Stability and Release Kinetics of Natural Oil Microemulsions Containing Nicotinamide

This research aimed to evaluate stability and release characteristics of nicotinamide-loaded microemulsions (MEs). Four MEs were prepared with Tween 80 as surfactant, Span 80 as cosurfactant, either virgin coconut oil or olive oil as oil phase, water as aqueous phase, and nicotinamide as an active ingredient. They were composed of 3% w/w nicotinamide and designated as MEC1-N, MEC2-N, MEO1-N, and MEO2-N. All samples were kept in clear glass containers at 4°C, room temperature (RT, 28° ± 2°C), and 45°C for 3 months. Afterward, they were observed for physical changes and analyzed for remaining nicotinamide by a validated high-performance liquid chromatography technique. MEC1-N and MEO1-N were compared for nicotinamide released through dialysis membrane using modified Franz diffusion cells. It was found that all samples were clear liquid and water-in-oil type. Phase separation was found in MEO2-N at all storage conditions. Discoloration was observed in all samples after being kept at 45°C for 3 months. MEC1-N, MEC2-N, and MEO1-N were both physically and chemically stable after being kept at 4°C and RT for 3 months. Release kinetics of MEC1-N and MEO1-N were the best fitted with the Higuchi model.