[Correlations between insulin sensitivity with anthropometric and metabolic parameters in type 2 diabetics]

AIM

The aim of the study was to evaluate correlations between insulin sensitivity and insulinosecretion with anthropometric and metabolic parameters in type 2 diabetics.

MATERIALS AND METHODS

We conducted a cross-sectional study among patients with type 2 diabetes mellitus treated with oral antidiabetic medications. The evaluation of insulin resistance and insulinosecretion was based on the calculation of the HOMA-IR and HOMA-β indices.

RESULTS

The mean age for the 100diabetes recruited was 56.4±8.4years. The mean body mass index (BMI) and waist circumference (WC) were 30.5±5.7kg/m² and 101.2±11.9cm respectively. The HOMA-IR and HOMA β indices were respectively 3.5±2.8 and 48.9±45.5. We have found a significantly positive correlation between HOMA-IR index and weight (r=0.406, p<10^-3), BMI (r=0.432, p<10^-3) and WC (r=0.412, p<10^-3). We noticed a significant negative correlation between HOMA β index and fasting glucose (r=-0.457, p<10^-3) and A1C (r=-0.399, p<10^-3). A positive statistically significant correlation was noted between HOMA-IR and HOMA-β (r=0.400, p<10^-3).

CONCLUSION

Insulin resistance is very related to overweight, especially the android distribution of fat hence the need for adequate management of this android obesity. It would also be interesting to evaluate the effects of weight loss on insulin resistance parameters.

Tiered approaches to chromatographic bioanalytical method performance evaluation: recommendation for best practices and harmonization from the Global Bioanalysis Consortium harmonization team

The A2 harmonization team, a part of the Global Bioanalysis Consortium (GBC), focused on defining possible tiers of chromatographic-based bioanalytical method performance. The need for developing bioanalytical methods suitable for the intended use is not a new proposal and is already referenced in regulatory guidance language. However, the practical implementation of approaches that differ from the well-established full validation requirements has proven challenging. Advances in technologies, the need to progress drug development more efficiently, and emerging new drug compound classes support the use of categorized tiers of bioanalytical methods. This paper incorporated the input from an international team of experienced bioanalysts to surmise the advantages and the challenges of tiered approaches and to provide recommendations on paths forward.

[Optic neuropathy in Behçet's disease: a series of 18 patients]

INTRODUCTION

The objective of this study was to analyse the incidence and the main characteristics of optic neuropathy in Behçet's disease.

METHODS

A retrospective review of a well-documented population of 376 Tunisian patients with Behçet's disease was performed. All patients fulfilled three or more criteria defined by the International Study Group for Behçet's Disease. The diagnosis of optic neuropathy was based on the clinical examination, visual field, visual evoked potentials and retinal angiography.

RESULTS

Eighteen patients (4.7 %) presented an optic nerve involvement. The mean age at presentation of these patients (10 men and nine women) was 39.11+/-12.9 years (range 17 to 73). The mean vision at presentation was 4.2/10+/-2.9, the vision was less than 1/10 in 34.5 % of eyes. The optic neuropathy was anterior in 89 % cases (26 eyes, 90 %), posterior in one case (2 eyes, 7 %); one patient (1 eye, 3 %) presented an optic atrophy. The optic neuropathy was associated with other ocular lesions in 13 cases (72.2 %). It was an inflammatory neuropathy in four cases (22.3 %) and a stasis papilledema complicating a benign intracranial hypertension in five cases (27.8 %). Corticosteroids were administrated in 17 cases (94.4 %), cyclophosphamide in six cases (33.3 %) and anticoagulant therapy in one patient (5.6 %). After a mean duration of 79 months (range: three months to 12 years), a third of the patients (8 eyes, 27.5 %) have a visual loss.

CONCLUSION

Optic neuropathy is a rare ocular involvement in Behçet's disease. It can be related to an inflammatory neuropathy, a stasis papilledema complicating a benign intracranial hypertension or an ischemic neuropathy. The association of optic neuropathy with other ocular lesions could be responsible for a diagnostic delay. Its treatment relies on systemic corticosteroids and immunosuppressive drugs. The prognosis remained poor, with a third of the patients having lost their sight.

Quantitative determination of the HIV protease inhibitor atazanavir (BMS-232632) in human plasma by liquid chromatography-tandem mass spectrometry following automated solid-phase extraction

A selective, accurate, and reproducible LC-MS-MS assay was developed for the determination of the HIV protease inhibitor atazanavir (BMS-232632) in human plasma samples. The method involved automated solid-phase extraction of atazanavir and a stable isotope analog internal standard (I.S.) using Oasis HLB 10 mg 96-well SPE plates. A portion of the reconstituted sample residue was injected onto a C(18) HDO analytical column which was configured with a triple quad mass spectrometer for analyte determination by positive ion electrospray. The assay was linear from 1.00 to 1,000 ng/ml with a lower limit of quantitation of 1.00 ng/ml. The inter- and intra-day coefficients of variation (C.V.) for the assay were <4%, and the accuracy was 99-102%. Atazanavir was stable in human plasma for at least 109 h at room temperature and for at least 1 year at -20 degrees C.

Pharmacodynamics and pharmacokinetics of omapatrilat in heart failure

The purpose of this study was to determine the pharmacodynamics and pharmacokinetics of omapatrilat, administered orally (25 mg) or intravenously (10 mg) in 19 New York Heart Association class II and class III congestive heart failure (CHF) patients versus 17 healthy controls matched for age, race, gender, and weight. The plasma concentrations of atrial natriuretic peptide (ANP) increased by approximately 20% and 30% in CHF and control subjects, respectively, at 4 hours after intravenous or oral omapatrilat administration. Similar elevation in the cyclic guanosine monophosphate concentration (25% to 35%) and ANP urinary excretion (21 ng/24 h to 22 ng/24 h) was seen in all treatment groups after omapatrilat administration. Angiotensin-converting enzyme activity was > 90% inhibited at 4 hours after dosing and remained approximately 60% to 70% inhibited at 24 hours after dosing. The levels of endothelin-1 and endothelin-2 remained unchanged after oral or intravenous administration of omapatrilat. The maximal reduction in seated blood pressure compared with baseline was similarfor CHF and control subjects. Clinical pharmacokinetic parameters were similar in both groups after intravenous dosing, but maximum concentration and area under the concentration-time curve were elevated in CHF patients compared with controls after oral dosing. Omapatrilat was well tolerated; differences in systemic exposure and metabolism between CHF patients and controls did not appear to be clinically significant.

LC/MS/MS determination of omapatrilat, a sulfhydryl-containing vasopeptidase inhibitor, and its sulfhydryl- and thioether-containing metabolites in human plasma

Omapatrilat, the most clinically advanced member of a new class of cardiovascular agents, vasopeptidase inhibitors, is under development at Bristol-Myers Squibb Pharmaceutical Research Institute for the treatment of hypertension and heart failure. An electrospray LC/MS/MS method has been developed and validated for the simultaneous determination of omapatrilat and its four metabolites in human plasma. Since omapatrilat and two of the metabolites are sulfhydryl-containing compounds, methyl acrylate was used to stabilize these compounds in human blood and plasma samples. Methyl acrylate reacted instantly with the sulfhydryl group to form a derivative that was stable in blood and plasma. Extraction of the analytes from plasma samples was achieved by semiautomated liquid-liquid extraction, where a robotic liquid handler performed the liquid-transferring steps. The mass spectrometer was operated in the negative ion selected-reaction-monitoring mode. The calibration curve ranges were 0.5-250 ng/mL for omapatrilat and one metabolite and 2.0-250 ng/mL for the other three metabolites.

Omapatrilat in patients with hepatic cirrhosis. Pharmacodynamics and pharmacokinetics

OBJECTIVE

The pharmacodynamics and pharmacokinetics of omapatrilat, a member of a new class of cardiovascular compounds, the vasopeptidase inhibitors, were evaluated in subjects with hepatic cirrhosis (n = 10) and in healthy subjects (n = 10) matched for age, weight, gender and smoking history.

METHODS

All subjects received omapatrilat 25 mg orally once daily for 14 days. Plasma renin and urinary atrial natriuretic peptide (ANP) levels were measured to assess the effect of omapatrilat on cirrhotic subjects. The effect of omapatrilat on blood pressure as well as changes in ANP and plasma renin levels were not altered by hepatic impairment. Pharmacokinetic parameters were determined from plasma omapatrilat concentrations.

RESULTS

There were no significant differences between the two subject groups with regard to log-transformed area under the curve or maximum observed plasma concentration. Systemic accumulation was similar in the two groups.

CONCLUSION

These results suggest, based on findings in otherwise healthy cirrhotic subjects, that no adjustment of standard dosing regimens is indicated for hypertensive patients with mild to moderate cirrhosis.

Increased throughput in quantitative bioanalysis using parallel-column liquid chromatography with mass spectrometric detection

The feasibility of quantitative bioanalysis by parallel-column liquid chromatography in conjunction with a conventional single-source electrospray mass spectrometer has been investigated using plasma samples containing a drug and its three metabolites. Within a single chromatographic run time, sample injections were made alternately onto each of two analytical columns in parallel at specified intervals, with a mass spectrometer data file opened at every injection. Thus, the mass spectrometer collected data from two sample injections into separate data files within a single chromatographic run time. Therefore, without sacrificing the chromatographic separation or the selected reaction monitoring (SRM) dwell time, the sample throughput was increased by a factor of two. Comparing the method validation results obtained using the two-column system with those obtained using the corresponding conventional single-column approach, the methods on the two systems were found to be equivalent in terms of accuracy and precision. The parallel-column system is simple and can be implemented using existing laboratory equipment with no additional capital outlays. A parallel-column system configured in this manner can be used not only for the within-a-run analysis of two samples containing two different sets of chemical entities, but also for the within-a-run analysis of two samples containing the same set of chemical entities.

Quantitative determination of pravastatin and its biotransformation products in human serum by turbo ion spray LC/MS/MS

A sensitive, specific, accurate and reproducible analytical method was developed and validated to quantify pravastatin (Prav), pravastatin-d5 (Prav-d5), SQ-31906, SQ-31906-d5, and pravastatin lactone (Prav-Lac) in human serum samples. Serum samples (0.5 ml) were acidified and extracted by a solid-phase extraction procedure to isolate all five analytes from human serum. Sample extracts were reconstituted and analyzed by turbo ion spray liquid chromatography/tandem mass spectrometry (LC/MS/MS) in the positive ion mode. The total run time was 9 min between injections. The assay demonstrated a lower limit of quantitation (LLQ) of 0.5 ng/ml for all five analytes. The calibration curves were linear from 0.5 ng ml to 100 ng/ml for all five analytes. The coefficients of determination of all calibration curves were > or = 0.999. Precision and accuracy quality control (QC) samples were prepared at concentrations of 2, 30, 80, and 500 ng/ml for all analytes. The intra-assay and inter-assay precision calculated from QC samples were within 8%, for all analytes. The inter-assay accuracy calculated from QC samples was within 8% for all analytes. The extraction recoveries were > or = 90% for all analytes. Benchtop stability experiments in an ice-water bath ( < or = 10 degrees C) demonstrated that over time, Prav-Lac hydrolyzes to Prav in serum. Prav, Prav-d5, SQ-31906, and SQ-31906-d5 were stable under these conditions for up to 24 h. Hydrolysis was minimized by buffering the serum to pH 4.5 and maintaining the serum sample in an ice-water bath. All analytes were stable after three freeze/thaw cycles and in reconstitution solution after 1 week at 4 degrees C. Stability of all analytes in human serum was demonstrated after storage at -70 degrees C for 77 days. The benchtop (< or = 10 degrees C) stability of pooled study samples was also investigated and the results were comparable to those obtained from serum QC samples.

High-throughput quantitative bioanalysis by LC/MS/MS

This review article discusses the most recent significant advances in the sample preparation and mass spectrometry aspects of high-throughput bioanalysis by LC/MS/MS for the quantitation of drugs, metabolites and endogenous biomolecules in biological matrices. The introduction and implementation of automated 96-well extraction has brought about high-throughput approaches to the biological sample preparation techniques of solid-phase extraction, liquid-liquid extraction and protein precipitation. The fast-flow on-line extraction technique is a different high-throughput approach that has also significantly speeded up analysis by LC/MS/MS. The use of pierceable caps for biological tubes further enhances the analysis speed and improves the safety in handling biological samples. The need for adequate chromatographic separation in order to eliminate interferences due to metabolites and/or matrix effects in LC/MS/MS is discussed. To highlight our limited understanding of atmospheric pressure ionization mass spectrometry, results from recent investigations that appear to be counter-intuitive are presented. Looking ahead to the future, multiplexed LC/MS/MS systems and capillary LC are presented as areas that can bring about further improvements in analysis speed and sensitivity to quantitative bioanalysis by LC/MS/MS.

An automated method of sample preparation of biofluids using pierceable caps to eliminate the uncapping of the sample tubes during sample transfer

Biological samples are normally collected and stored frozen in capped tubes until analysis. To obtain aliquots of biological samples for analysis, the sample tubes have to be thawed, uncapped, samples removed and then recapped for further storage. In this paper, we report an automated method of sample transfer devised to eliminate the uncapping and recapping process. This sampling method was incorporated into an automated liquid-liquid extraction procedure of plasma samples. Using a robotic system, the plasma samples were transferred directly from pierceable capped tubes into microtubes contained in a 96-position block. The aliquoted samples were extracted with methyl-tert-butyl ether in the same microtubes. The supernatant organic layers were transferred to a 96-well collection plate and evaporated to dryness. The dried extracts were reconstituted and injected from the same plate for analysis by liquid chromatography with tandem mass spectrometry.

Disposition and safety of omapatrilat in subjects with renal impairment

BACKGROUND

Omapatrilat, a vasopeptidase inhibitor, preserves natriuretic peptides and inhibits the renin angiotensin aldosterone system by simultaneously inhibiting neutral endopeptidase and angiotensin-converting enzyme.

METHODS

Oral omapatrilat, 10 mg/d, was administered for 8 to 9 days to three groups of eight subjects with varying degrees of renal function (CLCR values, normal > or = 80; mild to moderate impairment < 80 to > or = 30; severe impairment < 30 mL/min/1.73 mL2) and to six subjects undergoing maintenance hemodialysis. Omapatrilat and its metabolites (phenylmercaptopropionic acid, S-methylomapatrilat, S-methylphenylmercaptopropionic acid, and cyclic S-oxide-omapatrilat) were quantified in plasma by a validated liquid chromatography/mass spectrometry method. The model, Cmax or AUC(0-T) = intercept + slope x CLCR, was tested for a possible linear correlation between Cmax (peak plasma concentrations) or AUC(0-T) (area under plasma concentration versus time curve) and CLCR.

RESULTS

For omapatrilat and its inactive metabolites, phenylmercaptopropionic acid, S-methylomapatrilat, and S-methylphenylmercaptopropionic acid, the median times to peak plasma concentrations (tmax) were 1.5 to 2, 2 to 3, 2.5 to 3.5, and 7 to 10 hours, respectively, and were independent of renal function. After Cmax attainment, plasma concentrations declined rapidly to about 10% of Cmax values. Cyclic S-oxide-omapatrilat, a potentially active metabolite, was undetectable at all sampling time points. Hemodialysis did not decrease circulating levels of omapatrilat. There was minimal accumulation of omapatrilat and phenylmercaptopropionic acid and moderate accumulation of the S-methylated metabolites. For omapatrilat and S-methylphenylmercaptopropionic acid, neither Cmax nor AUC(0-T) was CLCR dependent. However, AUC(0-T) for phenylmercaptopropionic acid and both the Cmax and AUC(0-T) for S-methylomapatrilat were CLCR dependent.

CONCLUSIONS

The pharmacokinetics of omapatrilat, the only clinically relevant active compound studied, was independent of CLCR. For patients with reduced renal function, adjusting initial omapatrilat dose is not suggested. Hemodialysis did not significantly contribute to the clearance of omapatrilat. The long-term pharmacodynamic response to omapatrilat will dictate dose-adjustment needs.

Direct-injection LC-MS-MS method for high-throughput simultaneous quantitation of simvastatin and simvastatin acid in human plasma

A direct-injection liquid chromatography-mass spectrometry-mass spectrometry (LC-MS-MS) method was developed and validated for the simultaneous quantitation in human plasma of the widely used cholesterol-lowering prodrug simvastatin and its in vivo generated active drug, simvastatin acid. The plasma samples were injected into the LC-MS-MS system after simply adding the internal standard solution in an aqueous buffer and centrifuging. The analytes in the buffered plasma samples were found to be stable for at least 24 h at 4 degrees C. The method was successfully validated under the challenging condition of using a large number of quality control (QC) samples including those in which the ratio of the simvastatin concentration to the simvastatin acid concentration was different from the concentration ratio in the calibration curve standards. Under the dual stabilizing conditions of lower temperature (4 degrees C) and lower plasma pH of 4.9, the in-process hydrolysis of simvastatin to simvastatin acid or the lactonization of simvastatin acid to simvastatin was minimized to < or = 1.0%. Although the entire run time for on-line cleanup and analysis was only 2.5 min, chromatographic base-line separation of simvastatin from simvastatin acid, which was required to avoid the interference by simvastatin acid with the simvastatin selected reaction monitoring channel, was achieved. The desired lower limit of quantitation of 0.5 ng/ml was achieved by injecting only an equivalent of 8.0 microl of the plasma sample. The extraction column lasted for at least 500 injections.

Disposition of radiolabeled ifetroban in rats, dogs, monkeys, and humans

Ifetroban is a potent and selective thromboxane receptor antagonist. This study was conducted to characterize the pharmacokinetics, absolute bioavailability, and disposition of ifetroban after i.v. and oral administrations of [14C]ifetroban or [3H]ifetroban in rats (3 mg/kg), dogs (1 mg/kg), monkeys (1 mg/kg), and humans (50 mg). The drug was rapidly absorbed after oral administration, with peak plasma concentrations occurring between 5 and 20 min across species. Plasma terminal elimination half-life was approximately 8 h in rats, approximately 20 h in dogs, approximately 27 h in monkeys, and approximately 22 h in humans. Based on the steady-state volume of distribution, the drug was extensively distributed in tissues. Absolute bioavailability was 25, 35, 23, and 48% in rats, dogs, monkeys, and humans, respectively. Renal excretion was a minor route of elimination in all species, with the majority of the dose being excreted into the feces. After a single oral dose, urinary excretion accounted for 3% of the administered dose in rats and dogs, 14% in monkeys, and 27% in humans, with the remainder excreted in the feces. Extensive biliary excretion was observed in rats with the hydroxylated metabolite at the C-14 position being the major metabolite observed in rat bile. Ifetroban was extensively metabolized after oral administration. Approximately 40 to 50% of the radioactivity in rat and dog plasma was accounted for by parent drug whereas, in humans, approximately 60% of the plasma radioactivity was accounted for by ifetroban acylglucuronide.

Bioanalytical method validation design for the simultaneous quantitation of analytes that may undergo interconversion during analysis

In the analysis of post-dose biological samples for quantitative determination of two analytes that can potentially undergo interconversion, it is essential to minimize the interconversion during the multiple steps of the bioanalytical method. However, even after optimizing the conditions of each step, some interconversion may be unavoidable. Even then, a method can be developed for the accurate simultaneous determination of the two analytes in post-dose biological samples if the composition, in terms of the ratio of the concentrations of the two analytes, of the calibration standards and quality control (QC) samples are selected judiciously, in relation to the composition of the unknown samples to be analyzed. As an example of such interconverting analytes, a delta-hydroxy acid compound (analyte 1) and its delta-lactone (analyte 2) were selected as model compounds that can potentially undergo interconversion. The effects of changing the relative concentrations of the two analytes in QC samples vis-à-vis the calibration standards on the performance of the method under conditions were investigated where: (a) the interconversion between the two analytes was minimized; (b) the conversion of analyte 2 to analyte 1 was enhanced; (c) the interconversion between the two analytes was enhanced. The results showed that the method performance, as measured by the accuracy and precision of the QC samples, was not acceptable when the ratio of concentration of analyte 1 to that of analyte 2 in the QC samples was different from that in the calibration standards and the conditions used facilitated the conversion of one analyte to the other. However, when the relative concentration of the two analytes in the QC samples was identical to that of the calibration standards, the method performance was acceptable under all three conditions of interconversion. This was because the same degree of interconversion took place in the QC samples and calibration standards. The purpose of QC samples in bioanalytical methods is to gauge how the method will perform for the analysis of post-dose test samples and hence, ideally, the relative concentrations of the analytes in QC samples, should be selected to mimic the anticipated concentrations in the test samples. However, the relative concentrations of the analytes in test samples may not be known a-priori, or may change from sample to sample; therefore, it is not always possible to construct QC samples that exactly mimic the relative concentrations of analytes in the test samples. Thus, in order to cover the variety of test samples, the method should include, in addition to QC samples that contain the analytes at the same relative concentration as in the calibration standards, QC samples with relative concentrations that are different from those in the calibration standards, including those that contain only analyte 1 and only analyte 2. In addition, the conditions adopted for the method should favor the minimization of the conversion of the analyte that is expected to be the major component in the post-dose test samples.

Liquid chromatographic-electrospray tandem mass spectrometric method for the simultaneous quantitation of the prodrug fosinopril and the active drug fosinoprilat in human serum

A sensitive, specific, accurate and reproducible LC-MS-MS method was developed and validated for the simultaneous quantitation of the prodrug fosinopril and its active drug fosinoprilat in human serum. The method employed acidification of the serum samples to minimize the hydrolysis of fosinopril to fosinoprilat prior to purification by solid-phase extraction to isolate the two analytes and the two internal standards from human serum. The extracted samples were analyzed by turbo ionspray LC-MS-MS in the positive ion mode. Chromatography was performed on a polymer-based C18 column (Asahipak ODP PVA-C18, 2x50 mm) using gradient elution with methanol and 10 mM ammonium acetate, pH 5.5. The calibration curve, 1.17 to 300 ng/ml, was fitted to a weighted (1/x) linear regression model. Serum quality control (QC) samples used to gauge the accuracy and precision of the method were prepared at concentrations of 5.00, 100, 250 and 500 ng/ml of each analyte. The inter-assay accuracies were within 6% (DEV) for both analytes. The intra- and inter-assay precisions were within 7% and 11% (RSD), respectively, for both analytes. The hydrolysis of fosinopril to fosinoprilat during sample processing was < or = 6%. This degree of conversion would cause little error in the analysis of post-dose serum samples since such samples are known to contain low levels of the prodrug compared to the drug.

Ternary-column system for high-throughput direct-injection bioanalysis by liquid chromatography/tandem mass spectrometry

As a continuation of our efforts to improve our high-flow on-line bioanalytical approach for high-throughput quantitation of drugs and metabolites in biological matrices by high-performance liquid chromatography (LC) and tandem mass spectrometry (MS/MS), we have developed a ternary-column on-line LC/MS/MS system with dual extraction columns used in parallel for purification and an analytical column for analysis. The advantage of the dual extraction column system is that sample analysis can take place in one of the extraction columns while the other column is being equilibrated. Thus, the equilibration time does not add to the run time, hence shortening the injection cycle time and increasing the sample throughput. Moreover, the use of two extraction columns in parallel increases the number of samples that can be injected before the system fails due to an overused extraction column. Such a system has successfully been used to develop and validate a positive ion electrospray LC/MS/MS bioanalytical method for the quantitative determination of a guanidine-containing drug candidate in rat plasma. The system used for this work utilized two Oasis HLB extraction columns (1 x 50 mm, 30 microm), one C18 analytical column (3.9 x 50 mm, 5 microm), a ten-port switching value and a tandem mass spectrometer. The on-line analysis was accomplished by the direct injection of 10 microL of the sample, obtained by mixing a rat plasma sample 1:1 with an aqueous internal standard solution. Selected reaction monitoring (SRM) was utilized for the detection of the analyte and internal standard. The standard curve range was 1.00-200 ng/mL. The intra- and inter-day precision and accuracy were within 6.6%. The on-line purification step lasted for only 0.3 min and total run time was only 1.6 min.

Liquid chromatography/electrospray tandem mass spectrometry method for the quantitation of fosinoprilat in human serum using automated 96-well solid-phase extraction for sample preparation

A sensitive, specific, accurate and reproducible liquid chromatography/electrospray tandem mass spectrometry method was developed and validated for the quantitation of fosinoprilat in 0.2 mL of human serum. The method employed acidification (with pH 4.0 sodium acetate buffer) of the serum samples to minimize the hydrolysis of the prodrug fosinopril to fosinoprilat prior to purification by automated 96-well solid-phase extraction. The required chromatographic separation of fosinoprilat and fosinopril was achieved isocratically on a Luna C8 analytical column (2 x 50 mm, 3 microm). The total run time was 2 min. The mobile phase contained methanol and water with 10 mM ammonium acetate. Detection was by positive ion electrospray tandem mass spectrometry. The standard curve, which ranged from 2.00 to 500 ng/mL, was fitted to a 1/x(2) weighted linear regression model. Fosinoprilat quality control (QC) samples used to determine the accuracy and precision of the method were prepared in human serum at concentrations of 5.00, 200, 400 and 1000 ng/mL. The assay accuracy was within 8% (dev). The intra- and inter-assay precisions were within 6 and 3% (RSD), respectively. Fosinopril QC samples used to gauge the rate of hydrolysis of fosinopril to fosinoprilat during the assay procedure were prepared in human serum at 500 ng/mL. The hydrolysis of fosinopril to fosinoprilat was </=1%. This degree of conversion would cause little error in the analysis of post-dose serum samples since such samples are known to contain low levels of the prodrug compared with the drug.

The need for chromatographic and mass resolution in liquid chromatography/tandem mass spectrometric methods used for quantitation of lactones and corresponding hydroxy acids in biological samples

Because of the potential in-source conversion between a lactone and the corresponding hydroxy acid, it has been recognized that a liquid chromatography/tandem mass spectrometric (LC/MS/MS) method developed for quantitation of a lactone drug in the presence of its hydroxy acid metabolite (or vice versa) must incorporate chromatographic separation between the two compounds, unless in-source conversion between the two compounds has been eliminated by the appropriate selection of the LC/MS/MS parameters. We now report that chromatographic separation between a lactone and its hydroxy acid will be required under certain LC/MS/MS conditions used even in the absence of in-source conversion. This is due to the fact that the 18-mass-unit difference between a lactone and its hydroxy acid is, by coincidence, different by only one mass unit from the 17-mass-unit difference between the [M + H](+) and [M + NH(4)](+) ions of the lactone or the hydroxy acid. Thus, the [M + H](+) ion of a hydroxy acid is higher than the [M + NH(4)](+) ion of its lactone by only one mass unit. Therefore, in a method developed for quantitation of a hydroxy acid drug utilizing a selected-ion-monitoring (SRM) scheme that incorporates its [M + H](+) ion as the precursor ion, the quantitation would be inaccurate due to the interference by the contribution of the A + 1 isotope response from the [M + NH(4)](+) ion of the lactone metabolite present in the sample, unless there is a chromatographic separation between the two compounds. This is true even if Q1 is operated under a unit-mass resolution. The implication of this type of interference, arising from the presence of both the [M + H](+) and [M + NH(4)](+) ions of a drug and its metabolite, to the selection of LC and MS conditions (including mass resolution) will be discussed using the data obtained with a model lactone drug and its hydroxy acid metabolite.

Quantitation of cerivastatin and its seven acid and lactone biotransformation products in human serum by liquid chromatography-electrospray tandem mass spectrometry

A method for the simultaneous quantitation of cerivastatin (acid) and its biotransformation products, cerivastatin lactone, M-1 (acid), M-1 lactone, M-23 (acid), M-23 lactone, M-24 (acid) and M-24 lactone, in human serum by high-performance liquid chromatography (LC) with positive ion electrospray tandem mass spectrometry (MS-MS) was developed and validated. The method involves extraction of cerivastatin and its biotransformation products from acidified human serum (0.5 ml) using methyl tert.-butyl ether. The standard curve ranges in human serum were from 0.0100 to 10.0 ng/ml for cerivastatin and cerivastatin lactone, 0.0500 to 10.0 ng/ml for M-1 (acid) and M-1 lactone, 0.100 to 10.0 ng/ml for M-23 (acid) and M-23 lactone, and 0.500 to 10.0 ng/ml for M-24 (acid) and M-24 lactone. The lactone compounds in human serum at room temperature underwent considerable conversion to the corresponding acid compounds after only 4 h. Lowering the serum pH with a pH 5.0 buffer stabilized the lactone compounds for up to 24 h at room temperature. The degree of lactonization of the acid compounds was < or = 3.5% and the degree of hydrolysis of the lactone compounds was < or = 6.0% during the entire assay procedure. All the eight analytes eluted within 2.0 min and the total run time was only 3.5 min.

Comparison of plasma sample purification by manual liquid-liquid extraction, automated 96-well liquid-liquid extraction and automated 96-well solid-phase extraction for analysis by high-performance liquid chromatography with tandem mass spectrometry

Three extraction procedures were developed for the quantitative determination of a carboxylic acid containing analyte (I) in human plasma by high-performance liquid chromatography (HPLC) with negative ion electrospray tandem mass spectrometry (MS-MS). The first procedure was based on the manual liquid-liquid extraction (LLE) of the acidified plasma samples with methyl tert.-butyl ether. The second procedure was based on the automation of the manual LLE procedure using 96-well collection plates and a robotic liquid handling system. The third approach was based on automated solid-phase extraction (SPE) using 96-well SPE plates and a robotic liquid handling system. A lower limit of quantitation of 50 pg/ml was achieved using all three extraction procedures. The total time required to prepare calibration curve standards, aliquot the standards and plasma samples, and process a total of 96 standards and samples by manual LLE was three-times longer than the time required for 96-well SPE or 96-well LLE (4 h, 50 min vs. 1 h, 43 min). Even more importantly, the time the bioanalyst physically spent on the 96-well LLE or 96-well SPE procedure was only a small fraction of the time spent on the manual LLE procedure (<10 min vs. 4 h, 10 min). It should be noted that the 96-well SPE procedure incorporated the two steps of evaporation of the eluates to dryness and subsequent reconstitution of the dried extract. The total time required for the 96-well SPE could be reduced by 50% if the eluates were injected directly, eliminating the drying and reconstitution steps, which is achievable when sensitivity is less of an issue.

Fosinopril: pharmacokinetics and pharmacodynamics in Chinese subjects

This study examined thepharmacokinetics and pharmacodynamics of fosinopril (IVand oral) in Chinese subjects to determine whether they were different from a group of somewhat heavier and older Western control subjects previously published using the same methods. It was an open-label, randomized, balanced, two-way crossover study comparing oral and IV pharmacokinetics in 12 healthy Chinese subjects in a clinic in Taiwan. Each subject received 10 mg of oral fosinopril or 7.5 mg of IV fosinoprilatin a randomized sequence with sampling for fosinoprilat concentrations over 48 hours. Standard pharmacokinetics, including AUC, Cmax Tmax, T 1/2, Vss, bioavailability, total clearance, and renal and nonrenal clearance, were determined as well as pharmacodynamic effects on angiotensin-converting enzyme (ACE) activity. Following oral administration of 10 mg fosinopril, AUC0-T and AUCinf were 1,556 +/- 586 ng x hr/mL and 1,636 +/- 620 ng x hr/mL, respectively; T 1/2 was 17.4 +/- 11.4 hr; Cmax was 183.4 +/- 59.4 ng/mL; and median Tmax was 4.0 hr, with > 99% protein binding. Following IV administration of 7.5 mg fosinoprilat, AUC0-T and AUCinf were 7,727 +/- 2,638 ng x hr/mL and 7,816 +/- 2,693 ng x hr/mL, respectively; T 1/2 was 13.0 +/- 5.2 hr; and median Tmax was 4.0 hr, with 99.5% +/- 0.22% protein binding and a Vss of 5,850 +/- 2,780 mL. Bioavailability was 22.3% +/- 7.9%. Percent urinary excretion was 7.6% +/- 2.6% after oral dosing and 42.6% +/- 6.1% after IV dosing. After IV, dosing total clearance was 1,088 +/- 439 mL/hr, renal clearance was 472 +/- 213 mL/hr, and nonrenal clearance was 617 +/- 246 mL/hr. ACE inhibition was essentially complete through 12 hours and markedly reduced through 24 hours. Compared to a somewhat heavier and older previously reported control group, pharmacokinetic values were similar except for a slightly lower AUC and total clearance in Chinese and a statistically significantly lower nonrenal clearance. Pharmacodynamic effects on ACE activity were essentially identical. There is no reason to expect significant differences in fosinopril dosing or effect in a Chinese population compared to a Western population.

Direct injection versus liquid-liquid extraction for plasma sample analysis by high performance liquid chromatography with tandem mass spectrometry

Direct injection versus liquid-liquid extraction for post-dose human plasma sample analysis by high performance liquid chromatography with tandem mass spectrometry (LC/MS/MS) have been studied using a drug candidate compound. For the direct-injection method, an Oasis(R) HLB column (1 x 50 mm, 30 micrometer) was used as the on-line extraction column and a conventional Waters symmetry C18 column (3.9 x 50 mm, 5 micrometer) was used as the analytical column. Each plasma sample (100 microL) was mixed with 100 microL of a working solution of the internal standard in aqueous 0.05 M ammonium acetate (pH 6.9), and portions (10 microL) of these samples were then injected into the LC/MS/MS system. For the liquid-liquid extraction method, a YMC Basic C18 column (2.0 x 50 mm, 5 micrometer) was used as the analytical column. Each sample (0.5 mL) was extracted with methyl tert-butyl ether and the extract was reconstituted and injected into the LC/MS/MS system. The total analysis time for both methods was 2.0 min per sample. The accuracy, inter-day precision and intra-day precision obtained from the quality control samples were within 8% for both methods. The analysis results of post-dose human plasma samples showed that the deviations of 91% of the concentrations obtained using the direct-injection method were within +/-20% from the concentrations obtained using the liquid-liquid extraction method, and the overall average percentage deviation was -1.5%. The results showed that the two methods were equivalent in terms of total chromatographic run time, accuracy and precision. However, for a batch of 100 samples, the sample preparation time for the direct-injection method was only about 25% of the time required for liquid-liquid extraction. This decrease in sample preparation time resulted in the doubling of the overall sample analysis throughput.

A simple liquid-liquid extraction with hexane for low-picogram determination of drugs and their metabolites in plasma by high-performance liquid chromatography with positive ion electrospray tandem mass spectrometry

Four sensitive, specific and accurate methods, based on high-performance liquid chromatography (HPLC) with positive ion electrospray tandem mass spectrometry (MS/MS) coupled with liquid-Liquid extraction (LLE), have been developed and validated for the low-picogram determination of two drug candidates and a metabolite (compounds I-III) in human, monkey and rat plasma. In the LLE procedure, hexane or a mixture of hexane and methyl t-butyl ether was used to isolate these compounds from plasma of the different species after basification of each biological sample with sodium carbonate. The reconstituted extracts were then injected into a positive ion electrospray LC/MS/MS system for the quantitative analysis. The lower limit of quantitation of the methods ranged from 20 to 200 pg/mL. The use of hexane for the LLE proved to be simple, rapid and reproducible, and provided very clean extracts with little interference. The inter- and intra-day precision for the four methods was within 9%, and the accuracy was in the range 94-107%. The effect of pH on the isomerization of I (E-isomer) to its Z-isomer (II) showed that the rate of isomerization increased with decrease in pH and that there was no isomerization at pH >/=6.

Quantitation of the acid and lactone forms of atorvastatin and its biotransformation products in human serum by high-performance liquid chromatography with electrospray tandem mass spectrometry

A method for simultaneous quantitation of both the acid and lactone forms of atorvastatin, a new synthetic inhibitor of HMG-CoA reductase that is being marketed for the treatment of high serum cholesterol, and both the acid and lactone forms of its two biotransformation products, 2-hydroxyatorvastatin and 4-hydroxyatorvastatin, in human serum (a total of six analytes) by high-performance liquid chromatography with electrospray tandem mass spectrometry was developed and validated. A deuterium labeled analog was used as internal standard for each of the six analytes. Each point of the calibration standard curve, which ranged from 0.5 to 200 ng/mL, contained the six analytes at equal concentrations. Three groups of quality control (QC) samples were used. In the first group, combination QC samples contained all six analytes at equal concentrations. In the second group, acid-only QC samples contained only the acid forms (i.e. three analytes) at equal concentrations. In the third group, lactone-only QC samples contained only the lactone forms (i.e. three analytes) at equal concentrations. After adding the internal standard to 0.5 mL of each standard and the QC sample kept at 4 degrees C, the samples were acidified with sodium acetate buffer (pH 5.0) and then extracted with methyl tert-butyl ether. Detection was by positive ion electrospray tandem mass spectrometry using eight selected reaction monitoring channels. The acid compounds were stable in human serum at room temperature but the lactone compounds were unstable as they hydrolyzed rapidly to their respective acid forms. The conversion of the lactone compounds in both QC and post-dose human serum samples was nearly complete after 24 h at room temperature. The lactone compounds in serum could be stabilized by lowering the working temperature to 4 degrees C or lowering the serum pH to 6.0. The acid-only and the lactone-only QC samples showed that, under the sample processing conditions used, the degree of the hydrolysis of the lactone compounds or the lactonization of the acid compounds during the assay procedure was minimal (< 5%). The intra-day C.V., inter-day C.V. and the deviations from the nominal concentrations for all six analytes were within 15%, demonstrating good precision and accuracy. The required lower limit of quantitation (LLQ) of 0.5 ng/mL was achieved for each analyte.

A versatile system of high-flow high performance liquid chromatography with tandem mass spectrometry for rapid direct-injection analysis of plasma samples for quantitation of a beta-lactam drug candidate and its open-ring biotransformation product

A bioanalytical method has been developed and validated for quantitation of a beta-lactam drug candidate and its open-ring biotransformation product utilizing high-flow high-performance liquid chromatography (HPLC) for on-line purification of plasma samples and electrospray tandem mass spectrometry for detection and quantitation. The HPLC system used two columns: an Oasis column (1 x 50 mm, 30 microm) as the on-line extraction column and a conventional C18 column (2 x 50 mm, 5 microm) as the analytical column. Each plasma standard or quality control (QC) sample (50 microL) was mixed with 50 microL of a working solution of the internal standard in aqueous 0.5 M ammonium acetate (pH 4.0). Portions (10 microL) of these samples were then injected into an Oasis column with a mobile phase consisting of 100% aqueous 1 mM formic acid at a high flow rate (4.0 mL/min), with the effluent from the Oasis column directed to waste and not to the mass spectrometer. After the purification step, the Oasis column effluent was directed to the analytical column and the mass spectrometer and the analytes were eluted with methanol/aqueous 1 mM formic acid (70:30) at a flow rate of 1.0 mL/min. The total analysis time was 1.6 min per sample. The standard curve range was 0.980 to 250 ng/mL. The accuracy, inter-day precision and intra-day precision were within 10% for both compounds.

Gas chromatography-mass spectrometric method for quantitative determination in human urine of dicarboxylic (dioic) acids produced in the body as a consequence of cholesterol biosynthesis inhibition

A capillary gas chromatography-mass spectrometric (GC-MS) method in human urine has been developed and validated for the quantitative determination of dicarboxylic acids (dioic acids) which are produced in the body as a consequence of the administration of an inhibitor of the enzyme squalene synthase, which is involved in the biosynthesis of cholesterol. The standards and quality control (QC) samples were prepared by adding dioic acids into human urine. Internal standard (sebacic acid) was added to each urine sample (0.1 ml) and then dried by evaporation under nitrogen. The dried sample was reacted with pentafluorobenzyl (PFB) bromide under conditions that maximized the formation of the di-PFB ester (at the expense of the mono-PFB ester) of the dioic acids. After drying by evaporation, each sample residue was reconstituted in mesitylene and injected into a capillary GC-MS system via a splitless injection. The detection was by negative ion chemical ionization mass spectrometry with selected ion monitoring (SIM) of the [M-PFB]- of the analytes and the internal standard.

High performance liquid chromatography mobile phase composition optimization for the quantitative determination of a carboxylic acid compound in human plasma by negative ion electrospray high performance liquid chromatography tandem mass spectrometry

A systematic investigation was undertaken to study the effects of varying concentrations of additives in the acetonitrile/water high performance liquid chromatography mobile phase, especially formic acid and ammonium formate, on the negative ion electrospray response of a carboxylic acid compound. The study showed that the response progressively decreased with increase in the formic acid concentration. While such a decrease in the response could be qualitatively explained by the decrease in the concentration of the ionized form of the carboxylic acid compound due to the lower pH of the mobile phase, the change in response was not as large as expected from the change of the concentration of the ionized form. The response also progressively decreased with increase in the ammonium formate concentration but the decrease cannot be explained by the change in the pH of the mobile phase. Although the best negative ion electrospray response was obtained with a water/acetonitrile mobile phase that contained no additives at all, the retention time of the analyte was not found to be adequately reproducible on repeated injections. Thus, this mobile phase was deemed unacceptable for practical, routine use. Comparing formic acid against ammonium formate, the former was preferable since it caused a smaller attenuation of the negative ion response. Equally important was the fact that addition of formic acid had the desirable effect of maintaining a reasonably high capacity factor (k') for the analyte even at a relatively high acetonitrile concentration. A concentration of 1 mM formic acid in the mobile phase was large enough to achieve the reproducible elongated retention time for the analyte, with a loss in the analyte response of about 60% only. It should be noted that the sensitivity achieved with the 1 mM formic acid mobile phase, in which the carboxylic acid is expected to be about 10% in the ionized form, is about 9 times better than the sensitivity achieved in the 1 mM ammonium formate mobile phase, in which the carboxylic acid is expected to be about 99% in the ionized form.

The use of high-flow high performance liquid chromatography coupled with positive and negative ion electrospray tandem mass spectrometry for quantitative bioanalysis via direct injection of the plasma/serum samples

Two bioanalytical methods have been developed and validated utilizing high flow high performance liquid chromatography (HPLC) for on-line purification of plasma and serum samples and electrospray tandem mass spectrometry for detection and quantitation. Each plasma or serum sample, after mixing with an aqueous solution of the internal standard, was injected into a small diameter (1 x 50 mm) column packed with large particles of OASIS (30 microns), with a 100% aqueous mobile phase at a high flow rate (3-4 mL/min). The combination of the high linear speed (6-8 cm/s) of the aqueous mobile phase and the large particle size resulted in the rapid passage of the proteins and other large biomolecules through the column while the small-molecule analytes were retained on the column. During this purification period, the HPLC effluent was directed to waste. After the purification step, the HPLC mobile phase was rapidly changed from 100% aqueous to < or = 100% organic, the flow was reduced to 0.5-0.8 mL/min, and the column effluent was directed towards the mass spectrometer. The small molecule analytes were eluted during this period. In the method developed and validated for the quantitative determination of compound I in rat plasma (method A), the same OASIS column (1 x 50 mm, 30 microns) served as the purification and analytical (elution) column. In the method developed for the simultaneous determination of pravastatin and its positional isomer biotransformation product (SQ-31906) in human serum (method B), the purification column was connected to a conventional C18 analytical column (3.9 x 50 mm, 5 microns) to achieve the required chromatographic separation between the two isomers. For method A, where 50 microL of rat plasma mixed 1:1 with water containing the internal standard was injected, the standard curve range was 1 to 1,000 ng/mL. For method B, where 200 microL of a human serum sample mixed 4:1 with water containing the internal standard was injected, the standard curve range was 0.5 to 100 ng/mL. The total analysis time for each method was < or = 5 min per sample. The accuracy, inter-day precision and intra-day precision were within 10% for both methods.

Negative ion electrospray high-performance liquid chromatography-mass spectrometry method development for determination of a highly polar phosphonic acid/sulfonic acid compound in plasma. Optimization of ammonium acetate concentration and in-source collision-induced dissociation

A method, based on negative ion electrospray ionization (ESI) single-stage mass spectrometry coupled with HPLC, was developed for the determination of a squalene synthase inhibitor, BMS-187745, in human plasma. BMS-187745, a highly polar compound with both phosphonic acid and sulfonic acid groups, presented difficulties in developing plasma extraction and HPLC procedures. Precipitation of the plasma protein with methanol was finally chosen as the basis for sample preparation since extraction with water-immiscible solvents or with solid-phase extraction columns failed. It was essential to add ammonium acetate to the HPLC mobile phase, not only to enhance the retention of BMS-187745 but also to ensure a well-shaped chromatographic peak. While the use of ammonium acetate had the desired chromatographic effects, it had the undesirable consequence of suppressing the negative ion ESI signal. With the plasma extracts, the [M-H2O-H]- ion (m/z 367) showed significantly lower chemical noise than the [M-H]- ion (m/z 385), and was thus chosen as the analytical ion for the selected ion monitoring. The signal of the m/z 367 ion was significantly enhanced by the optimization of the in-source collision-induced dissociation (CID) of m/z 385 to m/z 367.

Quantitative determination of BMS-186716, a thiol compound, in rat plasma by high-performance liquid chromatography-positive ion electrospray mass spectrometry after hydrolysis of the methyl acrylate adduct by the native esterases

During method development in support of non-clinical studies in animal models, BMS-186716 was found to be extremely unstable in blood and plasma. Stabilization of the compound was achieved by reacting the compound with methyl acrylate (MA) in blood, from which the plasma was then prepared. While the resulting BMS-186716-MA adduct was found to be stable in dog plasma, and hence it was used as the basis for the method developed for analysis of dog plasma samples, the BMS-186716-MA adduct was found to be unstable in rat plasma as it was readily hydrolyzed to BMS-186716-acrylic acid (AA) by native esterases found in rat plasma. Although the finding of the instability of BMS-186716-MA in rat plasma was not the result of prospective planning, we were able to successfully develop a quantitative bioanalytical method using BMS-186716-AA as the analyte instead of the originally planned BMS-186716-MA analyte. The standard and quality-control (QC) samples were prepared by spiking blank plasma with BMS-186716-MA, and then allowing them to stand at room temperature for 1 h to convert BMS-186716-MA to BMS-186716-AA. After adding the internal standard BMS-188035-AA, each sample was acidified with HCl and then extracted with methyl tert.-butyl ether. The reconstituted extract was injected into a HPLC-electrospray ionization mass spectrometric system for detection by positive ion electrospray ionization. A lower limit of quantitation (LLQ) of 5 ng/ml was achieved, using 0.1 ml plasma and a standard curve range of 5-5000 ng/ml.

Quantitative determination of BMS186716, a thiol compound, in dog plasma by high-performance liquid chromatography-positive ion electrospray mass spectrometry after formation of the methyl acrylate adduct

As it is extremely unstable in blood, the thiol compound BMS186716 was stabilized by the addition of methyl acrylate (MA) to blood samples. The blood samples were then kept in ice for 10-15 min for completion of the Michael addition reaction to occur between the thiol group of BMS186716 and MA, after which the plasma was separated by centrifugation under refrigeration. For sample analysis, the standard and quality control samples were prepared by spiking blank plasma with the BMS186716-MA adduct. After addition of the internal standard, BMS 188035-MA, each sample was acidified with HCI and then extracted with methyl tert.-butyl ether. Each reconstituted extract was injected into a high-performance liquid chromatography-positive ion electrospray ionization mass spectrometric system. The electrospray condition was chosen to enhance the [M+NH4]+ signal at the expense of the [M+H]+ signal. Monitoring the [M+NH4]+ signal, a lower limit of quantitation of 2.5 ng/ml was achieved, with 0.5 ml plasma. We have thus shown that a sulfhydryl compound (BMS186716) in blood can successfully be stabilized by reacting it with MA and that the adduct produced is adequately stable in blood and plasma to allow the development of a rugged quantitative bioanalytical method.

Quantitative bioanalysis utilizing high-performance liquid chromatography/electrospray mass spectrometry via selected-ion monitoring of the sodium ion adduct [M+Na]+

A high-performance liquid chromatography (HPLC)/electrospray mass spectrometric method for quantitative determination of a compound in dog plasma was developed and validated via the selected-ion monitoring of the electrospray-generated [M+Na]+ adduct of the compound. The plasma samples were acidified with HCl and then extracted with methyl tert-butyl ether. The reconstituted extracts were injected into an HPLC/positive-ion electrospray ionization mass spectrometry system. The HPLC mobile phase consisted of acetonitrile, water, formic acid (3 mM) and sodium acetate (0.3 mM). This composition of mobile phase provided the optimum electrospray condition for the formation of the [M+Na](+)-ion. This work demonstrates that the addition of sodium acetate into the HPLC mobile phase and the subsequent selected-ion monitoring of the sodium ion adduct of the analyte is a viable approach in quantitative bioanalysis. The facile formation of the sodium ion adduct of the analyte, which does not contain functional groups that are known to be strong proton acceptors, appears to be a function of the particular electrospray instrument used.

Determination of BMS-186318 in dog, rat and monkey plasma by liquid chromatography-ionspray mass spectrometry

BMS-186318 is a member of the recently discovered "aminodiol" class of HIV protease inhibitors. A simple but sensitive method was developed for the determination of BMS-186318 in dog plasma and then applied to monkey and rat plasma. The compound was extracted from dog plasma with methyl tert-butyl ether at basic pH. The dried extract was reconstituted in mobile phase and injected into a 150 x 2.1 mm i.d. Zorbax Rx-C18 HPLC column. A portion of the effluent was directed into the LC-ionspray MS system, where the [M+H]+ ion of the secondary amine compound was monitored. The HPLC conditions were chosen in order to achieve a short run time and large sample throughput, with both analyte and internal standard eluting within 1.5 min. The liquid-liquid extraction procedure provided very clean extracts so that sufficient signal-to-noise ratio was obtained with single-stage mass spectrometry instead of the more costly tandem mass spectrometry. The required lower limit of quantitation of 2.5 ng ml-1 was easily achieved. The method has also been validated for BMS-186318 in monkey plasma without modification. The method has been modified for rat plasma. Owing to irreproducibility observed when applying the liquid-liquid extraction method to rat plasma, a solid-phase extraction method was developed. The addition of phenylmethylsulfonyl fluoride was necessary to stabilize BMS-186318 in rat blood and plasma.

Direct injection for high sample throughput capillary gas chromatographic-mass spectrometric bioanalysis

Because of the drawback of the relatively long analysis times inherent to temperature-programmed splitless injection capillary GC-MS, isothermal direct injection capillary GC-MS was investigated for quantitative bioanalysis. Using extracts from spiked plasma samples, we showed that high quality chromatography with a run time much shorter than that achievable with splitless injection can be achieved with direct injection. Sensitivity and other performance parameters were as good as or better than those of the splitless method. Since sample throughput is of great importance in laboratories that analyze thousands of biological samples, it is recommended that, when possible, splitless injection, which has traditionally been used in trace level GC-MS bioanalytical methods, be replaced by direct injection.

Effect of the amount of internal standard on the precision of an analytical method

In an earlier published paper, a confidence interval approach was used to show that the use of a large amount of internal standard (relative to the analyte) would adversely affect the precision of the analytical method. However, the confidence intervals were not calculated correctly. The authors recalculated the confidence intervals and found that there is no effect on the precision as measured by the confidence intervals.

Determination of SQ 33,600, a phosphinic acid containing HMG CoA reductase inhibitor, in human serum by high-performance liquid chromatography combined with ionspray mass spectrometry

A method for the determination of SQ 33,600 in human serum is presented. This compound, which contains both carboxylic and phosphinic acid functional groups, is an HMG CoA reductase inhibitor currently under clinical investigation at the Bristol-Myers Squibb Pharmaceutical Research Institute. Human serum extracts prepared using solid-phase techniques were analyzed by combining high-performance liquid chromatography and atmospheric pressure ionization mass spectrometry. Under the conditions of the analysis, SQ 33,600 and its fluorinated analog, SQ 33,547, used as the internal standard, existed as anions in solution and could be sampled directly using the ionspray technique. The method utilized a simple isocratic mobile-phase system. No sample derivatization was required for these polar molecules. The retention time of the analytes was 3.5 min with a total analysis time of 5 min. The limit of detection was 0.5 ng ml-1 serum with a minimum quantifiable limit of 2.0 ng ml-1. The method was linear to at least 400 ng ml-1.

Stereoisomeric purity determination of captopril by capillary gas chromatography

The GC method developed for the stereoisomeric purity determination of captopril is based on the combined information derived from the analyses of the captopril sample on two GC systems, one with a chiral and the other with an achiral column. The limit of detection has been determined to be 0.02% (w/w) for (R,S) or (S,R) and 0.03% for (R,R), with corresponding minimum quantifiable levels of 0.08% and 0.09%.

Simultaneous determination of the prodrug zofenopril and its active drug in plasma by capillary gas chromatography-mass-selective detection

After oral administration of zofenopril, the active sulfhydryl angiotensin-converting enzyme inhibitor is released. Zofenopril is currently under clinical investigation as an antihypertensive. Blood samples are reacted with N-ethylmaleimide, immediately after collection, processed into plasma and stored frozen for subsequent analysis. After addition of two internal reference standards, one each for the prodrug and the active compound, the plasma samples are purified by a combination of liquid-liquid and solid-phase extractions. The dried methylated extracts are reconstituted with tetramethylbenzene and chromatographed by automated splitless injection on a fused-silica capillary column, connected to a mass-selective detector. The analytes and the internal reference standards are chromatographically resolved and a common fragment ion is monitored for the analytes. A limit of quantitation of approximately 1 ng/ml of plasma is achieved.

Picogram level determination of fluphenazine in human plasma by automated gas chromatography/mass selective detection

An automated capillary column gas chromatography electron-impact mass selective detection method has been developed for the determination of a major tranquilizing agent, fluphenazine. Using a new purification method and incorporating a deuterated internal reference, a limit of quantitation of 50 pg per ml of plasma was obtained.