Simple method for maintaining serum lidocaine levels in the therapeutic range.

Lidocaine hydrochloride is commonly infused intravenously to prevent ventricular arrhythmias. In some patients, elevations in serum lidocaine levels can cause serious toxic effects. In a group of 19 patients given a constant infusion of lidocaine, we confirmed the observation that serum lidocaine levels rose significantly between four and 24 hours after initiation of therapy. One of these patients manifested a toxic reaction to lidocaine. The lidocaine infusion rate was modified in a second group of 32 patients on the basis of the four-hour serum level. In these patients, after dosage adjustment, the mean lidocaine level did not rise, and all levels remained within the 2- to 4-mg/L therapeutic range at 24 hours. Without dosage adjustment, half of these levels would have fallen outside the desired range. A simple formula can be used to adjust prophylactic lidocaine infusion rates to attain levels that remain therapeutic, yet nontoxic.