NONINVASIVE ASSESSMENT OF ANESTHETIC ACTIVITY OF TOPICAL LIDOCAINE FORMULATIONS

The effectiveness of a series of lidocaine formulations in producing a nesthesia after topical application was evaluated in human volunteers. The formulations, five suspensions in 20% propylene glycol and one cr eam, were applied to the forearms for 3 h with occlusion with Hilltop chambers. Testing for anesthesia was performed electrometrically. All lidocaine-containing formulations produced significantly greater anest hesia than the blanks. The formulation containing tetradecyltrimethyla mmonium bromide produced greater anesthesia than that containing octad ecyltrimethylammonium chloride. Changing the pH of the formulation fro m 7.9 to 10.0 had no significant effect. Other formulations (sodium la uryl sulfate and the cream) were no more effective than the plain form ulation without surfactants. The rank order for the suspension formula tions was the same as for steady-state permeation in in vitro experime nts. However, application of the cream formulation produced greater ef fect in vivo than was anticipated from in vitro flux values.