Babassu oil-based microemulsion promotes uniform in vitro release of diclofenac sodium and donepezil hydrochloride†

Microemulsions are nanostructured and thermodynamically stable systems with a reduced droplet size. They can improve drug absorption and distribution. Babassu oil has been investigated for various therapeutic properties reported by popular use. This work aimed to develop, optimize, and characterize babassu oil-based water-in-oil microemulsions to promote a controlled and uniform release of drugs with different physicochemical properties. The optimal microemulsion composition was investigated through pseudoternary diagrams, with water, surfactant mixture, and oil mixture as vertices. The formulations were characterized based on pH, conductivity, size, polydispersity index, and drug content. In vitro drug release was carried out using multidimensional and unidimensional techniques. An optimum microemulsion contains (w/w): 10% water, 17.8% babassu oil, 26.2% medium-chain triglycerides, 29.7% Span™ 83, 7.1% Tween® 80, and 9.2% Transcutol® HP. Diclofenac sodium (DS), donepezil hydrochloride (DH), and insulin were associated with the dispersed phase of the microemulsion. These formulations presented a droplet size of 26.9 ± 1.9, 22.6 ± 0.4, and 35.5 ± 0.7 nm, respectively. The polydispersity index was <0.1 for all formulations. Microemulsions controlled the outflow of drugs, showing a uniform release compared to the respective controls. It was evidenced that these profiles depend on the features of the molecule associated. According to the selection criteria, most experimental DS and DH release kinetics in water or pH 7.2 fit well with the Gompertz model. In conclusion, a babassu oil-based water-in-oil microemulsion was developed for the first time, optimized, and characterized, supporting further investigation of the formulation as a drug delivery system.