The effect of pentobarbital on lidocaine toxicity and brainstem concentration.

The effect of pretreatment with 20 mg/kg sodium pentobarbital on the acute intravenous toxicity of 2% lidocaine was determined in rats. Pretreatment increased the LD(50) of lidocaine from 20.2 mg/kg to 26.9 mg/kg (p<0.05). This 25% decrease in lethality was accompanied by similar decreases in the concentrations of lidocaine (relative to the injected dose) in serum and brainstem samples collected immediately after death. Under the conditions of this study, pentobarbital apparently protects against lidocaine lethality by increasing the relative distribution of local anesthetic to tissues outside of the central nervous system.