Continuous infusion of lidocaine in patients with cardiac arrhythmias. Unpredictability of plasma concentrations.

Recent studies suggest that lidocaine hydrochloride continues to accumulate during prolonged infusions. Plasma levels of lidocaine and monoethylglycinexylidide (MEGX) were measured in 26 patients with cardiac arrhythmias during lidocaine infusions of 15 to 69 hours' duration. Clearance varied, ranging from 3.2 to 14.7 mL/min/kg, and was significantly less in the ten patients with heart failure (5.8 +/- 1.7 mL/min/kg) as compared with the remaining 16 (8.4 +/- 2.6 mL/min/kg; P < .05). The MEGX levels were < 1 microgram/mL. In four patients, steady states were achieved at two different infusion rates, and changes in lidocaine plasma levels were generally proportional to changes in infusion rates. Lidocaine elimination half-lives ranged from 3.2 to 8.7 hours, and no accumulation continued beyond four half-lives. Clearance values, elimination half-lives, apparent volumes of distribution, and, consequently, steady-state levels were widely variable, which can be partly explained by the inclusion of patients with congestive heart failure. Monitoring of serum lidocaine levels may aid in individualization of therapy.