Excessive serum lidocaine levels during maintenance infusions: mechanisms and prevention.

Clinical and pharmacokinetic data were reviewed in 72 patients who developed excessive lidocaine serum levels during maintenance infusions. Fifty-one of the 72 (70%) were cardiac patients who had mean lidocaine excretory clearances less than one half of normal. Forty percent of these became toxic in spite of a reduced infusion rate (30 micrograms/kg/min). Seven patients with normal excretory mechanisms became toxic when they received large doses of lidocaine. The remaining 14 cases lacked an identifiable cause to explain the development of higher than therapeutic serum levels. Inordinately high serum levels of monoethylglycinexylidide (MEGX), an active lidocaine metabolite, were found in seven patients, but in only one was MEGX greater than lidocaine. Prolonged infusions (24 hours or greater) were not clearly associated with the worst lidocaine elimination clearances. Lidocaine toxicity was life-threatening or significantly complicated the management of 15 patients. Based on the data presented, guidelines are offered as an approach to the prevention of toxicity from maintenance lidocaine infusions.