Self-microemulsifying and microemulsion systems for transdermal delivery of indomethacin: Effect of phase transition

This study investigated the transdermal delivery of indomethacin (model drug) from self-microemulsifying system, microemulsions and their phase transition systems. The study selected five formulations with fixed surfactant–oil ratio and increasing water content. These included a water free self-microemulsifying drug delivery system (SMEDDS), microemulsions containing water at 5% (w/w) (ME 5%) or at 10% (w/w) (ME 10%), a liquid crystalline formulation containing water at 30% (w/w) (LC) and coarse emulsion containing water at 80% (w/w) (EM). To clarify the results the study evaluated a microemulsion containing 10% (w/w) of receptor fluid (30%, v/v ethanol in phosphate buffered saline, PBS) (MEEB 10%) and a supersaturated system of ME 10% (MESS 10%). The viscosity increased with increasing water content up to certain limit above which the viscosity started to reduce. These formulations increased the transdermal drug flux compared to saturated drug solution in PBS (control) with formulation being ranked as SMEDDS > MEEB 10% ≈ ME 10% ≈ ME 5% > LC > EM > control. SMEDDS produced the longest lag time. The MESS 10% produced a flux value similar to that of SMEDDS but with shorter lag time suggesting transformation of SMEDDS into microemulsion after topical application with possible supersaturation. These systems can provide the formula with high flexibility in selecting the optimum viscosity as the tested preparations were able to enhance transdermal delivery in the range between SMEDDS, ME and the LC preparations with some enhancing ability for the EM.