Optimization of self-microemulsifying drug delivery system for phospholipid complex of telmisartan using D-optimal mixture design

To improve the dissolution behavior of telmisartan (TMS), a poorly water-soluble angioten-sin II receptor blocker, TMS-phospholipid complex (TPC) was prepared by solvent evaporation method and characterized by differential scanning calorimetry and powder X-ray diffractometry. The crystalline structure of TMS was transited into an amorphous state by TPC formation. The equilibrium solubility of TPC (1.3-6.1 mg/mL) in various vehicles was about 100 times higher than that of TMS (0.009-0.058 mg/mL). TPC-loaded self-microemulsifying drug delivery system (SMEDDS) formulation was optimized using the D-optimal mixture design with the composition of 14% Capryol 90 (oil; X-1), 59.9% tween 80 (surfactant; X-2), and 26.1% tetraglycol (cosurfactant; X-3) as independent variables, which resulted in a droplet size of 22.17 nm (Y-1), TMS solubilization of 4.06 mg/mL (Y-2), and 99.4% drug release in 15 min (Y-3) as response factors. The desirability function value was 0.854, indicating the reliability and accuracy of optimization; in addition, good agreement was found between the model prediction and experimental values of Y-1, Y-2, and Y-3. Dissolution of raw TMS was poor and pH-dependent, where it had extremely low dissolution (< 1% for 2 h) in water, pH 4, and pH 6.8 media; however, it showed fast and high dissolution (< 90% in 5 min) in pH 1.2 medium. In contrast, the dissolution of the optimized TPC-loaded SMEDDS was pH-independent and reached over 90% within 5 min in all the media tested. Thus, we suggested that phospholipid complex formation and SMEDDS formulation using the experimental design method might be a promising approach to enhance the dissolution of poorly soluble drugs.