Descrição
The dissolution of powder drugs, besides being a topic of
utmost importance, especially for the sparingly soluble ones, is far from
being well-explained. The purpose of the present study is, on the one
hand, to obtain experimental dissolution profiles and, on the other hand,
to analyze and process the data for dissolution modeling. Three different
size fractions of a widely used sparingly soluble drugsibuprofenswere
fully characterized with regard to its particle size distribution, specific
surface area, density, solubility, and diffusion coefficient. The dissolution
profiles were obtained making use of a technique that counts and sizes
particlessthe Coulter counter techniqueswhich is capable of following
the number and size of the particles in suspension throughout time. The
knowledge of these parameters allowed a critical study of the assumptions
associated with the models currently used to describe the dissolution
process. It was concluded that most of the assumptions were not valid
for the present experimental conditions. This motivated the proposal of
a new methodology, which uses the experimentally determined characteristics
of the drug and takes into account the polydisperse nature of
the powder. By applying an adequate dissolution equation to each of
the many size classes in which the primary particle size distribution was
divided, it was possible to obtain a large agreement between the simulated
and the experimental dissolution profile.
; Simões, Sérgio 
