Development and validation of HPLC and CE methods for simultaneous determination of amlodipine and atorvastatin in the presence of their acidic degradation products in tablets.

Two methods were developed for separation and quantitation of amlodipine (AML) and atorvastatin (ATV) in the presence of their acidic degradation products. The first method was a simple isocratic RP-HPLC method while the second was capillary electrophoresis (CE). Degradation products were obtained by acidic hydrolysis of the two drugs and their structures were elucidated for the first time by IR and MS spectra. Degradation products did not interfere with the determination of either drug and the assays were therefore stability-indicating. The linearity of the proposed methods was established over the ranges 1-50 µg mL-1 for AML and ATV in the HPLC method and in the range of 3-50 and 4-50 µg mL-1 for AML and ATV, respectively, in the CE method. The proposed methods were validated according to ICH guidelines. The methods were successfully applied to estimation of AML and ATV in combined tablets.

Interaction of PEGylated anti-hypertensive drugs, amlodipine, atenolol and lisinopril with lipid bilayer membrane: A molecular dynamics simulation study.

The interaction of PEGylated anti-hypertensive drugs, amlodipine, atenolol and lisinopril with lipid bilayer membrane dimyristoylphosphatidylcholine (DMPC) has been studied in nine different simulation systems consisting of 128 lipid molecules and appropriate number of water molecules by molecular dynamics method and by utilizing GROMACS software. The influences of PEGylation on the mentioned drugs and the differences in application of two types of spacer molecules on the performance of drugs and DMPC membrane have been evaluated and mass density of the components in the simulation box, mean square displacement (MSD), electrostatic potential, hydrogen bonding, radial distribution function (RDF), area per lipid, order parameter, and angle distribution of the component molecules including drug, DMPC and PEG has been investigated. Furthermore, umbrella sampling analysis indicated that, PEGylation of the drugs made amlodipine to behave more hydrophilic, whereas in case of lisinopril and atenolol, PEGylation made these drugs to behave more hydrophobic. In almost all of the simulated systems, PEGylation increased the diffusion coefficient of the drugs.

[Comparative study of the effect of S-amlodipine nicotinate and amlodipine benzylate on the arterial pressure of awake rats].

We have performed a comparative study of the effects of two calcium channel blockers, S-amlodipine nicotinate and amnlodipine benzylate, on the arterial pressure (AP) of awake rats measured in the tail artery. The results of experiments showed that both preparations produce a statistically significant long-term decrease in the AP of animals. In respect of both strength and duration of the hypotensive effect, S-amlodipine nicotinate somewhat exceeds amnlodipine benzylate.

Interaction of CJY, an isoflavone, with ATPase of P-glycoprotein in doxorubicin-resistant human myelogenous leukemia (K562/DOX) cells.

OBJECTIVES: The previous study reported CJY, an isoflavone, can reverse P-glycoprotein (P-gp)-mediated multidrug-resistance (MDR) in doxorubicin-resistant human myelogenous leukemia (K562/DOX) cells. This study will investigate the exact mechanism of CJY on P-gp. METHODS: By assessment of ATPase activity, we gained further insight into the nature of the CJY interactions with P-gp. Kinetic studies on ATPase activity were applied to show the effects of Verapamil (Ver) on CJY-stimulated, CJX1 on Ver-stimulated, and CJX1 on CJY-stimulated P-gp ATPase activity. Furthermore, the combined effects of CJY with Ver, and CJY with CJX1 were also evaluated isobolographically in numerous fixed-ratio combinations of 1:1, 1:2, 1:4, 1:8, and 1:10. RESULTS: The results showed that basal P-gp ATPase activity was increased by CJY with half-maximal activity concentration (Km) of 2.9±0.3 µM and the maximal ATPase activity velocity (Vmax) of 265±21 nM · min-1 · mg-1. Kinetic studies on ATPase activity showed the effects of Verapamil (Ver) on CJY-stimulated, CJX1 on Ver-stimulated, and CJX1 on CJY-stimulated P-gp ATPase activity were all non-competitive inhibition, indicating that these substrates can simultaneously but independently bind to diverse sites on P-gp. The combined effects of CJY with Ver, and CJY with CJX1 show that mixtures of both drugs at these fixed-ratios displayed synergistic interactions. CONCLUSIONS: CJY, CJX1 and Ver bind P-gp on different sites. CJY could be applied combining with other P-gp inhibitors to get better reversal of multidrug resistance than it used alone.

CJX1, an amlodipine derivative, interacts with ATPase of human P-glycoprotein.

Our aim has been to elucidate the possible mechanism of CJX1, an amlodipine derivative, in the modulation of P-gp function by determining its effect on P-gp ATPase activity. Basal P-gp ATPase activity was increased by CJX1 with half-maximal activity concentration (Km) of 8.6+/-1.4 microM. Kinetic analysis indicated a non-competitive inhibition of Verapamil (Ver)-stimulated P-gp ATPase activity by CJX1 and competitive inhibition of CJX1-stimulated P-gp ATPase activity by tetrandrine (Tet). The effect of CsA on CJX1-stimulated and Ver-stimulated P-gp ATPase activity was non-competitive and competitive inhibition, respectively. These findings implying that CJX1 and Tet can bind P-gp either on overlapping sites or distinct but interacting sites, while CJX1 and Ver as well as CsA can bind P-gp on separated sites in K562/DOX cells. Furthermore, the combined effect of CJX1 and Ver has been evaluated isobolographically in numerous fixed-ratio combinations of 1:1, 1:2, 1:4, 1:8, 1:10 in K562/DOX cells. The results show that mixtures of both drugs at these fixed-ratios exerted synergistic interactions, indicating that when the two reverses that bind P-gp on separated sites are combined, each can contribute to the overall interaction with P-gp, leading to the greater effect than that by either agent alone.

S-amlodipine--the 2007 clinical review.

S-amlodipine is the only vaso-active enantiomer of amlodipine. This article reviews the published data in nearly 5000 patients. Randomised controlled trials of S-amlodipine at half the dose of racemate in the treatment of hypertension, have shown it to be as effective as racemic amlodipine. The postmarketing surveillance studies (n = 4089) of S-amlodipine confirmed its antihypertensive efficacy and showed that the incidence of peripheral oedema is negligible with S-amlodipine compared to racemic amlodipine. Further, the patients with peripheral oedema who were switched over from racemic amlodipine to S-amlodipine resolved their oedema associated with the racemate, while sustaining the blood pressure control. Subgroup analyses showed S-amlodipine to be effective and safe in elderly hypertensives and isolated systolic hypertension patients. A clinical study in normotensive angina patients confirmed the anti-anginal efficacy of S-amlodipine at half the dose of racemate. Fixed-dose combinations of S-amlodipine with atenolol and S-amlodipine with hydrochlorothiazide have been shown to be effective and well tolerated in clinical practice. In the light of its efficacy and favourable tolerability profile, S-amlodipine used alone or in combination with other antihypertensive or anti-anginal drugs, is a valuable treatment option in the management of hypertension and angina.

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.

The results of modipin monotherapy in coronary heart disease patients with arterial hypertension (secondary coronary prevention).

The goal of the present study was to evaluate the safety and efficacy of the third generation calcium antagonist -- modipin (amlodipin, Asfarma, Turkey) in 29 patients with coronary atherosclerosis and arterial hypertension. In addition, some pleiotropic actions were examined. On the background of 5-10 mg/day modipin monotherapy during the 3-month study period the target systolic and diastolic blood pressure were achieved in 64 and 51% of cases. Modipin revealed some antiatherogenic efficacy as well. Pleiotropic effects of the drug were particularly expressed in restoring endothelial function reducing degree of hyperlipoperoxidemia and inhibition of platelet aggregation. There were positive changes in functional class of angina. Clinical safety was good. Consequently the present trial supports the use of modipine in all coronary artery disease patients with moderate or severe arterial hypertension.

Reversal of p-glycoprotein-mediated multidrug resistance by CJX1, an amlodipine derivative, in doxorubicin-resistant human myelogenous leukemia (K562/DOX) cells.

P-glycoprotein-mediated drug efflux can yield a multidrug resistance (MDR) phenotype that is associated with a poor response to cancer chemotherapy. Development of safe and effective MDR reversing agents is an important approach in the clinic. The aim of this study was to observe the effects of CJX1, an amlodipine derivative, on the inhibition of P-gp function and P-gp-mediated MDR in K562/DOX cells and parental K562 cells. Based on the flow cytometric technology, the uptake, accumulation and efflux of rhodamine123 (Rh123) were detected in these cells by measuring Rh123-associated mean fluorescence intensity (MFI). The effects of CJX1 on the doxorubicin cytotoxicity were evaluated by assaying for MTT (3-(4,5-dimethylthiazol)-2,5-diphenyltetrazolium bromide) reduction and the reversal fold (RF) values. The DNA content, percentage of apoptosis and cell cycle analysis were monitored with flow cytometry. Intracellular accumulation of doxorubicin was also assessed by the determination of doxorubicin-associated MFI. Verapamil was employed as a comparative agent. Incubation of K562/DOX cells with CJX1 caused a marked increase in uptake and a notable decrease in efflux of Rh123, No such results were found in parental K562 cells. The inhibitory effect of the agent of P-gp function was reversible, but it persisted at least for 90 min after removal of 2.5 microM CJX1 from incubation medium. The doxorubicin-induced cytotoxicity, apoptosis and cell cycle perturbations were significantly potentiated by CJX1. The intracellular accumulation of doxorubicin was enhanced in the presence of various concentrations of CJX1. The CJX1 exhibited potent effects in vitro in the reversal of P-gp-mediated MDR, suggesting that the compound may become a candidate of effective MDR reversing agent in cancer chemotherapy.

Modulation of P-glycoprotein function by amlodipine derivatives in brain microvessel endothelial cells of rats.

AIM: To investigate whether the amlodipine derivatives, CJX1 and CJX2, have a modulative effect on P-glycoprotein (P-gp) function in rat brain microvessel endothelial cells (RBMEC). METHODS: Isolated RBMEC were cultured in DMEM/F12 (1:1) medium. The amount of intracellular rhodamine (Rh123) was determined, using a fluorescence spectrophotometer, to evaluate the function of P-gp. RESULTS: The accumulation of Rh123 in RBMEC was potentiated in a concentration-dependent manner after incubation with CJX1 and CJX2 at 1, 2.5, 5, and 10 micromol/L (P<0.01), but no accumulation of Rh123 was observed in human umbilical vein endothelial cells after incubation with CJX1 and CJX2 10 micromol/L (P>0.05). Accumulation of intracellular Rh123 was increased and efflux of intracellular Rh123 was decreased in a time-dependent manner from 0-100 min after CJX1 and CXJ2 at 10 micromol/L treatment. The inhibitory effect of CJX1 and CJX2 on P-gp function was reversible and remained even at 120 min after removal of CJX1 and CJX2 at 2.5 micromol/L from the medium. CONCLUSION: CJX1 and CJX2 exhibited a potent effect in the inhibition of P-gp function in vitro.

Multicentric, clinical trial of S-Amlodipine 2.5 mg versus Amlodipine 5 mg in the treatment of mild to moderate hypertension--a randomized, double-blind clinical trial.

OBJECTIVE: To compare the efficacy and tolerability of 2.5 mg of S-Amlodipine with 5 mg of Amlodipine in the treatment of mild to moderate hypertension in a double blind, double dummy, randomized, comparative clinical trial. METHOD AND MATERIALS: Two hundred OPD patients (97 women and 103 men) with mean age 53.4 +/- 5.58 years, with stage I and stage 2 hypertension were enrolled for the study after obtaining informed written consent. Twelve patients were dropped out as lost to follow up. Ninety seven patients in the S-Amlodipine 2.5 mg treatment group and ninety one patients in the Amlodipine 5 mg treatment group completed the study. Those with a history of angina pectoris, myocardial infarction or recent cerebrovascular accident in the past six months and those with stage 3 and stage 4 hypertension were excluded from the study. Those showing a history of secondary hypertension were also excluded from the study. For the first two weeks all patients received dummy tablets of both S-Amlodipine and Amlodipine, as a wash out therapy and to get the actual blood pressure reading. After two weeks, enrolled patients received a preparation containing either S-Amlodipine (containing 2.5 mg of S-Amlodipine) and dummy tablets of Amlodipine or Amlodipine besylate (containing 5 mg of racemic Amlodipine) and dummy tablets of S-Amlodipine once daily for a period of six weeks. RESULTS: The results were analyzed by Student's 't' test The reduction in the average systolic and diastolic blood pressure, in the standing, supine and sitting postures in the S-Amlodipine group as well as in the Amlodipine group after six weeks of treatment was highly significant (P < or = 0.0001). The baseline values for average systolic blood pressure in standing, supine and sitting positions in the S-Amlodipine 2.5 mg treatment group were found to be 164.12 +/- 10.28, 165.72 +/- 10.88 and 165.24 +/- 10.66 mm of Hg respectively, which after treatment of six weeks changed to 144.9 +/- 7.4, 146.04 +/- 8.56 and 145.36 +/- 8.32 mm of Hg. The baseline values for average systolic blood pressure in standing, supine and sitting positions in the Amlodipine 5 mg treatment group were found to be 164.57 +/- 10.36, 166.47 +/- 10.58 and 165.81 +/- 10.54 mm of Hg respectively, which after treatment of six weeks changed to 154.42 +/- 6.33, 147.23 +/- 7.11 and 146.57 +/- 7.54 mm of Hg. The baseline values for average diastolic blood pressure in standing, supine and sitting positions in the S-Amlodipine 2.5 mg treatment group were found to be 99.63 +/- 6.22, 101.13 +/- 7.18 and 100.59 +/- 6.6 mm of Hg respectively, which after treatment of six weeks changed to 86.0 +/- 4.70, 87.18 +/- 5.20 and 86.27 +/- 5.68 mm of Hg. While the baseline values for average diastolic blood pressure in standing, supine and sitting positions in the Amlodipine 5 mg treatment group were found to be 98.95 +/- 5.54, 100.86 +/- 6.71 and 100.38 +/- 6.38 mm of Hg respectively, which after treatment of six weeks changed to 86.19 +/- 4.77, 87.52 +/- 5.44 and 87.33 +/- 5.98 mm of Hg. However the difference in the average reduction in systolic and diastolic blood pressures, in the two treatment groups, in the sitting, supine and the standing positions was not found to be statistically significant (p > 0.1) (CI = 0.95). There was no statistically significant change in the levels of serum creatinine, SGOT, SGPT, HDL, LDL, triglyceride and total cholesterol in patients receiving Amlodipine 5 mg. The reduction in total cholesterol as well as triglyceride level in the S-Amlodipine 2.5 mg treatment group was found to be greater but it failed to show any statistically significant difference. CONCLUSION: S-Amlodipine 2.5 mg is found to be equivalent in its efficacy and tolerability when compared to Amlodipine 5 mg in the treatment of mild to moderate hypertension.