Analgesic efficacy of low doses of intravenously administered lidocaine on experimental laser-induced pain: a placebo controlled study.

The analgesic efficacy of low doses of intravenously administered lidocaine on experimental laser-induced pain was studied. Lidocaine or placebo was infused intravenously in ten healthy volunteers on 2 separate days according to a double-blind, randomized, cross-over design. Analgesia was assessed by argon laser-induced sensory and pain thresholds and pain evoked potentials after doses of 0.7, 1.85 and 3.7 mg/kg of lidocaine, infused over 15, 45 and 75 minutes, respectively. The plasma concentration of lidocaine was determined before each measurement. Although administration of the highest dose of lidocaine (mean plasma concentration, 8.5 mumol/l) caused significant increases in pain and sensory thresholds, the magnitude of these increases was no greater than those that occurred during placebo infusion. The power of the pain evoked potentials was significantly decreased by the highest dose of lidocaine (p = 0.0024) compared with placebo. These results probably reflect that the effect of lidocaine on subjective pain perception might be caused primarily by sedation.