Determination of four carboxylic acid metabolites of felodipine in plasma by high-performance liquid chromatography

Development of a high-performance liquid chromatography method for simultaneous determination of pioglitazone and felodipine in pig serum: application to pharmacokinetic study

A simple and sensitive high-performance liquid chromatographic method was developed and validated for simultaneous estimation of pioglitazone and felodipine in pig serum. The present method consists of protein precipitation, extraction of analytes from pig serum into dichloromethane and separation using reversed-phase C(18) column. Nitrendipine was used as an internal standard and the eluent was monitored by UV detector at 240 nm. The mobile phase used was acetonitrile and 50 mm ammonium acetate buffer at a flow rate of 1 mL/min. The retention times for pioglitazone, felodipine and nitrendipine were found to be 5.12, 10.53 and 7.14 min, respectively. The intraday and inter-day coefficient of variation and percent error values of assay method were less than 7% and mean recovery was more than 94% for each analyte, and the method was found to be precise, accurate and specific during study. The method was successfully applied for pharmacokinetic study of pioglitazone and felodipine from bioadhesive buccal tablet after buccal administration to pigs. The C(Max) , T(Max) , and AUC(0-24) of pioglitazone and felodipine from buccal tablet were found to be 394.6 ng/mL, 5.6 h, 2624.2 ng h/mL and 44.4 ng/mL, 5.5 h, 275.8 ng h/mL, respectively.

Titrimetric and spectrophotometric assay of felodipine in tablets using bromate–bromide, Methyl Orange and Indigo Carmine reagents

Three new methods based on titrimetric and spectrophotometric techniques are described for the determination of felodipine (FLD) in the bulk drug and in tablets using a bromate?bromide mixture and two dyes, Methyl Orange and Indigo Carmine. In the titrimetric method (method A), the drug solution was treated with a measured excess of the bromate?bromide mixture in acid medium and after the reaction was judged to be complete, the unreacted bromine was determined iodometrically. The two spectrophotometric methods are based on the bromination of the drug with a known excess of the bromate?bromide mixture under acidic conditions followed by the estimation of the surplus bromine by reaction with either Methyl Orange (Method B) or Indigo Carmine (Method C) and measuring the absorbance at 520 nm or 610 nm, respectively. In all the methods, the amount of reacted bromine corresponds to the drug content. The titrimetric procedure is applicable for between 6?15 mg and the reaction stoichiometry was found to be 1:1 (drug: BrO3?). The systems obey Beer?s law between 0.12 ? 0.87 ?gml-1 and 0.5 ? 6.0 ?gml-1 formethods B and C respectively. The limits of detection and quantification are reported for both the spectrophotometric methods. The methods could usefully be applied to routine quality control of pharmaceutical formulations containing FLD. Statistical comparison of the results with the reference method shows excellent agreement and indicates no significant difference in accuracy and precision.

Simultaneous determination of five 1,4-dihydropyridines in pharmaceutical formulations by high-performance liquid chromatography–amperometric detection

A high-performance liquid chromatographic method with electrochemical detection was developed for the simultaneous determination of five 1,4-dihydropyridines: amlodipine, nitrendipine, felodipine, lacidipine and lercanidipine. These drugs are widely used in the treatment of hypertension, angina pectoris and the therapy of cerebrovascular spasms of various origins. The chromatographic separation was performed on a Supelcosil LC ABZ + Plus C18 column with a mobile phase consisting of acetonitrile-10 mM acetate buffer (72:28, v/v) at a flow rate of 1 ml/min. The temperature was set at 30 +/- 0.2 degrees C. The amperometric detector, equipped with a glassy carbon electrode was operated at +1100 mV versus Ag/AgCl in the direct current mode. Under these chromatographic conditions, the drugs eluted in less than 12 min. The method showed to be linear over the range 4.5-15 microg/ml with a within-day and day-to-day repeatabilities in terms of R.S.D. lower than 15%, an accuracy greater than 98% and detection limits varying from 90 ng/ml (amlodipine) to 1.55 microg/ml (nitrendipine). The method was successfully applied to commercially available pharmaceuticals with relative errors lower than 5%. The validity of the method was examined comparing the results obtained with those of HPLC with photometric detection.

Sensitive spectrophotometric determination of amlodipine and felodipine using iron(III) and ferricyanide

A simple, accurate, sensitive and economical procedure for the estimation of amlodipine besylate and felodipine, both in pure form and in formulations has been developed. The method is based on the reduction of iron(III) by the studied drugs in acid medium and subsequent interaction of iron(II) with ferricyanide to form Prussian blue. The product exhibits absorption maximum at 760 nm in both cases. Beer's law is obeyed in the concentration ranges 5.0-15.0 and 1.5-5.0 microg/ml, for amlodipine and felodipine, respectively. The molar absorptivities are 1.76 x 10(4) and 4.24 x 10(4) l/mol cm. The corresponding Sandell sensitivities are 23.18 and 9.06 ng/cm(2). The limits of detection as well as quantification are reported. Seven replicate analyses of solutions containing three different concentrations of each drug were carried out and the percent error and the RSD values have been reported. The proposed method was applied to the determination of these drugs in pharmaceutical formulations and the results demonstrate that the method is equally accurate and precise as the official methods as found from the t- and F-values. The reliability of the method was established by recovery studies using standard-addition technique.

Hydrolytic degradation of nitrendipine and nisoldipine

The development of a new HPLC-UV diode array procedure applied to follow the hydrolytic degradation of two well-known 4-nitrophenyl-1,4-dihydropyridine derivatives, nitrendipine and nisoldipine is reported. Hydrolysis of each drug were carried out in ethanol/Britton-Robinson buffer at different pHs, stored into amber vials at controlled temperatures of 40, 60 and 80 degrees C and periodically sampled and assayed by HPLC. Nitrendipine degradation in different parenteral solutions was also evaluated. The HPLC procedure exhibited an adequate selectivity, repeatability (<1%) and reproducibility (<2%). The recoveries were higher than 98% with CV of 1.13 and 1.54% for nitrendipine and nisoldipine, respectively. A significant degradation was observed at alkaline pH (>pH 8) with a first order kinetic for both drugs. At pH 12, 80 degrees C, k values of 3.56x10(-2) x h(-1) and 2.22x10(-2) for nitrendipine and nisoldipine, respectively were obtained. Also, activation energies of 16.8 and 14.7 kcal x mol(-1) for nitrendipine and nisoldipine, respectively, were calculated. Furthermore, from the results obtained from hydrolytic degradation in different solutions for parenteral use, we can affirm that solutions significantly increased the degradation of nitrendipine. In conclusion, the HPLC proposed procedure exhibited adequate analytical requirements to be applied to the hydrolytic degradation studies of nitrendipine and nisoldipine. Furthermore, all tested parenteral solutions significantly increased the hydrolytic degradation of nitrendipine, the composition of solution being a relevant factor.

A stability indicating LC method for felodipine

A stability indicating reversed-phase liquid chromatographic (RP-LC) method was developed for the assay of felodipine as a bulk drug and in pharmaceuticals. The chromatography was performed on a C18 column. Eluents were monitored by UV detection at 238 nm using the mobile phase methanol-potassium dihydrogen orthophosphate (pH 3.5; 0.01 M) (75:25, v/v). The method was statistically validated for linearity, accuracy, precision and specificity. The linearity of felodipine peak area responses was demonstrated within the concentration range of 1-7 microg/ml. The limits of detection and quantitation were 150 and 500 ng/ml, respectively. The method was demonstrated to be precise, accurate and specific with no interference from the tablet excipients and separation of the drug peak from the peaks of the degradation products (oxidative degradation, photodegradation, acid and base degradation). The results indicated that the proposed method could be used in a stability assay.

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.

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.

Erythromycin-felodipine interaction: magnitude, mechanism, and comparison with grapefruit juice

OBJECTIVE

To investigate a potentially marked effect by erythromycin on felodipine pharmacokinetics, to characterize the mechanism, and to compare the interaction with that between grapefruit juice and felodipine.

METHODS

Felodipine, 10 mg extended release, was administered with 250 ml water, 250 mg erythromycin, or 250 ml grapefruit juice in a randomized crossover study of 12 healthy men. Erythromycin base, 250 mg four times a day, was started the day before and continued on that study day. Pharmacokinetic values of felodipine, the primary metabolite dehydrofelodipine, and the major secondary derivative M3 metabolite were studied.

RESULTS

Compared with water, erythromycin produced severalfold higher felodipine area under the plasma drug concentration-time profile (AUC), plasma peak drug concentration (Cmax), and apparent elimination half-life (t1/2); however, the effect was variable among individuals. Erythromycin augmented dehydrofelodipine AUC, Cmax, and t1/2 but decreased dehydrofelodipine/felodipine ratios. The AUC of the M3 metabolite and the M3 metabolite/dehydrofelodipine ratios were reduced. These findings support inhibition of both metabolic pathways likely mediated by CYP3A4. Grapefruit juice produced similar mean effects but did not prolong felodipine or dehydrofelodipine t1/2. Individually, felodipine AUC with erythromycin was greater than or similar to that with grapefruit juice. Relative felodipine AUC (erythromycin compared with grapefruit juice) correlated with relative felodipine Cmax but not with relative felodipine t1/2, suggesting felodipine AUC differed between these treatments, mainly from factors affecting presystemic drug elimination.

CONCLUSIONS

Erythromycin produced an important pharmacokinetic interaction with felodipine by inhibition of drug metabolism. Although erythromycin and grapefruit juice shared a common mechanism, erythromycin likely reduced felodipine biotransformation at the gut wall and liver, whereas single-dose grapefruit juice had an effect mainly at the gut wall.

Determination of felodipine, its enantiomers, and a pyridine metabolite in human plasma by capillary gas chromatography with mass spectrometric detection

Sensitive methods based on capillary gas chromatography (GC) with mass spectrometric (MS) detection in a selected-ion monitoring mode (SIM) for the determination of racemic felodipine, its enantiomers, and a pyridine metabolite in human plasma are described. Following liquid-liquid extraction from plasma, enantiomers of felodipine were separated on a chiral HPLC column (Chiralcel OJ) and fractions containing each isomer were collected on a continuous basis using a fraction collector. These fractions were later analyzed by GC-MS-SIM. A similar method based on GC-MS-SIM detection was developed for the determination of racemic felodipine and its pyridine metabolite with a minor modification of sample preparation. The limits of quantitation in plasma were 0.1 ng/ml for both the R(+)- and S(-)-enantiomers of felodipine and 0.5 ng/ml for both racemic felodipine and its pyridine metabolite. The stereoselective assay was used to support a clinical study with racemic felodipine, and was capable of analyzing more than 30 plasma samples per day.

Analysis of felodipine by packed column supercritical fluid chromatography with electron capture and ultraviolet absorbance detection

A reproducible and selective supercritical fluid chromatography (SFC) method was developed for the analysis of felodipine, a drug indicated for the treatment of hypertension. Methanol-modified carbon dioxide was employed as the SFC mobile phase with both electron capture detection (ECD) and multi-wavelength detection (MWD) being used simultaneously for analyte determination. Chromatography limit of detection (LOD) and limit of quantitation (LOQ), linear dynamic range (LDR) and injection precision were obtained in order to assess chromatographic and detector performance for both the SFC/MWD and SFC/ECD/MWD systems. The method was shown to be stability indicating since felodipine could be separated from its potential oxidative degradation product, H152/37, in under 6 min (felodipine k' = 2.44). Sample throughput was increased by 60% with the SFC assay vs LC. The optimized SFC method was shown to be equivalent to an existing LC/UV procedure for the analysis of a sustained-release tablet while realizing a 92% saving in disposable solvent waste. In order to achieve further solvent savings overall, supercritical fluid extraction (SFE) with 8% methanol-modified carbon dioxide as the extraction fluid was used to extract felodipine from a sustained-release tablet (as opposed to traditional solvent extraction). Comparable drug recoveries were obtained with SFE sample preparation technique when either SFC or LC extract analysis was utilized.