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Biomedical subjects

R Zelkó

Publications and source records attributed to R Zelkó.

At least 19 recordsLinked to original sources
PubMed2006

Metolose-PEG interaction as seen by positron annihilation spectroscopy.

The plasticizing effects of poly(ethylene glycol) (PEG 400) on methylcellulose (Metolose) cast films were studied by conventional physicochemical methods and positron annihilation spectroscopy. The PEG concentrations relative to the total polymer content were varied within the range 0-75% (w/w). At low concentrations (below 33.3%, w/w), the plasticizer was found to build in into the methylcellulose structure. On the other hand, at higher concentrations (above 50%, w/w), it formed small separate phases in the films. Positron annihilation spectroscopy (PALS) was applied to track the Metolose-PEG interaction. Controlled ageing of Metolose-PEG films at room temperature and at 75% RH revealed a significant difference between the ageing processes of the monophase and those of the separate phase films. The ageing involves two steps in both cases: a fast and a slow one. The PALS measurements demonstrated that the slow process is hindered in the phase-separated samples.

Elasticity↗
PubMed2006

Quantitative estimation of film forming polymer-plasticizer interactions by the Lorentz-Lorenz Law.

Molar refraction as well as refractive index has many uses. Beyond confirming the identity and purity of a compound, determination of molecular structure and molecular weight, molar refraction is also used in other estimation schemes, such as in critical properties, surface tension, solubility parameter, molecular polarizability, dipole moment, etc. In the present study molar refraction values of polymer dispersions were determined for the quantitative estimation of film forming polymer-plasticizer interactions. Information can be obtained concerning the extent of interaction between the polymer and the plasticizer from the calculation of molar refraction values of film forming polymer dispersions containing plasticizer.

Chemistry, Pharmaceutical↗
PubMed2005

Effect of beta-sitosterol concentration and high pressure homogenization on the chlorhexidine release from vesicular gels.

Previous studies have confirmed that the phase transition of vesicular gels of hydrogenated phospholipids to the less ordered fluid vesicular state was induced by the increase of the beta-sitosterol ratio in the whole gel system and consequently in the lipid bilayer. The purpose of the present study was to evaluate the influence of the beta-sitosterol portion in the lipid bilayer and the effect of high pressure homogenization on the structural characteristics of the prepared gel systems. In addition the influence of beta-sitosterol on the consequent chlorhexidine release from the obtained vesicles and liposomes was also examined. Lipid mixtures were prepared from different molar ratios of lecithin:sterol components (90:10-65:35 mol%). The obtained mixtures were hydrated with the aqueous solution of chlorhexidine digluconate in order to achieve a 30% (w/w) final concentration of the lipid mixtures and a 4% (w/w) concentration of the drug. One portion of the resultant multilamellar vesicles was homogenized by using high pressure. To characterize the homogenized and non-homogenized systems, transmission electron microscopy of the freeze-fractured samples and differential scanning calorimetry (DSC) were carried out. A vertical type diffusion cell was applied to determine the amount of released chlorhexidine digluconate. Along with the increase in beta-sitosterol concentration, the fluidity of the membrane as well as its permeability also increased. The increased permeability--caused by the higher beta-sitosterol concentration--and the high pressure homogenization, which increased the dispersity and therefore the surface area, enabled a higher amount of chlorhexidine to be released. The increase of drug release was more pronounced in the case of samples prepared with high pressure homogenization.

Anti-Infective Agents, Local↗
PubMed2004

Effect of beta-sitosterol on the characteristics of vesicular gels containing chlorhexidine.

Previous studies confirm that beta-sitosterol is very effective in altering the molecular packing of soybean lecithin bilayers even more than the cholesterol. The primary aim of the present study was to evaluate the influence of the beta-sitosterol portion in the lipid bilayer on the physical-chemical characteristics of the prepared gel systems, and its influence on the consequent drug release from the liposomes obtained from vesicular phospholipid gels (VPG-s) by redispersion. VPG-s were prepared of different molar ratios of lecithin:sterol components (10:90-35:65 mol%). The mixture was hydrated with the aqueous solution of chlorhexidin digluconate in order to achieve 30% (w/w) final concentration of the lipid mixtures and 4% (w/w) concentration of the drug in each homogenized VPG sample. To characterize the obtained VPG systems optical microscopic examinations using polarized light, differential scanning calorimetry (DSC), photon correlation spectroscopy (PCS), and dynamic surface tension measurements were carried out. Vertical type diffusion cell was applied to determine the amount of released chlorhexidine digluconate. As a result of the surface tension-decreasing effect of beta-sitosterol, the membrane deformability and the dispersity of the system increased. The increased dispersity and fluidity significantly increased the extent of released chlorhexidine from the vesicles.

Chlorhexidine↗
PubMed2004

Zinc sulphate release and morphology of matrices prepared for the individual therapy of Wilson's disease.

Hydrophobic zinc sulphate wax matrices with different drug loadings were prepared for the individual hospital therapy of Wilson's disease. The drug release parameters, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) of the samples were analysed. The release mechanisms from matrices of 75% and 80% w/w zinc sulphate loadings were described with good correlation by the semi-empirical Fikkian diffusion based release model. Besides the zinc sulphate diffusion through the pores of the wax matrices, the parallel diffusion of zinc sulphate from the matrix surface is dominant in the case of samples of 83% and 90%w/w drug loadings. The combination of SEM and EDS analysis visualizes the morphology of the matrices and the related composition thus explaining the differences in the release characteristics.

Algorithms↗
PubMed2004

Study of triethyl citrate migration from coating polymers to tablet cores.

Migration of plasticizers from film coating polymers towards the core and to the storage medium could result in serious changes in the mechanical properties and permeability of coatings thus greatly influencing rate and extent of drug release. The purpose of the present study was to follow the migration of water soluble triethyl citrate applied as a plasticizer in Acryl-Eze coating by Gas Chromatography/Mass Spectrometry (GC/MS). 20%w/w Acryl-Eze dispersions containing triethyl citrate of different concentrations were prepared. Placebo tablets were compressed and coated with the prepared dispersions. The coated tablets were stored under different relative humidity conditions for different time intervals. Considerable migration of triethyl citrate towards the tablet cores was found. The extent of the triethyl citrate migration was influenced by the relative humidity of the storage medium.

Citrates↗
PubMed2001

Influence of chlorhexidine species on the liquid crystalline structure of vehicle.

The aim of this study was to investigate the influence of three chlorhexidine species, chlorhexidine base and its salts (diacetate and digluconate), on the physico-chemical features of liquid crystalline systems and on drug transport through lipophilic membranes. Nonionic surfactant, Synperonic A7 (PEG(7)-C(13--15)) was selected for the preparation of the liquid crystalline systems. Mixtures of different ratios of Synperonic A7 and water were prepared. The liquid crystalline systems were characterized using polarizing microscopy, small-angle neutron scattering and transmission electron microscopy. Membrane transport was also examined. The addition of chlorhexidine species to the liquid crystalline system modified the structure of the liquid crystalline system. As a result of liquid crystal--drug interaction, the solubility of chlorhexidine base and its diffusion through lipophilic membranes increased in comparison with those of the chlorhexidine salts.

Chemical Phenomena↗
PubMed2001

[Analysis of antibiotic usage].

Economic analysis is founded on the assumption that resources are limited and that should be used in a way that maximizes the benefits gained. Pharmacoeconomics extends these assumptions to drug treatment. Therefore, a full pharmacoeconomic analysis must consider two or more alternative treatments and should be founded on measurement of incremental cost, incremental efficacy, and the value of successful outcome. Antibiotic policy based only on administrative restrictions is failed, instead of it disease formularies and infectologist consultation system are needed. Equally important are various programmes that encourage the cost-conscious use of the antibiotics chosen. Some of the methods evaluated in the literature include: streamlining from combination therapy to a single agent, early switching from parenteral to oral therapy, initiating treatment with oral agents, administering parenteral antibiotic at home from outset of therapy, and antibiotic streamlining programmes that are partnered with infectious disease physicians. The solution is the rational and adequate use of antibiotics, based on the modern theory and practice of antibiotic policy and infection control, that cannot be carried out without the activities of experts in this field.

Anti-Bacterial Agents↗
PubMed2000

The effect of liquid crystalline structure on chlorhexidine diacetate release.

The aim of this study was to examine different liquid crystalline preparations containing chlorhexidine diacetate and to find connection between their structure and the kinetic of drug release. Nonionic surfactant, Synperonic A7 (PEG(7)-C(13-15)) was selected for the preparation of the examined liquid crystalline systems. Mixtures of different ratios of Synperonic A7 and water were produced. By increasing the water content of the systems, lamellar and hexagonal liquid crystal structures were observed. For the analysis of the prepared liquid crystalline systems polarising microscopy, rheology study, differential scanning calorimetry and dynamic swelling tests were carried out. The chlorhexidine diacetate release was examined by Franz-type vertical diffusion cell apparatus. The chlorhexidine diacetate release from hexagonal liquid crystalline preparations was characterised by zero-order release kinetics, while the drug release from lamellar liquid crystalline systems was described by anomalous (non-Fickian) transport. The results indicate that the drug release kinetic is strongly dependent on the liquid crystalline structure.

Anti-Infective Agents, Local↗
PubMed2000

The effect of temperature and polymer concentration on dynamic surface tension and wetting ability of hydroxypropylmethylcellulose solutions.

The purpose of the present study was to evaluate quantitatively the changes of dynamic surface tension and contact angle of hydroxypropylmethylcellulose (HPMC) aqueous solutions as a function of temperature and polymer concentration of the examined solutions. HPMC aqueous solutions of different concentrations (1%, 2%, 3%, 4% w/w) were prepared without plasticizer and with 1% w/w Lutrol F127. Dynamic surface tension of the prepared solutions was determined by the Du Nouy ring method of the KSV Sigma 70 computer-controlled and programmable tensiometer. The dynamic contact angle of Avicel PH-101 tablets was measured against HPMC solutions of various concentrations by the plate method of the KSV Sigma 70 tensiometer. The obtained results indicate that dynamic surface tension measurement can be applied for the accurate determination of the thermal gelation temperature of the prepared HPMC solutions. With increasing concentration of HPMC, dynamic contact angle values of solutions also increased, thus decreasing the spreading behavior on the surface of Avicel tablets.

Anticholesteremic Agents↗
PubMed2000

Influence of drying temperature and granulation liquid viscosity on the inter- and intragranular drug migration in tray-dried granules and compacts.

The influence of the drying temperature and granulation liquid viscosity on the inter- and intragranular migration of a poorly water-soluble compound in a granulation mass and in a compact was quantitatively assessed. The intergranular migration kinetics were investigated by evaluating the drug distribution at different drying-time intervals. The results were analyzed by use of two-factor, three-level, face-centered, central composite designs. Riboflavin was mixed with alpha-lactose monohydrate 90 M and granulated with distilled water, except for the viscosity experiments in which an aqueous polyvinylpyrrolidone (PVP) (Kollidon K90) solution was used. The wet granules were dried in a hot-air oven or compacted prior to drying. The drug concentration at different locations inside the granulated mass and the compacts after drying was determined spectrophotometrically and by use of diffuse light reflectance measurements. The riboflavin distribution in the granulation masses and in the compacts was characterized by drug-enriched outer layers and drug-depleted inner regions, indicating a strong migration phenomenon. It was clear that the drying temperature had no influence on the inter- and intragranular drug distribution. The intergranular migration was avoided using the PVP as a binder in the granulation liquid, whereas a minimal granulation liquid viscosity of 100 mPa.sec was necessary to avoid the intragranular migration. The diffuse light reflectance measurements can be used for the in-process control of granule samples containing low drug concentrations without the destruction of the samples.

Hot Temperature↗
PubMed2000

Effect of the wettability characteristics of polyethylene glycol derivatives on the drug release of wax matrices.

The purpose of the present work was to study the relationship between the physicochemical characteristics of different polyethylene glycol aqueous solutions and the kinetics of potassium chloride release from wax matrix samples containing polyethylene glycol derivatives. Potassium chloride was embedded into thermosoftening matrix material to produce a sustained-release dosage form. Potassium chloride release was measured by the rotating paddle method of USP 23 and the dissolution process was characterized by a modified Nernst equation. Physicochemical characteristics--surface tension, dynamic contact angle, viscosity--of the polyethylene glycol aqueous solutions were also determined. The results indicate that the adhesion tension of surfactant containing aqueous solutions has a decisive impact on the prediction of the potassium chloride release rate from wax matrices.

Adhesiveness↗
PubMed1999

A comparison of the inter- and intragranular drug migration in tray- and freeze-dried granules and compacts.

The influence of the drying process (tray- or freeze-drying), the granulation liquid viscosity, and the drying time during tray-drying on the inter- and intragranular migration of both a water-soluble and a poorly water-soluble compound in a granulation mass and in a compact were quantitatively assessed. Quinidine bisulfate (QBS) and riboflavin (RB) were mixed with a model excipient (glass microspheres) and granulated with an aqueous povidone solution. The drug concentration at different locations inside the granulated mass and in the compacts after drying was determined spectrophotometrically. The RB distribution in the compacts was more homogeneous than the QBS distribution. For both drugs it was clear that the intragranular migration decreased as the granulation liquid viscosity increased. The RB distribution in oven-dried granulation masses showed no migration problem, whereas the QBS samples were characterized by drug-enriched outer layers and drug-depleted inner regions, indicating a strong migration phenomenon. The drug distribution in all freeze-dried samples was homogeneous. A homogeneous distribution of a small-dosed water-soluble and a water-insoluble drug in granules and in compacts was obtained by the use of freeze-drying. The intragranular migration of QBS was prevented by the use of twice the amount of binder compared to that in RB compacts.

Desiccation↗
PubMed1999

[Modification of drug release with application of pharmaceutical technological methods].

Pharmaceutical technological methods, which enable the development of controlled release, prolonged action solid oral dosage forms, are of great importance. The purpose of our study was to apply these methods and evaluate the prepared samples. The first type of the samples were individually coated separated particles, prepared by mixing with lubricant to built up a lubricant film layer on the surface of the drug crystals. The next group of the samples were separately coated particles--wall material was wax--prepared using the following two technologies: fluidisation atomisation process and hot-melt coating. The third group of the samples was the matrix type, where the core material was mixed into the molten mass of the thermosoftening natural coating material or into some synthetic polymer film material. In some cases several surface active agents were added to the molten mixture to achieve a modification in the drug release process and the examined parameters of the samples. For the comparative evaluation of the prepared dosage forms drug release determination and kinetical analysis of the process were maintainly used. The surface morphology was examined on the base of scanning electronmicroscopic and optical microscopic studies. Among the physical and physico-chemical studies particle size analysis was carried out and dynamic contact angles of the solid samples as well as the surface tension decreasing effect was measured to determine the modifying properties of surface active excipients. To sum up, our results demonstrate that the economical and environmentally acceptable melt coating technology was justified as applicable advantageously in a large number of cases for the development of controlled release devices of highly watersoluble drug, even the medical substance is an organic compound having adjustable thermostability.

Delayed-Action Preparations↗
PubMed1998

Effect of particle size and coating level on the diffuse reflectance of wax matrices.

The aim of this study was to examine the influence of particle size and extent of coating on the diffuse-reflectance spectra of wax matrices containing embedded potassium chloride. Near-infrared spectroscopy was used to analyse the diffuse-reflectance characteristics of the prepared multi-particulate matrices without destructive sample preparation. A 2-factor, 3-level face-centred central composite design was selected to construct a second-order polynomial model which described the effect of particle size and amount of coating on the intensity of the diffusely reflected light. A non-linear model was used to demonstrate the effect of the selected parameters on the intensity of the reflected light; good correlation was obtained between experimental and predicted results. The results indicated that the extent of coating and the particle size of the examined systems in the selected particle size-range modified the intensity of the reflected light. It can be concluded that near-infrared spectroscopy is a sensitive means of measuring not only the particle size of powders (substrates and their mixtures), but also that of coated multi-particulate systems.

Chemistry, Pharmaceutical↗
PubMed1998

Effect of polysorbates on drug release from wax matrices.

The purpose of this study was to investigate the effect of various types and amounts of polysorbates on potassium chloride release. Potassium chloride, which is a highly water-soluble model drug, was embedded into wax (containing surfactants) to produce a sustained-release dosage form. Various kinds of polysorbates were chosen as surfactants to control the dissolution profile. The release of the model drug was tested by rotating paddle method of USP 23 and the dissolution process was characterized by the Weibull distribution. The surface tension of the aqueous solutions of polysorbates was determined by a computer-controlled Sigma 70 tensiometer. The application of polysorbates in more than 2% concentration did not alter either the release rate of the embedded potassium chloride, or the surface tension values of the aqueous solutions. The results of this study allow the determination of the optimal concentration of polysorbates in the case of the potassium chloride release.

Administration, Oral↗