THE PHARMACOKINETICS OF EPIDURAL LIDOCAINE AND BUPIVACAINE DURING CESAREAN-SECTION

We studied the maternal pharmacokinetics of epidural lidocaine and bup ivacaine in 20 healthy parturients with institutional review board app roval and written, informed consent. Epidural anesthesia was induced u sing either 2% lidocaine with epinephrine 1:200,000, n = 10, or 0.5% p lain 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 mu g/mL; a nd Uv/Ma gradient 0.43 +/- 0.05 and 0.26 +/- 0.1. Peak Ma lidocaine co ncentrations in 2 of 10 patients reached potentially toxic levels with out producing clinical toxicity, whereas peak bupivacaine Ma concentra tions never approached levels considered unsafe. The results suggest t hat epidural bupivacaine reliably produces acceptable Ma concentration s below the toxic range.