Physicochemical properties and stability of nanoemulsions containing Clinacanthus nutans extract for postherpetic neuralgia

The leaf extract of Clinacanthus nutans (CNE), a medicinal plant widely distributed in South East Asia, has long been used in traditional medicine by applying topically for treatment of herpes zoster. Besides, it has an analgesic effects that could help relieve suffering from postherpetic neuralgia. The aims of this study were to develop nanoemulsions containing CNE obtained from extraction of dried leaves and evaluate their physicochemical properties, stability, and permeability. Forty formulations of oil-in-water emulsion bases containing various concentrations of sunflower oil and mixed emulsifiers were prepared by spontaneous emulsification and screened for further preparation of nanoemulsion bases by high presure homogenization. The results showed that particle sizes and viscosities of nanoemulsion bases were in the range of 85.9 – 120.9 nm and 339.4 – 1,362.0 cP, respectively. The content of vitexin, which was used as a marker in this study, in CNE and 4 %w/w CNE nanoemulsions were 0.130 and 0.005 %w/w, respectively. The 4 %w/w CNE nanoemulsions was found to be stable based on vitexin content under storage at 5 °C and 30 °C. The amount permeated of vitexin after 24-h permeation from 4 %w/w CNE nanoemulsion across Strat-M® membrane was 61.1 ± 1.95%. In conclusion, the promising formulation of nanoemulsions according to stability and permeability results was composed of 4 %w/w CNE, 20 %w/w sun flower oil, and 20 %w/w mixed emulsifiers of Span®80 and Brij®721 (weight ratio of 1.0:0.32), which could be a candidate as a herbal topical dosage form for postherpetic neuralgia. [Display omitted] •Proper nanoemulsion containing 20% sunflower oil, 15.2% Span®80 and 4.8% Brij®721.•Vitexin is a suitable marker of C. nutans extract for postherpetic neuralgia.•The 4% extract nanoemulsion stored at 30 ± 2 °C has shelf-life at least 90 days.•The 4% extract nanoemulsion could permeate through synthetic membrane imitating human skin.