Pretende-se com o presente trabalho abordar os aspectos teóricos e práticos dos estudos de dissolução das formas farmacêuticas sólidas orais de liberação modificada, em três partes. Na primeira parte faz-se referência à classificação, interesse terapêutico e teoria da liberação do fármaco. Na segunda parte abordam-se as teorias de dissolução, os modelos de liberação, os sistemas de dissolução e sua validação, as especificações e critérios de aceitação dos ensaios de dissolução e ainda os fatores condicionantes da dissolução, liberação e absorção. Na terceira parte confrontamse as condições em que são efetuados os ensaios de dissolução com os parâmetros fisiológicos, fazendo referência aos meios de dissolução e composição do lume do trato gastrintestinal e aos modelos hidrodinâmicos.

Different formulations of diclofenac sodium (DS) containing hydroxypropylmethylcellulose (HPMC) and/or chitosan were prepared, with a view to appraise the effect of the said polymers on the drug release behaviour from matrix tablets prepared by the direct compression method. The tablets were tested for different assays, including swelling and release performance. Differential scanning calorimetry (DSC) and Raman spectroscopy were performed in order to estimate the compatibility between the matrix components (DS and excipients). From the DSC and Raman results, non-negligible drug:excipient interactions were detected, although, these were found not to constitute an incompatibility effect. The dissolution tests and the kinetic analysis data indicated that the rate and the mechanism of DS release from tablets are mainly controlled by the drug/polymer ratio. The release rate became slower for a high polymer content of HPMC. Moreover, the results demonstrated that chitosan could accelerate the drug release with lower amount in the formulation. The analysis of the drug release profile was performed in the light of distinct kinetic mathematical models. Release from formulations F2 and F3 occurs by an anomalous transport mechanism (coupling of diffusion/erosion mechanisms), with Kosmeyer-Peppas exponent (n) values of 0.626 and 0.706, respectively. The balance between diffusion and polymer erosion competing mechanisms of drug release were assessed by the Peppas-Sahlin model.