PubMed · 4512817
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I Cuhadaroğlu. 1972. [A new method for constructing an acrylic bridge].. https://pubmed.ncbi.nlm.nih.gov/4512817/
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Stomach-specific drug delivery systems would be of value in treating diseases of the upper gastrointestinal tract. The present study measured in vitro and in vivo drug release from pH-sensitive membrane bags, constructed of poly(acrylic acid) grafted onto a poly(vinylidene fluoride) (PAA-PVDF) membrane, which might be suitable for stomach-specific drug delivery. The used model drugs were propranolol-HCl (1.0 mg) and FITC-dextran MW 4400 (1.0 mg). Drug release in vivo was studied by inserting membrane bags into the stomach and proximal duodenum of anesthetized rats and dogs. At 30 and 180 min, the bags were removed from the lumens and residual drug content was determined. The release of either propranolol or FITC-dextran were comparable in both stomach and duodenum, showing that in vivo drug release did not depend on environmental pH. In vitro results suggested that these results could be explained by interactions between PAA and the mucous layers of the stomach and duodenum.
The purpose of the present study was to generate mucoadhesive matrix-tablets based on thiolated polymers. Mediated by a carbodiimide, L-cysteine was thereby covalently linked to polycarbophil (PCP) and sodium carboxymethylcellulose (CMC). The resulting thiolated polymers displayed 100+/-8 and 1280+/-84 micromol thiol groups per gram, respectively (means+/-S.D.; n=6-8). In aqueous solutions these modified polymers were capable of forming inter- and/or intramolecular disulfide bonds. The velocity of this process augmented with increase of the polymer- and decrease of the proton-concentration. The oxidation proceeded more rapidly within thiolated PCP than within thiolated CMC. Due to the formation of disulfide bonds within thiol-containing polymers, the stability of matrix-tablets based on such polymers could be strongly improved. Whereas tablets based on the corresponding unmodified polymer disintegrated within 2 h, the swollen carrier matrix of thiolated CMC and PCP remained stable for 6.2 h (mean, n=4) and more than 48 h, respectively. Release studies of the model drug rifampicin demonstrated that a controlled release can be provided by thiolated polymer tablets. The combination of high stability, controlled drug release and mucoadhesive properties renders matrix-tablets based on thiolated polymers useful as novel drug delivery systems.
Eudragit RS/RL polymers were used to prepare microcapsules containing terbutaline-loaded ion-exchange resins, with the final aim of formulating this anti-asthmatic drug in a controlled-release liquid form. Oil-in-oil (o/o) and oil-in-water (o/w) solvent evaporation procedures were conveniently modified in order to encapsulate the resin cores. The microcapsules were then suspended in a hydroxypropylmethylcellulose solution of adequate viscosity and palatability, and stored at 20 degrees C and ambient humidity conditions for a 6-month period. Stability studies of the dispersed microparticles were performed in order to evaluate the changes occurred in the diffusion of the drug to the suspending medium and in the dissolution behaviour during storage. The morphological alterations of the stored microcapsules were followed throughout the duration of the study by scanning electron microscopy. The polymer coatings of microcapsules prepared by the o/o method broke up on the first day of storage, while those made by the aqueous procedure remained intact during all the storage period. This agreed with the modification observed in the controlled-release profiles of terbutaline in the case of microcapsules prepared by the o/o method, which completely changed after the first week of storage. On the contrary, the microcapsules prepared by the aqueous method showed identical controlled-release profiles for all the stability study. The different behaviour of both types of microcapsules was attributed to the swelling suffered by the resin particles in contact with the aqueous suspending medium, which was higher in the microcapsules prepared by the o/o technique. In fact, in the anhydrous procedure, the microencapsulation was carried out on the shrunken resin particles, whereas in the o/w method, the presence of water during the microencapsulation process allowed the coating of the swollen particles, thus avoiding the further problem of rupture of the polymer coating.