Evaluation of Tableted Microspheres of Dipyridamole

Sustained release properties of alginate microspheres and tabletted microspheres of diclofenac sodium

This study focused on the properties of diclofenac sodium (DNa) alginate (alg) microspheres and tabletted DNa alg microspheres using different polymers as additives. DNa alginate microspheres were prepared by the emulsification method and different polymers such as Eudragit (Eud) NE 30 D, Eudragit (Eud) RS 30 D and Aquacoat, which were incorporated into alg gel to control the release rate of drug. The release properties of DNa alg microspheres (1:1) were affected by the size, drug load of microspheres and also by the incorporated polymers, pH and ionic strength of dissolution medium. Tabletting of alg microspheres using carrageenan (carr), alg, pectin, NaCMC, tragacanth (trgh) and HPMC as additives in a (50:50) ratio produced tablets with good physical properties and also better controlled release of DNa. Dissolution studies were carried out in pH 7.2 phosphate buffer and phosphate buffers whose pH values were gradually changed from pH 3 to 7.4. The rank order of DNa release from tablets was carr < alg < pectin < NaCMC < trgh < HPMC which relates to the viscosity and swelling properties of polymers. The drug release was very slow from trgh and HPMC based tablets, but addition of carr or alg in different ratios could adjust the release rate of drug.

Mechanisms by which cyclodextrins modify drug release from polymeric drug delivery systems

For many drug candidates a modified in vivo drug release is desired to improve efficacy, sustain effect or minimise toxicity. Polymeric delivery systems, such as microspheres, nanospheres and polymeric films, have been extensively researched in an attempt to achieve modified drug release. Cyclodextrins offer an alternative approach. These cyclic oligosaccharides have the ability to form non-covalent complexes with a number of drugs and in so doing alter their physicochemical properties. In addition, the primary and secondary hydroxyl groups of the native (alpha, beta, gamma-) cyclodextrins are potential sites for chemical modification. It follows that the incorporation of these agents into polymeric drug delivery systems, as physical mixtures, covalently bound conjugates or cross-linking agents, frequently permits a greater degree of control of drug release. This paper reviews the incorporation of various cyclodextrins into polymeric formulations. The mechanisms by which cyclodextrin/polymer formulations act to modify drug release are considered.

Polymers for sustained release formulations of dipyridamole-alginate microspheres and tabletted microspheres

The preparation of dipyridamole (DIP) alginate (alg) microspheres by different methods or the incorporation of tragacanth (trgh), pectin or Eudragit L-100 55 (Eud) in alg microsphere formulations did not provide a prolonged release of DIP at pH 1.2. Tabletted microsphere formulations containing alg, trgh, pectin, sodium carboxymethyl cellulose (CMC), sodium starch glycolate (SSG), carrageenan (carrg) or Eud as diluents in different ratios, produced tablets with good physical properties which did prolong DIP release. The type, viscosity and the ratio of the diluent polymer, microsphere size and the compression pressure were found to be important factors to produce tablets with desired properties. No advantage of the tablets containing alg microspheres and granulated diluents was observed over the tablets containing powdered diluents.

Preparation and tabletting of dipyridamole alginate-Eudragit microspheres

Dipyridamole alginate-Eudragit microspheres were prepared by the emulsification technique of Monshipouri and Price. After modification of the formulation and process variables of this method it was possible to obtain spherical and discrete particles. Microspheres were free flowing and the release of drug was slow compared to granules and powder. To further control the release rate of the drug, tablets of microspheres were prepared, adding 20% HPMC 90 SH 4000 and 90 SH 100,000 and compressing at 98 mPa or 147 mPa. Increasing the amount of additive and the compression pressure decreased the release rate of drug.