Formulation and Evaluation of Isradipine Nanosuspension and Exploring its Role as a Potential Anticancer Drug by Computational Approach.

BACKGROUND: T-type calcium channels are aberrantly expressed in different human cancers and regulate cell cycle progression, proliferation, migration, and survival. FAK-1 can promote tumor protein degradation (p53) through ubiquitination, leading to cancer cell growth and proliferation. Similar findings are obtained regarding protease inhibitors' effect on cytokine-induced neutrophil activation that suppresses Granulocyte-macrophage colony-stimulatingfactor (GM-CSF) TNF-α-induced O2 release and adherence in human neutrophils without affecting phosphorylation of Extracellular signal-regulated kinase (ERK) and p38. Nanosuspensions are carrier-free, submicron colloidal dispersions, which consist of pure drugs and stabilizers. Incorporating drug loaded in nanosuspensions offer a great advantages of passive drug targeting with improved solubility, stability, and bioavailability, as well as lower systemic toxicity. OBJECTIVE: The present investigation objective was to establish a molecular association of Protease and Focal Adhesion Kinase 1 as cancer targets for isradipine, a calcium channel blocker (CCB). Furthermore, the study also aimed to formulate its optimized nanosuspension and how the physical, morphological, and dissolution properties of isradipine impact nanosuspension stability. METHODS: Five different molecular targets, namely Cysteine Proteases (Cathepsin B), Serine Proteases (Matriptase), Aspartate Proteases, Matrix Metalloproteases (MMP), and FAK-1 were obtained from RCSB-PDB, which has some potential associations with inhibition in cancer pathogenesis. Molecular interactions of these targets with CCB isradipine were identified and established by molecular simulation docking studies. Isradipine-loaded nanosuspension was prepared by precipitation technique by employing a 23 factorial design. PVP K-30, poloxamer 188, and sodium lauryl sulfate (SLS) were used as polymer, co-polymer, and surfactant, respectively. The nanosuspension particles were assessed for particle size, zeta potential, viscosity, polydispersity index (PDI), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), In-vitro drug release kinetics, and short-term stability study. RESULTS: Considerable interactions were found with Cysteine, Serine, Aspartate, Threonine, and Matrix metalloproteases with binding energies of -3.91, -6.7, -3.48, -8.42, respectively. Furthermore, the interaction of isradipine with FAK-1 was compared with 7 native ligands and was found to show significant interaction with binding energies of - 8.62, -7.27, -7.69, -5.67, -5.41, -7.44, -8.21, respectively. The optimized nanosuspension was evaluated and exhibited a particle size of 754.9 nm, zeta potential of 32.5 mV, viscosity of 1.287 cp, and PDI of 1.000. The In-vitro dissolution of the optimized formulation (F8) was found to be higher (96.57%) as compared to other formulations. CONCLUSION: Isradipine could act as a potential inhibitor of different proteases and FAK-1 associated with tumor growth initiation, progression, and metastasis. Furthermore, isradipine-loaded nanosuspension with optimized release could be utilized to deliver the anticancer drug in a more targeted way as emerging cancer nanotechnology.

Adaptation of Quality by Design-Based Development of Isradipine Nanostructured-Lipid Carrier and Its Evaluation for In Vitro Gut Permeation and In Vivo Solubilization Fate.

The present study demonstrated the systematic adaptation of quality by design-integrated approach for the development of novel nanostructured lipid carrier (NLC) of an anti-hypertensive drug isradipine (ISD) to address the inherent challenges such as low solubility and low oral bioavailability. Plackett-Burman design was used for preliminary screening of significant process and formulation variables (p <0.05), which were further processed using Box-Behnken design for the attainment of optimization goal that is, mean particle size (85.7 ± 7.3 nm), drug entrapment efficiency (87.4 ± 3.29%), and in vitro drug release characteristics (92.89 ± 5.47%). The optimized ISD-NLC formulation also demonstrated well-dispersed uniform-shaped particles (polydispersity index 0.207 ± 0.029), high gastrointestinal fluid stability (zeta potential -10.17 ± 0.59 mV), and higher in vitro gut permeation (21.69 ± 2.38 µg/cm2 of ISD-NLC as compared to 11.23 ± 1.74 µg/cm2 in ISD suspension). Furthermore, lipolysis studies were performed for the purpose of in vivo fate, and significantly higher drug content of ISD from ISD-NLC in aqueous phase was found (72.34 ± 4.62%) as compared to drug suspension (3.01 ± 0.91%). Relative bioavailability of ISD-NLC and ISD suspension was increased by 4.2-fold and 1.78-fold in the absence and presence of cycloheximide which is a lymphatic uptake inhibitor revealing lymphatic uptake of ISD-NLC in bioavailability improvement. Hence, systematic adaptation of quality by design integrated approach improved gut permeation and potential solubilizaton fate (dynamic lipolysis) of ISD-NLC, which further improved the lymphatic uptake and biodistribution of drug thereby promisingits in vivo prospect and clinical efficacy.

Role of Isradipine Loaded Solid Lipid Nanoparticles on the Pharmacodynamic Effect in Rats.

Isradipine (ID), is an antihypertensive drug, having low oral bioavailability (15-24%) due to poor aqueous solubility (0.01 mg/mL) and also hepatic first-pass metabolism. Among various approaches, Solid lipid nanoparticles (SLNs) were developed using stearic acid, glyceryl monostearate as lipid matrices for improving the oral bioavailability of ID. ID-SLNs were prepared by using hot homogenization followed by ultrasonication. The prepared SLNs were characterized for size, PDI, zeta potential (ZP), entrapment efficiency (EE) and drug content. In vitro release studies were performed in 0.1NHCl and pH 6.8 phosphate buffer of by open tube method. Physical stability of the SLNs was observed at refrigerated temperature and room temperature for 90 days. Further, pharmacodynamic study was conducted in wistar rats. SLNs prepared with GMS having size of 188.6±3.6 nm, PDI of 0.273±0.052, ZP of - 21.8±2.7 mV with 86.86±0.75% EE were optimized. Differential scanning calorimetric (DSC) study revealed that no interaction between drug and lipid. In vitro release studies showed that more cumulative release of ID in pH 6.8 phosphate buffer than in 0.1NHCl during 24 h. The lyophilized SLN formulation was used in knowing morphology of SLNs, and was found to have spherical shape with increased polydispersity by Scanning electron microscopy. Pharmacodynamic study of SLNs in fructose induced hypertensive rats showed a decrease in systolic blood pressure for 36 h, when compared to suspension, which showed a decrease in systolic blood pressure for only 2 h. Thus, the results conclusively demonstrated the role of SLNs for a significant enhancement in pharmacodynamic effect of ID.

Hydrophilic-hydrophobic polymer blend for modulation of crystalline changes and molecular interactions in solid dispersion.

This research study aimed to develop a new strategy for using a polymer blend in solid dispersion (SD) for dissolution enhancement of poorly water-soluble drugs. SDs with different blends of hydrophilic-hydrophobic polymers (zein/hydroxypropyl methylcellulose - zein/HPMC) were prepared using spray drying to modulate the drug crystal and polymer-drug interactions in SDs. Physicochemical characterizations, including power X-ray diffraction and Fourier transform infrared spectroscopy, were performed to elucidate the roles of the blends in SDs. Although hydrophobic polymers played a key role in changing the model drug from a crystal to an amorphous state, the dissolution rate was limited due to the wetting property. Fortunately, the hydrophilic-hydrophobic blend not only reduced the drug crystallinity but also resulted in a hydrogen bonding interaction between the drugs and the polymer for a dissolution rate improvement. This work may contribute to a new generation of solid dispersion using a blend of hydrophilic-hydrophobic polymers for an effective dissolution enhancement of poorly water-soluble drugs.

Practical Radiosynthesis and Preclinical Neuroimaging of [11C]isradipine, a Calcium Channel Antagonist.

In the interest of developing in vivo positron emission tomography (PET) probes for neuroimaging of calcium channels, we have prepared a carbon-11 isotopologue of a dihydropyridine Ca2+-channel antagonist, isradipine. Desmethyl isradipine (4-(benzo[c][1,2,5]oxadiazol-4-yl)-5-(isopropoxycarbonyl)-2,6-dimethyl-1,4-dihydropyridine -3-carboxylic acid) was reacted with [11C]CH3I in the presence of tetrabutylammonium hydroxide in DMF in an HPLC injector loop to produce the radiotracer in a good yield (6 ± 3% uncorrected radiochemical yield) and high specific activity (143 ± 90 GBq·µmol-1 at end-of-synthesis). PET imaging of normal rats revealed rapid brain uptake at baseline (0.37 ± 0.08% ID/cc (percent of injected dose per cubic centimeter) at peak, 15-60 s), which was followed by fast washout. After pretreatment with isradipine (2 mg·kg-1, i.p.), whole brain radioactivity uptake was diminished by 25%-40%. This preliminary study confirms that [11C]isradipine can be synthesized routinely for research studies and is brain penetrating. Further work on Ca2+-channel radiotracer development is planned.

Development of isradipine loaded self-nano emulsifying powders for improved oral delivery: in vitro and in vivo evaluation.

Isradipine (ISR) is a potent calcium channel blocker with low oral bioavailability due to low aqueous solubility, extensive first-pass metabolism and P-glycoprotein (P-gp)-mediated efflux transport. In the present investigation, an attempt was made to develop isradipine-loaded self-nano emulsifying powders (SNEP) for improved oral delivery. The liquid self-nano emulsifying formulations (L-SNEF/SNEF) of isradipine were developed using vehicles with highest drug solubility, i.e. Labrafil® M 2125 CS as oil phase, Capmul® MCM L8 and Cremophor® EL as surfactant/co-surfactant mixture. The developed formulations revealed desirable characteristics of self-emulsifying system such as nano-size globules ranging from 32.7 to 40.2 nm, rapid emulsification (around 60 s), thermodynamic stability and robustness to dilution. The optimized stable self-nano emulsifying formulation (SNEF2) was transformed into SNEP using Neusilin US2 (SNEP(N)) as adsorbent inert carrier, which exhibited similar characteristics of liquid SNEF. The solid state characterization of SNEP(N) by Fourier transform infrared spectroscopy, differential scanning calorimetry, powder X-ray diffraction and scanning electron microscopic studies shown transformation of crystalline drug into amorphous form or molecular state without any chemical interaction. The in vitro dissolution of SNEP(N) compared to pure drug was indicated by 18-fold increased drug release within 5 min. In vivo pharmacokinetic studies in Wistar rats showed significant improvement of oral bioavailability of isradipine from SNEP(N) with 3- and 2.5-fold increments in peak drug concentration (C(max)), area under curve (AUC(0-∞)) compared to pure isradipine. In conclusion, these results signify the improved oral delivery of isradipine from developed SNEP.

Amorphous isradipine nanosuspension by the sonoprecipitation method.

The aims of this study are to increase and explain the mechanism of dissolution enhancement of isradipine using the sonoprecipitation method for stable nanosuspensions. There have been still few of published researches on formulation of isradipine using nanoparticle engineering. Nanosuspension systems were prepared upon various factors including amplitude and the time length of ultrasonication. The dissolution test was performed according to the USP paddle method in intestinal fluid (pH 6.8). The crystalline structure of drug, the molecular interaction, morphology and size of nanosuspension were also investigated to determine the mechanism of dissolution enhancement. The sonoprecipitation method with use of HPMC 6 showed its potential in enhancement of the drug release rate. Stable nanosuspension was significantly depended on amplitude and time of ultrasonication since these factors affected on the size of nanoparticles. The synergistic effects of reduction of drug crystallinity and particle size could increase the dissolution rate of isradipine by providing a stable nanosuspension. This work may contribute to a new strategy for improvement dissolution rate of isradipine.

Physical properties and in vivo bioavailability in human volunteers of isradipine using controlled release matrix tablet containing self-emulsifying solid dispersion.

Poorly water-soluble drug with a short half-life such as isradipine (IDP) offer challenges in the controlled release formulation because of low dissolution rate and poor bioavailability. Self-emulsifying solid dispersions (SESD) of IDP consisted of surfactant and fatty acid in poloxamer 407 (POX 407) as a carrier and were manufactured by the melting method. Then, controlled release HPMC matrix tablet containing SESD were prepared via direct compression. The dissolution behaviors and in vivo bioavailability of controlled release matrix tablet in healthy human volunteers were investigated. The physical properties of solid dispersion were also examined using differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). It was shown that structure of IDP was amorphous in the solid dispersion. The dissolution rate of IDP from SESD was markedly enhanced because of increased solubility and wetting effect. Controlled release HPMC matrix tablets containing SESD released drug in a controlled manner and were stable during storage over 3 months at 40 °C/75% RH. Furthermore, the tablet containing 5mg IDP SESD showed significantly increased oral bioavailability and extended plasma concentration compared with the marketed 5 mg Dynacirc(®) capsule. A combined method of solid dispersion and controlled release technology could provide versatile dosage formulations containing IDP with poor water solubility and short half-life.

Effect of hydrophilic polymers on isradipine complexation with hydroxypropyl ß-cyclodextrin.

Complexation of isradipine with hydroxypropyl ß-cyclodextrin (HPßCD) in the presence and absence of 3 hydrophilic polymers-polyvinyl pyrrolidone (PVP), hydroxypropyl methylcellulose (HPMC), and polyethylene glycol (PEG)-was investigated with an objective of evaluating the effect of hydrophilic polymers on the complexation and solubilizing efficiencies of HPßCD and on the dissolution rate of isradipine from the HPßCD complexes. The phase solubility studies indicated the formation of isradipine-HPßCD inclusion complexes at a 1:1M ratio in solution in both the presence and the absence of hydrophilic polymers. The complexes formed were quite stable. Addition of hydrophilic polymers markedly improved the complexation and solubilizing efficiencies of HPßCD. Solid inclusion complexes of isradipine-HPßCD were prepared in 1:1 and 1:2 ratios by the kneading method, with and without the addition of hydrophilic polymers. The solubility and dissolution rate of isradipine were significantly improved by complexation with HPßCD. The isradipine-HPßCD (1:2) inclusion complex yielded a 9.66-fold increase in the dissolution rate of isradipine. The addition of hydrophilic polymers also markedly improved the dissolution rate of isradipine from HPßCD complexes: a 11.72-, 17.01-, and 39.23-fold increase was observed with PVP, PEG, and HPMC respectively. X-ray diffractometry and differential scanning calorimetry indicated stronger drug amorphization and entrapment in HPßCD because of the combined action of HPßCD and the hydrophilic polymers.

Design porosity osmotic tablet for delivering low and pH-dependent soluble drug using an artificial neural network.

In this paper formulation of porosity osmotic tablet containing isradipine (model drug) as a low and pH dependent solubility was optimized based on the simultaneous optimization technique in which an artificial neural network (ANN) was incorporated. Nonlinear relationships between the causal factors and the response variables were represented well with the response surface predicted by ANN. Three causal factors, i.e., drug, osmotic pressure promoting agent rate (Lactose: Fructose), PEG400 content in coating solution and coating weight, were evaluated based on their effects on drug release rate. In vitro dissolution profile time profiles at four different sampling times (1, 12, 20 and 24h) were chosen as output variables. Commercially available STATISTICA 7 (Stat soft, USA) was used throughout the study. The optimize values for the factors X1-X3 were 1.25:0.75, 22% and 2.5% respectively. Calculated difference (f1 = 11.19) and similarity (f2 = 70.07) factors indicate that there is no difference between predicted and experimental observed drug release profile. Artificial neural network technique can be particularly suitable in the pharmaceutical technology of controlled release dosage forms where systems are complex and nonlinear relationships between independent and dependent variables often exist.

Capillary electrophoresis method for the determination of isradipine enantiomers: stability studies and pharmaceutical formulation analysis.

A simple enantioselective method based on CE using CD as chiral selector was developed and validated for the determination of isradipine (IRD) enantiomers in a pharmaceutical formulation and for the determination of IRD enantiomers in degradation studies. After optimization, the best results were obtained using 15 mM borate buffer at pH 9.3 and sulfobutyl ether-ß-cyclodextrin (2.5%, w/v) as chiral selector. The applied voltage was +30 kV, and the sample injection was performed in the hydrodynamic mode. All analyses were carried out in a fused-silica uncoated capillary with an id of 50 µm and total length of 60.0 cm. Under these conditions, a complete separation between IRD enantiomers was achieved in less than 7 min. Linearity was obtained in the range 50-300 µg/mL for both enantiomers (r≥0.9978). The RSD (%) and relative errors (%) obtained in precision and accuracy studies (intra-day and inter-day) were lower than 5%. Therefore, this method was found to be appropriate for controlling pharmaceutical formulations containing IRD enantiomers and the assay was considered to be stability indicating. The drug was subjected to oxidation, hydrolysis and photolysis. In all stress conditions the drug presented considerable degradation when compared with a fresh sample (zero time).

Hollow fiber-based liquid-phase microextraction (HF-LPME) of isradipine and its main metabolite followed by chiral HPLC analysis: application to an in vitro biotransformation study.

An enantioselective liquid chromatographic method using two-phase hollow fiber liquid-phase microextraction (HF-LPME-HPLC) was developed for the determination of isradipine (ISR) enantiomers and its main metabolite (pyridine derivative of isradipine, PDI) in microsomal fractions isolated from rat liver. The analytes were extracted from 1 mL of microsomal medium using a two-phase HF-LPME procedure with hexyl acetate as the acceptor phase, 30 min of extraction, and sample agitation at 1,500 rpm. For the first time, ISR enantiomers and PDI were resolved. For this separation, a Chiralpak(®) AD column with hexane/2-propanol/ethanol (94:04:02, v/v/v) as the mobile phase at a flow rate of 1.5 mL min(-1) was used. The column was kept at 23 ± 2 °C. The drug and metabolite detection was performed at 325 nm and the internal standard oxybutynin was detected at 225 nm. The recoveries were 23% for PDI and 19% for each ISR enantiomer. The method presented quantification limits (LOQ) of 50 ng mL(-1) and was linear over the concentration range of 50-5,000 and 50-2,500 ng mL(-1) for PDI and each ISR enantiomer, respectively. The validated method was employed to an in vitro biotransformation study of ISR using rat liver microsomal fraction showing that (+)-(S)-ISR is preferentially biotransformed.

Evaluation of the tablet core factors influencing the release kinetics and the loadability of push-pull osmotic systems.

Push-pull osmotic systems have been developed to deliver poorly soluble drugs in a modified-release fashion. The aim of this study was to investigate the influence of the tablet core factors on the drug release kinetics and loadability. The release kinetics was efficiently modulated by varying either the proportion of osmotic agent or the drug layer polymer grade as an alternative to change the membrane characteristics. High osmotic agent proportions and viscous-grade polymers were recommended to formulate high drug loads up to 20% without losing both the release completeness and the zero-order drug release kinetics.

Benchtop-magnetic resonance imaging (BT-MRI) characterization of push-pull osmotic controlled release systems.

The mechanism of drug release from push-pull osmotic systems (PPOS) has been investigated by Magnetic Resonance Imaging (MRI) using a new benchtop apparatus. The signal intensity profiles of both PPOS layers were monitored non-invasively over time to characterize the hydration and swelling kinetics. The drug release performance was well-correlated to the hydration kinetics. The results show that (i) hydration and swelling critically depend on the tablet core composition, (ii) high osmotic pressure developed by the push layer may lead to bypassing the drug layer and incomplete drug release and (iii) the hydration of both the drug and the push layers needs to be properly balanced to efficiently deliver the drug. MRI is therefore a powerful tool to get insights on the drug delivery mechanism of push-pull osmotic systems, which enable a more efficient optimization of such formulations.

Proliferation of cultured human gingival fibroblasts caused by isradipine, a dihydropyridine-derivative calcium antagonist.

As it was reported earlier that isradipine, a Ca superset 2+ antagonist of dihydropyridine derivative class, caused regression of nifedipine-induced hyperplasia of human gingiva, experiments were performed to examine whether or not isradipine would solely inhibit the proliferation of cultured gingival fibroblasts. Normal human gingival fibroblast Gin-1 cells were used to test the impact of this medication. Fibroblast proliferation in the presence of isradipine (10 microM) was examined by using the reagent water-soluble tetrazolium-1 (WST-1). The level of basic fibroblast growth factor (bFGF) in the cell-free supernatant of each well was determined by using an enzyme-linked immunosorvent assay (ELISA) kit. The production of type I collagen was assayed by ELISA. Isradipine significantly enhanced the cell proliferation from the second day of the culture period. Also, isradipine raised the level of bFGF in the culture medium. The same concentration, also significantly enhanced the production of type I collagen. In conclusion, we were able to prove that isradipine causes the proliferation of cultured gingival fibroblasts as well as other dihydropyridine-derivative Ca superset 2+ antagonists do. In order to prevent the gingival overgrowth, it is advisable to be very careful in the use of isradipine as a therapy for hypertension and other indications.

Voltage-dependent acceleration of Ca(v)1.2 channel current decay by (+)- and (-)-isradipine.

Inhibition of Ca(v)1.2 by antagonist 1,4 dihydropyridines (DHPs) is associated with a drug-induced acceleration of the calcium (Ca(2+)) channel current decay. This feature is contradictorily interpreted as open channel block or as drug-induced inactivation. To elucidate the underlying molecular mechanism we investigated the effects of (+)- and (-)-isradipine on Ca(v)1.2 inactivation gating at different membrane potentials. alpha(1)1.2 Constructs were expressed together with alpha(2)-delta- and beta(1a)- subunits in Xenopus oocytes and drug-induced changes in barium current (I(Ba)) kinetics analysed with the two microelectrode voltage clamp technique. To study isradipine effects on I(Ba) decay without contamination by intrinsic inactivation we expressed a mutant (V1504A) lacking fast voltage-dependent inactivation. At a subthreshold potential of -30 mV a 200-times higher concentration of (-)-isradipine was required to induce a comparable amount of inactivation as by (+)-isradipine. At +20 mV the two enantiomers were equally efficient in accelerating the I(Ba) decay. Faster recovery from (-)- than from (+)-isradipine-induced inactivation at -80 mV in a Ca(v)1.2 construct (tau((-)-isr.(Cav1.2))=0.74 s

Redox properties of isradipine and its electrochemical detection in the HPLC determination of the compound in human serum.

The electrochemical behaviour of isradipine in a mixed solution of Britton-Robinson buffer (pH 11.8):acetonitrile:methanol (6:3:1, v/v) was studied by cyclic voltammetry and spectroelectrochemistry using an optically transparent thin layer electrode of carbon cloth. The cyclic voltammogram showed several peaks whose shape and potentials depended on the pH. The peak at 330 nm, corresponding to the absorbance of the dihydropyridine ring, disappeared after electrolysis at a potential that was more positive than the oxidation peak. The oxidation peak corresponds to the oxidation of the dihydropyridine ring. Peak height at pH 11.8 was proportional to isradipine concentration. On the basis of the redox properties of isradipine, HPLC was conducted applying electrochemical detection on a polybutadiene coated alumina column using an alkaline mobile phase. The method was applied for the determination of isradipine content in human serum. A good linear relationship between isradipine concentration and peak height was found in the concentration range of 2-200 ng/mL with a correlation coefficient of 0.9924. The detection limit was 0.5 ng/mL. The within-day and day-to-day variation were examined for control human serum and percentage relative standard deviation ranged from 0.5 to 6.7. Interference from many other coadministered drugs was studied in the specified experimental conditions. Photo and heat stabilities of the compound were also studied.

Dihydropyridine enantiomers block recombinant L-type Ca2+ channels by two different mechanisms.

1. The molecular basis of the state-dependent block of L-type Ca2+ channels by dihydropyridines is still poorly understood. Therefore, we studied the enantioselectivity of Ca2+ channel block by isradipine enantiomers at three holding potentials (-80, -60 and -40 mV) in Chinese hamster ovary (CHO) cells stably expressing the rabbit lung alpha1C-b-subunit. 2. The extent of enantioselectivity did not markedly change with the holding potential (IC50 ratios of 104-138), whereas the potency of both isradipine enantiomers increased with depolarisation of the holding potential. 3. In addition to its block of the peak Ca2+ channel current, Ipeak, (-)-isradipine inhibited the relative current at the end of the test pulse, the so-called Ilate, normalised to Ipeak (Ilate/Ipeak). This effect was unaffected by the holding potential and revealed distinct kinetics compared to the development of conventional block of Ipeak. 4. When these effects were studied using an alpha1C-b-mutant lacking the high-affinity dihydropyridine binding site, expressed in human embryonic kidney (HEK 293) cells, both enantiomers blocked Ilate/Ipeak to a similar degree. 5. Our data are discussed within the framework of the 'guarded receptor' and the 'modulated receptor' hypotheses. The very different properties of the block of Ilate/Ipeak compared to those of the conventional high-affinity block of Ipeak suggest the existence of an additional mechanism possibly mediated via a second, distinct binding site.

Photodegradation of inclusion complexes of isradipine with methyl-beta-cyclodextrin.

The paper presents results of the studies on photochemical decomposition of isradipine (IS) and its liquid inclusion complexes with methyl-beta-cyclodextrin (M-betaCD). The process of photodegradation was assessed by the methods of UV spectrophotometry, HPLC (reverse-phase) and HPTLC (normal phase) chromatographic methods. The process of photodegradation of IS was analysed in the conditions of version I of the document of International Chemical Harmonization (ICH)-HBO-200 lamp. Quantitative evaluation of the photochemical decomposition was performed on the basis of the calculated photodegradation rate constant (k), half-life period (t0.5) and time of degradation of 10% of the compound (t0.1). Formation of inclusion complexes of IS with M-betaCD was proved to increase twice the photostability of the drug. The analytical methods used were subjected to a validation procedure in which the limits of detectability and determinability as well as specificity, precision and sensitivity of the method were determined.

Determination of degradation products from the calcium-channel blocker isradipine.

Mass Spectrometry has been used to determine the identity of a number of degradation products from the bulk drug form of Isradipine (DynaCirc). Liquid chromatography coupled with mass spectrometry (LC/MS) was used to analyze the degraded samples and tentative identifications were made based upon the known reactivity of the molecule, molecular weight measurements and mass spectral fragmentation patterns. Isradipine was found to be stable to heating, acidic and basic conditions, but susceptible to degradation from exposure to UV light and oxidative processes.