[Pharmacokinetics of lidocaine in obstetric patients after its epidural single-dose administration]

To determine the concentrations of lidocaine in maternal plasma and to establish the kinetic constants following absorption of a single dose of lidocaine in obstetric epidural anesthesia.

Epidural blockade was provided to 10 patients by a single injection of lidocaine at doses of 200 to 300 mg (265 +/- 35 mg). The plasma concentrations of lidocaine were determined 1, 5, 10, 15, 20, 40, 60, 120 and 180 min later and at the moment of birth, by way of polarized immunofluorescence (PIF) with a Tdx automatic analyzer (Abbott).

Time until peak plasma concentration was 17.4 min. Peak concentrations ranged from 1.44 to 2.12 micrograms/ml. Plasma clearance took place at a rate of 10.1 +/- 1.7 ml/min/kg, more slowly than in surgical patients. Duration of anesthesia ranged from 40 to 80 min and was sufficient in all cases, even for women undergoing cesarean section. At birth (25 +/- 5 min after epidural injection), plasma concentration was 1.67 +/- 0.28 micrograms/ml.

Injection of 200-300 mg of lidocaine provides good analgesia during childbirth, even when cesarean section is practiced, with no toxic effects for the mother.