In vitro and in vivo evaluation of a water-in-oil microemulsion of platycodin D.

Platycodin D (PD) is the active metabolite of Platycodon grandiflorum. The main purpose of this study was to develop and evaluate a water-in-oil (W/O) microemulsion formulation of PD (PD-ME). The PD-ME was successfully prepared by the water titration method at K  = 2, to draw the pseudoternary phase diagrams. Physical characterization including the particle size, pH, refractive index, average viscosity, and polydispersity index (PDI) was performed. The in vivo characteristics were evaluated by intestinal permeability and pharmacokinetic studies. The optimized microemulsion formulation consisted of 100 mg/ml PD aqueous solution, soybean phospholipids, ethanol, and oleic acid (27:39:19:15, w/w). The average viscosity, pH, droplet size, PDI, and zeta potential of the PD-ME were 78.65 ± 0.13 cPa•s, 5.70 ± 0.05, 30.46 ± 0.20 nm, 0.33 ± 0.00, and -3.13 mV, respectively. The drug concentration of the PD-ME was 26.3 ± 0.6 mg/ml. The PD-ME showed significantly higher apparent permeability coefficients than PD (p < .01). The pharmacokinetic studies showed that the PD-ME had significantly higher values of T (2.26-fold), AUC (area under the curve; 1.65-fold), and MRT (1.58-fold) than PD (p < .01). It can be seen that W/O ME presents a strategy with great promise for enhancing the intestinal permeability and better oral absorption of drugs with high polarity and poor permeability.