Quantitative determination of amlodipine in serum by liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry

Intramolecular interactions and the neutral loss of ammonia from collisionally activated, protonated ω-aminoalkyl-3-hydroxyfurazans

Gas phase fragmentation reactions of monoprotonated 4-(3-aminopropyl)- and 4-(4-aminobutyl)-3-hydroxyfurazan were investigated to examine potential interactions between functional groups. The two heterocyclic alkyl amines were ionized by electrospray ionization (ESI, positive mode) and fragmented using tandem mass spectrometry (MS/MS). The fragmentation pathways were characterized using pseudo MS3 experiments, precursor-ion scans, and density functional computations. For both heterocyclic ions, loss of ammonia was the only fragmentation process observed at low collision energies. Computational analysis indicated that the most feasible mechanism was intramolecular nucleophilic displacement of ammonia from the protonated ω-aminoalkyl side chain by N5 of the furazan ring. The alkylated nitrogen in the resulting bicyclic product ion facilitated N-O bond cleavage; subsequent neutral losses of nitric oxide (NO) and carbon monoxide (CO) occurred by homolytic bond cleavages. Next in the multistep sequence, neutral loss of ethylene from a radical cation was observed. A less favorable, competing fragmentation pathway of protonated 4-(3-aminopropyl)-3-hydroxyfurazan was consistent with cleavage of the 3-hydroxyfurazan ring and losses of NO and CO. Overall, the similar fragmentation behavior found for protonated 4-(3-aminopropyl)- and 4-(4-aminobutyl)-3-hydroxyfurazan differed from that previously characterized for furazan analogs with shorter alkyl chains. These observations demonstrate that a small change in the structure of multifunctional, heterocyclic alkyl amines may significantly influence interactions between distinct functional groups and the nature of the fragmentation process.

A new stability-indicating HPLC-UV method for determination of amlodipine besylate and its impurities in drug substance

A new fast stability-indication high performance liquid chromatography method was developed and validated for the determination of amlodipine besylate and its organic impurities in drug substance. The separation of amlodipine and its seven impurities was achieved on a core shell C18 column, 100 mm × 4.6 mm; 2.6 μm, within 15 min. The mobile phase comprised of 0.4% ammonium hydroxide in water and methanol delivered in a gradient mode; the method detection wavelength is 237 nm. The selected column is stable at high pH and provided a good peak shape for basic compounds. Amlodipine besylate was subject to acid, base, oxidative, thermal, and photolytic stress conditions. The degradation products were well resolved from the amlodipine peak and its impurities. Major degradants were analyzed by liquid chromatography coupled with single-quadrupole mass detector. Amlodipine peak was shown to be free of co-elution by mass spectral analysis in all stress conditions. The method was validated in terms of specificity, linearity, accuracy, precision, and robustness. The developed method could be applied for routine quality control analysis of amlodipine besylate drug substance.

Analytical and Bioanalytical Techniques for the Quantification of the Calcium Channel Blocker - Amlodipine: A Critical Review

Hypertension is a condition in which blood pressure is elevated to an extent where benefit is obtained from blood pressure lowering. The risk of complications is proportional to the level that blood pressure raises. Calcium channel blockers are a class of compounds used in the treatment of hypertension. The dihydropyridine (DHP) group, a subclass of the calcium channel blocker works almost exclusively on L-type calcium channels in the peripheral arterioles and reduce blood pressure by reducing total peripheral resistant. Long acting DHP is preferred because they are more convenient for patients and avoid the large fluctuations in plasma drug concentration which are associated with side effects. Amlodipine is the most distinct DHP and the most popular. The drug was patented in the year 1986 and its commercial sale began by 1990. The current article provides a state of art about the analytical and bioanalytical techniques available for the quantification of drug as a single entity and in combined pharmaceutical formulations between 1989 and 2019.

Simulated space radiation: Investigating ionizing radiation effects on the stability of amlodipine besylate API and tablets

Efficacious pharmaceuticals with the adequate shelf life are essential for the well-being of the space explorers and successful completion of a space mission. Space is brimming with different types of radiations, which penetrate inside the spacecraft despite the shielding material. Such radiations can alter the stability of the pharmaceuticals during long duration space missions. The literature reporting the space radiation effects on the pharmaceuticals is scarce in a public domain. Ground-based simulation studies can be useful to predict the influence of the space radiations on the stability of the pharmaceuticals. Based upon these facts, the main objective of the present preliminary work was to investigate the effect of different types of ionizing radiations on the stability of amlodipine besylate API and tablets. Amlodipine besylate samples were irradiated by protons, neutrons (thermal and fast), gamma and heavy ion (⁵⁶Fe) radiations with their different doses. The samples were also irradiated with UV-visible radiation to compare the effect of selected ionizing radiations with photodegradation. The physical stability was examined through organoleptic evaluation and the chemical stability was evaluated by FTIR and HPLC. The results of the organoleptic evaluation showed colour changes from colourless to yellow in proton irradiated solid API and gamma irradiated API aqueous solution. The FTIR spectrum of proton irradiated API showed one additional absorption band at 1728 cm^-1 due to degradation products. HPLC analysis revealed that amlodipine degraded up to 10% and 21% after the highest doses of proton and gamma irradiation, respectively. No physical or chemical changes were observed after neutron and ⁵⁶Fe irradiation. The structures of major radiolytic products were elucidated using LC-MS/MS. Two new impurities were found in the API aqueous solution as a result of gamma irradiation. The drug degradation pathways were postulated by proposing the plausible mechanism of formation.

Comparative effectiveness of methylene blue versus intravenous lipid emulsion in a rodent model of amlodipine toxicity

Context: Calcium channel blocker (CCB) poisonings are the leading cause of death from cardiovascular medication-related overdoses. Current treatments (calcium salts, vasopressors, inotropes) are often insufficient. Intravenous lipid emulsion (ILE) and methylene blue (MB) show promise in treating CCB overdoses unresponsive to conventional therapy. Objective: To compare the effectiveness of MB versus ILE in a rodent model of amlodipine (AML) poisoning with survival as the primary outcome and hemodynamic parameters as secondary outcomes. Materials and methods: Sixty-four adult male albino rats were anesthetized and cannulated for non-invasive hemodynamic measurement. Rats received amlodipine intraperitoneally (42 mg/kg). We then divided the rats into four groups: AML only without antidote, AML followed by ILE (24.8 mL/kg over 10 min), AML followed by normal saline (an equivalent volume of ILE), and AML followed by IV MB (2 mg/kg over 5 min). They received study treatments at 5, 30, and 60 minutes from the start of the protocol and with observation for 2 hours. Results: Survival time in ILE group was greater than in the control and NS groups. Differences between ILE and MB and between MB and NS were not significant. Hemodynamic parameters significantly increased in ILE group compared to the MB group at the 30, 60 and 120 min assessments but not after induction of AML poisoning and at 5 min assessment. Conclusions: Survival was greatest in rats treated with ILE. Both MB and NS had little effect on survival when compared to control animals. Both ILE and MB improved hemodynamics.

Identification and structure elucidation of a new degradation impurity in the multi-component tablets of amlodipine besylate

New unknown impurity at m/z 421.15 was observed during the accelerated stability analysis (40 °C/75% relative humidity) in the multi-component tablets of amlodipine besylate by reversed-phase ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS). UHPLC-MS and nuclear magnetic resonance (NMR) techniques were employed to identify and fully characterize the degradation compound. The degradation product was unambiguously identified as 3-ethyl 5-methyl 4-(2-chlorophenyl)-6-methyl-2-(morpholin-2-yl)-1,4-dihydropyridine-3,5-dicarboxylate and mechanism of its formation was proposed. It was confirmed that the degradation product was formed by the reaction of amlodipine with formaldehyde originating from the excipients present in the dosage form.

Retinal Concentration and Protective Effect against Retinal Ischemia of Nilvadipine in Rats

Purpose

Several calcium entry blockers have neuroprotective effects on cellular damage in the brain induced by ischemia. The purpose of this study was to determine whether nilvadipine (NID) crosses the blood–retinal barrier, and if so, whether it can then protect the photoreceptors against retinal ischemia-reperfusion injury.

Methods

Rats received an intramuscular injection of 1 mg/kg of NID and nifedipine (NIF), and the retinal and serum concentrations were measured. Ischemia was induced by raising the intraocular pressure for 45 minutes. Twenty-four hours after the reperfusion, the number of TUNEL positive cells and retinal ganglion cells (RGCs) were counted, and the thickness of the retina was measured.

Results

After 60 minutes, the concentration of NID, but not NIF, was higher in retina than in the serum. The number of TUNEL-positive cells was fewer and the reduction in the number of RGCs and the thickness of retina was less in the eyes that had received NID than controls.

Conclusions

The findings show that NID has high permeability to retina compared with NIF, which has less fat solubility than NID, and neuroprotective effect to retinal cells. NID might be useful for the treatment of glaucoma or other retinal diseases that have some relation to apoptosis.

Pharmacokinetic Comparison of Isoalantolactone and Alantolactone in Rats after Administration Separately by Optimization of an UPLC-MS2Method

Isoalantolactone and alantolactone are two major active ingredients that are present in many medicinal plants. In this study, a sensitive and rapid ultraperformance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was developed for determination of the two compounds in rat plasma, separately. In this method, an electrospray ionization source was applied and operated in positive ion mode; multiple reaction monitoring (MRM) was selected for quantification using target fragment ions 233.2→187.1 for isoalantolactone (alantolactone) and 245.1→189.1 for internal standard (IS). Retention time of the lactones and IS was within 3.0 min. Further calibration suggested a linear regression can be calculated within 2.5–500 ng/mL for isoalantolactone and 4–500 ng/mL for alantolactone. This method was used to compare the pharmacokinetic characteristics of isoalantolactone and alantolactone at a single dose of 5 mg/kg into male Sprague-Dawley rats by intravenous administration separately. The levels oft1/2, Kel, CL,Cmax, and AUC were significantly increased in the alantolactone group compared to isoalantolactone. These results suggested that isoalantolactone was distributed and eliminated more rapidly than alantolactone in rats when administered, respectively.

Simultaneous estimation of amlodipine and atenolol in human plasma: a sensitive LC–MS/MS method validation and its application to a clinical PK study

Background: A highly sensitive, specific and rapid LC–ESI-MS/MS method has been developed and validated for simultaneous quantification of amlodipine (AMD) and atenolol (ATL) in human plasma (200 µl) using AMD-d4 and ATL-d7, respectively, as an internal standard (IS) as per the regulatory guidelines. Results: The SPE method was used to extract the analytes and IS from human plasma. The chromatographic resolution of AMD, ATL and corresponding IS was achieved using an isocratic flow on a C18 column. The total chromatographic run time was 3 min. A linear response function was established for the range of concentrations 50–8000 pg/ml and 10–800 ng/ml for AMD and ATL, respectively, in human plasma. Conclusion: The intra- and inter-day accuracy and precision values for AMD and ATL met the acceptance as per regulatory guidelines. The validated assay was applied to a fixed-dose combination of AMD and ATL (Adopin-AT®) PK study in humans.

Spectrofluorimetric determination of amlodipine in human plasma without derivatization

A rapid and sensitive spectrofluorimetric method was developed for the determination of amlodipine (AD), a calcium channel blocker, in the plasma. The type of solvent, the wavelength range, and the range of AD concentration were selected to optimize the experimental conditions. The calibration curves were linear (r² >0.997) in the concentration range of 0.1-12.5 ppm of AD. The limit of quantitation and limit of detection values for the method for plasma samples were 0.1 ppm and 0.07 ppm, respectively. The precision calculated as the relative standard deviation was less than 3.5%, and the accuracy (relative error) was better than 5.5% (n=6). The method developed in this study can be directly and easily applied for the determination of AD in the plasma without derivatization in plasma.

Fragmentation of toxicologically relevant drugs in positive-ion liquid chromatography-tandem mass spectrometry

The identification of drugs and related compounds by LC-MS-MS is an important analytical challenge in several application areas, including clinical and forensic toxicology, doping control analysis, and environmental analysis. Although target-compound based analytical strategies are most frequently applied, at some point the information content of the MS-MS spectra becomes relevant. In this article, the positive-ion MS-MS spectra of a wide variety of drugs and related substances are discussed. Starting point was an MS-MS mass spectral library of toxicologically relevant compounds, available on the internet. The positive-ion MS-MS spectra of ∼570 compounds were interpreted by chemical and therapeutic class, thus involving a wide variety of drug compound classes, such benzodiazepines, beta-blockers, angiotensin-converting enzyme inhibitors, phenothiazines, dihydropyridine calcium channel blockers, diuretics, local anesthetics, vasodilators, as well as various subclasses of anti-diabetic, antidepressant, analgesic, and antihistaminic drugs. In addition, the scientific literature was searched for available MS-MS data of these compound classes and the interpretation thereof. The results of this elaborate study are presented in this article. For each individual compound class, the emphasis is on class-specific fragmentation, as discussing fragmentation of all individual compounds would take far too much space. The recognition of class-specific fragmentation may be quite informative in determining the compound class of a specific unknown, which may further help in the identification. In addition, knowledge on (class-specific) fragmentation may further help in the optimization of the selectivity in targeted analytical approaches of compounds of one particular class.

Application of liquid chromatography-two-dimensional nuclear magnetic resonance spectroscopy using pre-concentration column trapping and liquid chromatography-mass spectrometry for the identification of degradation products in stressed commercial amlodipine maleate tablets

Application of the HPLC hyphenated techniques of LC-two-dimensional (2D) NMR using pre-concentration column trapping and LC-MS was demonstrated by the identification of two major degradation products, DP-1 and DP-2, in stressed commercial tablets of amlodipine maleate. The molecular formulas were estimated by LC-MS. Sample pre-concentration by column trapping was conducted to obtain adequate 2D-NMR signals by reducing the peak widths of the degradation products and making sure that the maximum amount of each component was inside the flow cell for NMR detection. Double-quantum filtered correlation spectroscopy (DQF-COSY) was applied to identify DP-1 as beta-N-lactosylamlodipine by suppressing the residual water signal without affecting the sample signal and by measuring the coupling constant of the lactose anomeric proton. Heteronuclear multiple bond coherence spectroscopy (HMBC) was applied to characterize DP-2 as an aspartic acid derivative of amlodipine by detecting long-range CH correlations. The chemical structures of the degradation products could be successfully elucidated unambiguously without an isolation process.

Simultaneous determination of 6 beta-blockers, 3 calcium-channel antagonists, 4 angiotensin-II antagonists and 1 antiarrhytmic drug in post-mortem whole blood by automated solid phase extraction and liquid chromatography mass spectrometry

A method for the simultaneous determination of the beta-blockers atenolol, sotalol, metoprolol, bisoprolol, propranolol and carvedilol, the calcium-channel antagonists diltiazem, amlodipine and verapamil, the angiotensin-II antagonists losartan, irbesartan, valsartan and telmisartan, and the antiarrhythmic drug flecainide, in whole blood samples from forensic autopsies was developed. Sample clean-up was achieved by precipitation and solid phase extraction (SPE) with a mixed-mode column. Quantification was performed by reversed phase high performance liquid chromatography with positive electrospray ionization mass spectrometric detection (HPLC-MS). The method has been developed and robustness tested by systematically searching for satisfactory conditions using experimental designs including factorial and response surface designs. With the exception of amlodipine, the concentration limit of quantification (cLOQ) covered low therapeutic concentration levels for all the compounds. Within assay precisions and accuracies (bias) were 3.4-21% RSD and from -24 to 21% for the concentration range 1.00-5.00 microM, respectively. Between assay precisions were 4.4-28% RSD for the concentration range from 0.1 to 5 microM and recoveries varied from 9 to 103%. The method is used for determination of cardiovascular drugs in post-mortem whole blood samples from forensic autopsy cases.

A qualitative study of amlodipine and its related compounds by electrospray ionization tandem mass spectrometry

A comprehensive structural analysis of amlodipine and certain related compounds was performed by electrospray ionization tandem mass spectrometry. Triple quadrupole and quadrupole time-of-flight instruments were used to provide collision-induced dissociation and accurate mass measurement for selected product and second-generation product ions. A unique ion rearrangement was observed, which was found to be characteristic of certain dihydropyridines. This study provides a fundamental understanding of the fragmentation of these compounds. The structural elucidation of an unknown impurity is presented as an example.

Sensitive and rapid liquid chromatography/tandem mass spectrometry assay for the quantification of amlodipine in human plasma

A simple, sensitive and rapid high-performance liquid chromatography/electrospray ionization tandem mass spectrometry method was developed and validated for the assay of amlodipine in human plasma. Following liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reverse-phase C(18) column and analyzed by MS in the multiple reaction monitoring mode using the respective [M+H]+ ions, m/z 409/238 for amlodipine and m/z 409/228 for the IS. The assay exhibited a linear dynamic range of 50-10,000 pg/mL for amlodipine in human plasma. The lower limit of quantification was 50 pg/mL with a relative standard deviation of less than 8%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The average absolute recoveries of amlodipine and the IS from spiked plasma samples were 74.7 +/- 4.6 and 72.1 +/- 2.0%, respectively. A run time of 1.5 min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies. The observed maximum plasma concentration (Cmax) of amlodipine (2.5 mg oral dose) was 1425 pg/mL, time to observed maximum plasma concentration (Tmax) was 8.1 h and elimination half-life (T(1/2)) was 50.1 h.

Development and validation of a selective and robust LC-MS/MS method for quantifying amlodipine in human plasma

A liquid chromatographic-tandem mass spectrometric method (LC-MS/MS) for quantifying amlodipine in human plasma was developed and validated. Sample preparation was based on liquid-liquid extraction using NaOH and a mixture of ethyl acetate/hexane (80/20; v/v). Chromatography was performed on a C-18 analytical column and the retention times were 1.9 and 3.0 min for amlodipine and nimodipine (internal standard), respectively. The ionization was optimized using ESI(+) and enhanced selectivity was achieved using tandem mass spectrometric analysis via two MRM functions, 409 --> 238 and 418 --> 343 for amlodipine and nimodipine. The calibration curve ranged from 0.2 to 20.0 ng/mL. The inter-day precision and accuracy and the relative standard deviation (RSD) were <15%. The analyte was shown to be stable over the time-scale of the whole procedure. The robustness of the method was demonstrated by the good reproducibility of the results obtained during the analysis of clinical samples.

Simple and rapid HPLC method for determination of amlodipine in human serum with fluorescence detection and its use in pharmacokinetic studies

A fast, sensitive and specific high performance liquid chromatographic method using fluorescence detection is described for analysis of amlodipine in human serum. Amlodipine is extracted from serum by ethyl acetate and involves precolumn derivatization with 4-chloro-7-nitrobenzofurazan (NBD-Cl) and reverse-phase chromatography on C18 column. The mobile phase was sodium phosphate buffer (pH 2.5) containing 1 ml/l triethylamine and methanol at flow rate of 2.8 ml/min. Propranolol was used as internal standard. The standard curve was linear over the range 0.25-16 ng/ml of amlodipine in human serum. The within-day and between-day precision studies showed good reproducibility with coefficients of variation less than 12% for all the analytes. The limit of quantification was 0.25 ng/ml of serum. The method has been applied to a bioequivalence study after administration of 10 mg amlodipine in 12 normal subjects.

Quantitative Determination of the Calcium Channel Antagonists Amlodipine, Lercanidipine, Nitrendipine, Felodipine, and Lacidipine in Human Plasma Using Liquid Chromatography-Tandem Mass Spectrometry

A sensitive and specific liquid chromatography-tandem mass spectrometric method has been developed and validated for the quantification of the five 1,4-dihydropyridine calcium channel antagonists amlodipine, lercanidipine, nitrendipine, felodipine, and lacidipine in human plasma. Sample preparation involved solid-phase extraction on RP-C18 cartridges with good recovery for all the compounds. Sample analysis was performed on a Luna RP-C18 analytical column (15 mm x 2 mm ID, 3.0 microm) with a Sciex API 365 triple quadrupole mass spectrometer with turboionspray source and multiple reaction monitoring. The method is sensitive with a limit of detection below 1 ng/mL for each drug in plasma, with good linearity (r(2) > 0.998), over the therapeutic concentration range (1 to 40 ng/mL). All the validation data, such as accuracy, precision, and interday repeatability, were within the required limits. The method can be used for pharmacokinetic studies and therapeutic drug monitoring of the compounds in humans.

Application of oxidants to the spectrophotometric determination of amlodipine besylate in pharmaceutical formulations

Three new spectrophotometric methods for the determination of amlodipine besylate have been proposed. The first two methods, i.e. A and B, are based on the oxidation of the drug with Fe(III) and the estimation of Fe(II) produced after chelation with either 1,10-phenanthroline or 2,2'-bipyridyl at 500 and 515 nm, respectively. The Beer's law was obeyed in the concentration ranges of 2-10 and 4-14 microg ml(-1) with molar absorptivity of 2.9 x 10(4) and 2.7 x 10(4) l mol(-1) cm(-1) for methods A and B, respectively. The third procedure depends on the interaction of amlodipine besylate with ammonium heptamolybdate tetrahydrate, which resulted in the formation of molybdenum blue (lambda(max) 825 nm). The linear dynamic range and the molar absorptivity values were found to be 15-59 microg ml(-1) and 1.8 x 10(4) l mol(-1) cm(-1), respectively. The results of the proposed procedures were validated statistically and compared with those obtained by the reference method. The proposed methods were applied successfully to the determination of amlodipine besylate in commercial tablets.

Determination of nateglinide in animal plasma by micellar electrokinetic chromatography and on-line sweeping technique

A micellar electrokinetic chromatography (MEKC) method was developed for the determination of nateglinide in animal plasma by on-line sweeping technique, in which plasma samples were simply deproteinized with acetonitrile, and analyzed with 16 mmol/L NaH2PO4 + 6 mmol/L Na2B4O7 + 60 mmol/L sodium dodecyl sulfate (SDS) (pH 7.14) as the running buffer, a fused-silica capillary as the separation tube, 21 kV as the running voltage and UV detection at 214 nm. Under these conditions, more than 100-fold enrichment of nateglinide was obtained with the good linear relation in the range of nateglinide plasma concentration 0.2-7 mg/L (R = 0.998). The method could be applied successfully to determine trace drugs in clinical analysis.

On-line coupling of solid-phase extraction with mass spectrometry for the analysis of biological samples. III. Determination of prednisolone in serum

Solid-phase extraction (SPE) was directly coupled to mass spectrometry (MS) to assess the feasibility of the system for the rapid determination of prednisolone in serum. A C(18) stationary phase allowed washing of the cartridge with 25% methanol. Elution was performed by switching the methanol percentage from 25% in the washing step to 50% during elution. The high flow-rates during the extraction (5.0 ml/min) combined with ion-trap MS detection resulted in a total analysis time of 4 min. Some tailing of the prednisolone peak was observed. However, the tailing was found acceptable, since by this elution procedure most matrix compounds were prevented from eluting from the cartridge. Some matrix interference was still observed with a triple-quadrupole MS, even in the multiple reaction monitoring mode. This resulted in a detection limit (LOD) of about 10 ng/ml. The matrix interference and the LOD were similar for atmospheric pressure chemical ionisation and atmospheric pressure photo ionisation. Applying an ion-trap MS in the MS-MS mode resulted in cleaner chromatograms. Due to extensive fragmentation of prednisolone, the LOD was not lower than about 5 ng/ml prednisolone in serum, and a limit of quantitation of about 10 ng/ml (relative standard deviation <15%) was observed.

Development and validation of a liquid chromatographic method for the determination of amlodipine residues on manufacturing equipment surfaces

In the pharmaceutical industry, an important step consists in the removal of possible drug residues from the involved equipment and areas. The cleaning procedures must be validated and the methods to determine trace amounts of drugs have therefore to be considered with special attention. A high performance liquid chromatographic method for the determination of amlodipine residues in swab samples was developed and validated in order to control a cleaning procedure. The swabbing procedure was optimized in order to obtain a suitable recovery of amlodipine from stainless steel. A mean recovery close to 90% was obtained when two swabs moistened with methanol were used. The residual amlodipine was chromatographed at 25 degrees C in the isocratic mode on a RP-18 stationary phase using a mobile phase consisting of acetonitrile, methanol and pH 3.0 triethylamine solution (15:35:50 v/v/v). UV detection was performed at 237 nm. The method was shown to be selective and linear into the concentration range varying from 0.39 to 1.56 microg/ml. Accuracy and precision of the method were also studied. The limits of detection and quantitation were evaluated to be 0.02 and 0.08 microg/ml, respectively. The stability of amlodipine at different steps of the sampling procedure and the precision of the swabbing procedure were also investigated.

Validated spectrophotometric methods for the determination of amlodipine besylate in drug formulations using 2,3-dichloro 5,6-dicyano 1,4-benzoquinone and ascorbic acid

Two simple and sensitive spectrophotometric methods have been proposed for the determination of amlodipine besylate either in pure form or in pharmaceutical formulations. The first method is based on the charge transfer complexation reaction of the drug with 2,3-dichloro 5,6-dicyano 1,4-benzoquinone (DDQ) to give coloured product having maximum absorbance at 580 nm. The second procedure depends on the measurement of purple red colour produced by the interaction of drug with ascorbic acid in N,N-dimethylformamide medium (DMF) which absorbed maximally at 530 nm. Under the optimized experimental conditions, Beer's law was obeyed in the concentration ranges of 1-125 and 10-140 microg ml(-1) with DDQ and ascorbic acid, respectively. Both the methods were applied successfully for the analysis of amlodipine besylate in dosage forms. Results of analyses were validated statistically and through recovery studies.

Ion suppression in the determination of clenbuterol in urine by solid-phase extraction atmospheric pressure chemical ionisation ion-trap mass spectrometry

Ion suppression effects were observed during the determination of clenbuterol in urine with solid-phase extraction/multiple-stage ion-trap mass spectrometry (SPE/MS(3)), despite the use of atmospheric pressure chemical ionisation. During SPE, a polymeric stationary phase (polydivinylbenzene) was applied. Post-cartridge infusion of analyte to the SPE eluate after the extraction of blank urine was performed to obtain a profile of the suppression. Single and multiple-stage MS were performed to provide insight in the suppressing compounds. The ion suppression was mainly ascribed to two m/z values, but still no identification of the compounds was achieved from the multiple-stage MS data. No ionisable and non-ionisable complexes and/or precipitation of clenbuterol with matrix compounds were observed. A concentration dependence of the percentage of suppression was observed. Up to 70% of the signal was suppressed upon post-cartridge infusion of 0.22 microg/mL (at 5 microL/min) clenbuterol into the eluate, and this decreased to about 4% at infusion of 22 microg/mL clenbuterol. Molecularly imprinted polymers were used to enhance the selectivity of the extraction. Although matrix components were still present after extraction, no interference of these compounds with the analyte was observed. However, the bleeding of the imprint from the polymer (brombuterol) caused significant ion suppression.

Enantiomeric determination of amlodipine in human plasma by liquid chromatography coupled to tandem mass spectrometry

A sensitive method for the separation and determination of amlodipine enantiomers in plasma has been developed based on solid-phase extraction (SPE) with disposable extraction cartridges (DECs) in combination with chiral liquid chromatography (LC). The SPE technique is used to isolate the drug from the biological matrix and to prepare a cleaner sample before injection and analysis by HPLC coupled to mass spectrometry. The DEC is filled with ethyl silica (50 mg) and is first conditioned with a 2.5% ammonia in methanol solution and then with ammonium acetate buffer. A 1.0-ml volume of plasma is then applied on the DEC. The washing step is first performed with ammonium acetate buffer and secondly with a mixture of water and methanol (65:35, v/v), while the final elution step is obtained by dispensing methanol containing 2.5% of ammonia. The eluate is then collected and evaporated to dryness before being dissolved in the LC mobile phase and injected into the LC system. The stereoselective analysis of amlodipine is achieved on a Chiral AGP column containing alpha(1)-acid glycoprotein as chiral selector by using a mobile phase consisting of a 10-mM acetate buffer (pH 4.5) and 1-propanol (99:1, v/v). The LC system is coupled to tandem mass spectrometry with an APCI interface in the positive-ion mode. The chromatographed analytes are detected in the selected reaction monitoring mode (SRM). The MS/MS ion transitions monitored are 409 to 238 for amlodipine, and 260 to 116 for S-(-)-propranolol used as internal standard (IS). The method was validated considering different parameters, such as linearity, precision and accuracy. The limit of quantitation was found to be 0.1 ng/ml for each amlodipine enantiomer.

Rapid pharmacokinetic screening for the selection of new drug discovery candidates using a generic isocratic liquid chromatography--atmospheric pressure ionization tandem mass spectrometry method

A generic isocratic HPLC-APCI-MS-MS method has been developed for the determination of plasma concentrations of bioactive compounds for the selection of potential new drug discovery candidates. A 4.6 x 50 mm cyano phase column eluted with an acetonitrile/water mobile phase containing 20 mM ammonium acetate and 0.4% TFA produces retention times of 1 min or less for a wide range of compounds. This is a great advantage in new drug discovery where many compounds are analyzed once and eliminated. No time is consumed developing chromatographic conditions for each new compound. The mass spectrometer can be optimized and the samples can be processed and analyzed, all in the same day. Multiple assays can be run consecutively without changing the column or mobile phase between assays.

Amlodipine bioequivalence study: quantification by liquid chromatography coupled to tandem mass spectrometry

OBJECTIVE

To assess the bioequivalence of two amlodipine tablet formulations (Amlodipine 5 mg tablet from Merck S.A. Indústrias Químicas, Brazil as test formulation and Norvasc 5 mg tablet from Laboratórios Pfizer Ltd., Brazil as reference formulation) in 24 healthy volunteers of both sexes.

METHODS

The study was conducted using an open, randomized two-period crossover design with a 4-week washout interval. Plasma samples were obtained over a 144 h period. Plasma amlodipine concentrations were analyzed by combined liquid chromatography coupled to tandem mass spectrometry (LC-MS-MS) with positive ion electrospray ionization using multiple reaction monitoring (MRM). From the amlodipine plasma concentration vs time curves, the following pharmacokinetic parameters were obtained: AUC(last), AUC(0-inf) and C(max). The statistical interval proposed was 80-125% according to the US Food and Drug Administration Agency.

RESULTS

The limit of quantification was 0.1 ng/ml for plasma amlodipine analysis. The geometric mean and the 90% confidence interval (CI) test/reference ratios were 101.2 (92.9-110.2%) for AUC(last), 99.6 (91.5-108.4%) for AUC(0-inf) and 98.5 (89.0-109.1%) for C(max).

CONCLUSION

Since the 90% CI for AUC(last), AUC(0-inf) and C(max) ratios were within in the 80-125% interval proposed by the US FDA, it was concluded that Amlodipine 5 mg tablet (test formulation) was bioequivalent to Norvasc 5 mg tablet, in terms of both rate and extent of absorption.

Spectrophotometric method for the determination of amlodipine besylate with ninhydrin in drug formulations

A spectrophotometric method has been developed for the determination of amlodipine besylate in pure form and in pharmaceutical preparations. The method is based on the reaction of the primary amino group of the drug with ninhydrin in N,N'-dimethylformamide (DMF) medium producing a coloured complex which absorbs maximally at 595 nm. Beer's law is obeyed in the concentration range of 10-60 microg ml(-1) with RSD of 0.66% and molar absorptivity of 6.52 x 10(3) l mol(-1) cm(-1). All variables were studied in order to optimize the reaction conditions. The proposed method has been applied successfully to the analysis of the bulk drug and its dosage forms. No interference was observed from common pharmaceutical adjuvants. Statistical comparison of the results with the reference method shows excellent agreement and indicates no significant difference in accuracy and precision.

Determination of amlodipine in human plasma by high-performance liquid chromatography with fluorescence detection

A sensitive and specific HPLC method has been developed for the assay of amlodipine in human plasma. The assay involves derivatization with 4-chloro-7-nitrobenzofurazan (NBD-Cl), solid-phase extraction on a silica column and isocratic reversed-phase chromatography with fluorescence detection. Nortriptyline hydrochloride was used as an internal standard. The assay was linear over the concentration range of 0.25-18.00 ng/ml. Both of the within-day and day-to-day reproducibility and accuracy were less than 11.80% and 12.00%, respectively. The plasma profile following a single administration of 10 mg amlodipine to a healthy volunteer was presented.

Enzyme linked immunosorbent assay for determination of amlodipine in plasma

Amlodipine is a calcium channel antagonist of the dihydropyridine group. It is effective for treating hypertension, chronic stable angina, and vasospastic angina. However, it is difficult clinically to pinpoint the maximum dosage for antihypertensive activity of the drug without having parallel data on the plasma drug concentrations. The methods for assaying amlodipine are either gas chromatography with electron capture detector or liquid chromatography coupled with tandem mass spectrometry (or with an electrochemical detector), which needs tedious derivatization, and is expensive and time consuming. Therefore, in this study we developed an enzyme immunoassay for determining amlodipine in plasma. Anti-amlodipine antibodies were produced following immunization of bovine serum albumin-amlodipine conjugate. These specific antibodies were used in a competitive biotin-avidin-based enzyme-linked immunosorbent assay to measure amlodipine in plasma. Biotin was linked to the antibodies in order to enhance the sensitivity of the assay. The assay was specific for the free form of amlodipine with a detection limit of 0.1 ng/ml and the intra- and interassay coefficient of variation ranged from 1.6-10.2%. This immunoassay provides a sensitive, reliable, rapid, and accurate method for determination of amlodipine in plasma, which can be used in therapeutic drug monitoring pharmacokinetic studies and pharmaceutical analysis.

On-line coupling of solid-phase extraction with mass spectrometry for the analysis of biological samples. I. Determination of clenbuterol in urine

The potential of the direct coupling of solid-phase extraction (SPE) with mass spectrometry (MS) for the analysis of biological samples is demonstrated. For SPE a cartridge exchanger is used and the eluate is directly introduced into the mass spectrometer. This system has been investigated for the determination of clenbuterol in urine. With mixed-mode cartridges, a considerable ion suppression has been obtained. The mass spectrum at the elution time of clenbuterol is dominated by that of creatinine and adduct formation of clenbuterol and creatinine has been observed. The whole procedure including injection of 1 ml urine, washing and desorption has been developed with cartridges containing 8-microm C18-bonded silica. If only a single MS step is used, the selectivity and, therefore, the sensitivity are insufficient. The detection limit is about 100 ng/ml. However, with atmospheric pressure chemical ionisation and the tandem MS mode the detection limit has been decreased to about 2 ng/ml and the ion suppression is only about 10%. For the electrospray ionisation the detection limit is about 10-times higher and the ion suppression is less favourable. The repeatability for the SPE-MS-MS procedure was 6.5% at 10 ng/ml (n=5) and the difference between the response factors at 10 ng/ml and 100 ng/ml was only 2.5%. The MS behaviour of clenbuterol and the matrix under the present conditions is discussed.

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.

Hyphenated liquid chromatographic techniques in forensic toxicology

The prerequisite of applicability of hyphenated methods in forensic analysis is the achievement of a stage of "final maturity". In the field of liquid chromatography, HPLC coupled with diode array detection (DAD) seems to fulfill this criterion, whilst the combination with atmospheric pressure ionization mass spectrometry (HPLC-API-MS) is still in a development stage. HPLC-DAD is broadly used as identification tool in forensic and in emergency toxicology. Two main approaches were observed; development of retention index scales for intra-laboratory exchange of data and establishing of databases only for intra-laboratory use. Using these approaches, several databases were established for toxicological relevant substances (illicit and therapeutic drugs and their metabolites, environmental poisons etc.) in biological fluids. Also, complete HPLC-DAD identification systems are commercially available. Further possibility of progress depends on the on-line combination ("triple hyphenation") with other detection methods, preferably API-MS. HPLC-API-MS, both in electrospray (ESI) and atmospheric pressure chemical ionization (APCI) options, underwent dramatic development in the last decade and is reaching its final shape. The method was broadly applied for various groups of toxicologically relevant substances, a lot of them unaccessible for other techniques, including GC-MS. Particularly important was application of HPLC-API-MS for detection and quantitation of active, polar metabolites of various drugs and for analysis of macromolecules. APCI seems to be more useful for analysis of less polar compounds, whereas ESI is particularly valuable for determination of polar, large molecules (e.g., toxic peptides, polar metabolites etc.) Up to now, HPLC-API-MS has been mainly applied for dedicated analyses, but the introduction of APCI or ESI in systematic toxicological screening may be expected in the near future.

Quantitative analysis of R-84760, a selective kappa-opioid receptor agonist, in plasma by liquid chromatography with electrospray ionization tandem mass spectrometry

A sensitive method for monitoring R-84760, a selective kappa-opioid receptor agonist, in plasma using liquid chromatography with electrospray ionization tandem mass spectrometry was explored. R-84760 and internal standard (I.S., d8-R-84760) were extracted from human or various animal plasmas with ethyl acetate. The analysis was performed by the selected reaction monitoring method, and the precursor-product combinations of m/z 399-328 for R-84760 and m/z 407-328 for I.S. were chosen for quantification. The calibration curve was linear in the range 5-500 pg/ml, and the limit of quantification was 5 pg/ml using 1 ml of human plasma. Pharmacokinetic studies of R-84760 in rats, dogs, and monkeys were performed by this method. The plasma concentration of unchanged form after administration at a trace dosage amount was able to be monitored. Interspecies correlations of pharmacokinetic parameters obtained in animals were utilized to estimate pharmacokinetic behavior in humans. The results showed that it is possible to perform pharmacokinetic studies on R-84760 by this quantitative analysis.

Liquid chromatography-mass spectrometry in forensic and clinical toxicology

This paper reviews liquid chromatographic-mass spectrometric (LC-MS) procedures for the identification and/or quantification of drugs of abuse, therapeutic drugs, poisons and/or their metabolites in biosamples (whole blood, plasma, serum, urine, cerebrospinal fluid, vitreous humor, liver or hair) of humans or animals (cattle, dog, horse, mouse, pig or rat). Papers published from 1995 to early 1997, which are relevant to clinical toxicology, forensic toxicology, doping control or drug metabolism and pharmacokinetics, were taken into consideration. They cover the following analytes: amphetamines, cocaine, lysergide (LSD), opiates, anabolics, antihypertensives, benzodiazepines, cardiac glycosides, corticosteroids, immunosuppressants, neuroleptics, non-steroidal anti-inflammatory drugs (NSAID), opioids, quaternary amines, xanthins, biogenic poisons such as aconitines, aflatoxins, amanitins and nicotine, and pesticides. LC-MS interface types, mass spectral detection modes, sample preparation procedures and chromatographic systems applied in the reviewed papers are discussed. Basic information about the biosample assayed, work-up, LC column, mobile phase, interface type, mass spectral detection mode, and validation data of each procedure is summarized in tables. Examples of typical LC-MS applications are presented.