Lidocaine Concentrations in Plasma and Cerebrospinal Fluid After Systemic Bolus Administration in Humans

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Abstract
Preclinical studies suggest that systemic lidocaine acts at the level of the spinal dorsal horn to inhibit hyperalgesia resulting from nerve injury, yet no clinical data are available to support this view.Therefore, we sought to characterize the time course of lidocaine in the plasma and cerebrospinal fluid (CSF) after an IV bolus injection of lidocaine 2 mg/kg in patients scheduled for surgery involving spinal anesthesia. Sixty-five patients were randomly allocated to one of five study groups (n = 13 per group) receiving IV lidocaine before CSF/plasma sampling at 5, 10, 15, 30, or 60 min. Gas chromatographic analysis of these samples revealed a fast but transient peak (5-15 min) in lidocaine plasma levels (1.7 +/- 0.16 [micro sign]g/mL), which declined rapidly thereafter. Only small concentrations of IV lidocaine were found in the CSF (6%-8% of plasma concentration), but this fraction remained stable from 15 min until termination of the experiment. No statistical correlation was observed between plasma and CSF lidocaine levels. These data suggest that because of the prolonged availability of lidocaine at the spinal dorsal horn level, systemic administration of lidocaine suppresses central sensitization within the spinal cord after nerve injury in humans. Implications: Cerebrospinal fluid concentrations of lidocaine after its systemic bolus delivery in humans indicate that the spinal cord may be the major site of antinociceptive action by this route of drug administration. (Anesth Analg 1998;87:601-4)