Intravascular lidocaine toxicity: influence of epinephrine and route of administration.

The intravenous (tail vein) and intra-arterial (internal carotid artery) toxicities of 2% lidocaine, 1:100,000 epinephrine, and the combination of drugs were tested in unanesthetized rats. At least 3 doses (normally 10 animals/dose) were used per drug and route of administration; the drugs were given by bolus injection. Probit analysis of lethal dose-response curve data revealed that lidocaine, with or without epinephrine, was significantly more toxic intravenously than by internal carotid artery injection and that epinephrine potentiated the intravascular toxicity of lidocaine. These results modify proposals suggesting that local anesthetics injected accidentally into a branch of the external carotid artery may cause serious adverse reactions by flowing in retrograde fashion down to the internal carotid artery and then directly to the brain.