Both quercetin and resveratrol are promising plant-derived compounds with various well-described biological activities; however, they are categorized as having low aqueous solubility and labile natural compounds. The purpose of the present study was to propose a drug delivery system to enhance the oral bioavailability of combined quercetin and resveratrol. The suitable self-microemulsifying formulation containing quercetin together with resveratrol comprised 100 mg Capryol 90, 700 mg Cremophor EL, 200 mg Labrasol, 20 mg quercetin, and 20 mg resveratrol, which gave a particle size of 16.91 ± 0.08 nm and was stable under both intermediate and accelerated storage conditions for 12 months. The percentages of release for quercetin and resveratrol in the self-microemulsifying formulation were 75.88 ± 1.44 and 86.32 ± 2.32%, respectively, at 30 min. In rats, an in vivo pharmacokinetics study revealed that the area under the curve of the self-microemulsifying formulation containing quercetin and resveratrol increased approximately ninefold for quercetin and threefold for resveratrol compared with the unformulated compounds. Moreover, the self-microemulsifying formulation containing quercetin and resveratrol slightly enhanced the in vitro antioxidant and cytotoxic effects on AGS, Caco-2, and HT-29 cells. These findings demonstrate that the self-microemulsifying formulation containing quercetin and resveratrol could successfully enhance the oral bioavailability of the combination of quercetin and resveratrol without interfering with their biological activities. These results provide valuable information for more in-depth research into the utilization of combined quercetin and resveratrol.
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