Long-acting tunable release of amlodipine loaded PEG-PCL micelles for tailored treatment of chronic hypertension

Hypertension is a chronic condition that requires lifelong therapeutic management. Strict adherence to drug administration timing improves efficacy, while poor adherence leads to safety concerns. In light of these challenges, we present a nanofluidic technology that enables long-acting drug delivery with tunable timing of drug administration using buried gate electrodes in nanochannels. We developed a poly(ethylene glycol) methyl ether-block-poly(ε-caprolactone) (PEG-PCL)-based micellar formulation of amlodipine besylate, a calcium channel blocker for hypertension treatment. The electrostatically charged PEG-PCL micellar formulation enhanced drug solubility and rendered amlodipine responsive to electrostatic release gating in nanochannels for sustained release at clinically relevant therapeutic dose. Using a low-power (<3 VDC) gating potential, we demonstrated tunable release of amlodipine-loaded micelles. Additionally, we showed that the released drug maintained biological activity via calcium ion blockade in vitro. This study represents a proof of concept for the potential applicability of our strategy for chronotherapeutic management of hypertension.

Direct Visualization of Amlodipine Intervention into Living Cells by Means of Fluorescence Microscopy

Amlodipine, a unique long-lasting calcium channel antagonist and antihypertensive drug, has weak fluorescence in aqueous solutions. In the current paper, we show that direct visualization of amlodipine in live cells is possible due to the enhanced emission in cellular environment. We examined the impact of pH, polarity and viscosity of the environment as well as protein binding on the spectral properties of amlodipine in vitro, and used quantum chemical calculations for assessing the mechanism of fluorescence quenching in aqueous solutions. The confocal fluorescence microscopy shows that the drug readily penetrates the plasma membrane and accumulates in the intracellular vesicles. Visible emission and photostability of amlodipine allow confocal time-lapse imaging and the drug uptake monitoring.

Structural Basis of the Modulation of the Voltage-Gated Calcium Ion Channel Cav 1.1 by Dihydropyridine Compounds*

1,4-Dihydropyridines (DHP), the most commonly used antihypertensives, function by inhibiting the L-type voltage-gated Ca2+ (Cav ) channels. DHP compounds exhibit chirality-specific antagonistic or agonistic effects. The structure of rabbit Cav 1.1 bound to an achiral drug nifedipine reveals the general binding mode for DHP drugs, but the molecular basis for chiral specificity remained elusive. Herein, we report five cryo-EM structures of nanodisc-embedded Cav 1.1 in the presence of the bestselling drug amlodipine, a DHP antagonist (R)-(+)-Bay K8644, and a titration of its agonistic enantiomer (S)-(-)-Bay K8644 at resolutions of 2.9-3.4 Å. The amlodipine-bound structure reveals the molecular basis for the high efficacy of the drug. All structures with the addition of the Bay K8644 enantiomers exhibit similar inactivated conformations, suggesting that (S)-(-)-Bay K8644, when acting as an agonist, is insufficient to lock the activated state of the channel for a prolonged duration.

A Drug Content, Stability Analysis, and Qualitative Assessment of Pharmacists' Opinions of Two Exemplar Extemporaneous Formulations

Despite a decline in the number of active pharmaceutical ingredients prepared extemporaneously using proprietary products, there remains a need for such products in the community (for example, liquid medicines for paediatrics which may be otherwise commercially unavailable). A lack of experience and quality assurance systems may have diminished pharmacist’s confidence in the extemporaneous preparation process; therefore, pharmacists were asked to prepare two proprietary products, omeprazole and amlodipine. The resulting products were characterised in terms of variability in drug quantity, stability, particle size and antimicrobial properties. Furthermore, a self-administered questionnaire was used to assess 10 pharmacists’ opinions on the perceived complexity of the extemporaneous compounding process and their overall confidence in the final extemporaneously compounded products. Drug content studies revealed that 88.5% and 98.0% of the desired drug content was obtained for omeprazole and amlodipine, respectively. Antimicrobial properties were maintained for both drugs, however variability in particle size, particularly for amlodipine, was evident between formulations. While pharmacists who partook in the study had some or high confidence in the final products, they reported difficulty formulating the suspensions. Findings from this study provide insight into pharmacists’ views on two extemporaneously prepared products and highlight the variability obtained in preparations prepared by different pharmacists.

Desorption of pharmaceuticals from pristine and aged polystyrene microplastics under simulated gastrointestinal conditions

Microplastics (MPs) in the environment usually undergo extensive weathering and can transport pollutants to organisms once being ingested. However, the transportation mechanism and effect of aging process are poorly understood. This study systematically investigated the desorption mechanisms of pharmaceuticals from pristine and aged polystyrene (PS) MPs under simulated gastric and intestinal conditions of marine organisms. Results showed that the increased desorption in stomach mainly depended on the solubilization of pepsin to pharmaceuticals and the competition for sorption sites on MPs via π-π and hydrophobic interactions. However, high desorption in gut relied on the solubilization of intestinal components (i.e. bovine serum albumin (BSA) and bile salts (NaT)) and the competitive sorption of NaT since the enhanced solubility increased the partition of pharmaceuticals in aqueous phase. Aging process suppressed the desorption of pharmaceuticals because aging decreased hydrophobic and π-π interactions but increased electrostatic interaction between aged MPs and pharmaceuticals, which became less affected by gastrointestinal components. Risk assessment indicated that the MP-associated pharmaceuticals posed low risks to organisms, and warm-blooded organisms suffered relatively higher risks than cold-blooded ones. This study reveals important information to understand the ecological risks of co-existed MPs and pollutants in the environment.

Effect of aging on adsorption behavior of polystyrene microplastics for pharmaceuticals: Adsorption mechanism and role of aging intermediates

In the environment, aging obviously changes physicochemical properties of microplastics (MPs), but the effects of aging process on adsorption behavior of MPs are not fully understood. In this study, the aging of polystyrene (PS) was accelerated by photo-Fenton reaction. The adsorption mechanism of different aged PS toward atorvastatin (ATV) and amlodipine (AML) and the role of PS-derived intermediates in adsorption process were investigated. Results showed that the adsorption of pristine PS toward pharmaceuticals relied on hydrophobic and π-π interaction, while for aged PS, electrostatic interaction and hydrogen bonding controlled the adsorption. The study revealed that the intermediates released from aging process in high concentration (TOC of 10 mg/L) significantly decreased the adsorption of ATV (10 mg/L) on PS (5.0 g/L) but increased the adsorption of AML (10 mg/L). However, those intermediates at environmental concentration (0.1 mg/L) exhibited low effects on adsorption of pharmaceuticals (1.0 mg/L) on MPs (0.5 g/L of PS). The impact mainly depended on electrostatic interaction between MPs and aging intermediates. Besides, the adsorption of low-degree aged PS was more susceptible to the aging intermediates than that of high-degree aged ones. These findings highlight significant implication of MP-derived intermediates in aquatic environments.

Investigation of complexation of amlodipine with lysozyme and its effect on lysozyme crystal growth

Lysozyme (LYZ) is a model protein frequently employed to study interaction with drugs and to understand the crystallization process of protein due to its small size and rapid crystallization behavior. Studies related to drug interaction and complexation with proteins will be significantly benefited if a suitable drug-lysozyme crystal is available. This can further aid in the understanding of the mechanism of nucleation, growth and the formation of drug-lysozyme complex. In the present study, amlodipine (AMLD) complexation with LYZ has been monitored, along with its effect on lysozyme crystallization. Different spectroscopic methods have been employed to monitor the nature of complexation, binding mode and changes in helix after interaction with AMLD. The absorbance and fluorescence spectroscopic measurement indicated the probability of a ground state complex between LYZ and AMLD. Further, the temperature dependent fluorescence studies showed an increase in binding constant with temperature, suggesting the static quenching mechanism involved in complex formation due to hydrophobic interactions. CD, FTIR, DLS and DSC techniques confirm the probability of changes in the tertiary structure of protein. Molecular docking was applied to investigate the interaction of amino acid residues of LYZ with AMLD. It was found that the complex formation is spontaneous and the ΔG value obtained (-21. 76 kJ/mol) very well matched with temperature dependent fluorescence study (-24.91 kJ/mol). Crystallization of LYZ was performed with different concentration ranges of AMLD to get a clear picture of its interference on the process. The time required for crystallization of AMLD-LYZ complex and the observed structure of crystal indicates that AMLD influences lysozyme crystallization process by changing the nature of nucleation and rate of crystal growth.

Physicochemical Stability of Compounded Amlodipine Besylate Suspensions in PCCA Base, SuspendIt

Amlodipine besylate is an antihypertensive agent recommended for the management of hypertension in children and adolescents. The commercially available 2.5-mg, 5-mg, and 10-mg amlodipine besylate tablets do not provide the necessary flexibility in dosing needed for treating children. This flexibility is readily achieved using an oral, liquid dosage form. However, no commercial liquid dosage form of amlodipine currently exists. An extemporaneously compounded suspension from pure drug powder or commercial tablets would provide a convenient option to meet unique patient needs. The purpose of this study was to determine the physicochemical stability of extemporaneously compounded amlodipine besylate suspensions in the PCCA Base, SuspendIt. This base is a sugar-free, paraben-free, dye-free, and gluten-free thixotropic vehicle containing a natural sweetener obtained from the monk fruit. The study design included two amlodipine besylate concentrations to provide stability documentation over a bracketed concentration range for eventual use by compounding pharmacists. A robust stabilityindicating high-performance liquid chromatographic assay for the determination of the chemical stability of amlodipine besylate in SuspendIt was developed and validated. Suspensions of amlodipine were prepared in SuspendIt at 0.5-mg/mL and 10.0-mg/mL concentrations, selected to represent a range within which the drug is commonly dosed. Samples were stored in plastic amber prescription bottles at two temperature conditions (5°C and 25°C). Samples were assayed initially, and at the following time points: 7 days, 14 days, 29 days, 46 days, 60 days, 90 days, 120 days, and 180 days. Physical data such as pH, viscosity, and appearance were also noted. All measurements were obtained in triplicate. A stable extemporaneous product is defined as one that retains at least 90% of the initial drug concentration throughout the sampling period. This study demonstrates that amlodipine besylate is physically and chemically stable in SuspendIt for 90 days in the refrigerator and 7 days at room temperature, retaining 90% of the label claim (initial drug concentration) at both concentrations. The pH values did not change significantly. The viscosity of the refrigerated samples at both concentrations decreased slightly, while that of the room temperature samples showed a marked increase in viscosity. This study provides a viable, compounded alternative for amlodipine in a liquid dosage form, with an adequate beyond-use-date to meet patient needs. The study further provides stability documentation over a bracketed amlodipine concentration range of 0.5 mg/mL to 10.0 mg/mL, allowing compounding pharmacists more flexibility in customizing their formulations.

UHPLC-MS/MS assay for simultaneous determination of amlodipine, metoprolol, pravastatin, rosuvastatin, atorvastatin with its active metabolites in human plasma, for population-scale drug-drug interactions studies in people living with HIV

Thanks to highly active antiretroviral treatments, HIV infection is now considered as a chronic condition. Consequently, people living with HIV (PLWH) live longer and encounter more age-related chronic co-morbidities, notably cardiovascular diseases, leading to polypharmacy. As the management of drug-drug interactions (DDIs) constitutes a key aspect of the care of PLWH, the magnitude of pharmacokinetic DDIs between cardiovascular and anti-HIV drugs needs to be more thoroughly characterized. To that endeavour, an UHPLC-MS/MS bioanalytical method has been developed for the simultaneous determination in human plasma of amlodipine, metoprolol, pravastatin, rosuvastatin, atorvastatin and its active metabolites. Plasma samples were subjected to protein precipitation with methanol, followed by evaporation at room temperature under nitrogen of the supernatant, allowing to attain measurable plasma concentrations down to sub-nanogram per milliliter levels. Stable isotope-labelled analytes were used as internal standards. The five drugs and two metabolites were analyzed using a 6-min liquid chromatographic run coupled to electrospray triple quadrupole mass spectrometry detection. The method was validated over the clinically relevant concentrations ranging from 0.3 to 480 ng/mL for amlodipine, atorvastatin and p-OH-atorvastatin, and 0.4 to 480 ng/mL for pravastatin, 0.5 to 480 ng/mL for rosuvastatin and o-OH-atorvastatin, and 3 to 4800 ng/mL for metoprolol. Validation performances such as trueness (95.4-110.8%), repeatability (1.5-13.4%) and intermediate precision (3.6-14.5%) were in agreement with current international recommendations. Accuracy profiles (total error approach) were lying within the limits of ±30% accepted in bioanalysis. This rapid and robust UHPLC-MS/MS assay allows the simultaneous quantification in plasma of the major currently used cardiovascular drugs and offers an efficient analytical tool for clinical pharmacokinetics as well as DDIs studies.

Metal organic framework HKUST-1 modified with carboxymethyl-β-cyclodextrin for use in improved open tubular capillary electrochromatographic enantioseparation of five basic drugs

This work shows that the metal organic framework (MOF) HKUST-1 of type Cu₃(BTC)₂ (also referred to as MOF-199; a face-centered-cubic MOF containing nanochannels) is a most viable coating for use in enantioseparation in capillary electrochromatography (CEC). A HKUST-1 modified capillary was prepared and characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, elemental analysis and thermogravimetric analysis. CEC-based enantioseparation of the basic drugs propranolol (PRO), esmolol (ESM), metoprolol (MET), amlodipine (AML) and sotalol (SOT) was performed by using carboxymethyl-β-cyclodextrin as the chiral selector. Compared with a fused-silica capillary, the resolutions are improved (ESM: 1.79; MET: 1.80; PRO: 4.35; SOT: 1.91; AML: 2.65). The concentration of chiral selector, buffer pH value, applied voltage and buffer concentration were optimized, and the reproducibilities of the migration times and R_s values were evaluated. Graphical abstract Schematic presentation of the preparation of a HKUST-1@capillary for enantioseparation of racemic drugs. Cu(NO₃)₂ and 1,3,5-benzenetricarboxylic acid (BTC) were utilized to prepare the HKUST-1@capillary. Then the capillary was applied to construct capillary electrochromatography system with carboxymethyl-β-cyclodextrin (CM-β-CD) for separation of basic racemic drugs.

Validated LC-MS/MS method for the determination of amlodipine enantiomers in rat plasma and its application to a stereoselective pharmacokinetic study

A rapid and sensitive method was established to determine amlodipine enantiomers using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Stereoselective separation was performed on CHIRALCEL OZ-RH column (150 mm × 4.6 mm i.d., 5 μm) with acetonitrile-water (10 mM ammonium acetate, 0.5% ammonia solution) (95:5, v/v) at a flow rate of 0.5 mL/min. The substances were detected by mass spectrometer equipped with an electrospray ionization source interface in positive ion mode. Multiple reaction monitoring was selected with the transition of the m/z 409.1 → 238.0 for amlodipine enantiomers and m/z 237.0 → 194.1 for carbamazepine (IS) respectively. Calibration curves were linear at the range of 0.9375-120 ng/mL for both isomers with r > 0.99, while using a lower sample volume (50 μL) compared with previously reported enantiospecific methods The accuracy was at the range of 84.1-119.0% for R-amlodipine, and 87.4-118.2% for S-amlodipine, respectively. The within- and between-run precision (CV%) was within 10% in all cases for both enantiomers. Enantiomers were stable under different conditions, e.g. processed sample, short-term, residue, long-term and freeze/thaw. The LC-MS/MS method was successfully applied in pharmacokinetic study of amlodipine enantiomers in rats. It was observed the concentration of the S- amlodipine was significantly higher than that of the R-amlodipine in racemate-treated group. And there was no significant difference in the pharmacokinetic profiles of the S-amlodipine between the 10 mg/kg racemate- and 5 mg/kg S-amlodipine-treated groups. In addition, it was the first time to find that the main pharmacokinetic parameters (AUC_(0-t), AUC_(0-∞) and C_max) of R-amlodipine were significantly lower in the 5 mg/kg R-amlodipine-treated group compared with the racemate-treated group.

Effect of Ginkgo Leaf Tablets on the Pharmacokinetics of Amlodipine in Rats

BACKGROUND AND OBJECTIVE

Ginkgo leaf tablet (GLT) is an effective traditional Chinese multi-herbal formula, which is often combined with amlodipine for treating senile hypertension in clinic. The aim of this study was to study the pharmacokinetics of amlodipine after oral administration of amlodipine and GLT and to investigate the potential for pharmacokinetic herb-drug interactions between GLT and amlodipine in rats.

METHODS

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) analytical method was developed for quantification of amlodipine in rat plasma. The accuracy, precision, linearity, selectivity and recovery were all within an acceptable range. Male Sprague-Dawley rats were randomly assigned to two groups: amlodipine group and amlodipine + GLT group. Plasma concentrations of amlodipine were determined at the designated time points after oral administration by using the developed LC-MS/MS method, and the main pharmacokinetic parameters were calculated and compared. As ginkgolides A, ginkgolides B, bilobalide, quercetin and kaempferol were the main components of GLT, the effects of these ingredients in GLT on metabolism of amlodipine were further investigated in rat liver microsomes.

RESULTS

The pharmacokinetic parameters, maximum plasma concentration (C _max), time to reach C _max (T _max), area under the concentration-time curve (AUC), area under the first moment plasma concentration-time curve (AUMC) and elimination half-life (t _1/2), of amlodipine were significantly increased in amlodipine + GLT group, which suggested that GLT may influence the pharmacokinetic behavior after oral co-administration with amlodipine. Amlodipine is metabolized by cytochrome P450 (CYP) 3A4, so it was speculated that GLT may change the pharmacokinetic parameters of amlodipine through modulating the metabolism of CYP3A4 enzymes. When ginkgolides B, bilobalide, or quercetin and amlodipine were co-incubated in the rat liver microsomes, the metabolic rate of amlodipine was prolonged to 533.1, 216.1 and 407.6 min, respectively, from 73.7 min.

CONCLUSIONS

These results suggested that these components in GLT inhibit the metabolism of amlodipine. So it can be speculated that the herb-drug interactions between GLT and amlodipine resulted from inhibiting the metabolism of amlodipine by GLT when they were co-administered.

Multiway analysis methods applied to the fluorescence excitation-emission dataset for the simultaneous quantification of valsartan and amlodipine in tablets

In this study, excitation-emission matrix datasets, which have strong overlapping bands, were processed by using four different chemometric calibration algorithms consisting of parallel factor analysis, Tucker3, three-way partial least squares and unfolded partial least squares for the simultaneous quantitative estimation of valsartan and amlodipine besylate in tablets. In analyses, preliminary separation step was not used before the application of parallel factor analysis Tucker3, three-way partial least squares and unfolded partial least squares approaches for the analysis of the related drug substances in samples. Three-way excitation-emission matrix data array was obtained by concatenating excitation-emission matrices of the calibration set, validation set, and commercial tablet samples. The excitation-emission matrix data array was used to get parallel factor analysis, Tucker3, three-way partial least squares and unfolded partial least squares calibrations and to predict the amounts of valsartan and amlodipine besylate in samples. For all the methods, calibration and prediction of valsartan and amlodipine besylate were performed in the working concentration ranges of 0.25-4.50μg/mL. The validity and the performance of all the proposed methods were checked by using the validation parameters. From the analysis results, it was concluded that the described two-way and three-way algorithmic methods were very useful for the simultaneous quantitative resolution and routine analysis of the related drug substances in marketed samples.

The capacity and effectiveness of diosmectite and charcoal in trapping the compounds causing the most frequent intoxications in acute medicine: A comparative study

The aim of the study was to compare the adsorption ability of two adsorbent materials, namely diosmectite and activated charcoal towards selected model compounds that are most commonly involved in acute intoxication. Eleven model compounds were selected: acetylsalicylic acid, α-amanitin, amlodipine, digoxin, phenobarbital, ibuprofen, imipramine, carbamazepine, oxazepam, promethazine, and theophylline. Of the tested compounds, promethazine and imipramine were the most effectively adsorbed to diosmectite. Their adsorption to diosmectite (0.356±0.029mg promethazine/mg diosmectite and 0.354±0.019mg imipramine/mg diosmectite, respectively) was significantly higher than their adsorption to activated charcoal. The effect of temperature and pH on the adsorption efficiencies was also evaluated. In the case of experiments with mixture of both adsorbents, they mostly behaved in a solution independently or in a slightly antagonistic way. Using various methods such as N₂ adsorption and thermogravimetric analysis, the structure and texture of diosmectite and activated charcoal were attained.

RP-HPLC ANALYSIS OF ACIDIC AND BASIC DRUGS IN SYSTEMS WITH DIETHYLAMINE AS ELUENTS ADDITIVE

The chromatographic behavior of some basic and acidic drugs was studied on Cl 8, Phenyl-Hexyl and Polar RP columns with methanol or acetonitrile as organic modifiers of aqueous mobile phases containing addition of diethylamine. Diethylamine plays a double function of silanol blocker reagent in analysis of basic drugs and ion-pair reagent in analysis of acidic drugs. Most symmetrical peaks and highest system efficiency were obtained on Phenyl-Hexyl and Polar RP columns in tested mobile phase systems compared to results obtained on C18 column. A new rapid, simple, specific and accurate reverse phase liquid chromatographic method was developed for the simultaneous determination of atorvastatin - antihyperlipidemic drug and amlodipine - calcium channel blocker in one pharmaceutical formulation. Atorvastatin is an acidic compounds while amlodipine is a basic substance. The chromatographic separation was carried out on Phenyl-Hexyl column by gradient elution mode with acetonitrile as organic modifier, acetate buffer at pH 3.5 and Q.025 M/L diethylamine. The proposed method was validated for specificity, precision, accuracy, linearity, and robustness. The linearity range of atorvastatin and amlodipine for 5 - 100 μg/mL was obtained with limits of-detection (LOD) 3.2750 gg/mL and 3.2102 μg/mL, respectively. The proposed method made use of DAD as a tool for peak identity and purity confirmation.

Structural basis for inhibition of a voltage-gated Ca2+ channel by Ca2+ antagonist drugs

Ca²⁺ antagonist drugs are widely used in therapy of cardiovascular disorders. Three chemical classes of drugs bind to three separate, but allosterically interacting, receptor sites on Ca_V1.2 channels, the most prominent voltage-gated Ca²⁺ (Ca_V) channel type in myocytes in cardiac and vascular smooth muscle. The 1,4-dihydropyridines are used primarily for treatment of hypertension and angina pectoris and are thought to act as allosteric modulators of voltage-dependent Ca²⁺ channel activation, whereas phenylalkylamines and benzothiazepines are used primarily for treatment of cardiac arrhythmias and are thought to physically block the pore. The structural basis for the different binding, action, and therapeutic uses of these drugs remains unknown. Here we present crystallographic and functional analyses of drug binding to the bacterial homotetrameric model Ca_V channel Ca_VAb, which is inhibited by dihydropyridines and phenylalkylamines with nanomolar affinity in a state-dependent manner. The binding site for amlodipine and other dihydropyridines is located on the external, lipid-facing surface of the pore module, positioned at the interface of two subunits. Dihydropyridine binding allosterically induces an asymmetric conformation of the selectivity filter, in which partially dehydrated Ca²⁺ interacts directly with one subunit and blocks the pore. In contrast, the phenylalkylamine Br-verapamil binds in the central cavity of the pore on the intracellular side of the selectivity filter, physically blocking the ion-conducting pathway. Structure-based mutations of key amino-acid residues confirm drug binding at both sites. Our results define the structural basis for binding of dihydropyridines and phenylalkylamines at their distinct receptor sites on Ca_V channels and offer key insights into their fundamental mechanisms of action and differential therapeutic uses in cardiovascular diseases.

Mean centering of double divisor ratio spectra, a novel spectrophotometric method for analysis of ternary mixtures

A novel spectrophotometric method was developed for determination of ternary mixtures without previous separation, showing significant advantages over conventional methods. The new method is based on mean centering of double divisor ratio spectra. The mathematical explanation of the procedure is illustrated. The method was evaluated by determination of model ternary mixture and by the determination of Amlodipine (AML), Aliskiren (ALI) and Hydrochlorothiazide (HCT) in laboratory prepared mixtures and in a commercial pharmaceutical preparation. For proper presentation of the advantages and applicability of the new method, a comparative study was established between the new mean centering of double divisor ratio spectra (MCDD) and two similar methods used for analysis of ternary mixtures, namely mean centering (MC) and double divisor of ratio spectra-derivative spectrophotometry (DDRS-DS). The method was also compared with a reported one for analysis of the pharmaceutical preparation. The method was validated according to the ICH guidelines and accuracy, precision, repeatability and robustness were found to be within the acceptable limits.

1,4-Dihydropyridine Derivatives: Dihydronicotinamide Analogues-Model Compounds Targeting Oxidative Stress

Many 1,4-dihydropyridines (DHPs) possess redox properties. In this review DHPs are surveyed as protectors against oxidative stress (OS) and related disorders, considering the DHPs as specific group of potential antioxidants with bioprotective capacities. They have several peculiarities related to antioxidant activity (AOA). Several commercially available calcium antagonist, 1,4-DHP drugs, their metabolites, and calcium agonists were shown to express AOA. Synthesis, hydrogen donor properties, AOA, and methods and approaches used to reveal biological activities of various groups of 1,4-DHPs are presented. Examples of DHPs antioxidant activities and protective effects of DHPs against OS induced damage in low density lipoproteins (LDL), mitochondria, microsomes, isolated cells, and cell cultures are highlighted. Comparison of the AOA of different DHPs and other antioxidants is also given. According to the data presented, the DHPs might be considered as bellwether among synthetic compounds targeting OS and potential pharmacological model compounds targeting oxidative stress important for medicinal chemistry.

Degradation kinetics and pathways of three calcium channel blockers under UV irradiation

Calcium channel blockers (CCBs) are a group of pharmaceuticals widely prescribed to lower blood pressure and treat heart diseases. They have been frequently detected in wastewater treatment plant (WWTP) effluents and downstream river waters, thus inducing a potential risk to aquatic ecosystems. However, little is known about the behavior and fate of CCBs under UV irradiation, which has been adopted as a primary disinfection method for WWTP effluents. This study investigated the degradation kinetics and pathways of three commonly-used CCBs, including amlodipine (AML), diltiazem (DIL), and verapamil (VER), under UV (254 nm) irradiation. The chemical structures of transformation byproducts (TBPs) were first identified to assess the potential ecological hazards. On that basis, a generic solid-phase extraction method, which simultaneously used four different cartridges, was adopted to extract and enrich the TBPs. Thereafter, the photo-degradation of target CCBs was performed under UV fluences typical for WWTP effluent disinfection. The degradation of all three CCBs conformed to the pseudo-first-order kinetics, with rate constants of 0.031, 0.044 and 0.011 min(-1) for AML, DIL and VER, respectively. By comparing the MS(2) fragments and the evolution (i.e., formation or decay) trends of identified TBPs, the degradation pathways were proposed. In the WWTP effluent, although the target CCBs could be degraded, several TBPs still contained the functional pharmacophores and reached peak concentrations under UV fluences of 40-100 mJ cm(-2).

Formulation and bioequivalence of two Valsartan/Amlodipine immediate release tablets after a single oral administration

The aim of this study was to formulate a film-coated Valsartan/Amlodipine (VS/AM) immediate release tablets and to evaluate their in vivo release profile. VS/AM core tablets were manufactured using dry granulation method. Opadry aqueous coating dispersion was used as film coating material. Dissolution of the film coated tablets was tested in 900 ml of 0.5% SLS media, bioequivalence of tablets was tested by comparisons against the reference brand product. The ICH guidelines were used to evaluate the stability of the obtained tablets. The coated tablets were subjected to gastric pH, and drug release was analyzed using HPLC system to evaluate the efficiency of the film coat. The coated tablets had no defects. VS/AM release met the FDA guidelines for bioequivalence studies. Statistical comparison of the main pharmacokinetic parameters showed no significant difference between test and reference. These findings suggest that aqueous film coating with Opadry system is an easy and economical approach for preparing stable film coated VS/AM tablets without compromising their in vivo drugs release.

Testing the capability of a polynomial-modified gaussian model in the description and simulation of chromatographic peaks of amlodipine and its impurity in ion-interaction chromatography

In this paper, the capability of a polynomial-modified Gaussian model to relate the peak shape of basic analytes, amlodipine, and its impurity A, with the change of chromatographic conditions was tested. For the accurate simulation of real chromatographic peaks the authors proposed the three-step procedure based on indirect modeling of peak width at 10% of peak height (W0.1), individual values of left-half width (A) and right-half width (B), number of theoretical plates (N), and tailing factor (Tf). The values of retention factors corresponding to the peak beginning (k(B)), peak apex (k(A)), peak ending (k(E)), and peak heights (H0) of the analytes were directly modeled. Then, the investigated experimental domain was divided to acquire a grid of appropriate density, which allowed the subsequent calculation of W0.1, A, B, N, and Tf. On the basis of the predicted results for Tf and N, as well as the defined criteria for the simulation the following conditions were selected: 33% acetonitrile/67% aqueous phase (55 mM perchloric acid, pH 2.2) at 40°C column temperature. Perfect agreement between predicted and experimental values was obtained confirming the ability of polynomial modified Gaussian model and three-step procedure to successfully simulate the real chromatograms in ion-interaction chromatography.

Spectrophotometric methods for simultaneous determination of ternary mixture of amlodipine besylate, olmesartan medoxomil and hydrochlorothiazide

Four, accurate, precise, and sensitive spectrophotometric methods are developed for the simultaneous determination of a ternary mixture containing amlodipine besylate (AM), olmesartan medoxomil (OL) and hydrochlorothiazide (HZ), where AM is determined at its λ(max) 364.6 nm ((0)D), while (OL) and (HZ) are determined by different methods. Method (A) depends on determining OL and HZ by measuring the second derivative of the ratio spectra ((2)DD) at 254.4 and 338.6 nm, respectively. Method (B) is first derivative of the double divisor ratio spectra (D-(1)DD) at 260.4 and 273.0 nm for OL and HZ, respectively. Method (C) based on successive spectrophotometric resolution technique (SSRT). The technique starts with the ratio subtraction method then measuring OL and HZ at their isoabsorptive point at 260.0 nm, while HZ is measured using the amplitude of first derivative at 335.2 nm. Method (D) is mean centering of the ratio spectra (MCR) at 252.0 nm and 220.0 nm for OL and HZ, respectively. The specificity of the developed methods is investigated by analyzing laboratory prepared mixtures containing different ratios of the three drugs and their combined dosage form. The obtained results are statistically compared with those obtained by the official or reported methods, showing no significant difference with respect to accuracy and precision at p=0.05.

The effects of amlodipine and S(-)-amlodipine on vascular endothelial function in patients with hypertension

BACKGROUND

Amlodipine has been shown to improve vascular endothelial function in hypertensive patients, but whether S(-)-amlodipine has a similar effect remains controversial. This study compared the effects of amlodipine and S(-)-amlodipine on vascular endothelial function in hypertensive patients and investigated relevant mechanisms of action in cell culture.

METHODS

Twenty-four patients with essential hypertension received amlodipine and S(-)-amlodipine for 6 weeks in a randomized, crossover study. Associated flow-mediated dilation (FMD), nitric oxide (NO), and endothelial nitric oxide synthase (eNOS) levels were determined. NO levels were measured after exposure of human umbilical vein endothelial cells (HUVECs) to amlodipine, S(-)-amlodipine, the eNOS inhibitor N w-nitro-L-arginine (L-NA), and the Protein Kinase C (PKC) inhibitor Ro 31-8220. Phosphorylation levels of Ser(1177) and Thr(495) in eNOS were determined after exposure to amlodipine, S(-)-amlodipine, and Ro 31-8220.

RESULTS

FMD, NO, and eNOS levels significantly improved after treatment with amlodipine and S(-)-amlodipine. The levels were all higher with amlodipine, although the between-treatment difference was not statistically significant. Amlodipine and S(-)-amlodipine significantly increased NO levels in cultured HUVECs, but increases in NO levels were more marked with amlodipine. Western blot assay showed that both amlodipine and Ro31-8220 induced Ser(1177) phosphorylation and weakened Thr(495) phosphorylation in eNOS. S(-)-amlodipine had no similar effects. Amlodipine, but not S(-)-amlodipine, decreased the PKC phosphorylation in a time-dependent manner.

CONCLUSIONS

Amlodipine and S(-)-amlodipine can both improve endothelial function in hypertensive patients. Amlodipine has greater potential for vascular endothelial protection than S(-)-amlodipine. It affects eNOS phosphorylation at Ser(1177) and Thr(495) by the PKC pathway, further enhancing eNOS activation.

Comparative study between derivative spectrophotometry and multivariate calibration as analytical tools applied for the simultaneous quantitation of Amlodipine, Valsartan and Hydrochlorothiazide

Four simple, accurate and specific methods were developed and validated for the simultaneous estimation of Amlodipine (AML), Valsartan (VAL) and Hydrochlorothiazide (HCT) in commercial tablets. The derivative spectrophotometric methods include Derivative Ratio Zero Crossing (DRZC) and Double Divisor Ratio Spectra-Derivative Spectrophotometry (DDRS-DS) methods, while the multivariate calibrations used are Principal Component Regression (PCR) and Partial Least Squares (PLSs). The proposed methods were applied successfully in the determination of the drugs in laboratory-prepared mixtures and in commercial pharmaceutical preparations. The validity of the proposed methods was assessed using the standard addition technique. The linearity of the proposed methods is investigated in the range of 2-32, 4-44 and 2-20 μg/mL for AML, VAL and HCT, respectively.

Three different methods for determination of binary mixture of Amlodipine and Atorvastatin using dual wavelength spectrophotometry

Three simple, specific, accurate and precise spectrophotometric methods depending on the proper selection of two wavelengths are developed for the simultaneous determination of Amlodipine besylate (AML) and Atorvastatin calcium (ATV) in tablet dosage forms. The first method is the new Ratio Difference method, the second method is the Bivariate method and the third one is the Absorbance Ratio method. The calibration curve is linear over the concentration range of 4-40 and 8-32 μg/mL for AML and ATV, respectively. These methods are tested by analyzing synthetic mixtures of the above drugs and they are applied to commercial pharmaceutical preparation of the subjected drugs. Methods are validated according to the ICH guidelines and accuracy, precision, repeatability and robustness are found to be within the acceptable limit. The mathematical explanation of the procedures is illustrated.

The physicochemical equivalence of eight brands of amlodipine tablets in Lagos, Nigeria

BACKGROUND

Amlodipine is a dihydropyridine calcium channel antagonist that is useful in the treatment of hypertension and angina pectoris. In addition to the innovator brand of this molecule, several generic brands are marketed in Nigeria.

OBJECTIVE

To evaluate the physicochemical equivalence of eight brands of amlodipine tablets marketed in Lagos, Nigeria.

METHODS

Physicochemical properties such as identity, weight uniformity, friability, hardness test, disintegration test, dissolution test and assay of active ingredients were performed using the methods described in the British and the United States Pharmacopoeia. Ultra-violet spectrophotometric and High performance liquid chromatographic methods were used for assay of the labelled amount of amlodipine in the products.

RESULTS

All the products passed weight uniformity and disintegration tests. Only one brand failed the friability test. Two brands had mean crushing strength less than 4 kg/cm²; while only 4 brands passed dissolution test by releasing >75% of the labelled amlodipine within 45 minutes. One brand failed both assay and dissolution tests by returning less than official specifications in the general monograph for conventional tablets. In all, four of the eight sample products analyzed passed all the tests. These can be said to be physicochemically equivalent and may be clinically interchangeable or substituted.

CONCLUSION

This study further highlights the concerns over the quality of drug products marketed in a developing country.

Efficacy, safety, and palatability of RACTAB(®) formulation amlodipine orally disintegrating tablets

OBJECTIVE

The aim of this study was to confirm the efficacy, safety, and expected palatability of amlodipine orally disintegrating tablets (ODT) [RACTAB(®) formulation (Towa, Osaka, Japan)]. We report the re-analyzed results of 1687 cases in clinical settings obtained through postmarketing surveillance in Japan.

METHOD

Study subjects were patients receiving treatment for the first time with amlodipine ODT for hypertension under routine care. A multicenter central registration system was used for this prospective survey. The survey was conducted from October 2008 to October 2010. The observational period was 12 weeks, during which time surveys on outpatient blood pressure, adverse events, palatability, etc. were conducted.

RESULTS

Blood pressure stabilized following treatment, and both systolic and diastolic blood pressures were favorably controlled. Adverse events observed were not significantly different from those observed during drug use trials of amlodipine formulations reported in 2003. Moreover, palatability of amlodipine ODT showed a 99.6% (227 of 228 cases) favorable patient acceptance, which is consistent with the initial design concept of RACTAB(®) formulation.

CONCLUSIONS

The results of this postmarketing surveillance study indicated that the efficacy, safety, and palatability of amlodipine ODT met our expectations (dissolves quickly in the mouth, tastes good, and is not rough on the tongue). Accordingly, amlodipine ODT are believed to be an easy-to-use formulation for prescribing doctors, dispensing pharmacists, and patients receiving treatment.

Characterization of cyanide-trapped methylated metabonates formed during reactive drug metabolite screening in vitro

Reactive metabolites are estimated to be one of the main reasons behind unexpected drug-induced toxicity, by binding covalently to cell proteins or DNA. Due to their high reactivity and short lifespan, reactive metabolites are analyzed after chemical trapping with nucleophilic agents such as glutathione or cyanide. Recently, unexplained and uncharacterized methylated reaction products were reported in a human liver microsome based reactive metabolite trapping assay utilizing potassium cyanide as a trapping agent. Here, a similar assay was utilized to produce mono- or dimethylated and further cyanide-trapped reaction products from propranolol, amlodipine and ciprofloxacin, followed by ultra-performance liquid chromatography/time-of-flight mass spectrometry (UPLC/TOF-MS) and ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) experiments for their more detailed structural elucidation. Formation of all observed cyanide-trapped products was clearly NADPH-dependent and thus metabolism-mediated. The suggested reaction pathways included N-methylation leading to iminium formation in primary and/or secondary amines preceded by cytochrome P450 (CYP)-mediated reactions. As the methylation reaction was suggested to be involved in formation of the actual reactive iminium ion, the observed cyanide-trapped products were experimental artifacts rather than trapped reactive metabolites. The results stress that to avoid overestimating the formation of reactive metabolites in vitro, this methylation phenomenon should be taken into account when interpreting the results of cyanide-utilizing reactive metabolite trapping assays. This in turn emphasizes the importance of identification of the observed cyano conjugates during such studies. Yet, metabolite identification has a high importance to avoid overestimation of in vitro metabolic clearance in the cases where this kind of metabonate formation has a high impact in the disappearance rate of the compound.

Validation of a capillary electrophoresis method for the simultaneous determination of amlodipine besylate and valsartan in pharmaceuticals and human plasma

A rapid, simple, and sensitive capillary electrophoresis (CE) method was developed and validated for the simultaneous determination of amlodipine (AML) and valsartan (VAL) in pharmaceuticals and human plasma using a UV photodiode array detector. Electrophoretic conditions were optimized to improve separation, sensitivity, and rapidity. The optimal conditions were 25 mM phosphate buffer at pH 8.0, injection time 10.0 s, voltage 25 kV, and column temperature 25 degrees C, with detection at 214 nm. The method was found to be linear in the range of 1.0-35 and 1.0-350 mg/L, with weighted regression 0.9999 and 0.9994, for AML and VAL, respectively. Validation of the method showed acceptable intraday and interday accuracy (85.5-95.3%) and precision (RSD 1.64-4.2%) in pharmaceutical formulation and human plasma analysis. The sensitivity of the method was enhanced by both optimization of the CE procedure and preconcentration performed by liquid-liquid extraction. The LOD for both AML and VAL was 0.03 mg/L, which allows analysis at the level of the drugs possibly found in human plasma. Therefore, the proposed method is suitable for QC in pharmaceutical laboratories and therapeutic drug monitoring in clinical laboratories.

[Comparative estimation of efficiency and safety of racemic amlodipine and its S-enantiomer in hypertensive patients]

The authors conducted comparative estimation of efficiency and safety of racemic (R+S-) AMLODIPINE and sinistrorotatory isomer--S(-)AMLODIPINE besylate in 63 hypertensive patients from which 32 patients were administered (R+S-) amlodipine and 31--S(-)amlodipine besylate. It was established identity of antihypertensive effect according daily monitoring of blood pressure and monitoring of blood pressure in the office. However, daily dose of S(-)enantiomer was two times less than the dose of (R+S-) amlodipine. Adverse effects (headache, excessive heartbeat, peripheral edema) were less in patients who have received S(-)AMLODIPINE besylate that contributed to more expressed positive clinical dynamic of the state of patients of this group.

Effects of (S)-amlodipine and (R)-amlodipine on L-type calcium channel current of rat ventricular myocytes and cytosolic calcium of aortic smooth muscle cells

OBJECTIVE

Amlodipine (Aml) has R- and S-isomers with different pharmacological effects. However, no data are available on the influence of (S)-Aml and (R)-Aml on L-type calcium channel current (I(Ca-L)) or cytosolic calcium (Ca2+). This study is to investigate effects on I(Ca-L) and cytosolic Ca2+.

METHODS

I(Ca-L), peak currents, I-V curves, steady state activation curves, steady state inactivation curves and recovery curves from inactivation with (S)-Aml and (R)-Aml were recorded by whole-cell patch clamp configuration. Cytosolic Ca2+ of smooth muscle cells was assayed by Fura-2/AM.

RESULTS

At the concentrations of 0.1, 0.5, 1, 5, and 10 micromol/L, 1.5 +/- 0.2%, 25.4 +/- 5.3%, 65.2 +/- 7.3%, 78.4 +/- 8.1%, and 94.2 +/- 5.0% of I(Ca-L) were blocked by (S)-Aml. I-V curves were shifted upward. Half-activation voltages were -16.01 +/- 1.65 mV, -17.61 +/- 1.60 mV, -20.17 +/- 1.46 mV, -21.87 +/- 1.69 mV and -24.09 +/- 1.87 mV (P < 0.05). Half-inactivation voltages were -27.16 +/- 4.48 mV, -28.69 +/- 4.52 mV, -31.19 +/- 4.17 mV, -32.63 +/- 4.34 mV and -35.16 +/- 4.46 mV (P < 0.05). Recovery time were prolonged gradually (P < 0.05). 10.3 +/- 1.2%, 35.2 +/- 3.5%, 60.1 +/- 5.0%, 78.9 +/- 6.1%, and 91.2 +/- 7.6% of cytosolic Ca2+ were reduced at different concentrations (P < 0.05). However, (R)-Aml at different concentrations had no effect on I(Ca-L) and cytosolic Ca2+ (P > 0.05).

CONCLUSION

Only (S)-Aml has calcium channel blockade activity, while (R)-Aml has none of the pharmacologic actions associated with CCBs.

Structure elucidation of thermal degradation products of amlodipine

Thermal degradation of amlodipine base causes intramolecular reactions affording three cyclic products, referred to as AMLDEG-I, AMLDEG-II, and AMLDEG-III, respectively. AMLDEG-I is a cyclized product formed by intramolecular elimination of ammonia from amlodipine. AMLDEG-II is a positional isomer of AMLDEG-I. AMLDEG-III is also intramolecular cyclisation product. The three degradation products were isolated by column chromatography and characterized by FT-IR and 1H and 13C NMR spectroscopy data. The AMLDEG-III was crystallized and its structure was solved by single crystal X-ray diffraction (SXRD).

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.

Determination and pharmacokinetic study of amlodipine in human plasma by ultra performance liquid chromatography–electrospray ionization mass spectrometry

A novel, specific and sensitive ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was developed for the determination and pharmacokinetic study of amlodipine in human plasma. The analysis was carried out on an ACQUITY UPLC BEH C(18) column (50 mm x 2.1 mm, i.d., 1.7 microm) with gradient elution at a flow-rate of 0.35 ml/min. The mobile phase was water and acetonitrile under gradient conditions (both containing 0.3% formic acid) and nimodipine was used as the internal standard. Detection was performed on a triple-quadrupole tandem mass spectrometer by multiple reaction monitoring (MRM) mode via Turbo ion spray ionization (ESI). Linear calibration curves were obtained over the concentration range 0.15-16.0 ng/ml, with a lower limit of quantification of 0.15 ng/ml. The intra- and inter-day precision (R.S.D.) values were below 15% and the accuracy (R.E.) was -2.3% to 6.9% at all three QC levels. The method was used to support clinical pharmacokinetic studies of amlodipine in healthy volunteers following oral administration.

Stability Indicating RP-HPLC Method for Simultaneous Determination of Atorvastatin and Amlodipine from Their Combination Drug Products

The study describes development and subsequent validation of a stability indicating reverse-phase HPLC method for the simultaneous estimation of atorvastatin (ATV), and amlodipine (AML) from their combination drug product. The proposed RP-HPLC method utilizes a Lichrospher 100 C18, 5 microm, 250 mm x 4.0 mm i.d. column, at ambient temperature, optimum mobile phase consisted of acetonitrile and 50 mM potassium dihydrogen phosphate buffer (60 : 40, v/v), apparent pH adjusted to 3+/-0.1 with 10% phosphoric acid solution, effluent flow rate monitored at 1.0 ml/min, and UV detection at 254 nm. ATV, AML, and their combination drug product were exposed to thermal, photolytic, hydrolytic, and oxidative stress conditions, and the stressed samples were analyzed by proposed method. The method was applied for the in vitro dissolution of marketed combination drug products. The described method was linear over the range of 1-90 microg/ml and 1-80 microg/ml for ATV and AML, respectively. The mean recoveries were 99.76 and 98.12% for ATV and AML, respectively. The intermediate precision data obtained under different experimental setup, the calculated value of coefficient of variation (CV, %) was found to be less than critical value. The limit of detection for ATV and AML were found to be 0.4 and 0.6 mug/ml, respectively and the limit of quantification was 1.0 microg/ml for both drugs. The average percentage drug release was found to be more than 70% within 30 min for both drugs. Chromatographic peak purity data of ATV and AML indicated no co-eluting peaks with the main peaks of drugs which demonstrated the specificity of assay method for their estimation in presence of degradation products. The proposed method can be useful in the quality control and in vitro dissolution of combination drug products.

Pharmacokinetic and pharmacodynamic characteristics of a new S-amlodipine formulation in healthy Korean male subjects: A randomized, open-label, two-period, comparative, crossover study

BACKGROUND

Amlodipine, a dihydropyridine calcium channel antagonist, is prescribed for the management of angina and hypertension. It is used therapeutically as a racemic mixture, composed of S- and R-enantiomers, but its calcium channel-blocking effect is confined to S-amlodipine; R-amlodipine has 1000-fold less activity than its S-enantiomer.

OBJECTIVE

The objective of this study was to compare the pharmacokinetic and pharmacodynamic properties and safety profiles of a newly developed amlodipine formulation, composed wholly of S-amlodipine, with those of the conventionally prescribed racemic formulation.

METHODS

This randomized, open-label, 2-period, comparative, crossover study was conducted with healthy volunteers at the Gil Medical Center and Gachon Medical School, Incheon, Korea. Male subjects, aged 20 to 50 years, were eligible to participate if their weight was within 20% of ideal body weight and if they were judged by physicians to be healthy. All subjects were randomly assigned in a 1:1 ratio to 1 of 2 treatment sequences: (1) a single dose of the test amlodipine formulation (S-enantiomer amlodipine 5 mg p.o.) (Lodien [Hanlim Pharmaceutical Co., Seoul, Korea]) in the first study period, followed by a single dose of the reference amlodipine formulation (racemate 10 mg p.o.) (Norvasc [Pfizer Pharmaceuticals Korea Ltd., Seoul, Korea]) in the second study period, or (2) a single dose of the reference formulation in the first study period, followed by a single dose of the test formulation in the second period. A 3-week washout occurred between study periods. Blood samples for pharmacokinetic analysis of S-amlodipine were collected at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 24, 48, 72, 96, 120, 144, and 168 hours after drug administration. Pharmacodynamic variables (ie, systolic and diastolic blood pressure and heart rate) were measured at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 24, 48, and 72 hours after administration. Safety profiles were also assessed. Hematology, biochemistry, electrocardiography, and urinalysis were performed at baseline and end of study. Adverse events were monitored throughout the study period. Pharmacokinetic characteristics were compared using noncompartmental analysis. Pharmacokinetic equivalence was concluded if the geometric mean ratios of the plasma Cmax and AUC were within the predetermined range of 80% to 125%.

RESULTS

Twenty-six healthy Korean male volunteers were screened and 18 subjects (mean [SD] age, 23.4 [1.5] years [range, 21-26 years]; mean [SD] weight, 69.3 [6.8] kg [range, 60-88 kg]) were enrolled and completed the study. The plasma concentration-time profiles of S-amlodipine were comparable after administration of both formulations. The mean (SD) values for Cmax AUC from time 0 to the last available measurement (AUC(last)), and AUC from 0 to infinity (AUC(0-infinity)) for the reference formulation (3.0 [0.6] ng/mL, 151.4 [35.7] ng x h/mL, and 175.3 [45.1] ng x h/mL, respectively) did not differ significantly from those for the test formulation (3.1 [0.6] ng/mL, 139.7 [40.3] ng x h/mL, and 161.7 [43.8] ng x h/mL, respectively). The calculated 90% Cls for the corresponding ratios of log-transformed Cmax, AUCO(0-infinity), and AUC(last) were 97.56% to 112.51%, 86.31% to 98.74%, and 83.46% to 100.04%, respectively, which met the predetermined criteria for pharmacokinetic equivalence. Despite the single administration, significant changes in maximal blood pressure and heart rate were observed after drug administration for both formulations, compared with baseline values (all, P < 0.001). However, no significant differences were observed between the 2 formulations in terms of pharmacodynamic profiles, and no clinically relevant changes were observed for either formulation with respect to physical examination, hematology, biochemistry, electrocardiography, or urinalysis. Neither formulation caused any serious adverse events.

CONCLUSIONS

Two amlodipine formulations were found to be equivalent in terms of the pharmacokinetics of S-amlodipine. The newly developed formulation, comprised of only S-amlodipine, had pharmacodynamic profiles comparable to those of the conventional racemic amlodipine formulation in these healthy Korean male subjects. Both formulations were well tolerated.

Thermal stability of 1,4-dihydropyridine derivatives in solid state

The effect of temperature and air humidity on the stability of 7 derivatives of 1,4-dihydropyridine (nifedipine, nisoldipine, nitrendipine, nimodipine, nicardipine, felodipine and amlodipine) in solid state has been studied by accelerated testing. Quantitative analysis of the compounds studied was made by UV spectrophotometry, identification of the thermodegradation products and reference to the standard were made by thin layer chromatography (TLC), UV spectra and the reaction with KMnO4. Thermodegradation of the derivatives studied was found not to occur in dry air, whereas at air humidity it occurred according to the first order reaction at a similar rate for all derivatives. The main product of thermodegradation of the derivatives with the nitro substituent was a nitrozoderivative formed as a result of dihydropyridine ring aromatisation accompanied by water molecule elimination.

Improvement of bioavailability and photostability of amlodipine using redispersible dry emulsion

To improve the bioavailability and photostability of poorly water-soluble and photosensitive amlodipine, dry emulsion (DE) was prepared by spray-drying the oil-in-water emulsion of amlodipine. Labrafil M 1944 CS and dextrin were employed as oil phase and matrix material, respectively. Dispersing DE in distilled water formed an emulsion with a mean droplet size 1.4-fold larger than that of the homogenized amlodipine emulsion before spray-drying (0.24 +/- 0.30 microm versus 0.17 +/- 0.02 microm). The mean droplet size of DE remained unchanged during 6-month storage at room temperature. 94.4% versus 33.1% of amlodipine remained intact after 24-h UV irradiation of amlodipine as DE formulation or as powder. These data suggest that DE formulation greatly improved the photostability of amlodipine, as well as increasing the physical stability of emulsion systems. In vitro release of DE was higher than that of amlodipine powder (66% versus 48% release at 60 min). Consequently, DE formulation resulted in 2.6- and 2.9-fold higher Cmax and AUC0-24 h of amlodipine compared after oral administration of amlodipine powder in rats. Our data suggest that the DE may be a potential oral dosage form for amlodipine to improve its bioavailability.

Interaction of verapamil with lipid membranes and P-glycoprotein: connecting thermodynamics and membrane structure with functional activity

Verapamil and amlodipine are calcium ion influx inhibitors of wide clinical use. They are partially charged at neutral pH and exhibit amphiphilic properties. The noncharged species can easily cross the lipid membrane. We have measured with solid-state NMR the structural changes induced by verapamil upon incorporation into phospholipid bilayers and have compared them with earlier data on amlodipine and nimodipine. Verapamil and amlodipine produce a rotation of the phosphocholine headgroup away from the membrane surface and a disordering of the fatty acid chains. We have determined the thermodynamics of verapamil partitioning into neutral and negatively charged membranes with isothermal titration calorimetry. Verapamil undergoes a pK-shift of DeltapK(a) = 1.2 units in neutral lipid membranes and the percentage of the noncharged species increases from 5% to 45%. Verapamil partitioning is increased for negatively charged membranes and the binding isotherms are strongly affected by the salt concentration. The electrostatic screening can be explained with the Gouy-Chapman theory. Using a functional phosphate assay we have measured the affinity of verapamil, amlodipine, and nimodipine for P-glycoprotein, and have calculated the free energy of drug binding from the aqueous phase to the active center of P-glycoprotein in the lipid phase. By combining the latter results with the lipid partitioning data it was possible, for the first time, to determine the true affinity of the three drugs for the P-glycoprotein active center if the reaction takes place exclusively in the lipid matrix.

Effect of gamma radiation on amlodis and its potential for radiosterilization

In the present work, radiation sensitivity of amlodis (AML) and its active ingredient Amlodipin Besylate (AML-B) were separately investigated by electron spin resonance (ESR) spectroscopy using radiolytic products induced in these drugs. Irradiation in the dose range of 2.5-25kGy did not create any ESR resonance line in AML-B, but it create five characteristic ESR resonance lines associated with more than one radical species in the case of AML. This signal is attributed to the radical species created upon irradiation of inactive ingredients such as microcrystalline cellulose and sodium starch glycolate of AML. Five resonance lines were observed to be divided into three sub groups of different characteristic behaviors associable with three different radical species. Radical species responsible from observed ESR lines were unstable at room and above room temperatures, however, they conserved their identities over a storage period of 92 days. This permitted to discriminate irradiated AML from unirradiated one. A quadratic function was found to describe best the variations of the intensities of observed resonance lines with applied radiation dose. A model based on three tentative radical species with a pyranose ring formed by the rapture of CH bonds in positions 1 and 4 was proposed to explain the observed five lines experimental ESR spectra. AML was considered not providing the characteristic features of a good dosimetric material due to its low radiation yield and relatively fast decays of the created radical species, but very low radiation sensitivity of its active ingredient, namely AML-B makes AML a good candidate for radiosterilization.

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.

Clinic blood pressure responses to two amlodipine salt formulations, adipate and besylate, in adult Korean patients with mild to moderate hypertension: A multicenter, randomized, double-blind, parallel-group, 8-week comparison

BACKGROUND

The commercially available formulation of amlodipine is conjugated with besylate salt to increase water solubility. Recently, a new amlodipine salt formulation has been developed in which the free base of amlodipine is conjugated with a chemically different salt, adipate.

OBJECTIVE

The goal of this study was to compare the antihypertensive effect and tolerability of amlodipine adipate with those of amlodipine besylate in patients with mild to moderate hypertension.

METHODS

This was a multicenter, randomized, doubleblind, parallel-group study in which patients received 8 weeks of treatment with either amlodipine adipate or amlodipine besylate. The primary efficacy variable was noninferiority of the difference in mean changes from baseline in trough diastolic blood pressure (DBP) after 8 weeks of treatment. Secondary efficacy variables included mean changes in DBP, systolic blood pressure (SBP), and response rate (defined as the proportion of patients whose DBP was <90 mm Hg or whose DBP had decreased from baseline by > or =10 mm Hg). The incidence of adverse events (AEs) was also assessed.

RESULTS

Two hundred eleven patients were randomly assigned to receive amlodipine adipate (n = 106) or amlodipine besylate (n = 105). Study patients were primarily female (54.5%), with a mean (SD) age of 52.2 (9.6) years and a mean body weight of 67.1 (10.2) kg; there were no between-group differences in demographic profiles. After 4 weeks of randomized treatment, 58 (27.5%) patients (29 [27.4%] amlodipine adipate, 29 [27.6%] amlodipine besylate) had not achieved a mean DBP <90 mm Hg, and their dose was doubled. Mean DBP changes at 8 weeks were -15.2 (7.3) mm Hg in the amlodipine adipate group and -14.2 (7.4) mm Hg in the amlodipine besylate group (P = NS). Because the 95% CI for the difference in mean DBP changes between groups (-0.53 to 2.55) was within the prespecified lower limit (-4 mm Hg), amlodipine adipate was considered noninferior to amlodipine besylate. Mean SBP changes were -24.9 (12.1) mm Hg in the amlodipine adipate group and -22.0 (14.7) mm Hg in the amlodipine besylate group (P = NS). The response rates were 92.0% for amlodipine adipate and 95.4% for amlodipine besylate (P = NS). The overall incidence of clinical AEs was 20.8% in the amlodipine adipate group and 25.7% in the amlodipine besylate group (P = NS). Drug-related clinical AEs occurred in 5.7% and 12.4% of patients in the respective treatment groups (P = NS). Serum uric acid levels decreased significantly from base-line in both groups (P < 0.001).

CONCLUSIONS

Eight weeks of treatment with amlodipine adipate produced significant reductions from baseline in blood pressure in these patients with mild to moderate hypertension. The efficacy of amlodipine adipate was not inferior to that of amlodipine besylate. Tolerability was comparable between the 2 treatment groups.

Ionization, lipophilicity, and molecular modeling to investigate permeability and other biological properties of amlodipine

This paper uses a recent approach toward drug discovery, in which in silico tools and experimental data are combined together to study the structural features of amlodipine and their relevance in the peculiar pharmacodynamic and pharmacokinetic profiles of this long acting calcium antagonist. Results reveal for amlodipine two families of conformers (folded and extended) but also demonstrate that protonation is the predominant factor governing amlodipine intermolecular interactions among which ionic forces play a major role.

Application of oxidants to the spectrophotometric determination of amlodipine besylate in pharmaceutical formulations

Three new spectrophotometric methods for the determination of amlodipine besylate have been proposed. The first two methods, i.e. A and B, are based on the oxidation of the drug with Fe(III) and the estimation of Fe(II) produced after chelation with either 1,10-phenanthroline or 2,2'-bipyridyl at 500 and 515 nm, respectively. The Beer's law was obeyed in the concentration ranges of 2-10 and 4-14 microg ml(-1) with molar absorptivity of 2.9 x 10(4) and 2.7 x 10(4) l mol(-1) cm(-1) for methods A and B, respectively. The third procedure depends on the interaction of amlodipine besylate with ammonium heptamolybdate tetrahydrate, which resulted in the formation of molybdenum blue (lambda(max) 825 nm). The linear dynamic range and the molar absorptivity values were found to be 15-59 microg ml(-1) and 1.8 x 10(4) l mol(-1) cm(-1), respectively. The results of the proposed procedures were validated statistically and compared with those obtained by the reference method. The proposed methods were applied successfully to the determination of amlodipine besylate in commercial tablets.

[Enantioseparation of amlodipine maleate by capillary electrophoresis using colominic acid as a chiral selector and the mechanism of chiral recognition]

AIM

Colominic acid, a novel chiral selector, was applied to enantioseparation of dihydropyridine derivative by capillary electrophoresis. A new method was developed for enantioseparation of amlodipine maleate, a novel calcium channel blocking therapeutic agent. The chiral recognition mechanism of colominic acid to amlodipine maleate was studied.

METHODS

Capillary electrophoresis was performed, and the effects of separation conditions on chiral separation were examined, including concentration of chiral selector, buffer pH, capillary temperature, applied voltage and molecular mass of colominic acid.

RESULTS

The optimum conditions were additive concentration of 8.0%, buffer pH at 3.00, capillary temperature at 15 degrees C, 12 kV for applied voltage and 3 x 10(4) for molecular mass of colominic acid. Under optimum conditions complete separation was achieved between the enantiomers of amlodipine maleate with resolution as high as 2.20.

CONCLUSION

The cliral separation was based on the multipoint recognition between colominic acid and amlodipine maleate. It is recommended that this simple, rapid and selective method be used for enantioseparation of amlodipine maleate. As far as polysaccharides were concerned, colominic acid was first used for enantioseparation of amlodipine maleate.

Amlodipine Besylate–Excipients Interaction in Solid Dosage Form

This article studies the compatibility of amlodipine besylate in its solid formulations with various drug excipients. The various factors affecting amlodipine besylate stability were studied using high-performance liquid chromatography (HPLC). It has been found that binary 1:1 mixtures of amlodipine besylate and an excipient are stable at 65 degrees C and 40 degrees C/75% RH. Further investigations were conducted to study the stability of amlodipine besylate in multicomponent mixtures, including mixtures with actual formulations. The study reveals that mixtures of lactose, magnesium stearate, and water induce some instability on amlodipine besylate. The major degradation product confirmed by HPLC-mass spectrometry is amlodipine besylate glycosyl. This is in conformity with the well-known Maillard reaction between primary amines and lactose. Thus, lactose-free amlodipine formulations are recommended from the safety, quality, efficacy, and process cost points of view.

Design and monitoring of photostability systems for amlodipine dosage forms

Photostability of amlodipine (AML) has been monitored in several pharmaceutical inclusion systems characterized by plurimolecular aggregation of the drug and excipients with high molecular weight. Several formulations including cyclodextrins, liposomes and microspheres have been prepared and characterized. The photodegradation process has been monitored according to the conditions suggested by the ICH Guideline for photostability testing, by using a light cabinet equipped with a Xenon lamp and monitored by spectrophotometry. The formulations herein tested have been found to be able to considerably increase drug stability, when compared with usual pharmaceutical forms. The residual concentration detected in the inclusion complexes with cyclodextrins and liposomes was 90 and 77%, respectively, while a very good value of 97% was found for microspheres, after a radiant exposure of 11,340 kJm(-2).

Enantiomeric separation by HPLC of 1,4-dihydropyridines with vancomycin as chiral selector

The macrocyclic antibiotics represent a relatively new class of chiral selectors in CE, HPLC, and TLC. We have examined the use of the macrocyclic antibiotic vancomycin as a chiral selector in HPLC for the separation of 1,4-dihydropyridines (DHPs) calcium antagonists (CAs). Chromatographic data of six 1,4-dihydropyridine calcium channel blockers obtained on the vancomycin chiral stationary phase (Chirobiotic V) were compared with those obtained on an alpha(1)-acid glycoprotein (AGP) HPLC stationary phase. Optimization of pH and organic modifier was carried out in order to modulate the retention properties of each system. All chiral neutral DHPs were resolved on the AGP column, whereas on Chirobiotic V only basic DHPs showed a split peak. The analytical chromatographic procedure on Chirobiotic V proved suitable for semipreparative separation, since the separation factor on the analytical column was high enough to obtain pure enantiomers with high yields.