Insights into the role of polymer-surfactant complexes in drug solubilisation/stabilisation during drug release from solid dispersions

To evaluate the role of polymer-surfactant interactions in drug solubilisation/stabilisation during the dissolution of spray-dried solid dispersions and their potential impact on in vivo drug solubilisation and absorption. Dissolution/precipitation tests were performed on spray-dried HPMC-Etravirine solid dispersions to demonstrate the impact of different surfactants on the in vitro performance of the solid dispersions. Interactions between HPMC and bio-relevant and model anionic surfactants (bile salts and SDS respectively) were further characterised using surface tension measurements, fluorescence spectroscopy, DLS and SANS. Fast and complete dissolution was observed in media containing anionic surfactants with no drug recrystallisation within 4 h. The CMCs of bile salts and SDS were dramatically reduced to lower CACs in the presence of HPMC and Etravirine. The maximum increases of the apparent solubility of Etravirine were with the presence of HPMC and SDS/bile salts. The SANS and DLS results indicated the formation of HPMC-SDS/bile salts complexes which encapsulated/solubilised the drug. This study has demonstrated the impact HPMC-anionic surfactant interactions have during the dissolution of non-ionic hydrophilic polymer based solid dispersions and has highlighted the potential relevance of this to a fuller understanding of drug solubilisation/stabilisation in vivo.