Trace analysis of quinapril and its active metabolite, quinaprilat, in human plasma and urine by gas chromatography-negative-ion chemical ionization mass spectrometry

LC–MS/MS assay of quinapril and its metabolite quinaprilat for drug bioequivalence evaluation: prospective, concurrential and retrospective method validation

Background: The bioequivalence of two pharmaceutical formulations containing 10 mg quinapril was assessed by assaying the untransformed drug and its active metabolite quinaprilat from plasma samples. Results: A gradient elution liquid chromatographic separation coupled to positive atmospheric pressure electrospray ionization and tandem mass spectrometry detection was used and validated. Sample preparation is simple and uses protein precipitation through addition of an acetonitrile:methanol (8:2 v/v) mixture. The method has a run time of 6.3 min. Carvedilol was used as an internal standard. The multiple reactions monitoring mode was used for both quantitation and structural confirmation of target compounds. Linear 1/x2-weighted regressions characterize detector response function up to concentrations of 1000 ng/ml for quinapril and 2000 ng/ml for quinaprilat. Low limits of quantitation of 5 ng/ml for quinapril and 10 ng/ml for quinaprilat were found. Intra- and inter-day variability of the results were found below 15%. Long- (-20°C/6 months) and short-term (25°C/48 h) stability of analytes in plasma, as well as freeze and thaw stability (six cycles) were demonstrated. Conclusion: The method was found to be selective, precise, accurate and robust when applied to a large number of unknown samples.

An overview of chromatographic methods coupled with mass spectrometric detection for determination of angiotensin-converting enzyme inhibitors in biological material

Gas and liquid chromatography-mass spectrometry (GC-MS, LC-MS) methods for the determination of angiotensin-converting enzyme inhibitors (ACEIs) and their metabolites in biological material have been reviewed. Since 1980s those hyphenated techniques have been applied to quantitate ACE inhibitors and the dynamic increase in the number of relevant publications can be observed in recent years. Although most of the methods available in the literature were analyses of plasma or serum, assays of blood and urine were also included. Additionally, sample pretreatment methods, separation conditions and ionization modes were overviewed. Some information on chemical structures, cis-trans izomerization and stability of compounds in question was also included. Most of the reported methods were successfully applied to the pharmacokinetic studies in humans.

Interference from a glucuronide metabolite in the determination of ramipril and ramiprilat in human plasma and urine by gas chromatography–mass spectrometry

In the course of development and validation of a gas chromatography-mass spectrometry (GC-MS) method for ramipril and its biologically active metabolite ramiprilat, evidence was found for an unknown interfering metabolite. Sample treatment included isolation from plasma or urine by solid-phase extraction, methylation with trimethylsilyldiazomethane and acylation with trifluoroacetic anhydride (TFAA). When liquid chromatography was used to fractionate plasma extracts prior to derivatization, the alkyl, acyl-derivative of ramipril was obtained from two separate LC fractions. Electrospray ionization mass spectral data, together with circumstances for the derivatization, were consistent with the presence of an N-glucuronide of ramipril. Interference from the metabolite was eliminated by including a wash step after extraction/alkylation, prior to acylation. The final assay had a lower limit of quantification at 1.0 nmol/L and a linear range of 1-300 nmol/L. Intra- and inter-batch precision for ramipril and ramiprilat in plasma or urine were better than 10 and 5% at 2 and 80 nmol/L, respectively.

Mass spectral fragmentation reactions of angiotensin-converting enzyme (ACE) inhibitors

A variety of mass spectrometric techniques have been employed in the study of a series of structurally similar compounds used in the treatment of hypertension. The compounds, known collectively as angiotensin-converting enzyme (ACE) inhibitors, all share the amino acid residue proline or some variant thereof, as a common structural element. The gas phase fragmentation behavior of these compounds has been explored systematically using various instruments and techniques. An interesting dissociation process (rearrangement) unique to one of the compounds, lisinopril, has been investigated using isotopic labeling experiments and exact mass measurements. The general nature of the process has been probed through both the positive and negative ion analyses of fourteen related compounds exhibiting structural homology.

Voltammetric determination of cilazapril in pharmaceutical formulations

A sensitive adsorptive stripping voltammetric method for the measurement of cilazapril in 0.04 M Britton-Robinson buffer (pH 9.0) solution was described. The method was based on the adsorptive accumulation of the drug at a hanging mercury drop electrode (HMDE), followed by differential pulse voltammetry. The response was evaluated with respect to pre-concentration time, pH effect, accumulation potential, accumulation time and scan rate. The peak potential was -0.60 V (vs. Ag/AgCl). The peak current was directly proportional to the concentration of cilazapril with a detection limit of 17.6 ng ml(-1) at an accumulation time of 10 s. The reduction process was irreversible and the wave showed adsorptive characteristics. The results were compared to those obtained using a HPLC procedure. A reversed-phase C18e column with aqueous phosphate buffer (pH 3.5; 0.125 M)-acetonitrile (67:33, v/v) mobile phase and benazapril as internal standard was used. UV detector was set at 254 nm. Results obtained in HPLC were comparable to those obtained by adsorptive stripping voltammetric method.

Determination of the antihypertensive drug cilazapril and its active metabolite cilazaprilat in pharmaceuticals and urine by solid-phase extraction and high-performance liquid chromatography with photometric detection

A liquid chromatographic method with photometric detection for the determination of cilazapril and its active metabolite and degradation product cilazaprilat in urine and pharmaceuticals has been developed. The chromatographic method consisted of a microBondapak C18 column maintained at 30+/-0.2 degrees C, using a mixture of methanol-10 mM phosphoric acid (50:50 v/v) as mobile phase at a flow-rate of 1.0 ml/min. Enalapril maleate was used as internal standard. The detection was performed at a wavelength of 206 nm. A study of the retention of cilazapril and cilazaprilat using solid-liquid extraction has been carried out in order to optimise the clean-up procedure for urine samples, which consisted of a solid-liquid extraction using C(R) cartridges. Recoveries greater than 85% are obtained for both compounds. The method was sensitive, precise and accurate enough to be applied to the determination of urine samples obtained from three hypertensive patients up to 24 h after intake of a therapeutic dose (detection limit of 70 ng/ml for cilazapril and cilazaprilat in urine). A comparison of the method developed using photometric and amperometric detection has been carried out.

Systematic toxicological analysis procedures for acidic drugs and/or metabolites relevant to clinical and forensic toxicology and/or doping control

This paper reviews systematic toxicological analysis (STA) procedures for acidic drugs and/or metabolites relevant to clinical and forensic toxicology or doping control using gas chromatography, gas chromatography-mass spectrometry, liquid chromatography, thin-layer chromatography and capillary electrophoresis. Papers from 1992 to 1998 have been taken into consideration. Screening procedures in biosamples (whole blood, plasma, serum, urine, vitreous humor, brain, liver or hair) of humans or animals (horse, or rat) are included for the following drug classes: angiotensin-converting enzyme (ACE) inhibitors and angiotensin II (AT-II) blockers, anticoagulants of the 4-hydroxy coumarin type, barbiturates, dihydropyridine calcium channel blockers (calcium antagonists), diuretics, hypoglycemic sulfonylureas and non-steroidal anti-inflammatory drugs (NSAIDs). Methods for confirmation of preliminary results obtained by screening procedures using immunoassay or chromatographic techniques are also included. Furthermore, procedures for the simultaneous detection of several drug classes are reviewed. The toxicological question to be answered and the consequences for the choice of an adequate method, the sample preparation and the chromatography itself are discussed. The basic information about the biosample assayed, work-up, separation column, mobile phase or separation buffer, detection mode and validation data of each procedure is summarized in 16 tables. They are arranged according to the drug class and the analytical method. Examples of typical applications are presented. Finally, STA procedures are reviewed and described allowing simultaneous screening for different (acidic) drug classes.

Screening for the detection of angiotensin-converting enzyme inhibitors, their metabolites, and AT II receptor antagonists

A gas chromatography-mass spectrometry (GC-MS) screening procedure was developed for the detection of angiotensin-converting enzyme (ACE) inhibitors, their metabolites, and angiotensin (AT) II receptor antagonists in urine as part of a systematic toxicologic analysis procedure for acidic drugs and poisons after extractive methylation. The part of the phase-transfer catalyst remaining in the organic phase was removed by solid phase extraction on a diol phase. The compounds were separated by capillary GC and identified by computerized MS in the full scan mode. Using mass chromatography with the ions m/z 157, 160, 172, 192, 204, 220, 234, 248, 249, and 262, the possible presence of ACE inhibitors, their metabolites, and AT II antagonists could be indicated. The identity of positive signals in such mass chromatograms was confirmed by comparison of the peaks underlying full mass spectra with the reference spectra recorded during this study. This method allowed detection of therapeutic concentrations of ACE inhibitors (benazepril, enalapril, perindopril, quinapril, ramipril, trandolapril, their metabolites, or both) and therapeutic concentrations of the AT II antagonist, valsartan, in human urine samples. Human urine samples were not available for testing cilazapril, moexipril, and losartan; they were detected only in rat urine. The overall recoveries of ACE inhibitors ranged between 80% and 88%, with a coefficient of variation (CV) of less than 10% and the limit of detection of at least 10 ng/ml (signal to noise ratio 3) in the full-scan mode. The overall recovery of the valsartan was 68%, with a CV of less than 10%; the limit of detection was at least 10 ng/ml (S/N 3) in the full scan mode.

Quantitative determination of the angiotensin-converting enzyme inhibitor cilazapril and its active metabolite cilazaprilat in pharmaceuticals and urine by high-performance liquid chromatography with amperometric detection

A rapid and simple high-performance liquid chromatographic method with amperometric detection has been developed for the quantitation of cilazapril and its active metabolite and degradation product cilazaprilat in urine and tablets. The chromatographic system consisted of a microBondapak C18 column, using a mixture of methanol-5 mM phosphoric acid (50:50, v/v) as mobile phase, which was pumped at a flow-rate of 1.0 ml/min. The column was kept at a constant temperature of (40+/-0.2) degrees C. Detection was performed using a glassy carbon electrode at a potential of 1350 mV. Sample preparation for urine consisted of a solid-phase extraction using C8 cartridges. This procedure allowed recoveries greater than 85% for both compounds. The method proved to be accurate, precise and sensitive enough to be applied to pharmacokinetic studies and it has been applied to urine samples obtained from four hypertensive patients (detection limit of 50 ng/ml for cilazapril and 40 ng/ml for cilazaprilat in urine). Results were in good agreement with pharmacokinetic data.

Simultaneous determination of moexipril and moexiprilat, its active metabolite, in human plasma by gas chromatography-negative-ion chemical ionization mass spectrometry

A sensitive and selective method for the simultaneous determination of moexipril and moexiprilat, its active metabolite, in human plasma is described using quinapril and quinaprilat as internal standards. The analytes are isolated from human plasma by means of Bond Elut C18 cartridges, methylated with diazomethane, purified by acid-base partitioning and converted to the corresponding trifluoroacetamides using trifluoroacetic anhydride. Moexipril and moexiprilat were analysed by gas chromatography-negative-ion chemical ionization mass spectrometry (GC-NICI-MS) at the fragment ions m/z 302 and m/z 288, respectively. The lower limit of quantitation both for moexipril and moexiprilat is 0.5 ng/ml of human plasma. Linear calibration curves are obtained over the concentration range 0.5-300 ng/ml of human plasma. In any case the imprecision and the inaccuracy are < 15%. The present method has been successfully applied to various pharmacokinetic studies in human subjects and patients.

Determination of dioxopiperazine metabolites of quinapril in biological fluids by gas chromatography-mass spectrometry

The dioxopiperazine metabolites of quinapril in plasma and urine were extracted with hexane-dichloroethane (1:1) under acidic conditions. Following derivatization with pentafluorobenzyl bromide and purification of the desired reaction products using a column packed with silica gel, the metabolites were analysed separately by capillary column gas chromatography-electron-impact mass spectrometry with selected-ion monitoring. The limits of quantitation for the metabolites were 0.2 ng/ml in plasma and 1 ng/ml in urine. The limits of detection were 0.1 ng/ml in plasma and 0.5 ng/ml in urine, at a single-to-noise ratio of greater than 3 and greater than 5, respectively. The proposed method is applicable to pharmacokinetic studies.