[Sensory nerve anesthesia with 4% liposomal lidocaine cream in healthy subjects by use of the neuroselective current perception threshold].

Background: ELA-Max, an external liposomal preparation of lidocaine (4%) available without prescription in United States, has a recommended application time of 15 to 45 min without occlusive dressing, and the side effect has been reported to be rare. To investigate external anesthetic preparations to reduce neuropathic pain, we evaluated sensory nerve anesthesia by ELA-Max in comparison with placebo and other lidocaine topical preparations by double blind method.

Methods: We measured the neuroselective current perception threshold (N-CPT) 30 min after the application of ELA-Max on 30 healthy Japanese volunteers. Evaluation of anesthetic effect was performed by change in N-CPT rate before and after the application of 0.025 g x cm(-2) to the skin where stimulation was performed.

Results: ELA-Max increased N-CPT ratio in 4 out of 9 subjects stimulated at 5 Hz. However these CPT values were within normal ranges, and the change in N-CPT ratio was not statistically significant throughout all stimulation frequencies.

Conclusions: The application of 0.025 g x cm(-2) ELA-Max for 30 min was not effective to induce therapeutic level of anesthesia. Extended application times as well as occlusive dressing may be needed for this preparation to be used clinically.