Lidocaine plasma concentrations obtained with a standardized infusion in the awake and anaesthetized dog

Lidocaine was administered intravenously on several occasions to three healthy mongrel dogs. The lidocaine treatment consisted of an infusion of 0.8 mg/kg/min over 10 min, followed by an infusion of 0.085 mg/kg/min over 3 h. This lidocaine treatment was given once in the awake state and on two other occasions the infusion was started before or during the following anaesthetic regimen: atropine-meperidine premedication, thiopental induction and maintenance nitrous oxide-methoxyflurane anaesthesia. In most instances plasma levels were somewhat higher at the end of the loading infusion (greater than 5 micrograms/ml) than subsequently, but steady-state values were obtained soon after starting the 3-h infusion. There were no striking differences between the plasma profiles and half-lives found in the three series of experiments: mean plasma concentrations of lidocaine during steady state were between 3.5 and 5.0 micrograms/ml and the half-life of lidocaine was 1 to 2 h. Signs of intoxication were not seen in any of the dogs at any stage of the procedures. It is concluded that with the loading and maintenance doses used in this study steady-state values, probably within the therapeutic range, are obtained within a few minutes. The plasma concentrations are not influenced by the anaesthetic regimen used.