Biomedical subjects

R M Alonso

Publications and source records attributed to R M Alonso.

At least 19 recordsLinked to original sources

PubMed2006

Validation of a solid phase extraction-high performance liquid chromatographic method for the determination of eprosartan in human plasma.

In this work, a solid phase extraction-reversed phase high performance liquid chromatographic (SPE-RP-HPLC) method with photometric detection for monitoring the antihypertensive drug eprosartan has been validated in order to assure good quantitation of eprosartan in plasma samples obtained from patients under cardiovascular treatment. This analytical method was developed by using experimental design and quantitation was accomplished with the internal standard method. No interferences were observed from endogenous compounds of plasma and other drugs which are commonly co-administered in elderly patients. The recoveries of eprosartan from plasma samples, measured at three levels of the linear concentration range (150-4000 ng/mL) were found to be between 93.4 and 102.8%. The intraday and interday precision and accuracy (measured by relative standard deviation, RSD, and relative error, RE, respectively) were always lower than 13% (RSD) and 4% (RE). Stability studies showed that eprosartan stock solutions are stable for at least 3 months when stored at 8 degrees C and plasma samples containing the drug were stable at least during the whole analytical method.

Acrylates↗

PubMed2004

Capillary electrophoresis as a useful tool for the analysis of chemical tracers applied to hydrological systems.

A capillary electrophoretic method was optimised for the separation and determination of iodide used as artificial tracer in hydrology. The influence of the buffer concentration and pH, electroosmotic flow modifier concentration (cetyltrimethylammonium bromide (CTAB)), the injection time and voltage applied, on the electrophoretic separation was studied. A running buffer of 20 mM phosphate (pH 8) containing 1 mM CTAB was found to provide the optimum separation of iodide with respect to resolution, migration time and selectivity. The water samples were injected hydrostatically at 10 cm for 110 s, the voltage applied was -20 kV and a detection wavelength of 214 nm. The influence of the sulphite added to water samples in order to prevent the oxidation of iodide to iodate was also studied. This method can be applied to the determination of iodide free of sulphite interference up to at least a ratio of 1:1000 (I(-):SO3(2-)). The other inorganic anions, which are present in the water samples (mainly chloride, sulphate, nitrate, carbonate), do not interfere with the determination of iodide. This method allows the simultaneous determination of bromide, nitrite, and nitrate together with iodide. The electrophoretic method showed to be linear from 0.5 to 5 mg l(-1) of iodide (the migration time was 2.6 min) with a quantitation limit of 0.45 mg l(-1) and a intraday repeatability lower than 4% of R.S.D. at different concentration levels.

Electrophoresis, Capillary↗

PubMed2004

Experimental design optimization of a capillary zone electrophoresis method for the screening of several diuretics and ACE inhibitors.

Experimental design methodologies are applied to the development of a capillary zone electrophoretic method for the separation of the angiotensin-converting enzyme inhibitor enalapril and its derivative enalaprilat and the diuretics xipamide and hydrochlorothiazide. The effects of pH, buffer concentration, proportion of boric acid in the mixed boric acid-potassium dihydrogen phosphate background electrolyte, temperature, applied voltage, and percentage of organic modifier are studied. Critical factors are identified in a screening design (a 2(6-2) fractional factorial design), and afterwards, optimal conditions for the separation are reached by means of an optimization design (a 2(2) + 2 x 2 + k central composite design). The studied response is the resolution between peaks. The four studied compounds can be separated in less than 3.5 min using an electrolyte of 20mM boric acid-potassium dihydrogen phosphate (75:25, v/v) with 5% MeOH adjusted to pH 8.0 with KOH, at a potential of 30 kV. The detection wavelength and temperature are 206 nm and 35 degrees C, respectively.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2003

Experimental design approach for the optimisation of a HPLC-fluorimetric method for the quantitation of the angiotensin II receptor antagonist telmisartan in urine.

A high performance liquid chromatographic method with fluorimetric detection has been developed for the quantitation of the angiotensin II receptor antagonist (ARA II) 4-((2-n-propyl-4-methyl-6-(1-methylbenzimidazol-2-yl)-benzimidazol-1-yl)methyl)biphenyl-2-carboxylic acid (telmisartan) in urine, using a Novapak C18 column 3.9 x 150 mm, 4 microm. The mobile phase consisted of a mixture acetonitrile-phosphate buffer (pH 6.0, 5 mM) (45:55, v/v) pumped at a flow rate of 0.5 ml min(-1). Effluent was monitored at excitation and emission wavelengths of 305 and 365 nm, respectively. Separation was carried out at room temperature. Chromatographic variables were optimised by means of experimental design. A clean-up step was used for urine samples consisting of a solid-phase extraction procedure with C8 cartridges and methanol as eluent. This method proved to be accurate (RE from -12 to 6%), precise (intra- and inter-day coefficients of variation (CV) were lower than 8%) and sensitive enough (limit of quantitation (LOQ), ca. 1 microg l(-1)) to be applied to the determination of the active drug in urine samples obtained from hypertensive patients. Concentration levels of telmisartan at different time intervals (from 0 up to 36 h after oral intake) were monitored.

Angiotensin Receptor Antagonists↗

PubMed2002

Quantitative determination of oxprenolol and timolol in urine by capillary zone electrophoresis.

A simple capillary zone electrophoretic method with UV detection has been developed for the quantitative determination of the beta-adrenoreceptor antagonists (beta-blockers) oxprenolol and timolol in human urine, preceded by a solid-phase extraction step. The electrophoretic separation was performed on a 78 cm x 75 microm I.D. fused-silica capillary (effective capillary length: 70 cm). The electrolyte consisted of a Na2B4O7-H3BO3 (50 mM), pH 9. The introduction of the sample was made hydrostatically for 20 s and the running voltage 25 kV at the injector end of the capillary. Photometric detection was used at a wavelength of 229 nm for oxprenolol and 280 nm for timolol. Under these conditions oxprenolol migrated at 4.76+/-0.05 min and timolol at 4.97+/-0.05 min. The solid-phase extraction methods were optimised for each beta-blocker and provided recoveries of 72.8% for timolol and 94.52% for oxprenolol. Good resolution from the endogenous compounds present in the urine matrix were achieved for both compounds. The method was applied to the determination of both beta-blockers in pharmaceutical formulations and urine samples obtained from hypertensive patients after the ingestion of a therapeutic dose (in a 24-h time interval after the ingestion). The quantitative results were compared with results previously obtained at our laboratories by HPLC and were found to be in good agreement. Good reproducibility, linearity, accuracy and quantitation limits (in urine) of 0.19 microg/ml for timolol and 0.20 microg/ml for oxprenolol were obtained, allowing the method to be applied to pharmacokinetic studies of these compounds.

Adrenergic beta-Antagonists↗

PubMed2002

Fast screening method for the determination of angiotensin II receptor antagonists in human plasma by high-performance liquid chromatography with fluorimetric detection.

A selective, accurate and precise high-performance liquid chromatographic assay coupled to fluorescence detection was developed for the detection of some angiotensin II receptor antagonists (ARA II): Losartan, Irbesartan, Valsartan, Candesartan cilexetil and its metabolite Candesartan MI. The analytes and the internal standard (bumetanide, a high-ceiling diuretic) were extracted from plasma under acidic conditions by means of solid-phase extraction using C8 cartridges. This procedure allowed recoveries close to 80% for all these drugs excluding Candesartan cilexetil (70%) which presented adsorption processes on glass and plastic walls. The analytes and potential interferences were separated on a reversed-phase column, muBondapak C18, at room temperature. A gradient elution mode was used to carry out the separation, the optimal mobile phase being composed of acetonitrile-5 mM acetate buffer, pH 4, at variable flow-rates (from 1.0 to 1.2 ml/min). Fluorescence detector was set at an excitation wavelength of 250 nm and an emission wavelength of 375 nm. Intra- and inter-day relative standard deviations for all the compounds were lower than 8% except for Losartan (12%) and the method assesses a quite good accuracy (percentage of relative error approximately 6% in most of the cases). The limit of quantitation for these compounds was 3 ng/ml for Candesartan cilexetil and M1, 16 ng/ml for Losartan and 50 ng/ml for Irbesartan and Valsartan, which allows their determination at expected plasma concentration levels. This assay method has been successfully applied to plasma samples obtained from hypertensive patients under clinical studies after oral administration of a therapeutic dose of some of these ARA II compounds.

Angiotensin II↗

PubMed2001

Determination of the beta-blocker atenolol in plasma by capillary zone electrophoresis.

A capillary zone electrophoretic method was optimised for the determination of the beta-blocker atenolol in plasma. Separation was performed in an uncoated silica capillary of 58.5 cm (effective length 50 cm) x 75 microm I.D., and detection was at 194 nm. The effects of the buffer (concentration and pH), the injection time, the voltage applied and the plasma clean-up procedure were studied. The determination of atenolol was achieved in less than 3 min, using an electrolyte of 50 mM H3BO3-50 mM Na2B4O7 (50:50, v/v) pH 9, injected hydrodynamically for 4 s at 50 mbar and applying a voltage of +25 kV. This method was applied to the determination of atenolol in plasma of nine hypertensive patients (male and female, aged from 39 to 73 years). Atenolol concentrations found vary from 30 to 585 ng/ml.

Adrenergic beta-Antagonists↗

PubMed2001

Capillary zone electrophoresis applied to the determination of the angiotensin-converting enzyme inhibitor cilazapril and its active metabolite in pharmaceuticals and urine.

A capillary zone electrophoresis method has been developed for the quantitation of antihypertensive drug cilazapril and its active metabolite cilazaprilat in pharmaceuticals and urine. The separation of the compounds was performed in a fused-silica capillary filled with the running electrolyte, which consisted of a 60 mM borate buffer solution at pH 9.5. Under the optimized experimental conditions, the separation took less than 5 min. The analysis of urine samples required a previous solid-phase extraction step using C8 cartridges. The method was successfully applied to the determination of the drug and its metabolite in urine samples obtained from three hypertensive patients (detection limits of 115 ng ml(-1) for cilazaprilat and 125 ng ml(-1) for cilazapril) and to pharmaceutical dosage forms. The method was validated in terms of reproducibility, linearity and accuracy.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2001

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.

Antihypertensive Agents↗

PubMed2001

pK(a) determination of angiotensin II receptor antagonists (ARA II) by spectrofluorimetry.

The acid-base equilibrium constants of a new family of antihypertensive drugs, the angiotensin II receptor antagonists (ARA II), Losartan, Irbesartan, Valsartan, Candesartan cilexetil, its metabolite Candesartan M1 and Telmisartan were determined by spectrofluorimetry. Relative fluorescent intensity (I(F,rel))-pH data were treated by graphical (derivatives and curve-fitting) and numerical methods (LETAGROP SPEFO). The resultant pK(a) values at an ionic strength of 0.5 M were (3.15+/-0.07) for Losartan, (4.70+/-0.06) for Irbesartan, (4.90+/-0.09) for Valsartan, (6.0+/-0.1) for Candesartan cilexetil, (3.9+/-0.1) for Candesartan M1, and (4.45+/-0.09) for Telmisartan.

Angiotensin Receptor Antagonists↗

PubMed2001

Quantitative determination of the loop diuretic bumetanide in urine and pharmaceuticals by high-performance liquid chromatography with amperometric detection.

A high-performance liquid chromatographic method with amperometric detection has been developed for the determination of the diuretic bumetanide using a microBondapak C18 column. The mobile phase consists of a 50:50 acetonitrile-water mixture containing 5mM KH2PO4-K2HPO4 (pH 4.0). The compound is monitored at +1350 mV with an amperometric detector equipped with a glassy carbon working electrode. A liquid-liquid or solid-liquid extraction is done prior to chromatographic analysis in order to avoid the interferences found in the urine matrix. The percentages of recovery obtained are 71%+/-1% for liquid-liquid extraction and 84.2%+/-0.7% for solid-liquid extraction. The method developed has a linear concentration range from 50 to 499 ng/mL with a reproducibility in terms of relative standard deviation of 1.73% and 3.85% for a concentration level of 70 ng/mL and 237 ng/mL, respectively, and a detection limit of 0.25 ng/mL (3:1 signal-to-noise ratio). The method is applied to the determination of bumetanide in pharmaceutical formulations and urine obtained from hypertensive patients and healthy volunteers after the ingestion of a therapeutic dose of Fordiuran (1 mg bumetanide).

Adult↗

PubMed2001

Simultaneous determination of torasemide and its major metabolite M5 in human urine by high-performance liquid chromatography-electrochemical detection.

A high-performance liquid chromatographic method with electrochemical detection is described for the simultaneous determination of the loop diuretic 1-isopropil-3-[4-(3-methylphenylamino)-3-pyridinesulphonyl]urea (torasemide) and its major metabolite M5 in human urine. The assay is simple, fast, and easy. It requires a sample cleanup consisting of a solid-phase extraction under acidic conditions followed by chromatographic separation with a C18 microBondapack column. The use of a water-acetonitrile mobile phase (80:20, v/v, pH 3) ensures total separation from urine-interfering substances, and both compounds can be quantitated amperometrically at a glassy carbon electrode set to +1300 mV versus Ag-AgCl. The method demonstrates linearity for both the parent drug and the metabolite over a wide concentration range (up to 7 microg/mL) and reproducibility with relative standard deviation lower than 2% in intraday and 5% in interday assays. The mean extraction recoveries are 78% for M5 and 60% for torasemide, and the limits of quantitation are 1 and 8 ng/mL, respectively. The method developed is applied to the analysis of healthy volunteers' urine samples collected at different time intervals after the oral ingestion of a single dose of 10 mg torasemide, and the results obtained are in agreement with the pharmacokinetic profile of torasemide.

Chromatography, High Pressure Liquid↗

PubMed2001

Solid-phase extraction and high-performance liquid chromatography applied to the determination of quinapril and its metabolite quinaprilat in urine.

Quinapril is an antihypertensive drug that belongs to the family of angiotensin-converting enzyme inhibitors. It is metabolized to quinaprilat, which is the compound that is really responsible for the therapeutic action. In this study, a rapid and simple liquid chromatographic method with photometric detection is described and applied to the determination of quinapril and quinaprilat in urine. The cleanup procedure for the urine samples consists of a solid-liquid extraction using C8 cartridges. Under these conditions, both compounds and the internal standard (enalapril maleate) are separated in less than 9 min. Recoveries for quinapril and quinaprilat are greater than 80%. The method is sensitive enough (detection limit of 60 ng/mL for quinapril and 50 ng/mL for quinaprilat) to be applied for the determination of quinapril and quinaprilat in urine samples obtained from four hypertensive patients after the intake of a therapeutic dose.

Antihypertensive Agents↗

PubMed2000

Determination of the pKa values of beta-blockers by automated potentiometric titrations.

The acid-base equilibrium constants of the beta-blockers atenolol, oxprenolol, timolol and labetalol were determined by automated potentiometric titrations. The pKa values were obtained in water-rich or water methanol medium (20% MeOH) to obviate the solubility problems associated with the compounds. The initial estimates of pKa values were obtained from Gran's method and then, were refined by the NYTIT and ZETA versions of the LETAGROP computer program. The resultant values were 9.4 (I = 0.1 M KCl, 20% methanol) for atenolol, 9.6 (I = 0.1 M KCl) for oxprenolol, 9.4 (I = 0.1 M KCl, 20% methanol) for timolol and 7.4 and 9.4 (I = 0.1 M KCl) for labetalol. The potentiometric method was found to be accurate and easily applicable. The operational criteria for applying the methodology are indicated.

Adrenergic beta-Antagonists↗

PubMed2000

Determination of aldicarb, aldicarb sulfoxide and aldicarb sulfone in some fruits and vegetables using high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

An analytical method for the determination of aldicarb, and its two major metabolites, aldicarb sulfoxide and aldicarb sulfone in fruits and vegetables is described. Briefly the method consisted of the use of a methanolic extraction, liquid-liquid extraction followed by solid-phase extraction clean-up. Afterwards, the final extract is analyzed by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (LC-APCI-MS). The specific fragment ion corresponding to [M-74]+ and the protonated molecular [M+H]+ ion were used for the unequivocal determination of aldicarb and its two major metabolites. The analytical performance of the proposed method and the results achieved were compared with those obtained using the common analytical method involving LC with post-column fluorescence detection (FL). The limits of detection varied between 0.2 and 1.3 ng but under LC-FL were slightly lower than when using LC-APCI-MS. However both methods permitted one to achieve the desired sensitivity for analyzing aldicarb and its metabolites in vegetables. The method developed in this work was applied to the trace determination of aldicarb and its metabolites in crop and orange extracts.

Aldicarb↗

PubMed2000

High-performance liquid chromatography with amperometric detection applied to the screening of 1,4-dihydropyridines in human plasma.

A high-performance liquid chromatographic method with electrochemical detection has been developed for the determination of six 1,4-dihydropyridines: nifedipine, nimodipine, nisoldipine, nicardipine, felodipine and lacidipine. The chromatographic separation was performed using a Supelcosil LC-ABZ+Plus C18 column. A mobile phase of methanol-water (70:30), containing 2 mM CH3COOH-CH3COONa at a flow-rate of 1 ml/min and a pH of 5.0, was used. The temperature was optimized at 30+/-0.2 degrees C. The amperometric detector, equipped with a glassy carbon electrode, was operated at 1000 mV versus Ag/AgCl in the direct current mode. The method was applied to the determination of these compounds at ng/ml concentrations, obtaining intra-day reproducibilities of lower than 5.0% in terms of relative standard deviations and detection limits ranging from 16 to 44 ng/ml. The method was applied to the screening of 1,4-dihydropyridines in spiked plasma samples, with a total elution time of lower than 18 min, obtaining the best recoveries for nimodipine and felodipine (91 and 88%, respectively). These recoveries together with the low detection limits achieved allow its application to the analysis of these drugs in human plasma.

Calcium Channel Blockers↗

PubMed2000

In vitro and in vivo evaluation of the antihypertensive drug atenolol in cultured human lymphocytes: effects of long-term therapy.

The genotoxicity of atenolol, a beta-blocker antihypertensive drug, both in vitro and in vivo, was cytogenetically tested for its ability to induce sister chromatid exchange (SCE) and micronuclei (MN) in cultured peripheral lymphocytes. Also, fluorescence in situ hybridization (FISH) with a centromeric probe was performed to determine the origin of the induced MN. The in vivo study was carried out, on the one hand, on four patients under antihypertensive treatment with atenolol and, on the other hand, on four matched control individuals taking an oral dose of atenolol. The in vitro study was performed on the control individuals by adding the drug to the culture medium at a final concentration similar to the levels found in plasma. When a comparison was made, the frequency of SCE did not show significant differences in any case. A statistically significant increase in the frequency of MN was detected in patients but not in control individuals either in vitro or in vivo. FISH analysis revealed statistically significant differences between patients and control individuals without the drug with respect to the frequency of centromeric signals in MN. Taking all these observations together, our data suggest that chronic exposure to atenolol resulted mainly in the induction of chromosome loss, so an aneugenic activity could be predicted. Different sensitivity to the compound was observed among control individuals. Nevertheless, all of them responded to the presence of atenolol in the same way in both assays. Interindividual variability was also reported. The intervariability seen in patients suggested an adaptive response to the chemical after long-term therapy.

Antihypertensive Agents↗

PubMed1999

Micellar electrokinetic chromatography as a fast screening method for the determination of 1,4-dihydropyridine calcium antagonists.

A micellar electrokinetic chromatographic method (MEKC) was optimized for the separation of six calcium antagonists. The effects of the buffer (concentration and pH), concentration of sodium dodecyl sulphate (SDS), the organic modifier, the injection time, and the voltage applied were studied. A final appropriate electrolyte of 50 mM borate buffer, pH 8.2, containing 20 mM SDS and 15% (v/v) acetonitrile was found to provide the optimum separation with respect to resolution and migration time. The samples were introduced hydrostatically for 4 s at 50 mbar injection pressure and the applied voltage was +25 kV. The screening of the six compounds was achieved in less than 15 min: nifedipine (migration time, tm = 6.9 min), nimodipine (tm = 10.1 min), felodipine (tm = 12.2 min), nicardipine hydrochloride (tm = 12.7 min), lacidipine (tm = 13.5 min) and amlodipine besylate (tm = 14.1 min, tm = 8 min). The method developed showed to be linear at least up to 70 micrograms/ml with a detection limit of about 5 micrograms/ml for each compound. The within-day and inter-day area reproducibility (R.S.D.) were, respectively, lower than 4.8 and 8.6% for six replicate samples.

Acetonitriles↗