AN INVESTIGATION INTO THE CRITICAL SURFACTANT CONCENTRATION FOR SOLIDSOLUBILITY OF HYDROPHOBIC DRUG IN DIFFERENT POLYETHYLENE GLYCOLS

Solid dispersions of 10% w/w griseofulvin in different polyethylene gl ycols (PEGs) with or without incorporation of alkali dodecyl sulphates (MDS) were prepared by the melting method. The investigations concern ed the solid state (X-ray powder diffraction), the transition from sol id to liquid stale (Oscillating DSC) and the liquid state (low frequen cy dielectric spectroscopy). The critical concentrations of SDS for th e formation of solid solutions in varying PEGs were evaluated. In PEG 3000 this formation occurs at 1.4% w/w SDS, whereas PEG 6000 and PEG 2 0000 require solely 1.0% ww SDS to transfer a dispersion into a solid solution. PEG 3000 was also investigated with the addition of MDS. The critical surfactant concentrations for the formation of solid solutio ns with the counterions Li+, Na+ and K+ were 1.0%, 1.4% and 2.1% w/w, respectively. The investigated systems had varying degrees of crystall inity. With the addition of SDS to PEGs with a range of molecular weig hts, the highest crystallinity was seen in the PEG 3000 sample. The di fferent polymers contained different amounts of folded and extended ch ains which influences the amount of amorphous material within the poly mer structure. When surfactants with different counterions were added to PEG 3000, the lithium sample showed the highest crystallinity. In t he melt the Li+ sample showed the lowest dielectric mobility. The resu lts show that concentration and structure of surfactant together with the presence of folded and extended chains form the conditions for the formation of solid solutions.