Quantitative analysis of the dihydropyridines, 3-(2-furoyl)-5-methoxycarbonyl-2,6-dimethyl-4-(2-nitrophenyl)- 1,4-dihydropyridine and nifedipine, by high-performance liquid chromatography with electrochemical detection

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.

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.

Redox properties of isradipine and its electrochemical detection in the HPLC determination of the compound in human serum

The electrochemical behaviour of isradipine in a mixed solution of Britton-Robinson buffer (pH 11.8):acetonitrile:methanol (6:3:1, v/v) was studied by cyclic voltammetry and spectroelectrochemistry using an optically transparent thin layer electrode of carbon cloth. The cyclic voltammogram showed several peaks whose shape and potentials depended on the pH. The peak at 330 nm, corresponding to the absorbance of the dihydropyridine ring, disappeared after electrolysis at a potential that was more positive than the oxidation peak. The oxidation peak corresponds to the oxidation of the dihydropyridine ring. Peak height at pH 11.8 was proportional to isradipine concentration. On the basis of the redox properties of isradipine, HPLC was conducted applying electrochemical detection on a polybutadiene coated alumina column using an alkaline mobile phase. The method was applied for the determination of isradipine content in human serum. A good linear relationship between isradipine concentration and peak height was found in the concentration range of 2-200 ng/mL with a correlation coefficient of 0.9924. The detection limit was 0.5 ng/mL. The within-day and day-to-day variation were examined for control human serum and percentage relative standard deviation ranged from 0.5 to 6.7. Interference from many other coadministered drugs was studied in the specified experimental conditions. Photo and heat stabilities of the compound were also studied.

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.

Determination of nifedipine in human plasma by flow-injection tandem mass spectrometry

For use in clinical studies, a fast and sensitive assay method was developed for the determination of nifedipine in human plasma samples. The assay method is based on tandem mass spectrometry detection (HPLC-MS-MS). The effect of flow injection as well as HPLC separation on the results of the nifedipine determination were evaluated. The limit of quantification is 0.5 ng/ml and the accuracy (as determined by spiking recovery) was found to be good.

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).

Liquid chromatographic determination of manidipine in serum with electrochemical detection

A highly sensitive and selective method for determining a dihydropyridine calcium antagonist, manidipine, by liquid chromatography using column switching with electrochemical detection was developed. Manidipine in serum was extracted by a rapid and simple procedure based on C8 bonded-phase extraction and then silica extraction. Manidipine and nilvadipine as an internal standard were separated on a C8 bonded-phase HPLC column and detected by high conversion efficiency amperometric detection at +0.7 V. Manidipine and nilvadipine (I.S.) were separated from an endogenous interference peak in serum and concentrated on a pre-column (C18) by column switching using an isocratic mobile phase, and then the corresponding fractions were introduced to an analytical column with a C8 stationary phase. Determination of manidipine was possible over the concentration range 0.5-10 ng/ml: the limit of detection was 0.3 ng/ml. The recovery of manidipine added to serum was 93.1-98.4% with coefficients of variation of less than 7.1%. The method is applicable to drug level monitoring in the serum of healthy volunteers treated with manidipine and to the analysis of pharmacokinetics.

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.

Determination of nifedipine in human serum by gas chromatography-mass spectrometry: validation of the method and its use in bioavailability studies

A procedure for the determination of nifedipine in human serum is described. The light-sensitive substance is isolated from serum by liquid-liquid extraction and analyzed using capillary gas chromatography with a mass-selective detector. The validation of the method shows that the extraction recovery is ca. 85%, the limit of detection is 2 ng/ml and the standard deviations of the intra-day precision test range from 5.8 to 7.4% with respect to the concentration. The procedure is highly selective and sensitive. It is especially suited for bioavailability studies because of its stability and high sampling rate.

Sensitive high-performance liquid chromatographic assay for nifedipine in human plasma utilizing ultraviolet detection

A rapid, simple, sensitive and selective reversed-phase high-performance liquid chromatographic (HPLC) technique is reported for the determination of nifedipine in human plasma. The procedure involves extraction of nifedipine from plasma under alkaline conditions (pH 12), separation via reversed-phase HPLC and ultraviolet detection (350 nm). The peak corresponding to nifedipine was free of interference from its photodegradation products or metabolites. The method was validated over the range 5-250 ng/ml nifedipine using weighted least-squares linear regression analysis. Accuracy and precision were within approximately 10% or less over the concentration range, except for the lowest concentration point which, nonetheless, was acceptable and approached 15%. The minimum quantifiable concentration of nifedipine was determined to be 5 ng/ml. The minimum detectable concentration was in the order of 1 ng/ml. Analysis of plasma samples collected from healthy volunteers demonstrate that this assay is applicable to clinical and pharmacokinetic studies.

Quantitative analysis of nifedipine in plasma by high-performance liquid chromatography

A rapid, sensitive and specific high-performance liquid chromatographic assay for the quantification of nifedipine in human plasma was developed, satisfactorily validated and applied to samples of plasma from healthy volunteers. The sample pre-treatment incorporating protein denaturation by urea and ethyl acetate extraction compared favourably in terms of selectivity with previously published methods. The limit of quantitation of this reversed-phase LC method was 7.0 ng ml-1 for the analysis of 0.5 ml samples.

The influence of nifedipine on microvascular vein graft intimal thickening

The influence of high-dose Nifedipine on the intimal thickening seen in experimental vein grafts was studied in an established rat model. The iliolumbar vein was grafted to the common iliac artery in 28 control and 30 Nifedipine-treated animals. There was one death in the control group and 10 deaths due to drug aspiration in the treated group; a further six control and four treated grafts were excluded from analysis due to occlusion or histological artefact. Animals were killed at 3 weeks, at which time a Nifedipine assay was performed. Longitudinal sections of the graft were prepared and the intimal thickness in the proximal, mid and distal graft measured using an eyepiece graticule. Median (range in brackets) intimal thicknesses for the control group were as follows: proximal 50 microns (10-120), mid 30 microns (10-70), and distal 30 microns (10-100). Results for the treated group were: proximal 65 microns (10-110), mid 30 microns (5-90), and distal 35 microns (20-120). There was no statistically significant difference between the two groups suggesting that Nifedipine is not of value in the inhibition of early vein graft intimal thickening.

Simultaneous determination of a new dihydropyridine calcium antagonist (MPC-1304) and its metabolite in dog plasma by high-performance liquid chromatography with electrochemical detection

A rapid and sensitive high-performance liquid chromatographic analysis, with electrochemical detection, has been developed for the simultaneous determination of a new calcium-channel antagonist, (+/-)-methyl 2-oxopropyl-1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridinedi carboxylate (I, MPC-1304), and its active metabolite in dog plasma. The plasma extract with toluene was chromatographed on a reversed-phase column and detected by an electrochemical detector at + 0.92 V. Calibration curves were linear from 2.0 to 100.0 ng/ml, and the detection limit was ca. 0.25 ng/ml. This method is applicable to the simultaneous determination of I and its metabolite in dog plasma following the oral administration of I.

Analysis of nifedipine and its pyridine metabolite dehydronifedipine in blood and plasma: review and improved high-performance liquid chromatographic methodology

A reversed-phase HPLC method is described for the simultaneous determination of nifedipine and its primary pyridine metabolite dehydronifedipine in blood and plasma, that involves UV detection and neutral (blood) or alkaline (plasma) extraction. The limit of reliable determination is found to be 3 ng ml-1 with an inter-assay RSD of below 11%. In the presence of haemoglobin, nifedipine is unstable at pH greater than 10, necessitating neutral extraction for the measurement of nifedipine in haemolysed blood. Published methods for analysis of nifedipine are reviewed, emphasizing the lack of specificity and sensitivity which render many of them unsuitable for the investigation of nifedipine disposition in man.

Chromatography of calcium channel blockers

Numerous publications during the past ten years have described the determination of various calcium channel blockers in biological fluids, using gas and liquid chromatographic techniques. Diltiazem, verapamil, flunarizine and a growing number of dihydropyridines belong to this group of drugs, which in most instances are active at low plasma concentrations. From a bioanalytical point of view these compounds have many features in common, such as high lipophilicity and favourable detection properties.