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

Utility of Cilefa Pink B, a foodstuff dye as a fluoro-substrate in the devising of the first facile green Molecular-mass-Related Fluorescence Sensor for quantifying amlodipine in batched material and dosage forms; content uniformity evaluation

This study introduces the first and unique Molecular-mass-Related Fluorescence Sensor as the first fluorimetric strategy for determining amlodipine. An environmentally friendly, single-step, and direct spectrofluorimetric approach was utilized to evaluate the analyte. In an acidic setting, combining the amlodipine medication and the fluorescent dye Cilefa Pink B generated an instantaneous ultra-fluorescent product. An increase in dye response after adding amlodipine was proportional to the molecular weight of the generated complex, as measured at 329 nm. was the idea ofthe applied fluorimetric analysis. The complexing process increased the molecular mass from 879.86 to 1288.739 g mol-1. The medication's range of 0.050-1.00 µg mL-1 is directly correlated with this molecular massenlargement. The ideal settings for the changeable parameters of the system were established through an analysis of the response of the amlodipine-Cilefa Pink B system. Furthermore, the developed sensor complied with ICH (International Council for Harmonization) standards. The sensitivity limits were 0.0139 µg mL-1 (for the detection limit, LOD) and 0.042 µg mL-1 (for the quantification limit, LOQ). Additionally, this method effectively recovered the drug in its original and therapeutic dosage forms. Finally, the proposed process's environmental impact was also assessed through different modern greenness evaluation tools.

An LC-MS/MS Method for Determination of Triple Drugs Combination of Valsartan, Amlodipine and Hydrochlorothiazide in Human Plasma for Bioequivalence Study

Background:

Current guidelines for the treatment of hypertension recommend combination therapy, which intends to control blood pressure and enhance cardiovascular protection.

Materials and Methods:

A sensitive, reliable and selective tandem mass spectrometry (LC-MS/MS) method has been developed for simultaneous quantification of amlodipine (AML), valsartan (VAL) and hydrochlorothiazide (HCTZ) in human plasma. The chromatographic system was equipped with ACE 5 C8 (50 X 2.1 mm) column and utilized a mobile phase composition of 0.5 mM Ammonium Chloride & 0.04% FA-Methanol (45:55% v/v). The method used three internal standards; AML-D4, HCTZ-D2 C13 and VAL-D3 with 10% intra- and inter-day precision, and 6% bias for all the analytes.

Results:

The assay was found to be linear with R-2 > 0.998, and the limits of quantification for AML, VAL and HCTZ were 0.2, 50.0 and 2.0 ng/mL, respectively. The analytes were found to be stable in plasma samples over short and long term storage.

:

The developed method is rapid with a run time of 3.5 min and cost-effective since the simple sample preparation method is adopted. This method was successfully applied for the bioequivalence study of AML, VAL, and HCTZ in human plasma after administration of the fixed-dose combination tablet of (10/160/25 mg). Pharmacokinetic parameters (Cmax and AUC0-72) for AML and (Cmax, AUC0-t, AUC0-∞) for VAL and HCTZ were used for bioequivalence assessment. These were determined by noncompartmental analysis of concentration data.

Conclusion:

The result showed 90% confidence intervals (obtained by ANOVA) which were within the predefined ranges. As a consequence, this method can be successfully applied for measuring and quantifying a large number of samples.

High performance liquid chromatographic assay of amlodipine, valsartan and hydrochlorothiazide simultaneously and its application to pharmaceuticals, urine and plasma analysis

A Simple, Specific, Precise, Accurate, Linear, Rugged, Robust High Performance Liquid Chromatographic method of analysis for simultaneous determination of assay of Amlodipine, Valsartan and Hydrochlorothiazide drugs in the pharmaceuticals tablet formulations using Pioglitazone as a common internal standard was developed and validated. The assay was accomplished using a mixture of acetonitrile & methanol in the volume ratio of 20:80 v/v (mobile phase B) and Ammonium acetate buffer (Mobile phase A) in gradient flow as mobile phase on an Hibar RP-18e, 250 × 4.6 mm, 5µ as chromatographic column at a flow rate of 1.300 mLmin-1, injection volume 10 µL and at a wavelength 235 nm with UV detector. Linearity of the analytical method was evaluated at a concentration range of 2.5-45.3 µg/ml for Amlodipine, 32.0-720.1 µg/ml for valsartan and 5.0-112.6 µg/ml for Hydrochlorothiazide respectively with Correlation coefficient (r) value more than 0.9997. The limit of detection (LOD) for Amlodipine, Valsartan and Hydrochlorothiazide was found to be 1.1 µg/ml, 8.0 µg/ml & 1.0 µg/ml respectively. Specificity, Method Precision, System Precision, Ruggedness, Robustness, Recovery, Stability of analytical solution, Filter paper selection study, Stress testing (Force Degradation) at various conditions were performed as per the ICH (Q2) recommendations. The chromatographic method may also be applied for simultaneous estimation of analytes in plasma and urine.

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.

Development of UV spectrophotometry methods for concurrent quantification of amlodipine and celecoxib by manipulation of ratio spectra in pure and pharmaceutical formulation

Recently, the United States Food and Drug Administration approved a new oral dosage preparation of amlodipine besylate (AML) and celecoxib (CEL) for the management of hypertension and osteoarthritis. However, no simultaneous estimation procedures for these two analytes have been described. Hence, two simple, accurate, and precise ultraviolet spectroscopic procedures that manipulated the ratio spectra were established for concurrent quantification of AML and CEL using ethanol as a solvent. The first method involves determining the peak-to-trough amplitude difference of the ratio spectra of AML and CEL. The second method involves determining the peak amplitude of the ratio first derivative (Δλ 4 nm) spectra of AML and CEL at 334.2 nm and 254.2 nm, correspondingly. Both methods showed linearity in the range of 1–6 μg mL-1 for AML and 5–40 μg mL-1 for CEL with an excellent correlation coefficient (<0.999). The proposed procedures were validated by following the International Conference on Harmonization guidelines for accuracy, precision, selectivity, recovery, and stability studies. It is evident from the low %RSD and %RE that both analytical procedures were found to be accurate and precise, respectively. The percent recovery of AML and CEL from the formulation was found to be 99.79% and 99.34% using the ratio-difference method and 100.13% and 99.70% using the ratio first-derivative method, with a low percent relative standard deviation. Further, the proposed techniques permit concurrent quantification of AML and CEL in different concentration ratios without interference from each other; hence, these techniques can be adopted for regular quality-control studies.

Simultaneous colorimetric detection of four drugs in their pharmaceutical formulations using unmodified gold nanoparticles as a probe

Schematic representation for the aggregation of unmodified Au NPs induced by four drugs (venlafaxine, imipramine, amlodipine, and alfuzosin).

Adsorption behavior of a computer-aid designed magnetic molecularly imprinted polymer via response surface methodology

A combined computer simulation and experimental study of magnetic a molecularly imprinted polymer was put forward and verified.

Development and validation of a HPLC-PDA bioanalytical method for the simultaneous estimation of Aliskiren and Amlodipine in human plasma

A simple, unique and selective HPLC-PDA method was developed and validated for the simultaneous estimation of aliskiren (ALS) and amlodipine (AML) in human plasma. Extraction of the sample was accomplished by protein precipitation. Plasma proteins were precipitated by employing acetonitrile containing hydrochlorothiazide as internal standard. The compounds were analyzed by HPLC by using PDA detector on a Hibar C18 (250 × 4.6 mm) column with a mobile phase comprising acetonitrile and phosphate buffer (pH 4.2 and 25 mm; 60:40 v/v) with a flow rate of 0.8 mL/min. Different sample pretreatment techniques were evaluated but protein precipitation was found to be satisfactory, offering good recovery values of 97.11-98.45% for ALS and 97.5-99.12% for AML. The within-day precisions for ALS were 96.66, 99.16 and 99.41% at 90, 240 and 480 ng/mL, respectively, and for AML they were 97.27, 99.54 and 99.31% at 3.3, 8.8 and 17.6 ng/mL, respectively. The between-day precisions for ALS were 96.66, 99.16 and 99.41% at 90, 240 and 480 ng/mL, respectively and the between-day precisions for AML were 98.18, 99.20 and 99.40% at 3.3, 8.8 and 17.6 ng/mL, respectively. The limit of quantitation was 30 and 1.0 ng/mL for ALS and AML respectively. Different constituents of plasma proteins did not interfere with the absolute recovery of ALS and AML.

Development and Validation of a LC-MS/MS Method for the Simultaneous Estimation of Amlodipine and Valsartan in Human Plasma: Application to a Bioequivalence Study

A reliable, simple, and robust liquid chromatography-tandem mass spectro-metric (LC-MS/MS) method has been developed and validated that employs solid-phase extraction for the simultaneous estimation of amlodipine and valsartan in human K₃EDTA plasma using amlodipine-d4 and valsartan-d9 as internal standards. Chromatographic separation of amlodipine and valsartan was achieved on the Luna C18 (2)100A (150 × 4.6 mm, 5 μm) column using acetonitrile: 5 mM ammonium formate solution (80:20, v/v) as the mobile phase at a flow rate of 0.8 mL/min in isocratic mode. Quantification was achieved using an electrospray ion interface operating in positive mode, under multiple reaction monitoring (MRM) conditions. The assay was found to be linear over the range of 0.302–20.725 ng/mL for amlodipine and 6.062–18060.792 ng/mL for valsartan. The method has shown good reproducibility, as intra- and interday precisions were within 10% and accuracies were within 8% of nominal values for both analytes. The method was successfully applied for the bioequivalence study of amlodipine and valsartan after oral administration of a fixed dose of the combination. Additionally, as required by the current regulatory bodies, incurred sample reanalysis was performed and found to be acceptable.

Simultaneous determination of amlodipine, valsartan and hydrochlorothiazide by LC-ESI-MS/MS and its application to pharmacokinetics in rats

Polypill is a fixed-dose combination that contains three or more active ingredients used as a single daily pill to achieve a large effect in preventing cardiovascular disease with minimal adverse effects. A novel and accurate liquid chromatography tandem mass spectrometry method using electrospray ionization mode has been developed and validated for the simultaneous determination of amlodipine (AMD), valsartan (VAL) using losartan (LOS) as an internal standard (IS), and hydrochlorothiazide (HCT) using furosemide (FSD) as an IS. The separation was carried on Aquasil C₁₈ (50 mm×2.1 mm, 5 µm) reversed phase column using acetonitrile and water containing 0.1% formic acid (50:50, v/v) as the mobile phase. The method was validated in terms of linearity, accuracy and precision over the concentration range of 1–1000 ng/mL. The intra and inter-day precision and accuracy, stability and extraction recoveries of all the analytes were in the acceptable range. This method can be successfully applied to the pharmacokinetic study of AMD, VAL and HCT when given as a polypill.

Simultaneous Quantitative Analysis of Olmesartan Medoxomil and Amlodipine Besylate in Plasma by High-performance Liquid Chromatography Technique

A rapid, simple and sensitive high-performance liquid chromatography (HPLC) method has been developed for quantification of olmesartan medoxomil (OLM) and amlodipine besylate (AM) in plasma. The assay enables the measurement of OLM and AM for therapeutic drug monitoring with a minimum detectable limit of 2 ng mL. The method involves a simple, one-step extraction procedure and analytical recovery was above 50%. The separation was performed on an analytical 250 × 4.6 mm Eurospher 100^-5 C18 column. The wavelength was set at 239 nm. The mobile phase was a mixture of acetonitrile:0.05 M ammonium acetate buffer: 0.1 mL triethylamine at pH 6.8 was selected at a flow rate of 1.0 mL min. The calibration curve for the determination of OLM and AM in plasma was linear over the range 2–2500 and 8–10,000 ng mL AM and OLM. The coefficients of variation for interday and intraday assay were found to be <15%. The method can be applied to a pharmacokinetic and pharmacodynamic study of OLM and AM in a combined dosage form.

Glucose-β-CD interaction assisted ACN field-amplified sample stacking in CZE for determination of trace amlodipine in beagle dog plasma

A simple, sensitive and low-cost method using CE coupled with glucose-β-CD interaction assisted ACN stacking technique has been developed for quantification of trace amlodipine in dog plasma. The plasma samples were extracted with methyl tert-butyl ether. The separation was performed at 25°C in a 31.2 cm × 75 μm fused-silica capillary with an applied voltage of 15 kV. The BGE was composed of 6.25 mM borate/25 mM phosphate (pH 2.5) and 5 mg/mL glucose-β-CD. The detection wavelength was 200 nm. Because CD could diminish the interaction between drugs and matrix, and derivation groups of CD play an important role in separation performance, the effects of β-CD, and its derivatives on the separation were studied at several concentrations (0, 2.5, 5.0, 10.0 mg/mL). In this study, organic solvent field-amplified sample stacking technique in combination with glucose-β-CD enhanced the sensitivity about 60-70 folds and glucose-β-CD could effectively improve the peak shape. All the validation data, such as accuracy, precision extraction recovery, and stability, were within the required limits. The calibration curve was linear for amlodipine from 1 to 200 ng/mL. The method developed was successfully applied to the pharmacokinetic studies of amlodipine besylate in beagle dogs.

Clinical applications of fast liquid chromatography: a review on the analysis of cardiovascular drugs and their metabolites

One of the major challenges facing the medicine today is developing new therapies that enhance human health. To help address these challenges the utilization of analytical technologies and high-throughput automated platforms has been employed; in order to perform more experiments in a shorter time frame with increased data quality. In the last decade various analytical strategies have been established to enhance separation speed and efficiency in liquid chromatography applications. Liquid chromatography is an increasingly important tool for monitoring drugs and their metabolites. Furthermore, liquid chromatography has played an important role in pharmacokinetics and metabolism studies at these drug development stages since its introduction. This paper provides an overview of current trends in fast chromatography for the analysis of cardiovascular drugs and their metabolites in clinical applications. Current trends in fast liquid chromatographic separations involve monolith technologies, fused-core columns, high-temperature liquid chromatography (HTLC) and ultra-high performance liquid chromatography (UHPLC). The high specificity in combination with high sensitivity makes it an attractive complementary method to traditional methodology used for routine applications. The practical aspects of, recent developments in and the present status of fast chromatography for the analysis of biological fluids for therapeutic drug and metabolite monitoring, pharmacokinetic studies and bioequivalence studies are presented.

Estimation of Amlodipine Besylate, Valsartan and Hydrochlorothiazide in Bulk Mixture and Tablet by UV Spectrophotometry

A simple, precise, accurate and economic simultaneous UV spectrophotometric method has been developed for the estimation of amlodipine besylate, valsartan and hydrochlorothiazide in combination in bulk mixture and tablet. The estimation was based upon measurement of absorbance at absorbance maxima of 359 nm, 317 nm and 250 nm for amlodipine besylate, hydrochlorothiazide and valsartan in methanol, respectively in bulk mixture and tablet. The Beer Lambert's law obeyed in the concentration range 5-25 μg/ml, 10-50 μg/ml and 5-25 μg/ml for amlodipine besylate, hydrochlorothiazide and valsartan, respectively. The estimation of bulk mixture and tablet was carried out by simultaneous equation, Q-analysis and area under curve method for estimation of amlodipine besylate and hydrochlorothiazide and standard curve method for estimation of valsartan. The results were found to be in the range of 99.6±1.52% to 102±0.51%. Method was validated with respect to specificity, linearity, range, accuracy, precision, LOD, LOQ, robustness, ruggedness and can be applied for routine analysis of tablet dosage forms.

Determination and validation of duloxetine hydrochloride in capsules by HPLC with pre-column derivatization and fluorescence detection

A high-performance liquid chromatographic (HPLC) method is described for the determination of duloxetine hydrochloride in capsules. The method was based on pre-column derivatization with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole using the fluorimetric detection technique. Duloxetine hydrochloride was analyzed by HPLC using an Inertsil C18 column (5 μm, 150 × 4.6 mm) and mobile phase consisted of methanol and water (65:35, v/v). The fluorescence detector was adjusted at excitation and emission wavelengths of 461 and 521 nm, respectively. The linearity of the method was in the range of 10-600 ng/mL. Limits of detection and quantification were 0.51 and 1.53 ng/mL, respectively. The proposed method was successfully applied for determination of duloxetine hydrochloride in its pharmaceutical preparation. The results were in good agreement with those obtained using a reference method.

Simultaneous determination of amlodipine and valsartan

A spectrophotometric method was developed for simultaneous determination of amlodipine (Aml) and valsartan (Val) without previous separation. In this method amlodipine in methanolic solution was determined using zero order UV spectrophotometry by measuring its absorbency at 360.5 nm without any interference from valsartan.

Valsartan spectrum in zero order is totally overlapped with that of amlodipine. First, second and third derivative could not resolve the overlapped peaks.

The first derivative of the ratio spectra technique was applied for the measurement of valsartan. The ratio spectrum was obtained by dividing the absorption spectrum of the mixture by that of amlodipine, so that the concentration of valsartan could be determined from the first derivative of the ratio spectrum at 290 nm. Quantification limits of amlodipine and valsartan were 10–80 μg/ml and 20–180 μg/ml respectively. The method was successfully applied for the quantitative determination of both drugs in bulk powder and pharmaceutical formulation.

Simultaneous spectrofluorimetric determination of amlodipine besylate and valsartan in their combined tablets

Amlodipine, a dihydropyridine calcium channel blocker, and valsartan, an angiotensin II receptor blocker, are co-formulated in a single-dose combination for the treatment of hypertension. The combination is used by patients whose blood pressure is not adequately controlled on either component monotherapy. This work describes a simple, sensitive, and reliable spectrofluorimetric method for the simultaneous determination of the two antihypertensive drugs; amlodipine besylate (AML) and valsartan (VAL) in their combined tablets. The method involved measurement of the native fluorescence at 455 nm (λ(Ex) 360 nm) and 378 nm (λ(Ex) 245 nm) for AML and VAL, respectively. Analytical performance of the proposed spectrofluorimetric procedure was statistically validated with respect to linearity, ranges, precision, accuracy, selectivity, robustness, detection, and quantification limits. Regression analysis showed good correlation between fluorescence intensity and concentration over the concentration ranges 0.2-3.6 and 0.008-0.080 µg mL⁻¹ for AML and VAL, respectively. The limits of detection were 0.025 and 0.0012 µg mL⁻¹ for AML and VAL, respectively. The proposed method was successfully applied for the assay of the two drugs in their combined pharmaceutical tablets with recoveries not less than 98.85%. No interference was observed from common pharmaceutical additives. The results were favourably compared with those obtained by a reference spectrophotometric method.

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 stability-indicating high performance liquid chromatographic (HPLC) assay for the simultaneous determination of atorvastatin and amlodipine in commercial tablets

A simple, rapid, precise and accurate isocratic reversed-phase stability-indicating HPLC method was developed and validated for the simultaneous determination of atorvastatin (AT) and amlodipine (AM) in commercial tablets. The method has shown adequate separation for AM, AT from their associated main impurities and their degradation products. Separation was achieved on a Perfectsil Target ODS-3, 5 microm, 250 mm x 4.6 mm i.d. column using a mobile phase consisting of acetonitrile-0.025 M NaH(2)PO(4) buffer (pH 4.5) (55:45, v/v) at a flow rate of 1 ml/min and UV detection at 237 nm. The drugs were subjected to oxidation, hydrolysis, photolysis and heat to apply stress conditions. The linearity of the proposed method was investigated in the range of 2-30 microg/ml (r=0.9994) for AT and 1-20 microg/ml (r=0.9993) for AM. The limits of detection were 0.65 microg/ml and 0.35 microg/ml for AT and AM, respectively. The limits of quantitation were 2 microg/ml and 1 microg/ml for AT and AM, respectively. Degradation products produced as a result of stress studies did not interfere with the detection of AT and AM and the assay can thus be considered stability-indicating.

Effect of ABCB1 (MDR1) haplotypes derived from G2677T/C3435T on the pharmacokinetics of amlodipine in healthy subjects

AIM

We aimed to investigate the effect of the ABCB1 gene on the pharmacokinetics of amlodipine.

METHODS

Based on polymorphisms of the ABCB1 gene at positions 2677 and 3435, 26 healthy male participants were divided into three groups: subjects with 2677GG/3435CC (n = 9), 2677GT/3435CT (n = 9) and 2677TT/3435TT (n = 8). After a single-dose administration of 5 mg amlodipine, plasma concentrations of amlodipine were measured and its pharmacokinetic characteristics were compared according to ABCB1 genotype.

RESULTS

The area under the plasma concentration-time curve was significantly lower in subjects with 2677TT/3435TT (140.8 +/- 35.6 ng h(-1) ml(-1)) and 2677GT/3435CT (149.8 +/- 40.1 ng h(-1) ml(-1)) than in those with 2677GG/3435CC (208.6 +/- 39.2 ng h(-1) ml(-1)) [95% confidence interval (CI) on the difference, 2677GG/3435CC vs. 2677GT/3435CT 12.0, 105.6, P < 0.01; 2677GG/3435CC vs. 2677TT/3435TT 19.6, 116.0, P < 0.01; 2677GT/3435CT vs. 2677TT/3435TT - 39.2, 57.2, P > 0.05]. The peak plasma concentrations were highest in subjects with 2677GG/3435CC (3.8 +/- 0.5 ng ml(-1)), lower in subjects with 2677GT/3435CT (3.2 +/- 0.5 ng ml(-1)) and 2677TT/3435TT (2.7 +/- 0.5 ng ml(-1)) in rank and showed a significant difference between those with 2677GG/3435CC and with 2677TT/3435TT (95% CI on the difference 0.4, 2.0, P < 0.01). However, the oral clearance was higher in subjects with 2677TT/3435TT (37.7 +/- 10.2 l h(-1)) than in those with 2677GT/3435CT (35.7 +/- 9.9 l h(-1)) and with 2677GG/3435CC (24.8 +/- 5.4 l h(-1)) and exhibited a significant difference between ABCB1 genotype groups (95% CI on the difference, 2677GG/3435CC vs. 2677GT/3435CT - 21.5, - 0.3, P < 0.05; 2677GG/3435CC vs. 2677TT/3435TT - 23.8, - 2.0, P < 0.05).

CONCLUSION

Amlodipine pharmacokinetics was affected by the genetic polymorphisms of the ABCB1 gene in humans. These findings may provide a plausible explanation for interindividual variation in the disposition of amlodipine, although our study could not explain the exact mechanism(s) by which the polymorphic ABCB1 gene paradoxically reduces the plasma levels of amlodipine. Further evaluation is thus warranted.

Liquid chromatographic separation and UV determination of certain antihypertensive agents

Three antihypertensive agents were extracted and isolated from commercial formulations. These were purified and characterized by melting point, lambdamax and IR. The percentage recovery by extraction process was in the range 81-91%. Active ingredients from binary formulations were separated by RP-HPLC using methanol-water (50:50 v/v) and by TLC using CHCl3-CH3OH (6:1) as mobile phase. Detection was by UV at 210 nm in HPLC, and by iodine vapors in TLC. The solvent conditions from TLC were transferred to open column chromatographic separation. Quantitative determination was carried out using TLC and column chromatography supplemented with UV spectrophotometry. Recovery was in the range 82-93%. Two combination of drugs, viz. amlodipine+ramipril and amlodipine+enalapril, were separated by the three modes of liquid chromatography. The percentage recovery was in the range 80-92% by open column.

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.

Validated HPLC method for determination of amlodipine in human plasma and its application to pharmacokinetic studies

A rapid, simple and sensitive high-performance liquid chromatography (HPLC) method has been developed for quantification of amlodipine in plasma. The assay enables the measurement of amlodipine for therapeutic drug monitoring with a minimum detectable limit of 0.2 ng ml(-1). The method involves simple, one-step extraction procedure and analytical recovery was about 97%. The separation was performed on an analytical 125 x 4.6 mm i.d. Nucleosil C8 column. The wavelength was set at 239 nm. The mobile phase was a mixture of 0.01 M sodium dihydrogen phosphate buffer and acetonitrile (63:37, v/v) adjusted to pH 3.5 at a flow rate of 1.5 ml min(-1). The calibration curve was linear over the concentration range 0.5-16 ng ml(-1). The coefficients of variation for inter-day and intra-day assay were found to be less than 10%.