Influence of congestive heart failure on blood levels of lidocaine and its active monodeethylated metabolite

The blood concentrations of lidocaine and its active monodeethylated metabolite, monoethylglycinexylidide (MEGX), were measured in 31 patients who were receiving infusions of lidocaine intravenously. In 3 patients who were studied intensively, the elimination half-life of MEGX was 120 min, which was similar to the elimination half-life of lidocaine (139 min). An additional 3 patients demonstrated a higher ratio of the concentration in blood of MEGX to lidocaine, and the MEGX may have contributed, in 1 patient, to the central nervous system toxicity that occurred during the infusion. Elevated concentrations of MEGX in blood were associated with congestive heart failure (r = 0.5, p = 0.004). Our data suggest that the elimination of MEGX may be decreased in patients with depressed cardiac output and sympathomimetic compensation.