Characterization of the in vitro metabolic profile of amlodipine in rat using liquid chromatography–mass spectrometry

Comprehensive metabolite identification study of arterolane using hydrophilic interaction liquid chromatography with quadrupole-time-of-flight mass spectrometry

RATIONALE

In 2012, arterolane (ART) in combination with piperaquine received approval in India for the treatment of plasmodium-induced malaria; however, to date, a detailed metabolite identification study of ART has not been reported. Being polar in nature, ART shows early elution on reversed-phase columns which might be the rate-limiting factor of its systematic analytical studies. We have utilized hydrophilic interaction liquid chromatography (HILIC) to separate in vitro and in vivo metabolites of ART.

METHODS

The possible sites of metabolism were predicted by XenoSite software to obtain an initial assessment. In vitro studies were conducted by incubating the drug with liver microsomes such as human, rat and human S9 fractions. Later, in vivo studies were performed to check the metabolites in urine, faeces and plasma. The samples were pooled and subjected to the protein precipitation method before analysis by liquid chromatography/quadrupole-time-of-flight mass spectrometry (LC/QTOFMS).

RESULTS

We have observed 15 metabolites in this study which were phase I metabolites formed due to hydroxylation, dihydroxylation, peroxide bond scission and oxidation. Here, we report 11 metabolites of ART for the first time. The metabolic pathways and plausible structures were proposed according to accurate mass measurements and its MS/MS data.

CONCLUSIONS

The present study comprehensively reports the in vitro and in vivo metabolism of ART mentioning 11 novel metabolites. Here, extensive use of HILIC has helped to efficiently separate various metabolites. These findings would help prospects of ART disposition and its congeners.

Pharmacokinetics, plasma protein binding, and metabolism of a potential natural chemosensitizer from Marsdenia tenacissima in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Marsdenia tenacissima (Roxb.) Wight et Arn is a medicinal plant mainly distributed in southwest China. It is used in folk medicine for the treatment of tumors and is synergistic with chemotherapies. In our previous study, 11α-O-2-methybutyryl-12β-O-tigloyl-tenacigenin B (MT2), a main steroid aglycone isolated from the total aglycones of M. tenacissima, significantly enhanced the in vivo antitumor effect of paclitaxel in mice bearing human tumor xenografts, showing its potential as a chemosensitizer. However, the pharmacokinetic characteristics, plasma protein binding rate, and metabolic profile of MT2 remain unclear.

AIM OF THE STUDY

To elucidate the pharmacokinetic characteristics, plasma protein binding rate, and metabolic profile of MT2 in rats.

MATERIALS AND METHODS

MT2 in rat plasma and phosphate-buffered saline was quantified using ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method, while the MT2 metabolites in rat liver microsomes were analyzed using UPLC-triple time-of-flight MS/MS.

RESULTS

For intravenously administered MT2, the maximum plasma concentration and the area under the plasma concentration-time curve indicated dose dependency, while the elimination half-life time, the mean residence time, apparent volume of distribution and total apparent clearance values remained relatively unchanged in both the 5 mg/kg and 10 mg/kg groups. For orally administered MT2, the bioavailability was 1.08-1.11%. In rat plasma, MT2 exhibited a protein binding rate of 93.84-94.96%. In rat liver microsomes, MT2 was metabolized by oxidation alone or in combination with demethylation, and five MT2 metabolites were identified.

CONCLUSION

MT2 has low oral bioavailability and a high plasma protein binding rate in rats. After administration, MT2 is transformed into oxidative metabolites in the liver. To achieve a high blood concentration of MT2, it should be administered intravenously. These findings would serve as a reference for further MT2-based pharmacological study and drug development.

Self-management using crude herbs and the health-related quality of life among adult patients with hypertension living in a suburban setting of Malaysia

PURPOSE

To determine the prevalence of crude herbs' use in the self-management of hypertension and the health-related quality of life (HRQOL) in patients with hypertension.

METHODS

This cross-sectional study was performed among patients with hypertension attending a government health clinic. Socio-demographic characteristics, lifestyle modifications, medical history and predictors of crude herbs users were obtained. The diversity of crude herbs used was assessed using a modified international complementary and alternative medicine questionnaire (I-CAM-Q) and the HRQOL was assessed using the SF36 instrument.

RESULTS

Out of the 294 patients recruited, 52.4% were female, 41.5% were Malay and 38.8% were within the 60 to69 age category. The prevalence of crude herbs users was 30.6% and the most common herbs used were pegaga (Centella asiatica), peria (Momordica charantia) and betik (Carica papaya). Using the regression analysis, significantly higher odds of using crude herbs are noted among Malay or Indian patients who have these characteristics: attained secondary education, experienced falls or muscle pain, and had systolic blood pressure of more than 140 mmHg. There was no significant difference in HRQOL domains between the crude herb users and non-users (p>0.05).

CONCLUSION

Besides taking allopathic medications, certain patients with hypertension use crude herbs as a form of self-management. Although patients are adamant about integrating crude herbs as a form of self-management, the effects of doing so have not been properly investigated. This implies that the healthcare staff members need to communicate with the patients regarding the use of crude herbs together with conventional drugs.

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.

Magnetic Nanoparticles with Dual Surface Functions-Efficient Carriers for Metalloporphyrin-Catalyzed Drug Metabolite Synthesis in Batch and Continuous-Flow Reactors

The dual functionalization of magnetic nanoparticles with inert (methyl) and reactive (aminopropyl) groups enables efficient immobilization of synthetic metalloporphyrins (such as 5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)iron(II) porphyrin and 5,10,15,20-tetrakis-(4-sulfonatophenyl)iron(II) porphyrin) via covalent or ionic interactions. The proportion of reactive function on the surface has significant effect on the biomimetic activity of metalloporphyrins. The optimized magnetic nanocatalyst containing porphyrin was successfully applied for biomimetic oxidation of antihypertensive drug Amlodipine in batch and continuous-flow reactors as well.

Exploring in vivo metabolism and excretion of QO-58L using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry

QO-58 lysine (QO-58L) as a new potassium channel opener, reported to have a potential activity to cure neuropathic pain. The aim of this research is to develop and validate a high-performance liquid chromatography with tandem spectrometry (LC-MS/MS) method for the quantification of QO-58L in rat urine, feces and bile. In addition, analyze and identify the metabolites in urine and bile. The assay for this compound in samples detected with multiple reaction monitoring mode (MRM), and take nimodipine as internal standards (IS). To better understand the biotransformation of QO-58L, metabolites in urine and bile were identified by using ultra high performance liquid chromatography tandem quadrupole/time of flight mass spectrometry (UHPLC-Q-TOF-MS) in the positive and negative ion mode. Urine, feces and bile were quantified by three new methods. The results showed that: QO-58L was mainly eliminated through fecal route (92.94%), a small amount of it via biliary excretion (2.05%), and rarely through urinary excretion (0.024%). As a result, there are 11 metabolites were identified, including 8 phase I metabolites resulting from elimination, hydroxylation and dihydroxylation, and 3 phase II metabolites originating from sulfation, N-acetylcysteine conjugation and glucuronidation. Furthermore, the newly discoveries of excretion and metabolism significantly expanded our understanding and was going to be greatly helpful for QO-58L's further pharmacokinetic study in vivo.

Effect of microneedles on transdermal permeation enhancement of amlodipine

The present study aimed to investigate the effect of microneedle (MN) geometry parameters like length, density, shape and type on transdermal permeation enhancement of amlodipine (AMLO). Two types of MN devices viz. AdminPatch® arrays (ADM) (0.6, 1.2 and 1.5 mm lengths) and laboratory-fabricated polymeric MNs (PM) of 0.6 mm length were employed. In the case of PMs, arrays were applied thrice at different places within a 1.77-cm² skin area (PM-3) to maintain the MN density closer to 0.6 mm ADM. Scaling analyses were done using dimensionless parameters like concentration of AMLO (C_t/C_s), thickness (h/L) and surface area of the skin (Sa/L²). Microinjection moulding technique was employed to fabricate PM. Histological studies revealed that the PM, owing to their geometry/design, formed wider and deeper microconduits when compared to ADM of similar length. Approximately 6.84- and 6.11-fold increase in the cumulative amount (48 h) of AMLO permeated was observed with 1.5 mm ADM and PM-3 treatments respectively, when compared to passive permeation amounts. Good correlations (R ² > 0.89) were observed between different dimensionless parameters with scaling analyses. The enhancement in AMLO permeation was found to be in the order of 1.5 mm ADM ≥ PM-3 > 1.2 mm ADM > 0.6 mm ADM ≥PM-1 > passive. The study suggests that MN application enhances the AMLO transdermal permeation and the geometrical parameters of MNs play an important role in the degree of such enhancement.

The potential role of amlodipine on experimentally induced bacterial rhinosinusitis

Introduction

Antibiotics are frequently used for the treatment of rhinosinusitis. Concerns have been raised regarding the adverse effects of antibiotics and growing resistance. The lack of development of new antibiotic compounds has increased the necessity for exploration of non-antibiotic compounds that have antibacterial activity. Amlodipine is a non-antibiotic compound with anti-inflammatory activity.

Objective

In this study we aimed to investigate the potential role of amlodipine in the treatment of rhinosinusitis by evaluating its effects on tissue oxidative status, mucosal histology and inflammation.

Methods

Fifteen adult albino guinea pigs were inoculated with Staphylococcus aureus and treated with saline, cefazolin sodium, or amlodipine for 7 days. The control group was composed by five healthy guinea pigs. Animals were sacrificed after the treatment. Histopathological changes were identified using Hematoxylin-Eosin staining. Inflammation was assessed by Polymorphonuclear Leukocyte infiltration density. Tissue levels of antioxidants (superoxide dismutase, glutathione) and an oxidative product (malondialdehyde) were determined.

Results

In rhinosinusitis induced animals, amlodipine reduced loss of cilia, lamina propria edema and collagen deposition compared to placebo (saline) and although not superior to cefazolin, amlodipine decreased polymorphonuclear leukocyte infiltration. The superoxide dismutase activity and glutathione levels were reduced, whereas the malondialdehyde levels were increased significantly in all three-treatment groups compared to the control group. Amlodipine treated group showed significantly increased superoxide dismutase and glutathione levels and decreased malondialdehyde levels compared to all treatment groups.

Conclusion

The non-antibiotic compound amlodipine may have a role in acute rhinosinusitis treatment through tissue protective, antioxidant and anti-inflammatory mechanisms.

Effects of orally administered antibiotics on the bioavailability of amlodipine: gut microbiota-mediated drug interaction

BACKGROUND

Amlodipine is a representative calcium channel blocker that is frequently prescribed for the treatment of hypertension. In this study, the possibility of drug-drug interactions between amlodipine and coadministered antibiotics (ampicillin) was investigated in rats; thus, changes in the metabolic activities of gut microflora and the consequent pharmacokinetic pattern of amlodipine following ampicillin treatment were characterized.

METHODS AND RESULTS

In human and rat fecalase incubation samples, amlodipine was metabolized to yield a major pyridine metabolite. The remaining amlodipine decreased and the formation of pyridine metabolite increased with incubation time, indicating the involvement of gut microbiota in the metabolism of amlodipine. Pharmacokinetic analyses showed that systemic exposure of amlodipine was significantly elevated in antibiotic-treated rats compared with controls.

CONCLUSION

These results showed that antibiotic intake might increase the bioavailability of amlodipine by suppressing gut microbial metabolic activities, which could be followed by changes in therapeutic potency. Therefore, coadministration of amlodipine with antibiotics requires caution and clinical monitoring.

Urinary antihypertensive drug metabolite screening using molecular networking coupled to high-resolution mass spectrometry fragmentation

INTRODUCTION

Mass spectrometry is the current technique of choice in studying drug metabolism. High-resolution mass spectrometry in combination with MS/MS gas-phase experiments has the potential to contribute to rapid advances in this field. However, the data emerging from such fragmentation spectral files pose challenges to downstream analysis, given their complexity and size.

OBJECTIVES

This study aims to detect and visualize antihypertensive drug metabolites in untargeted metabolomics experiments based on the spectral similarity of their fragmentation spectra. Furthermore, spectral clusters of endogenous metabolites were also examined.

METHODS

Here we apply a molecular networking approach to seek drugs and their metabolites, in fragmentation spectra from urine derived from a cohort of 26 patients on antihypertensive therapy. The mass spectrometry data was collected on a Thermo Q-Exactive coupled to pHILIC chromatography using data dependent analysis (DDA) MS/MS gas-phase experiments.

RESULTS

In total, 165 separate drug metabolites were found and structurally annotated (17 by spectral matching and 122 by classification based on a clustered fragmentation pattern). The clusters could be traced to 13 drugs including the known antihypertensives verapamil, losartan and amlodipine. The molecular networking approach also generated clusters of endogenous metabolites, including carnitine derivatives, and conjugates containing glutamine, glutamate and trigonelline.

CONCLUSIONS

The approach offers unprecedented capability in the untargeted identification of drugs and their metabolites at the population level and has great potential to contribute to understanding stratified responses to drugs where differences in drug metabolism may determine treatment outcome.

Antihypertensive drugs metabolism: an update to pharmacokinetic profiles and computational approaches

Drug discovery and development is a high-risk enterprise that requires significant investments in capital, time and scientific expertise. The studies of xenobiotic metabolism remain as one of the main topics in the research and development of drugs, cosmetics and nutritional supplements.

Antihypertensive drugs are used for the treatment of high blood pressure, which is one the most frequent symptoms of the patients that undergo cardiovascular diseases such as myocardial infraction and strokes. In current cardiovascular disease pharmacology, four drug clusters - Angiotensin Converting Enzyme Inhibitors, Beta-Blockers, Calcium Channel Blockers and Diuretics - cover the major therapeutic characteristics of the most antihypertensive drugs. The pharmacokinetic and specifically the metabolic profile of the antihypertensive agents are intensively studied because of the broad inter-individual variability on plasma concentrations and the diversity on the efficacy response especially due to the P450 dependent metabolic status they present.

Several computational methods have been developed with the aim to: (i) model and better understand the human drug metabolism; and (ii) enhance the experimental investigation of the metabolism of small xenobiotic molecules. The main predictive tools these methods employ are rule-based approaches, quantitative structure metabolism/activity relationships and docking approaches.

This review paper provides detailed metabolic profiles of the major clusters of antihypertensive agents, including their metabolites and their metabolizing enzymes, and it also provides specific information concerning the computational approaches that have been used to predict the metabolic profile of several antihypertensive drugs.

Comparison of trapping profiles between d-peptides and glutathione in the identification of reactive metabolites

Qualitative trapping profile of reactive metabolites arising from six structurally different compounds was tested with three different d-peptide isomers (Peptide 1, gly–tyr–pro–cys–pro–his-pro; Peptide 2, gly–tyr–pro–ala–pro–his–pro; Peptide 3, gly–tyr–arg–pro–cys–pro–his–lys–pro) and glutathione (GSH) using mouse and human liver microsomes as the biocatalyst. The test compounds were classified either as clinically “safe” (amlodipine, caffeine, ibuprofen), or clinically as “risky” (clozapine, nimesulide, ticlopidine; i.e., associated with severe clinical toxicity outcomes). Our working hypothesis was as follows: could the use of short different amino acid sequence containing d-peptides in adduct detection confer any add-on value to that obtained with GSH? All “risky” agents’ resulted in the formation of several GSH adducts in the incubation mixture and with at least one peptide adduct with both microsomal preparations. Amlodipine did not form any adducts with any of the trapping agents. No GSH and peptide 2 and 3 adducts were found with caffeine, but with peptide 1 one adduct with human liver microsomes was detected. Ibuprofen produced one Peptide 1-adduct with human and mouse liver microsomes but not with GSH. In conclusion, GSH still remains the gold trapping standard for reactive metabolites. However, targeted d-peptides could provide additional information about protein binding potential of electrophilic agents, but their clinical significance needs to be clarified using a wider spectrum of chemicals together with other safety estimates.

Identification of metabolites produced by Phanerochaete chrysosporium in the presence of amlodipine orotate using metabolomics

Pharmaceuticals are very useful in treating human diseases but they are excreted to the environment sometimes in their original form or as byproducts of human metabolism. Pharmaceuticals and their metabolites have been proven by studies to be harmful to non-target ecological species and may be persistent in different water matrices. In this regard, there is an emergent need to eliminate these compounds to prevent their adverse effects on aquatic species. Biodegradation using white-rot fungi is a promising technology for the removal of recalcitrant compounds; however, products of fungal biodegradation can also be detrimental. In this novel study, we evaluated the ability of Phanerochaete chrysosporium to degrade amlodipine, an anti-hypertensive drug which was recently found in water systems. Analysis of amlodipine metabolites was done using quadrupole time-of-flight liquid chromatography mass spectrometry after the degradation set-up of 120 hours. Pharmaceutical degradation was seen using triple quadrupole liquid chromatography tandem mass spectrometry. Ninety-two significant metabolites (P-value ≤ 0.05) were significantly expressed after false discovery rate adjustment at a significance threshold of q = 0.05. Pyridine derivatives which were identified from samples became the basis of the proposed degradation pathway of amlodipine in this study.

A liquid chromatography-tandem mass spectrometric assay for the antihypertensive agent azelnidipine in human plasma with application to clinical pharmacokinetics studies

A robust and sensitive high-performance liquid chromatographic-tandem mass spectrometric (HPLC-MS/MS) assay for the high-throughput quantification of the antihypertensive drug azelnidipine in human plasma was developed and validated following bioanalytical validation guidelines. Azelnidipine and internal standard (IS), telmisartan, were extracted from human plasma by precipitation protein and separated on a C18 column using acetonitrile-methanol-ammonium formate with 0.1% formic acid as mobile phase. Detection was performed on a turbo-spray ionization source (ESI) and mass spectrometric positive multiple reaction monitoring mode (+MRM) using the respective transitions m/z 583.3 → 167.2 for azelnidipine and m/z 515.3 → 497.2 for IS. The method has a wide analytical measuring range from 0.0125 to 25 ng/mL. For the lowest limit of quantitation, low, medium and high quality controls, intra- and interassay precisions (relative standard deviation) were 3.30-7.01% and 1.78-8.09%, respectively. The drug was sufficiently stable under all relevant analytical conditions. The main metabolite of azelnidipine, M-1 (aromatized form), was monitored semiquantitatively using the typical transition m/z 581.3 → 167.2. Finally, the method was successfully applied to a clinical pharmacokinetic study in human after a single oral administration of azelnidipine 8 mg. The assay meets criteria for the analysis of samples from large research trials.

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

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

High throughput screening of high-affinity ligands for proteins with anion-binding sites using desorption electrospray ionization (DESI) mass spectrometry

A high throughput screening system involving a linear ion trap (LTQ) analyzer, a house-made platform and a desorption electrospray ionization (DESI) source was established to screen ligands with a high affinity for proteins with anion-binding sites. The complexes were analyzed after incubation, ultrafiltration, washing, and displacement. A new anionic region inhibited dissociation (ARID) mechanism that was suitable for a protein with anion-binding site was proposed. We utilized the differences in detectable dissociation of protein-ligand complexes, combined with displacement experiments, to distinguish free ligands displaced from anion-binding sites from liberated ligands dissociated from nonspecific interactions. The method was validated by α1-acid glycoprotein (AGP) and (R), (S)-amlodipine. Site-specific enantioselectivity shown in our experiments was consistent with earlier studies. Obtaining all of the qualitative information of 15*3 samples in 2.3 min indicates that the analysis process is no longer the time-limiting step in the initial stage of drug discovery. Quantitative information verified that our method was at least a semiquantitative method.

Amlodipine metabolism in human liver microsomes and roles of CYP3A4/5 in the dihydropyridine dehydrogenation

Amlodipine is a commonly prescribed calcium channel blocker for the treatment of hypertension and ischemic heart disease. The drug is slowly cleared in humans primarily via dehydrogenation of its dihydropyridine moiety to a pyridine derivative (M9). Results from clinical drug-drug interaction studies suggest that CYP3A4/5 mediate metabolism of amlodipine. However, attempts to identify a role of CYP3A5 in amlodipine metabolism in humans based on its pharmacokinetic differences between CYP3A5 expressers and nonexpressers failed. Objectives of this study were to determine the metabolite profile of amlodipine (a racemic mixture and S-isomer) in human liver microsomes (HLM), and to identify the cytochrome P450 (P450) enzyme(s) involved in the M9 formation. Liquid chromatography/mass spectrometry analysis showed that amlodipine was mainly converted to M9 in HLM incubation. M9 underwent further O-demethylation, O-dealkylation, and oxidative deamination to various pyridine derivatives. This observation is consistent with amlodipine metabolism in humans. Incubations of amlodipine with HLM in the presence of selective P450 inhibitors showed that both ketoconazole (an inhibitor of CYP3A4/5) and CYP3cide (an inhibitor of CYP3A4) completely blocked the M9 formation, whereas chemical inhibitors of other P450 enzymes had little effect. Furthermore, metabolism of amlodipine in expressed human P450 enzymes showed that only CYP3A4 had significant activity in amlodipine dehydrogenation. Metabolite profiles and P450 reaction phenotyping data of a racemic mixture and S-isomer of amlodipine were very similar. The results from this study suggest that CYP3A4, rather than CYP3A5, plays a key role in metabolic clearance of amlodipine in humans.

Development of a pharmacokinetic interaction model for co-administration of simvastatin and amlodipine

A model for drug interaction between amlodipine and simvastatin was developed using concentration data obtained from a multiple-dose study consisting of single- and co-administration of amlodipine and simvastatin conducted in healthy Koreans. Amlodipine concentrations were assumed to influence the clearance of simvastatin and simvastatin acid, which as well as the oral bioavailability was allowed to vary depending on genetic polymorphisms of metabolic enzymes. Covariate effects on drug concentrations were also considered. The developed model yielded a 46% increase in simvastatin bioavailability and a 13% decrease in simvastatin clearance when amlodipine 10 mg was co-administered. When CYP3A4/5 polymorphisms were assessed by a mixture model, extensive metabolizers yielded a decrease in simvastatin bioavailability of 81% and a decrease in simvastatin clearance by 4.6 times as compared to poor metabolizers. Sixty percent of the usual dose was the optimal simvastatin dose that can minimize the interaction with amlodipine 10 mg. Age and weight had significant effects on amlodipine concentrations. In conclusion, this study has quantitatively described the pharmacokinetic interaction between simvastatin and amlodipine using a modeling approach. Given that the two drugs are often prescribed together, the developed model is expected to contribute to more efficient and safer drug treatment when they are co-administered.

Simultaneous determination of losartan, losartan acid and amlodipine in human plasma by LC-MS/MS and its application to a human pharmacokinetic study

INTRODUCTION

A simple, rapid and sensitive liquid chromatography-tandem mass spectrometric assay method has been developed and fully validated for simultaneous quantification of losartan and its active metabolite, losartan carboxylic acid, and amlodipine in human plasma. Irbesartan was used as an internal standard.

MATERIALS AND METHODS

The analytes were extracted from human plasma samples by solid-phase extraction technique using Oasis HLB cartridges, (Waters Corporation, Mumbai, India). The reconstituted samples were chromatographed on a C18 column by using an 85:15, v/v mixture of methanol and 0.1% v/v formic acid as the mobile phase at a flow rate of 1.0 mL/min. A detailed validation of the method was performed as per the FDA guidelines.

RESULTS

The calibration curves obtained were linear (r ≥ 0.99) over the concentration range of 0.5-1000 ng/mL for losartan and for its active metabolite losartan acid and 0.05-10.1 ng/mL for amlodipine. The results of the intra- and inter-day precision and accuracy studies were well within the acceptable limits.

CONCLUSIONS

A run time of 2.5 min for each sample made it possible to analyze more than 300 plasma samples per day. The proposed method was found to be applicable to clinical studies.

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

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

Recent advances in metabolite identification and quantitative bioanalysis by LC–Q-TOF MS

The need for rapid, sensitive and effective identification and quantitation of drugs and metabolites to accelerate drug discovery and development has given MS its central position in drug metabolism and pharmacokinetic research. This review attempts to orient the readers with respect to hybrid Q-TOF MS, which enables accurate mass measurement and generates information-rich datasets. The key properties of the Q-TOF MS system, including mass accuracy, resolution, scan speed and dynamic range, are herein discussed. Developments on tandem separation techniques (e.g., UHPLC® and ion mobility spectrometry), data acquisition and data-mining methods (e.g., mass defect, product/neutral loss, isotope pattern filters and background subtraction) that facilitate qualitative and quantitative analysis are then examined. The performance and versatility of LC–Q-TOF MS are thoroughly illustrated by its applications in metabolite identification and quantitative bioanalysis. Future perspectives are also discussed.

Simultaneous determination of telmisartan and amlodipine in human plasma by LC-MS/MS and its application in a human pharmacokinetic study

A rapid and sensitive liquid chromatography–tandem mass spectrometric (LC–MS/MS) assay method has been developed and fully validated for the simultaneous quantification of telmisartan and amlodipine in human plasma. Carbamazepine was used as an internal standard. Analytes and the internal standard were extracted from human plasma by solid-phase extraction technique using Waters Oasis^® HLB 1 cm³ (30 mg) extraction cartridge. The reconstituted samples were chromatographed on a Hypurity advance C₁₈ column (50 mm×4.6 mm, 5 μm) using a mixture of acetonitrile–5 mM ammonium acetate buffer (pH-4.0) (50:50, v/v) as the mobile phase at a flow rate of 0.8 mL/min. The calibration curve obtained was linear (r≥0.99) over the concentration range of 2.01–400.06 ng/mL for telmisartan and 0.05–10.01 ng/mL for amlodipine. Method validation was performed as per FDA guidelines and the results met the acceptance criteria. A run time of 2.5 min for each sample made it possible to analyze more than 400 human plasma samples per day. The proposed method was found to be applicable to clinical studies.

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.

Potential role of the cardiovascular non-antibiotic (helper compound) amlodipine in the treatment of microbial infections: scope and hope for the future

The appearance of multiresistant bacterial strains coupled with the globally ongoing problem of infectious diseases point to the imperative need for novel and affordable antimicrobial drugs. The antibacterial potential of cardiovascular non-antibiotics such as amlodipine (AML), dobutamine, lacidipine, nifedipine and oxyfedrine has been reported previously. Of these drugs, AML proved to have the most significant antibacterial activity against Gram-positive and Gram-negative bacteria. Time-kill curve studies indicate that this Ca(2+) channel blocker exhibits bactericidal activity against Listeria monocytogenes and Staphylococcus aureus. AML could protect against murine listeriosis and salmonellosis at doses ranging within its maximum recommended human or non-toxic ex vivo dose. AML acts as a 'helper compound' in synergistic combination with streptomycin against several Gram-positive and Gram-negative bacterial strains in vitro as well as in the murine salmonellosis model in vivo. The present review focuses on the possible use of cardiovascular non-antibiotics such as AML as auxiliary compound targets for synergistic combinations in infections and hypertension conditions, rationalised on the basis of the activities of the compounds.