Novel anhydrous emulsions: Formulation as controlled release vehicles

Novel anhydrous emulsions, which may offer some advantages as depot or reservoir vehicles for lipophilic drugs in controlled delivery systems, were formulated using castor oil as the disperse phase and dimethicone or cyclopentasiloxane as the continuous phase. Among the emulsifiers studied only silicone surfactants (cyclomethicone/dimethicone copolyols) which were miscible in silicone oil stabilized the emulsions. Cyclomethicone/PEG/PPG-18/18 Dimethicone and Cyclopentasiloxane/PEG/PPG-18/18 Dimethicone were more effective in lowering the interfacial tension between castor oil and both dimethicone and cyclopentasiloxane. Emulsions formulated using either of these two surfactants were found to be stable against phase separation and exhibited least globule growth over 168 h. The average particle size was found to be 2-6 μm in these systems formed by probe sonication. Slow release patterns of 3H-dehydroepiandrosterone (DHEA) and 3H-dexamethasone solubilized in the disperse castor oil phase into an aqueous dialyzing medium were observed over 48 h.