A systematic procedure is presented for selecting the carrier material and stabilizer for drug-loaded solid lipid microparticles (SLMs). Heuristics criteria as well as investigation methods are proposed. The proposed procedure is based on the summaries of the authors' investigation and the accumulated heuristics derived from the available literature works. The physical properties of carrier materials, drug distribution in the carrier matrix, the compatibility between drugs and carrier materials, and the crystal structures of carrier matrices are taken into account in the selection of the carrier materials. In stabilizer selection, the coverage of stabilizer molecules on particle surfaces and the electrostatic repulsion and steric repulsion of stabilizers should be considered. The presented heuristics and criteria are to assist with decision making in new SLM development. This is demonstrated with an application case, in which a clozapine-loaded SLM formulation is designed, to illustrate the selection of carrier materials and stabilizers. Experiments and testing have confirmed the effectiveness of the proposed procedure and heuristics.
Controlled release behaviours of nifedipine loaded poly (D,L-lactide) (PLA) and poly(D,L-lactide-co-glycolide) (PLGA) microspheres are investigated and modelled in this paper. Based on the integrated consideration of diffusion, fi nite dissolution rate, moving front of dissolution and size distribution of microspheres, a mathematic model is presented to quantitatively describe the drug release kinetics. The coupled partial differential equations are numerically solved. Dynamic concentration profi les of both dissolved and undissolved drug in the microspheres are analyzed. In comparison with the diffusion model and Higuchi model, the proposed dissolution-diffusion model is characteristic of describing the whole release process without limitation of different dissolution rate or dissolubility. The diffusion coeffi cient and the dissolution rate constants are evaluated from measured release profi les. The effects of microstructures of polymer microspheres on release behaviours are related to parameters of the model. Based on the mathematical model and in vitro release data, intrinsic mass transfer mechanism is further investigated.Dans cet article, on a étudié et modélisé les comportements de libération contrôlée de microsphères de poly (D,L-lactide) (PLA) et poly (D,L-lactide-co-glycolide) (PLGA) chargées en nifédipine. Un modèle mathématique est présenté pour décrire quantitativement la cinétique de libération du médicament, en considérant de façon intégrée la diffusion, la vitesse de dissolution fi nie, le front de dissolution en déplacement et la distribution de tailles des microsphères. Les équations différentielles partielles couplées sont résolues numériquement. En comparaison au modèle de diffusion et au modèle de Higuchi, le modèle de dissolution-diffusion proposé caractérise bien la description du procédé de libération entier sans limitation de vitesse de dissolution ou de dissolubilité différente. Le coeffi cient de diffusion et les constantes de vitesse de dissolution sont évalués à partir des profi ls de libération. Les effets de la microstructure des microsphères de polymère sur le comportement de libération sont reliés aux paramètres du modèle. D'après le modèle mathématique et des données de libération in vitro, le mécanisme de transfert de matière intrinsèque est étudié plus en profondeur.
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