Quantitative Investigation of the Effect of Sensory Nerve Anesthesia with 9% Lidocaine Ointment on Healthy Subjects by Use of the Neuroselective Current Perception Threshold

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We measured the current perception threshold (CPT) before and 2 h after an application of 9% lidocaine ointment on healthy subjects and investigated the effect of this ointment on sensory nerve function. The application of 9% lidocaine ointment significantly decreased the CPT within site ratios: 2 kHz/5 Hz (11.20±2.07 (0 h), 3.54±0.26 (2 h); p<0.01), 2 kHz/250 Hz (4.39±0.36 (0 h), 2.64±0.14 (2 h); p<0.01), and 250 Hz/5 Hz (2.71±0.56 (0 h), 1.36±0.11 (2 h); p<0.05), compared with those immediately before the application (0 h). The rate of change in CPT was highest at 5 Hz (4.36±1.04); the rate then decreased in the order of 250 Hz (2.25±0.27) and 2 kHz (1.31±0.09). These findings showed that an application of 9% lidocaine ointment decreased the sensory nerve function and that the A δ fiber and C fiber rather than the A β fiber may be closely involved in this reduction of the sensory nerve function. The experiment was also performed with 10% lidocaine cream, which is clinically used for postherpetic neuralgia, and this concentration reduced the sensory nerve function to a degree similar to that caused by 9% lidocaine ointment. The 9% lidocaine ointment may be an effective topical agent indicated for postherpetic neuralgia.