Formulation and in vitro evaluation of pH-responsive ethosomes for vaginal delivery of metronidazole

pH-responsive metronidazole ethosomes (ME) were formulated by solvent evaporation method using Phospholipon 90 H (P90H) and evaluated for vaginal delivery. Differential scanning calorimetry showed no interaction between metronidazole and P90H. Scanning electron microscopy (SEM) showed formation of spherically-shaped vesicles. The average vesicle size was 179.9 nm with PDI of 0.338. The entrapment efficiency (EE) and loading capacity (LC) were 50.31 ± 3.38 % and 39.89 ± 0.02 %, respectively. Over pH of 6.5-5.0, the permeation and flux were of the order: ME 5.6 > ME 5.0 > ME 6.5, respectively, with ME 5.6 showing, significantly (P < 0.05) the highest release profile. Ethosome vesicles were formed which entrapped the metronidazole molecules. The optimized ethosome gel (ME 5.6) exhibited pseudo-plastic flow behaviour typical of non-Newtonian fluids and showed potentials for sustained delivery compared to the aqueous dispersion. This may be replicated in the vagina to cause increased local and systemic bioavailability of metronidazole.