolites and its application to a pharmacokinetics related to CYP2C19 genotypes

Studies investigating the relationship between CYP2C19 genotype and the stereoselective metabolism of omeprazole have not been reported. In the present study, we developed a simple and sensitive analytical method based on column switching reversed phase high-performance liquid chromatography (HPLC) with UV detection to determine the concentrations of (R)- and (S)-omeprazole and of its principal metabolites, (R)- and (S)-5-hydroxyomeprazole, and the non-chiral, omeprazole sulfone, in human plasma. Sample preparation involved liquid-liquid extraction with diethyl ether:dichloromethane (60:40, v/v) followed by clean-up on a TSK BSA-ODS/S column (5 μm, 10 mm × 4.6mm i.d.) using phosphate buffer:acetonitrile (97:3, v/v, pH 6.4). After column switching, separation was performed on a Shiseido CD-ph chiral column (5 μm, 150 mm × 4.6mm i.d.) using phosphate buffer:methanol (45:55, v/v, pH 5.0) as mobile phase. The limit of quantitation (LOQ) was 5 ng/mL for all analytes with intra- and inter-day precisions (as coefficient of variation) of <9.5% and <9.6%, respectively for all analytes. The present method was successfully applied to a chiral pharmacokinetic study of omeprazole in human volunteers with different CYP2C19 genotypes. The results show that the formation of (R)-5-hydroxyomeprazole gives the best correlation with CYP2C19 genotype.     

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.     

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

A practical and selective HPLC method for the separation and quantification of omeprazole enantiomers in human plasma is presented. C18 solid phase extraction (SPE) cartridges were used to extract the enantiomers from plasma samples and the chiral separation was carried out on a Chiralpak AD column protected with a CN guard column, using ethanol:hexane (70:30) as the mobile phase, at a flow rate of 0.5 ml/min. The detection was carried out at 302 nm. The method proved to be linear in the range of 10-1000 ng/ml for each enantiomer, with a quantification limit of 5 ng/ml. Precision and accuracy, demonstrated by within-day and between-day assays, were lower than 10%.     

Inhibitor effect of omeprazole in isolated human myometrial smooth muscle.

The aim of the present study was to investigate the effect of omeprazole, an H+-K+-ATPase inhibitor, in myometrial smooth muscle strips from women undergoing elective caesarean section at term. Isolated myometrial strips taken with informed consent were obtained from eight pregnant women undergoing elective caesarean section at term (not in labour) and mounted in organ baths for recording of isometric tension. We recorded the effect of increasing concentrations of omeprazole on spontaneous and Ca2+-induced contractions of myometrial smooth muscle and on contractions of myometrial smooth muscle pretreated with indomethacin (3 x 10(-6) M) and L-NAME (3 x 10(-5) M). Omeprazole (10(-4)-10(-3) M) decreased the amplitude and frequency of spontaneous contractions in a time- and concentration-dependent manner in all myometrial smooth muscle isolated from pregnant women. The decrease in amplitude of contractions in myometrial smooth muscle reached statistical significance beginning from the concentration of 3 x 10(-4) M. Addition of indomethacin (3 x 10(-6) M) and L-NAME (3 x 10(-5) M) in to the organ baths 30 min before did not change relaxation responses to omeprazole. When 8 mM Ca2+-precontracted in Ca2+-free medium myometrial smooth muscle were exposed to increasing concentrations of omeprazole (10(-5)-10(-3) M), omeprazole produced relaxation responses in a time- and concentration-dependent manner, reaching statistical significance at 10(-4) M. These results show: (1) omeprazole time- and concentration-dependently decreased spontaneous contractile activity in myometrial smooth muscle isolated from pregnant women, (2) omeprazole-induced relaxations was not influenced by indomethacin and N(G)-nitro-L-arginine methyl ester (L-NAME), suggesting that it is not mediated by cyclooxygenase products and nitric oxide, and (3) omeprazole brought about time- and concentration-dependently relaxation of myometrial smooth muscle precontracted by 8 mM Ca2+ in Ca2+-free medium. This effect of omeprazole may be due to blockade of the calcium channels.     

HPLC separation technique for analysis of bufuralol enantiomers in plasma and pharmaceutical formulations using a vancomycin chiral stationary phase and UV detection

A sensitive and selective high-performance liquid chromatographic (HPLC) method has been developed for the simultaneous determination of bufuralol enantiomers in plasma and pharmaceutical formulations. Enantiomeric resolution was achieved on a vancomycin macrocyclic antibiotic chiral stationary phase (CSP) known as Chirobiotic V with UV detection set at 254 nm. The polar ionic mobile phase (PIM) consisting of methanol-glacial acetic acid-triethylamine (100:0.015:0.010, v/v/v) has been used at a flow rate of 0.5 ml/min. The method is highly specific where other coformulated compounds did not interfere. The stability of bufuralol enantiomers under different degrees of temperature was also studied. The results showed that the drug is stable for at least 7 days at 70 degrees C. The method was validated for its linearity, accuracy, precision and robustness. An experimental design was used during validation to evaluate method robustness. The calibration curves in plasma were linear over the range of 5-500 ng/ml for each enantiomer with detection limit of 2 ng/ml. The mean relative standard deviation (RSD) of the results of within-day precision and accuracy of the drug were 0.05) between inter- and intra-day studies for each enantiomer which confirmed the reproducibility of the assay method. The mean extraction efficiency for S-(-)- and R-(+)-bufuralol from plasma was in the range 97-102% at 15-400 ng/ml level for each enantiomer. The overall recoveries of bufuralol enantiomers from pharmaceutical formulations was in the range 99.6-102.2% with %RSD ranging from 1.06 to 1.16%. The assay method proved to be suitable as chiral quality control for bufuralol formulations by HPLC and for therapeutic drug monitoring.     

Double-blind, Multicenter, Placebo-Controlled Evaluation Of Clarithromycin And Omeprazole For Helicobacter Pylori-Associated Duodenal Ulcer

Background. Eradication of Helicobacter pylori leads to faster ulcer healing and a significant decrease in ulcer recurrence. Clarithromycin is the most effective monotherapy for eradicating H. pylori from the gastric mucosa, and omeprazole frequently is used for the treatment of duodenal ulcer disease, prompting the interest to investigate rigorously the combination of clarithromycin and omeprazole for eradicating H. pylori. Materials and Methods. The aim of this double-blind, randomized, multicenter (n=30), multinational (n=10) study was to compare clarithromycin and omeprazole with omeprazole monotherapy for the eradication of H. pylori from the gastric mucosa, endoscopic healing, and reduction of symptoms and ulcer recurrence in patients with active duodenal ulcer. Patients with active duodenal ulcer associated with H. pylori infection were randomized to receive omeprazole, 40 mg every morning for 14 days, with either clarithromycin, 500 mg, or placebo three times daily, which was followed by omeprazole, 20 mg every morning for 14 days. Patients underwent endoscopy before enrolling in the study, immediately after finishing treatment, and at 4- to 6-week and 6-month follow-up evaluations or at the recurrence of symptoms. Results. Two hundred and eight patients with active duodenal ulcer associated with confirmed H. pylori infection were randomized to treatment with either clarithromycin and omeprazole (n=102) or omeprazole and placebo (n=106). Four to six weeks after treatment was completed, H. pylori was eradicated in 74% (95% confidence interval, 63.0%–82.4%) of patients receiving clarithromycin and omeprazole, compared with 1% (0.0%–6.2%) of patients receiving omeprazole monotherapy (p < .001). Clarithromycin resistance developed in eight patients treated with clarithromycin and omeprazole and in none given omeprazole and placebo. Ulcers, which were healed following treatment in more than 95% of study patients, recurred by the 6-month follow-up visit in 10% (5%–19%) of dual therapy recipients, compared with 50% (39%–61%) of those who took omeprazole alone (p <.001). Conclusion. Clarithromycin and omeprazole dual therapy is simple and well-tolerated and leads to consistently high eradication rates for patients with duodenal ulcer associated with H. pylori infection.     

Lansoprazole quantification in human plasma by liquid chromatography-electrospray tandem mass spectrometry

An analytical method based on liquid chromatography with positive ion electrospray ionization (ESI) coupled to tandem mass spectrometry detection was developed for the determination of lansoprazole in human plasma using omeprazole as the internal standard. The analyte and internal standard were extracted from the plasma samples by liquid-liquid extraction using diethyl-ether-dichloromethane (70:30; v/v) and chromatographed on a C(18) analytical column. The mobile phase consisted of acetonitrile-water (90:10; v/v)+10 mM formic acid. The method has a chromatographic total run time of 5 min and was linear within the range 2.5-2000 ng/ml. Detection was carried out on a Micromass triple quadrupole tandem mass spectrometer by Multiple Reaction Monitoring (MRM). The intra- and inter-run precision, calculated from quality control (QC) samples, was less than 3.4%. The accuracy as determined from QC samples was less than 9%. The method herein described was employed in a bioequivalence study of two capsule formulations of lansoprazole.     

Omeprazole and ranitidine in treatment of reflux oesophagitis: double blind comparative trial

One hundred and sixty two patients with endoscopically proved reflux oesophagitis stratified for severity, 66 with grade 1 disease (erythema and friability) and 96 with grade 2 or 3 disease (including erosions or ulcerations), were allocated at random to double blind treatment with omeprazole 40 mg in the morning or ranitidine 150 mg twice daily for up to 12 weeks. A patient could be evaluated sooner if symptomatic relief and endoscopically normal mucosa (grade 0) were noted after four to eight weeks'' treatment. Patients treated with omeprazole responded significantly more rapidly than those treated with ranitidine (p<0.0001), cumulative healing rates at four, eight, and 12 weeks being 90%, 100%, and 100% respectively for those with grade 1 disease and 70%, 85%, and 91% respectively for those with grade 2 or 3 disease in the omeprazole group. Corresponding rates in the ranitidine group were 55%, 79%, and 88% (grade 1) and 26%, 44%, and 54% (grade 2 or 3). Relief of the major symptoms of heartburn, regurgitation, and dysphagia and improvements in the histological appearance of the mucosa occurred earlier and were again more pronounced during treatment with omeprazole than with ranitidine.This observed superiority of omeprazole 40 mg in the morning over ranitidine 150 mg twice daily in the short term treatment of reflux oesophagitis was obtained without major clinical or biochemical side effects, but further research is needed into longer term use of omeprazole and the effects of the acid inhibition it induces.     

Design,synthesis and pharmacological evaluation of omeprazole-like agents with anti-inflammatory activity

A new series of novel benzimidazole derivatives containing substituted pyrid-2-yl moiety and polyhydroxy sugar conjugated to the N-benzimidazole moiety has been synthesized and evaluated as orally bioavailable anti-inflammatory agents with anti-ulcerogenic activity. The anti-inflammatory and anti-ulcerogenic activities of these compounds were compared to diclofenac and omeprazole, respectively. In carrageenan-induced paw oedema assay, 2-methyl-N-((3,4-dimethoxypyridin-2-yl)methyl)-1H-benzimidazol-5-amine (12d) and 1-(1,2,3,5-tetrahydroxy-α-d-mannofuranose)-5-(((3,4-dimethoxypyridin-2yl)methyl)amino)-2-methyl-1H-benzimidazole (15d) displayed dose-dependent anti-inflammatory activities by decreasing the inflammation by 62% and 72%, respectively which is comparable to that of diclofenac (73%). In contrast to diclofenac, the anti-inflammatory activity of these compounds was not only free from any side effects on the gastric mucosa but also showed significant anti-ulcerogenic activity in rat pyloric ligation and ethanol-induced gastric ulcer models similar to that of omeprazole. Together, these findings suggest that 12d and 15d are potent anti-inflammatory agents with concurrent anti-ulcerogenic activity and support its clinical promise as a component of therapeutic strategies for inflammation, for which the gastric side effects are always a major limitation.     

Comparative Treatment of Helicobacter pylori–Positive Duodenal Ulcer Using Pantoprazole at Low and High Doses Versus Omeprazole in Triple Therapy

Background. Helicobacter pylori eradication has become the standard treatment for peptic ulcer disease. H. pylori –eradicating triple therapy with omeprazole plus two antibiotics has been used until recently; however, the efficacy of pantoprazole and antibiotics for H. pylori eradication has not been researched thoroughly until now. The aim of this randomized clinical trial was to verify the efficacy of triple oral therapy comparing the effects of pantoprazole using two different doses versus omeprazole twice daily in H. pylori eradication, in ulcer healing and relapses, and in gastritis improvement.
Materials and Methods. We enrolled 243 patients with H. pylori– positive duodenal ulcer and randomized them into three treatment groups: 84 patients (group Ome40) were assigned to receive omeprazole, 20 mg twice daily, plus amoxicillin, 1 gm twice daily, and clarithromycin, 500 mg twice daily for 10 days; 79 patients (group Pan40) were treated with pantoprazole, 40 mg daily, plus amoxicillin and clarithromycin at the same doses as those of group Ome40; and 80 patients (group Pan80) were treated with pantoprazole, 40 mg twice daily, plus amoxicillin and clarithromycin at the same doses as those of group Ome40.
Results. Ulcer healing was observed in 81 of 84 patients (96.4%) in group Ome40; in 66 of 79 patients (83.5%) in group Pan40; and in 77 of 80 patients (96.2%) in group Pan80. H. pylori was eradicated in 79 of 84 patients (94%) in group Ome40; in 63 of 79 patients (79.7%) in group Pan40; and in 75 of 80 patients (93.7%) in group Pan80.
Conclusions. We found that 10-day triple therapy with amoxicillin, clarithromycin, and either pantoprazole, 80 mg daily, or omeprazole, 40 mg daily, is highly effective in ulcer healing and is very well tolerated, achieving the 90% cure recommended for an ideal first-line anti– H. pylori positive duodenal ulcer treatment regimen.     

Omeprazole, a specific inhibitor of gastric (H+-K+)-ATPase, is a H+-activated oxidizing agent of sulfhydryl groups

Omeprazole (5-methoxy-2-[[(4-methoxy-3,5- dimethylpyridinyl)methyl]sulfinyl]-1H-benzimidazole) appeared to inhibit gastric (H+-K+)-ATPase by oxidizing its essential sulfhydryl groups, since the gastric ATPase inactivated by the drug in vivo or in vitro recovered its K+-dependent ATP hydrolyzing activity upon incubation with mercaptoethanol. Biological reducing agents like cysteine or glutathione, however, were unable to reverse the inhibitory effect of omeprazole. Moreover, acidic environments enhanced the potency of omeprazole. For example, in vivo pretreatment of rats with carbachol, a secretagogue, enhanced the activity of omeprazole to inhibit gastric (H+-K+)-ATPase, while pretreatment with cimetidine, an antisecretory agent, reduced its potency. In vitro, lowering pH of incubation media from 7.4 to 5.0 improved the ability of omeprazole to inhibit hog gastric (H+-K+)-ATPase almost 60-fold. The inhibitory effect of the drug was accompanied by a dose-dependently decreased amount of free sulfhydryl groups in the isolated hog gastric membranes. The chemical reactivity of omeprazole with mercaptans is also consistent with the biological action of omeprazole. The drug, only under acidic conditions, reacted with a stoichiometric amount of ethyl mercaptan (or beta-mercaptoethanol) to produce regio-isomers of N-sulfenylated omeprazole sulfide (5-methoxy-2[[(4-methoxy-3,5- dimethyl-2-pyridinyl)methyl]thio]-1- or 3-(ethylthio)benzimidazole). The N-sulfenylated compound reacted at neutral pH with another stoichiometric amount of ethyl mercaptan to produce omeprazole sulfide quantitatively. The gastric polypeptides of 100 kilodaltons representing (H+-K+)-ATPase in the rat gastric mucosa or isolated hog gastric membranes were covalently labeled with [14C]omeprazole. The radioactive label bound to the ATPase, however, could not be displaced by mercaptoethanol under the identical conditions where the ATPase activity was fully restored. These observations suggest that the essential sulfhydryl groups which reacted with omeprazole did not form a stable covalent bond with the drug, but rather that they further reacted with adjacent sulfhydryl groups to form disulfides which could be reduced by mercaptoethanol.     

Determination of mitiglinide in rat plasma by high-performance liquid chromatography with UV detection

A selective and sensitive high-performance liquid chromatography method has been developed and validated for determination of mitiglinide (MGN) in rat plasma using 2-(4-biphenylyl) propionic acid (BPA) as internal standard. Liquid-liquid extraction was used for sample preparation. Chromatographic separation was achieved on a C(18) column using acetonitrile and 0.02 mol/l KH(2)PO(4) buffer (pH 4.0) (45:55, v/v) as mobile phase delivered at 1.0 ml/min. The UV detector was set at 210 nm. The assay was linear over the range 0.1-20 microg/ml for MGN. The average extraction recoveries of MGN and BPA from rat plasma were 98.6 and 97.4%, respectively. The developed method has been applied to the pharmacokinetic study of MGN in rats.     

Rapid determination of omeprazole in human plasma by protein precipitation and liquid chromatography-tandem mass spectrometry

A rapid, sensitive and reliable method was developed to quantitate omeprazole in human plasma using liquid chromatography-tandem mass spectrometry. The assay is based on protein precipitation with acetonitrile and reversed-phase liquid chromatography performed on an octadecylsilica column (55 mm x 2mm, 3 microm particles), the mobile phase consisted of methanol-10 mM ammonium acetate (60:40, v/v). Omeprazole and flunitrazepam, the internal standard, elute at 0.80+/-0.10 min with a total run time 1.35 min. Quantification was through positive ion mode and selected reaction monitoring mode at m/z 346.1-->197.9 for omeprazole and m/z 314.0-->268.0 for flunitrazepam, respectively. The lower limit of quantitation was 1.2 ng/ml using 0.25 ml of plasma and linearity was observed from 1.2 to 1200 ng/ml. Within-day and between-day precision expressed by relative standard deviation was less than 5% and inaccuracy did not exceed 12%. The assay was applied to the analysis of samples from a pharmacokinetic study.     

Method for analysis of polybrominated biphenyls by gas chromatography mass spectrometry

Gas chromatography using a short packed column (45 cm, 0.2 cm i.d., 2% OV-101 on Gas-Chrom Q) with mass spectrometric detection in the selected ion monitoring mode has been found satisfactory for the analysis of lower as well as higher polybrominated biphenyls. Acceptable sensitivity (< 1 ng) may be achieved for this method by focusing selectively at either the low (m/z 20-600) or the high m/z 600-1000) range of the quadrupole filter (low range for mono- through hexabromobiphenyl, high range for hexa- through decabromobiphenyl). A tuning technique has been developed for low range and high range polybrominated biphenyls using the ion abundances of perfluorotributylamine as a standard. Standard ions for the quantitation of mono- through decabromo-biphenyls were selected and validated. The technique was applied to the analysis of a variety of environmental samples.