There are many factors influencing the drug release behaviour from a pharmaceutical formulation as the particle size of the drug and excipient, porosity of the system or geometrical phase
transitions of the components. Therefore, the choice of the adequate excipient to achieve a specific drug release profile is mainly based on the experience and the trial and error method. Taking
into account the directives towards the application of the “Quality by Design” approach, in this study the Excipient Efficiency (EE), a parameter able to quantify the capability of an excipient
to control the drug release, has been developed. EE was initially calculated dividing the total porosity of the system by its diffusional release rate constant. The influence of several factors
on this parameter has been evaluated. As a result, the final parameter has been corrected based on the drug solubility and the excipient particle size. EE provides a rational basis for
identifying the most adequate excipients for a concrete formulation.
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