Effects of Intravenous Infusion of Lidocaine on Its Pharmacokinetics in Conscious Instrumented Dogs

In this study, potential alterations in hepatic blood flow, plasma protein binding, hepatic tissue binding, and enzyme activities induced by LD iv infusion of lidocaine (LD) were evaluated using a chronically instrumented dog model. Four conscious female mongrel dogs (19.0-23.5 kg) were each given, on days 1 and 10, a 5-min infusion of a mixture of unlabeled LD at approximately 2 mg/kg and 14C-labeled LD at approximately 25 microCi and, on day 8, a 12-h constant rate iv infusion of LD (approximately 76 microg/kg/min). During LD infusion, there was a 11-79% increase in total hepatic blood flow, mainly due to a 1.6-9.2-fold increase in hepatic arterial flow. Despite similar blood clearance (27.5 +/- 6.0 mL/min/kg vs 27.5 +/- 3.5 mL/min/kg), volume of distribution at steady state (1.38 +/- 0.08 L/kg vs 1.36 +/- 0.17 L/kg), and free fraction values of LD between days 1 and 10 (p > 0.05), intrinsic clearance values were consistently reduced (1224 +/- 859 mL/ min/kg vs 285 +/- 104 mL/min/kg; p = 0.034). Furthermore, hepatic tissue uptake of LD and/or its metabolites was less on day 10 than on day 1 (39.7 +/- 14.5 micromol vs 30.1 +/- 15.1 micromol; p = 0.072). The extent of N-dealkylation of LD to MEGX was unaltered, whereas sequential biotransformation of MEGX was impaired. Hence, these findings suggested that LD infusion led to a reduction of hepatic intrinsic clearance, although the change was not significant enough to alter its conventional kinetic parameters.