Influence of drug polarity upon the solid-state structure and release properties of self-emulsifying drug delivery systems in relation with water affinity.

To overcome low oral bioavailability of poorly water-soluble drugs, self-emulsifying drug delivery systems (SEDDS) have been noted as a promising strategy. However, incorporation of drugs into SEDDS composed of Gelucire44/14 could induce interactions not yet well understood. The aim of this study was to investigate the influence of drug polarity upon the solid-state structure of SEDDS formulation, particularly in terms of wettability, thermal behaviour and microscopic aspects and their effect upon the release properties of the SEDDS. Model drugs were naproxen and sodium naproxen (10% w/w), two drugs with similar chemical structure but different water solubilities. Both drugs had an effect on the structure and behaviour of SEDDS: sodium naproxen mainly increased surface wettability while naproxen modified its thermal behaviour. Moreover, influence of Gelucire44/14 as self-emulsifying matrix was very marked for naproxen with a huge increase of naproxen release, the less water-soluble drug in condition where the solubility was the limiting parameter (at pH 1.2). Study of SEDDS structure and its physico-chemical properties using different techniques brought novel findings about the behaviour of SEDDS with different kinds of drugs (various water solubilities) and could be linked to their performances during in vitro dissolution.