Dry adsorbed emulsion: 1. Characterization of an intricate physicochemical structure

A recent solid pharmaceutical form called "Dry Adsorbed Emulsion" (DAE) was characterized in morphological and structural fields. A DAE is an intricate system initiated by a water-in-oil emulsion including the active drug (i.e., theophylline). Each emulsion phase is adsorbed on pulverulent adsorbents with a suitable polarity (silica) to obtain a free-flowing powder with nonporous particles of size from 125 to 710 microm, with small specific surface area and a spherical shape. Different methods, such as scanning electron microscopy combined with chemical microanalysis, dying tests, and electron spin resonance studies, allow the formulator to follow the behavior of DAE aqueous and oily phases during the manufacturing process and then to set up a structural model for DAE particles. These DAE particles appear to be made up of a random pack of hydrophilic and hydrophobic particles, containing a liquid phase adsorbed on silica by weak bonds.