The pharmacokinetics of epidural lidocaine and bupivacaine during cesarean section.

We studied the maternal pharmacokinetics of epidural lidocaine and bupivacaine in 20 healthy parturients with institutional review board approval and written, informed consent. Epidural anesthesia was induced using either 2% lidocaine with epinephrine 1:200,000, n = 10, or 0.5% plain bupivacaine, n = 10. Maternal arterial (Ma) blood was sampled at regular intervals and umbilical venous (Uv) blood at delivery. Results for lidocaine and bupivacaine, respectively, were (mean +/- SEM): age 30.4 +/- 1.5 and 24.7 +/- 1.6 yr; weight 74.0 +/- 4.2 and 74.9 +/- 4.5 kg; duration of surgery 55.5 +/- 4.3 and 53.1 +/- 3.5 min; epidural dosage 6.1 +/- 0.6 and 1.5 +/- 0.2 mg/kg; elimination half-life 113.9 +/- 5.6 and 110.4 +/- 20.4 min; plasma clearance 6.1 +/- 0.4 and 13.6 +/- 1.3 mL.kg-1.min-1; volume of distribution 0.98 +/- 0.1 and 1.67 +/- 0.3 L/kg; time to peak concentration 31 +/- 2.3 and 40.5 +/- 1.7 min; peak Ma concentration 6.4 +/- 0.65 and 0.8 +/- 0.1 microgram/mL; and Uv/Ma gradient 0.43 +/- 0.05 and 0.26 +/- 0.1. Peak Ma lidocaine concentrations in 2 of 10 patients reached potentially toxic levels without producing clinical toxicity, whereas peak bupivacaine Ma concentrations never approached levels considered unsafe. The results suggest that epidural bupivacaine reliably produces acceptable Ma concentrations below the toxic range.