RESUMO
Directly compressed theophylline tablets, containing commercial xanthan (X) (Keltrol) and a highly hydrophilic galactomannan (G) from the seeds of Mimosa scabrella (a brazilian leguminous tree called bracatinga) as release-controlling agents, were obtained. Gums were used at 4, 8, 12.5 and 25% (w/w), either alone or in mixture (X:G 1:1). During galactomannan extraction process, the biopolymer was dried in a scale up, by vacuum oven (VO) or spray dryer (SD). The in vitro drug release was evaluated at different time intervals during 8 h using apparatus 1 (USP 26) at 100 rpm. The pH of the dissolution medium (1.4) was changed to 4.0 and 6.8 after 2 and 3 h, respectively. Tablets containing G(SD) resulted in more uniform drug release than G(VO) ones, due to their smaller particle size. The drug release decreased with the increase of polymer concentration and all formulations at 25% w/w of gums showed excessive sustained release effect. The matrices made with alone X showed higher drug retention for all concentrations, compared with G matrices that released the drug too fast. The XG matrices were able to produce near zero-order drug release. The XG(SD) 8% tablets provided the required release rate (about 90% at the end of 8 h), with zero-order release kinetics. Tablets containing G(VO) in low concentration showed a complete erosion, while the others demonstrated fast hydration and swelling in contact with the dissolution medium. The release mechanism was a combination of diffusion and relaxation. The relative importance of these two processes varied with matrix composition. The XG(SD) 8% matrix showed higher contribution of polymer relaxation.
Assuntos
Sistemas de Liberação de Medicamentos/métodos , Mananas/farmacocinética , Mimosa , Polissacarídeos Bacterianos/metabolismo , Teofilina/farmacocinética , Administração Oral , Galactose/análogos & derivados , Mananas/administração & dosagem , Polissacarídeos Bacterianos/administração & dosagem , Comprimidos , Teofilina/administração & dosagemRESUMO
A highly substituted galactomannan (G) from Mimosa scabrella Bentham (Man:Gal 1.1:1), isolated from the seeds of a Brazilian leguminous tree and xanthan (X), an exopolysaccharide secreted by Xanthomonas campestris (Keltrol), were evaluated as a hydrophilic matrix system (XG) for controlled release (CR) of diclofenac sodium (DS) in tablets and capsules. The performance of XG (2:1) matrices containing 50 mg (A) or 100 mg (B) of DS was compared with a commercial CR product of DS. The drug release studies were carried out using a dissolution apparatus (paddle method) with gradual increase of pH values, from pH 1.4, to pH 4.0 (after 1 h) and to pH 6.8 (after 2 h). The results suggested the potential of XG systems as release retarding materials, which released 78.6 and 35.1% of drug after 24 h for capsules (A) and tablets (A), respectively. Drug release decreased with the increase of amount of drug and it is dependent of dosage form. Analysis of release data indicate a rather zero-order drug release with the erosion mechanism playing a dominant role.