that affect sodium channel activation. Lidocaine decreases ion permeability across the sodium channel acting in the opposite manner. The aim of this work is to determine whether lidocaine antagonized the toxic effect of the crude poison of Centruroides limpidus limpidus. Methods: One half the lethal dose of the crude poison was determined alone and in the presence of different doses of lidocaine. Experiments with crude poison at LD(50) and crude poison plus lidocaine were carried out after 30, 90, and 180 min of poison inoculation; lung, heart, and brain were obtained for histopathologic analysis. Results: Lidocaine (7 mg/kg dose) increased LD(50) of crude poison (2.95 +/- 0.22 to 6.68 +/- 0.25, p