1,720,968 research outputs found
Preparation and in vitro evaluation of chitosan matrices for the colonic controlled release of proteins
No full textMatrices for colonic controlled release of the model protein drug bovine serum albumin (BSA) were prepared by direct compression of chitosan (CH) or chitosan hydrochloride (CHHCl) microspheres containing 4% BSA, without the aid of any other ingredient. The matrices (6 mm diameter, 50 mg weight each) are destined to be filled into enteric coated size 00 capsules and thereby conveyed to the proximal colon. Protein release was studied in vitro using pH 7.4 buffer as the elution medium. Release from microspheres was exceedingly fast, whereas the matrices were able to control release over prolonged periods. In the elution medium both the CH- and the CHHCl-based matrices swelled without disintegrating. The latter matrix type swelled to a much higher degree. Protein release from matrices was diffusion-controlled and independent of external medium hydrodynamics. The time for release of 50 % dose was much shorter for the CHHCl-based than for the CH-based matrix (0.9 vs. 12.0 h), so the latter is more suitable as a controlled-release system for proteins
Evaluation of the solution impregnation method for loading drugs into suspension-type polymer matrices: a study of factors determining the patterns of solid drug distribution in matrix and drug release from matrix
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A novel polyelectrolyte complex (PEC) hydrogel for controlled drug delivery to the distal intestine
No full textThis work was aimed at preparing and evaluating a physically crosslinked hydrogel for the controlled release of
diverse drugs to the distal intestine. A solution of fluorescein isothiocyanate dextran, MW 4400 Da (FD4), or a dispersion
of micronized dexamethasone (DMS) was microencapsulated into a PEC hydrogel, composed of polycationic N-trimethyl
chitosan (TMC) and polyanionic N-carboxymethyl chitosan (CMCh). A fine spray of a 1% CMCh solution containing 1%
FD4 in solution or 0.1% DMS in dispersion was directed into a 2% TMC solution, then the resulting microcapsules
(MCPS) were lyophilized. MCPS were analyzed by SEM and solid-state NMR. Drug release from MCPS was too fast, so
these were compressed into matrices (weight 20 mg; diameter 6 mm; drug load 2.5%, with FD4, or 3.7%, with DMS)
which were enteric coated. Drug release from matrices was studied simulating matrix transit across GI environments of
different pHs, from stomach to proximal colon. The enteric film hindered release in stomach and proximal small intestine.
After film dissolution at ileum pH, release occurred with a pattern described by the Peppas equation (n=0.6, with DMS;
n=0.7, with FD4). As the pH changed from 7.4 to 6 (from ileum to ascending colon) MCPS were liberated from matrix
surface. This phenomenon sustained the release rate. The present MCPS allow controlled doses of macromolecular or microparticulate
drugs being uniformly loaded into controlled-release matrices based on a physically crosslinked, biodegradable
hydrogel
Matrices for site-specific controlled-delivery of 5-fluorouracil to descending colon
No full textColon-specific controlled-delivery 5-fluorouracil (5-FU) matrices for the treatment of colorectal carcinoma were prepared and evaluated. Matrices are destined to be introduced into enteric-coated capsules and thereby carried to and liberated in the ileum. There, drug release should be prevented until matrices reach descending colon where release should occur. Matrices (50 mg, diameter 0.6 mm) were prepared by compression of powders or of granules prepared by melt granulation. The ingredients comprised 30-70% w/w 5-FU, glyceryl palmitostearate as rate-controlling material and 5% w/w Aerosil as glidant. Drug release was measured by the rotating basket method. The matrix containing 60% w/w drug, prepared by compression of powders, was appropriate to make the planned system, in virtue of its fairly high drug load and its nearly constant and reasonable release rate. This matrix was spray-coated with Eudragit S100 (EUD). Subsequently, an external layer of chitosan hydrochloride (CH-HCl) was applied by a dipping-drying technique. When transit of coated matrix through ileum (phosphate buffer (PB) pH 7.4), ascending colon (PB pH 6 containing rat cecal contents) and descending colon (PB pH 7.4) was simulated in vitro, the pH 4.7 of the CH-HCl gel layer and the pH 6 of the ascending colon prevented dissolution of the protective EUD film until descending colon was reached, then controlled release started. The present small matrices can enter size no. 00 capsules. Considering that each capsule contains 10 matrices, the maximal dose is 300 mg
Methyl-DEAE-dextran: a candidate biomaterial
No full textThe full quaternisation of DEAE-dextran was successfully attempted and an application of the quaternised product was suggested. Commercial DEAE-dextran was reacted with iodomethane at 60°C in the presence of NaOH. The raw product was purified by dialysis, during which the iodide ion was replaced by chloride. N-methylation and O-methylation resulted from the 1H NMR spectrum. A second methylation step produced no further changes in the molecule. Alkalimetry indicated the absence of amino groups in the methylated polymer molecule, thus testifying to a complete quaternisation. N-acetylcysteine (AcCy) was neutralised with the polymer in the hydroxide form, thus obtaining the methyl DEAE-dextran salt of AcCy (Me-DEAE-dextran/AcCy), whereby an ophthalmic formulation for the treatment of the Dry Eye Syndrome was prepared. For comparison, the neutral AcCy salt of commercial DEAE-dextran (DEAE-dextran/AcCy) was prepared. The AcCy content in Me-DEAE-dextran/AcCy was higher than in DEAE-dextran/AcCy (23 vs 13%), while the viscosity of a solution containing the salt concentration corresponding to the therapeutic AcCy concentration (4% w/v) was lower with the former compared to the latter salt (20.5 vs 23.9 mPa s). Both solutions were ipotonic (245 mOsm/kg) and nonirritant in rabbit eyes, whereas the commercial Tirocular is strongly hypertonic (900 mOsm/kg) and irritant
Polyoxyethylene-poly(methacrylic acid-co-methyl methacrylate)compounds for site-specific peroral delivery
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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