Improved oral bioavailability of lipophilic substances can be achieved using self-emulsifying drug delivery systems. However, because the properties of self-emulsifying are greatly influenced by surfactant amount and type, type of oil used, droplet size, charge, cosolvents, and physiological variables, the synthesis of self-emulsifying is highly complex; consequently, only a small number of excipient self-emulsifying formulations has been developed so far for clinical use. This study reports a highly effective procedure for developing self-emulsifying formulations using a novel approach based on the hydrophilic-lipophilic difference theory. Microemulsion characteristics, such as the constituents and amounts of oil and surfactant electrolyte concentration and temperature, were optimized to produce high-quality self-emulsifying drug delivery systems. Furthermore, in vitro lipolysis and in vivo bioavailability studies of fenofibrate, a highly lipophilic oral drug, loaded self-emulsifying dosage form were conducted. The self-emulsifying drug delivery system used in this study comprised soybean oil, water with a specific salinity, sodium dioctyl sulphosuccinate as a surfactant, and orlistat as a lipase inhibitor. The hydrophilic-lipophilic difference-based approach involved fewer experiments and allowed for the development of an efficient self-emulsifying dosage form with a relatively low surfactant concentration when compared to previous works. The salinity and equivalent alkane carbon number were optimized, with the proper selection of the type and amount of surfactant, to obtain a bicontinuous microemulsion (Winsor type III) that can be fully diluted with water. In vitro lipolysis was investigated in fasting and feeding settings, which showed a significant dosage form digestion by lipase enzyme; orlistat was successfully used to overcome dosage digestion and drug precipitation problem. In vivo experiments in rats involved oral gavage with a self-emulsifying dosage form containing fenofibrate (20 mg/kg). The pharmacokinetic profile of fenofibric acid showed remarkable enhancement in the bioavailability (F-95%). These findings demonstrate that the hydrophilic-lipophilic difference approach is a practical, scalable, and easy technique for self-emulsifying drug delivery system formulation development. Keywords: HLD theory, fenofibrate, SEDDS, lipolysis
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