Formulation and In Vivo Pain Assessment of a Novel Niosomal Lidocaine and Prilocaine in an Emulsion Gel (Emulgel) of Semisolid Palm Oil Base for Topical Drug Delivery

This study aimed to formulate semisolid niosomal encapsulated lidocaine and prilocaine using the patented palm oil base Hamin-C® for further characterization and in vivo pain assessment. Seven formulations were initially studied with various chemical compositions. A thin-layer film hydration method was used to produce niosome using a mixture of surfactant (Span® 40 or Span® 60) and cholesterol (CHOL) at a 1:1 ratio, with/without a charge-inducing agent (diacetyl phosphate) (DCP) and with/without labrasol®. Niosome F1 formulation had been identified as the highest %EE achieved, at 53.74 and 55.63% for prilocaine and lidocaine, respectively. Furthermore, NIO-HAMIN F1 emulgel indicated the best formulation with higher permeability of prilocaine and lidocaine compared to the rest of the formulations. The reformulation of optimization of NIO-HAMIN F1 emulgel using a cold process to NIO-HAMIN F1-C emulgel to improve the viscosity resulted in higher diffusion of prilocaine and lidocaine by 5.71 and 33.38%, respectively. In vivo pain perception studies by verbal rating score (VRS) and visual analogue score (VAS) on healthy subjects show a comparable local anesthetic effect between NIO-HAMIN F1-C emulgel and EMLA® cream.