High-performance liquid chromatographic determination of nifedipine, nicardipine and pindolol using a carbon fibre flow-through amperometric detector

Rapid and simultaneous determination of nifedipine and dehydronifedipine in human plasma by liquid chromatography-tandem mass spectrometry: Application to a clinical herb-drug interaction study

Nifedipine (NIF), a calcium channel antagonist, is metabolized primarily by cytochrome P450 (CYP3A4) to dehydronifedipine (DNIF). As such, NIF is often used as a probe drug for determining CYP3A4 activity in human studies. A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed and validated to simultaneously determine NIF and DNIF in human plasma using nitrendipine as the internal standard (IS). After extraction of the plasma samples by ether-n-hexane (3:1, v/v), NIF, DNIF and the IS were subjected to LC/MS/MS analysis using electro-spray ionization (ESI). Chromatographic separation was performed on a Hypersil BDS C(18) column (50 mm x 2.1 mm, i.d., 3 microm). The method had a chromatographic running time of approximately 2.5 min and linear calibration curves over the concentrations of 0.5-100 ng/mL for NIF and DNIF. The recoveries of the one-step liquid extraction method were 81.3-89.1% for NIF and 71.6-80.4% for DNIF. The lower limit of quantification (LLOQ) of the analytical method was 0.5 ng/mL for both analytes. The intra- and inter-day precision was less than 15% for all quality control samples at concentrations of 2, 10, and 50 ng/mL. The validated LC/MS/MS method has been successfully used to study pharmacokinetic interactions of NIF with the herbal antidepressant St. John's wort in healthy volunteers. These results indicated that the developed LC/MS/MS method was efficient with a significantly shorter running time (2.5 min) for NIF and DNIF compared to those methods previously reported in the literature. The presented LC/MS/MS method had acceptable accuracy, precision and sensitivity and was used in a clinical pharmacokinetic interaction study of NIF with St. John's wort, a known herbal inducer of CYP3A4. St. John's wort was shown to induce NIF metabolism with increased plasma concentrations of DNIF.

Room-temperature, phosphorimetric determination of the beta-blocking agent pindolol in pharmaceutical tablets, urine and blood serum

It is already recognised that heavy-atom-induced, room-temperature phosphorescence can be used to determine pindolol in pharmaceutical samples and biological fluids. We describe here a new, simple, rapid and selective development of this technique. The phosphorescence signals derive from the interaction of pindolol with a relatively high concentration of heavy-atom salts in the presence of sodium sulphite as oxygen scavenger. Phosphorescence was registered in the presence of 1.2 M potassium iodide, 15 mM sodium sulphite and 30% v/v methanol at 450 nm, exciting at 285 nm. The detection limit was 21.1 ng mL(-1). The method has been successfully applied to the determination of pindolol in commercial pharmaceutical tablets, urine and blood serum.

Sensitive and simple liquid chromatographic method with ultraviolet detection for the determination of nifedipine in canine plasma

An isocratic high-performance liquid chromatographic method with detection at 240 nm was developed, optimized and validated for the determination of nifedipine in canine plasma. Liquid-liquid extraction was used as the sample preparation technique. Carbamazepine was used as internal standard. A Hypersil BDS RP-C18 column (250 mm x 4.6 mm, 5 microm) was equilibrated with a mobile phase composed of water and methanol, 45:55 (v/v). Its flow rate was 1 ml min(-1). The elution time for nifedipine and carbamazepine was approximately 12 and 8 min, respectively. Calibration curves of nifedipine in plasma were linear in the concentration range of 1-200 ng ml(-1). Limits of detection and quantification in plasma were 0.5 and 1.5 ng ml(-1), respectively. Recovery was greater than 98%. Intra- and inter-day relative standard deviation for nifedipine in plasma was less than 8.5 and 10%, respectively. This method was applied to the determination of nifedipine plasma levels after administration of commercially available soft gelatine capsules to dogs.

Determination of nifedipine in human plasma by solid-phase extraction and high-performance liquid chromatography: validation and application to pharmacokinetic studies

Nifedipine, a dihydropyridine calcium channel antagonist, is widely used in the treatment of hypertension and other cardiovascular disorders. A simple, rapid, sensitive, precise and accurate HPLC method, using solid-phase extraction, for the quantitation of nifedipine in human plasma was developed and validated. The calibration graphs were linear in the 5-400 ng/ml concentration range (r>0.999). Recovery for nifedipine was greater than 93.9% and for internal standard nitrendipine was 96.1%. Intra-day and inter-day precision ranged from 1.4 to 4.2 and 3.9 to 5.6%, respectively. Intra-day and inter-day accuracy was ranged from 94.5 to 98.0 and 93.1 to 98.0%, respectively. The method was not interfered with by other plasma components and was applied for the determination of nifedipine in pharmacokinetic study after single oral administration of 10 mg nifedipine to 18 healthy male subjects.

Cathodic adsorptive stripping square-wave voltammetric determination of nifedipine drug in bulk, pharmaceutical formulation and human serum

Nifedipine is a calcium-channel antagonist drug used in the management of angina pectoris and hypertension through inhibition of calcium influx. A fully validated sensitive cathodic adsorptive stripping square-wave voltammetry procedure was optimized for the determination of the drug at trace levels. The procedure was based on the reduction of the nitrophenyl group after the interfacial accumulation of the drug onto a hanging mercury drop electrode in Britton-Robinson buffer of pH 11.0. The optimal conditions of the procedure were found to be: accumulation potential=-0.9 V vs. Ag/AgCl/KCl(s)), accumulation time=30 s, scan increment=10 mV, pulse amplitude=50 mV and frequency=120 Hz. Under these conditions, a well-defined peak was obtained; its peak current showed a linear dependence on drug concentration in the range of 2x10(-9)-2x10(-7) mol L(-1) bulk nifedipine. The mean recoveries based on eight replicate measurements for 1x10(-8) and 5x10(-8) mol L(-1) bulk nifedipine solutions were 98.46+/-0.86% and 98.23+/-0.92%, respectively. A detection limit of 3.42x10(-10) mol L(-1) bulk nifedipine was achieved. The procedure was successfully applied for assay of the drug in tablets and spiked human serum with mean recoveries of 101.95+/-1.42% and 98.70+/-0.63%, respectively. The limit of detection of the drug in spiked human serum was found to be 3.90x10(-10) mol L(-1).

A simple method for nicardipine hydrochloride quantification in plasma using solid-phase extraction and reversed-phase high-performance liquid chromatography

A simple and sensitive reversed-phase liquid chromatography method was developed and validated for the determination of nicardipine hydrochloride (NC) in rabbit plasma. Nicardipine hydrochloride and nimodipine, used as internal standard, were initially extracted from plasma by a rapid solid-phase extraction using C(18) cartridges. After extraction, nicardipine hydrochloride was separated by HPLC on a C(18) column and quantified by ultraviolet detection at 254 nm. A mixture of acetonitrile-0.02 M sodium phosphate buffer-methanol (45:40:15) with 0.2% of triethylamine of pH of 6.1 was used as mobile phase. The mean (+/-SD) extraction efficiency of NC was 77.56 +/- 5.4, 84.23 +/- 4.32 and 83.94 +/- 3.87% for drug concentrations of 5, 25 and 100 ng/mL, respectively. The method proved to be linear in the range of 5-100 ng/mL with a regression coefficient of 0.9993. The relative standard deviations of intra- and inter-day analysis for NC in plasma were 3.26-6.52% (n = 5) and 4.71-9.38% (n = 5), respectively. The differences of the mean value measured from the concentration prepared, expressed in percentages (bias percentage), were only - 5.2, 0.4 and 0.8% at NC 5, 25 and 50 ng/mL, which confirmed the accuracy of the method. The analytical technique was used to determine NC plasma concentration after drug oral administration to rabbits. The results inferred that NC is rapidly absorbed in rabbits and has a short half-life (t(1/2) = 1.34 h).

Liquid chromatographic assay of nifedipine in human plasma and its application to pharmacokinetic studies

A highly sensitive, selective and reproducible reversed-phase high-performance liquid chromatographic method has been developed for the determination of nifedipine in human plasma with minimum sample preparation. The method is sensitive to 3 ng/ml in plasma, with acceptable within- and between-day reproducibilities and linearity (r2 > 0.99) over a concentration range from 10-200 ng/ml. Acidified plasma samples were extracted using diethyether containing diazepam as internal standard and chromatographic separation was accomplished on C18 column using a mobile phase consisting of acetonitrile, methanol and water (35:17:48, v/v). The within-day precision ranged from 2.22 to 4.64% and accuracy ranged from 102.4-106.4%. The day-to-day precision ranged from 2.34-7.07% and accuracy from 95.1-100.1%. The relative recoveries of nifedipine from plasma ranged from 91.0-107.3% whereas extraction recoveries were 88.6-93.3%. Following eight 6-week freeze-thaw cycles, nifedipine in plasma samples proved to be stable with accuracy ranging from 0.64 to 3.0% and precision ranging from 3.6 to 4.15%. Nifedipine was also found to be photostable for at least 120 min in plasma, 30 min in blood and for 60 min in aqueous solutions after exposure to light. The method is sensitive and reliable for pharmacokinetic studies and therapeutic drug monitoring of nifedipine in humans after the oral administration of immediate-release capsules and sustained-release tablets to five healthy subjects.

Quantitation of nifedipine in human plasma by on-line solid-phase extraction and high-performance liquid chromatography

An analytical methodology for nifedipine quantitation in plasma by on-line solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) is described. The SPE cartridges contain C2 and the analytes nifedipine and nitrendipine (internal standard) are separated on a C18 column with a mobile phase consisting of acetonitrile-13 mM phosphate buffer pH 7 (65:35, v/v) followed by UV detection at 338 nm. Validation of the method demonstrated good recoveries (>90%), sensitivity (limit of quantification, 2 ng/ml), based on a 500 microl sample volume, accuracy and precision (<5.5% in concentrations greater than the limit of quantitation). This methodology has been used for bioequivalence studies.

Sensitive high-performance liquid chromatographic determination of nifedipine in cat plasma following improved sample treatment

A simple, easy and accurate reversed-phase high-performance liquid chromatographic method is described for the determination of nifedipine in cat plasma. The procedure involves extraction of nifedipine from plasma using a Sep-Pak C18 cartridge and ultraviolet detection at 350 nm. The present method provides the required reproducibility and sensitivity for the determination of low concentrations of nifedipine without interference from plasma components or photodegradation products. The method was validated over the range 1-50 ng/ml nifedipine. Accuracy and precision were, respectively, 97% or more and 5% or less over the concentration range examined. The minimum quantifiable concentration of nifedipine was found to be 1 ng/ml.

Simultaneous determination of nifedipine and dehydronifedipine in human plasma by liquid chromatography-tandem mass spectrometry

Quantitative analysis of therapeutic compounds and their metabolites in biological matrix (such as plasma, serum or urine) nowadays requires sensitive and selective methods to allow the determination of concentrations in the ng/ml range. A new on-line LC-MS-MS method using atmospheric pressure chemical ionisation (APCI) as interface for the simultaneous determination of nifedipine (NIF) and its metabolite in human plasma, dehydronifedipine (DNIF) has been developed. The compounds were extracted from plasma using solid-phase extraction (SPE) on disposable extraction cartridges (DECs). The SPE operations were performed automatically by means of a sample processor equipped with a robotic arm (ASPEC system). The DEC filled with phenyl modified silica was first conditioned with methanol and water. The washing step was performed with water. Finally, the analytes were successively eluted with methanol and water. The liquid chromatographic (LC) separation of NIF and DNIF was achieved on a RP-18 stationary phase (4 microm). The mobile phase consisted of methanol-50 mM ammonium acetate solution (50:50, v/v). The LC was then coupled to tandem mass spectrometry with an APCI interface in the positive ion mode. The method developed was validated. The absolute recoveries evaluated over the whole concentration range were 95+/-2% and 95+/-4% for NIF and DNIF, respectively. The method was found to be linear in the 0.5-100 ng/ml concentration range for the two analytes (r2 = 0.999 for both NIF and DNIF). The mean R.S.D. values for repeatability and intermediate precision were 2.9 and 3.0% for NIF and 2.2-4.7% for the metabolite. The method developed was successfully used to investigate the plasma concentration of NIF and DNIF in the pharmacokinetic studies.

Electroanalytical study of nifedipine using activated glassy carbon electrode

The electrochemical properties of nifedipine have been investigated in aqueous solution by linear sweep and cyclic voltammetry. The method is based both on the reduction and on the oxidation of the drug at a glassy carbon electrode activated by applying a new pre-treatment. The voltammograms of nifedipine on pH, concentration and scan rate have been carefully examined. Both the electroreduction and electrooxidation of nifedipine allow its determination at pH 1.5 in the concentration range of 2 x 10(-5)-6 x 10(-4) M and 8 x 10(-5)-1 x 10(-3) M, respectively. The method has been applied to commercial samples (tablets and capsules).

Sensitive high-performance liquid chromatographic determination of nifedipine in dog plasma using an automated sample preparation system with laboratory robot

Nifedipine, a calcium-channel blocking drug was analysed in dog plasma after oral dosing with two different formulations. Sample preparation was automated with a laboratory robot. Quantitative determination of the drug was performed on a reversed-phase HPLC system with electrochemical detection (ED) using an internal standard. Validation of the analytical method showed that the system is well suited for pharmacokinetic studies on dogs. The assay was linear in the range 1-50 ng/ml. Inter-day and intra-day variability were between 6.43-18.15% C.V. and 1.57-5.53% C.V., respectively.

Selective extraction of beta-blockers from biological fluids by column-switching high-performance liquid chromatography using an internal-surface phenylboronic acid precolumn

A column-switching HPLC method using an internal-surface phenylboronic acid precolumn for the selective extraction of beta-blockers from biological fluids has been developed. Filtered urine and plasma samples (50 microliters) were injected onto the precolumn equilibrated with methanol-0.05 M disodium hydrogenphosphate (5:95, v/v). After the precolumn had been washed briefly, the selectively retained beta-blockers were eluted with methanol-0.05 M phosphate buffer (pH 2.0) and transferred to a reversed-phase analytical column, on which they were then separated. Even after exposure to at least 160 injections of non-treated urine and plasma samples, the retention efficiency of the precolumn was maintained with no increase in back pressure. Quantitative recoveries and good reproducibility were demonstrated with pindolol.

Adsorptive stripping voltammetry of nicardipine at a HMDE; determination of trace levels nicardipine in blood and urine

The redox behaviour of nicardipine, a 1,4-dihydropyridine calcium antagonist, has been studied in different media on mercury, glassy carbon, gold and platinum electrodes using various voltammetric techniques. A highly sensitive adsorptive stripping voltammetric method for the determination of nicardipine based on adsorption of the drug onto mercury, followed by differential pulse voltammetric determination of the surface species, is described. All factors (pH, supporting electrolyte, accumulation potential and time, etc.) influencing adsorption as well as voltammetric response are discussed. The application of adsorptive stripping voltammetry at the hanging mercury drop electrode (HMDE) to the determination of trace levels of nicardipine in human urine and blood is illustrated, without an extraction procedure being necessary prior to the voltammetric measurement. A limit of detection of 4.8 ng per ml urine and 34 ng per ml blood is found with a mean recovery of nicardipine in urine and blood of 97%. The mean relative error does not exceed 6.5%.

Knowledge-based system for the automated solid-phase extraction of basic drugs from plasma coupled with their liquid chromatographic determination. Application to the biodetermination of beta-receptor blocking agents

Techniques for the preparation of biological samples are often based nowadays on solid-phase extraction (SPE). The different SPE steps can be performed automatically on disposable extraction cartridges (DECs) by means of a sample processor. A knowledge-based system was developed to facilitate the development of fully automated methods for the solid-phase extraction of relatively hydrophobic basic drugs from plasma, coupled with their determination by high-performance liquid chromatography (HPLC). The DEC filled with 50 mg of cyanopropyl-bonded silica phase is first conditioned with methanol and buffer solution (pH 7.4). After sample application, the DEC sorbent is washed with the same buffer. The analytes are then desorbed with an appropriate eluent and the eluate is finally diluted with the same buffer as used in the HPLC mobile phase before injection. Under these conditions, only three variables are still to be optimized: the composition and volume of the elution solvent and the volume of buffer to be added to the eluate. On the basis of this general strategy, a decision tree providing information about suggested starting conditions and guidelines for the optimization of the three variables was developed and implemented by use of a hypermedia software. This didactic expert system was evaluated using several beta-receptor blocking agents as model compounds and the operating conditions obtained for the automated SPE of these compounds are presented. A method for the determination of propranolol in plasma using the SPE conditions deduced from the knowledge-based system was validated. The absolute recovery of propranolol is ca. 93% and the limit of detection is 1.3 ng ml-1. The mean within-day and between-day reproducibilities are 2.3 and 3.6%, respectively.