ABSTRACT
OBJECTIVE: The aim of this research is to analyze analgesic efficacy of the 5% lidocaine medicated plaster in two randomized, double-blinded, placebo-controlled, crossover studies in 16 healthy volunteers using capsaicin and sunburn pain models. METHODS: Lidocaine and placebo plasters were simultaneously applied to forearms and thighs at contralateral body sites for three alternating 12-h plaster-on/plaster-off periods. Between the second and third plaster-on period, 4.2-cm circular spots on both pretreated thighs were irradiated with three times the individual minimal erythema dose of UVB light. After the last plaster-on period, 20 µl of 0.1% capsaicin was injected intradermally into both forearms. The study was repeated using a single 12-h plaster application. RESULTS: The area of pinprick hyperalgesia was diminished by 53% (p < 0.003) in the capsaicin model and by 84% (p < 0.0001) in the sunburn model; the intensity of mechanical hyperalgesia to rigid filaments (8 - 512 mN) was reduced in both models. Cold pain perception threshold was reduced (19.7°C ± 8.0 vs 21.8°C ± 6.8 for placebo, p < 0.05, sunburn). Similar effects were observed in the 12-h exposure study. No effect was seen on capsaicin-induced spontaneous pain and flare size, or blood flow in the sunburn area, and heat hyperalgesia in either study. CONCLUSIONS: Lidocaine plaster effectively treats mechanical hyperalgesia and cold pain.
