The Base in Four Types of Lidocaine Preparation (Formulated in Hospital)

Abstract

  PL cream (combination of lidocaine and procaine) was launched on the market in April 2012 in Japan. We investigated differences in the anesthetic effect by employing two types of base: Carbopol and methylcellulose. Electron microscopy showed a distinct difference in appearance: densely-scattered, fine particles for Carbopol and sparse, large particles for methylcellulose. Accordingly, the extensibility of the cream was significantly greater at 4 and 25 degrees centigrade for methylcellulose, but was greater at 34 degrees centigrade for Carbopol. The steady flow viscosity (1 s⁻¹) was greater for the Carbopol than methylcellulose base. The difference in the cutaneous permeability between the two bases increased over time: the methylcellulose base was removed at 90 min after application and, 30 min later, showed a significant difference. These results suggest that the methylcellulose base has a superior anesthetic effect in clinical settings.