Biomedical subjects

A Mrhar

Publications and source records attributed to A Mrhar.

40 records · Page 3Linked to original sources

PubMedDate not supplied

The influence of stirring rate on biopharmaceutical properties of Eudragit RS microspheres.

Eudragit RS microspheres containing pipemidic acid, as a model drug, were prepared by the solvent evaporation method using an acetone/liquid paraffin solvent system. The aim of the work was to evaluate the influence of stirring rate on the average particle size, particle morphology, drug content and release kinetics, as well as the influence of particle size on microsphere morphology, drug content and release kinetics. Stirring rate has been found to significantly influence the average diameter of microspheres. The average diameter decreases as the stirring rate increases. This can be explained by production of a finer dispersion of droplets when higher stirring rates are applied and, consequently, by the formation of smaller microspheres. With increasing stirring rate and increasing fraction particle size the drug content also increases. It is assumed that this dependence is a consequence of an uneven diffusion of the drug from the inner to the outer emulsion phase, and an uneven encapsulation of drug particles during the preparation. Drug release follows the Higuchi model. As seen from SEM photographs, larger microspheres are more porous and the microspheres produced at higher stirring rates are more porous than those produced at lower stirring rates. This explains the unexpected finding that the release rate increases as the fraction particle size and the stirring rate increase.

Acrylic Resins↗

PubMedDate not supplied

The influence of magnesium stearate on the characteristics of mucoadhesive microspheres.

Microspheres containing the mucoadhesive polymer chitosan hydrochloride, with matrix polymer Eudragit RS, pipemidic acid as a model drug and agglomeration preventing agent magnesium stearate were prepared by the solvent evaporation method. The amount of magnesium stearate was varied and the following methods were used for microsphere evaluation: sieve analysis, drug content and dissolution determination, scanning electron microscopy, x-ray diffractometry, DSC and FTIR spectroscopy. The results showed that average particle size decreased with increasing amount of magnesium stearate used for microsphere preparation. This is probably a consequence of stabilization of the emulsion droplets with magnesium stearate. Higher pipemidic acid content in the microspheres was observed in larger particle size fractions and when higher amounts of magnesium stearate were used. It was also found that these two parameters significantly influenced the dissolution rate. The important reason for the differences in drug content in microspheres of different particle sizes is the diffusion of pipemidic acid from the acetone droplets in liquid paraffin during the preparation procedure. The physical state of pipemidic acid changed from crystalline to mostly amorphous with its incorporation in microspheres, as shown by x-ray diffractometry and differential scanning calorimetry. No differences were observed in the physical state of pipemidic acid and in microsphere shape and surface between different size fractions of microspheres, prepared with different amounts of magnesium stearate. Additionally, no correlation between the physical state of the drug in different microspheres and their biopharmaceutical properties was found.

Acrylic Resins↗

PubMedDate not supplied

Eudragit E microspheres containing bacampicillin: preparation by solvent removal methods.

Eudragit E microspheres containing bacampicillin hydrochloride were prepared by solvent evaporation and solvent extraction methods. Three different systems of solvents were used: methyl acetate, acetone and methanol/liquid paraffin. The success of the procedures depended mostly on the lipophilicity of the solvent. The particle size of microspheres was determined by sieve analysis. The results showed that the average size of microspheres is influenced greatly by the type of solvent. Scanning electron microscopy was used for observation of the shape of microspheres. Microspheres prepared by the solvent evaporation method in systems with acetone and methyl acetate were all of a regular spherical shape. The surface of all other microspheres were folded. The influence of magnesium stearate content in microspheres was also studied in terms of different methods, solvents and processing conditions.

Acrylic Resins↗

PubMedDate not supplied

Formulation and evaluation of vinylpyrrolidone/vinylacetate copolymer microspheres with griseofulvin.

Regular spherical microspheres of 220-260 microns average size have been prepared from vinylpyrrolidone/vinylacetate copolymer using a solvent evaporation method. Griseofulvin has been incorporated into these microspheres and its physical characterization has been carried out by differential scanning calorimetry (DSC), X-ray diffractometry and X-ray photoelectron spectroscopy. An increase of solubility was observed only with the 1:3 drug/polymer microspheres and the comparison of the dissolution profiles of microspheres with pure griseofulvin resulted in an enhancing effect. Furthermore the release rate of griseofulvin, incorporated into the microspheres, was shown to be biphasic and dependent upon the penetration of water into the microspheres, hydration and dissolution of the polymer and finally dissolution of the drug.

Chemical Phenomena↗