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Dynamic dialysis for the drug release evaluation from doxorubicin-gelatin nanoparticle conjugates
No full textThe drug release from doxorubicin (DXR)-gelatin nanoparticle conjugates was evaluated by means of a dynamic dialysis technique. The study was carried out in absence and in presence of a proteolytic enzyme (trypsin) able to degrade the carrier. In a preliminary study the apparent permeability constant (K-cv) of the drug through the dialysis bag was evaluated in several media. On the basis of this screening, a saline solution (NaCl 0.9%, w/v) resulted appropriate to carry out the dialysis study since, in this medium, the K-cv did not depend on the drug concentration in the donor solution. In absence of the enzyme only a little fraction (from 9 to 13%, w/w of the drug content) was released from nanoparticles. This fraction was considered as the evidence of the free drug fraction. After the addition of trypsin, the diffusion of a further drug fraction was observed. This fraction is probably due to a fraction of the DXR-peptide conjugates characterised by a molecular weight lower than membrane cut-off (3500 Da). (C) 1999 Elsevier Science B.V. All rights reserved
Influence of drug loading level on drug release and dynamic swelling of crosslinked gelatin microspheres
No full textThe effect of drug loading level both on dynamic swelling and drug releae was evaluated using crosslinked gelatin microspheres. Owing to water penetration the microsphere diameter went first to a maximum value, wich was not affected by the payload; the diameter gradually approached to an equilibrium swollen value, which was affected by drug loading level. Water absorption increases and drug diffusion decreases the microsphere diameter. Obviolusly, the diameter variation depends on the factor (water absorption and drug diffusion) predominating in the process. As the payload affected only the equilibrium swollen level it is reasonable to hypothesize that drug loading level has a greater effect on drug diffusion than on polymer relaxation. This rationale could explain the increase of the diffusion component of the drug release process as the payload increased
Selective coating of cylindrical matrices with a central hole. II. An interpretation of the release process
No full textA swellable perforated matrix was prepared and coated on one or more of its surfaces. Two drugs having different water solubility were chosen to load the matrix. To clarify the effect of the matrix swelling on the release process, the release rate was analysed according to the swelling area, i.e., the surface area from which the drugs could be released. According to the experimental release data, the drug solubility usually predominated at the beginning and the matrix swelling at the end of the release process. When the interior hole was the only uncoated surface, pseudo-zero order kinetics were obtained when the drug solubility allows the control of the drug release by the matrix swelling
The effect of the cross-linking time period upon the drug release and the dynamic swelling of gelatin microspheres
No full textThe cross-linking time period affected both the swelling and release processes of cross-linked gelatin microspheres. In the dynamic swelling procedure, the combination of both phenomena of microparticle swelling and drug diffusion produced at first the increase and then the decrease of the diameter of a loaded microsphere. The increase of the cross-linking time period produced the shift of the penetrant transport from anomalous to super-case II kinetics. This behaviour could justify the decrease of the diffusion component of the drug release as the cross-linking time period increased
General and cardiac toxicity of doxorubicin-loaded gelatin nanoparticles
No full textGeneral and cardiac toxicity of doxorubicin loaded gelatin nanoparticles cross-linked by glutaraldheyde were investigated in healthy rats. The rats were treated with free doxorubicin (DXR), unloaded nanoparticles (UNp), physical mixture of doxorubicin, and unloaded nanoparticles (DRX/UNp), and DXR-loaded nanoparticles (DXR-Np). Each group of animals received the same dose of DXR (3 mg/kg) via i.p. once a week. Both electrocardiogram (EGG) parameters and body weight were measured 24h before each administration. Rats treated with UNp behaved as controls. DXR/UNp provoked the same toxic effects as free DXR. On the contrary, DXR-Np resulted more toxic since significant variations of both the body weight and the ECG parameters were observed during the first week of treatment. In addition, the rats treated with DXR-Np died between the 3(rd) and the 5(th) day after the 2(nd) administration. These results demonstrate that, in these experimental conditions, the couplage of DXR to nanoparticles enhanced the cardiotoxicity of the drug. Since DXR was linked to the protein matrix of nanoparticles via glutaraldehyde, the high toxicity of DXR-loaded nanoparticles could be due to the covalent binding of the drug to the carrier
Dissolution and enzymatic hydrolysis of chloramphenicol palmitic and stearic esters
No full textThe dissolution rate of the polimorphs A and B of chloramphenicol palmitic and stearic esters, has been compared to the enzymatic hydrolysis rate by pancreatine in the same experimental conditions.The enzymatic hydrolysis rate does not depend on a normal process of dissolution and the assumption is made that the pancreatic enzyme acts at the solid-liquid interface on the film of molecules of the esters which are going into solution, thus favouring an "eased release" of the molecules from the crystal according to the conformational differences of the molecules themselves.As for polymorphs B, it has also been possible to note a good correlation between the in vitro data related to chloramphenicol release in enzymatic hydrolysis and the in vivo data concerning the absorption rate and the blood levels of the antibiotic after peroral administration of its esters
The influence of 2-hydroxypropyl-beta-cyclodextrin on the haemolysis induced by bile acids
No full textCyclodextrins improve the water-solubility of drugs and can mask their haemolytic effect in parenteral use. Because the mechanism by which bile acids induce haemolysis is poorly understood, it has been investigated in the presence of 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD). The haemolytic effect of 1.8 mM solutions of cholic acid, chenodeoxycholic acid (CDCA), deoxycholic acid and ursodeoxycholic acid (UDCA) in isotonic buffer at pH 7.4 was investigated at 37 degrees C in the presence of HP-beta-CyD at concentrations from 0.18 to 32 mM. No haemolytic effect was evident for cholic acid and UDCA. The haemolytic effect of the other bile acids was reduced by addition of HP-beta-CyD and was prevented at a molar ratio of 1:1 owing to complex formation. An HP-beta-CyD:bile acid molar ratio greater than 5:1 had a different effect on the erythrocyte membrane, irrespective of the identity of the bile acid; the effect was in accordance with the complexion affinities. In the absence of HP-beta-CyD, the haemolytic effect of CDCA and deoxycholic acid appeared related to their capacity to form a surface monolayer and to solubilize the components of the erythrocyte membrane. The haemolytic effect observed after complexation of the bile acids appeared to be solely the effect of HP-beta-CyD, which was able to form a reversible inclusion complex with lipophilic components of the erythrocyte membranes at concentrations higher than 12 mM
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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