Pharmacokinetics of 450 mg ropivacaine with and without epinephrine for combined femoral and sciatic nerve block in lower extremity surgery. A pilot study

Abstract

No pharmacokinetic data exist on doses of ropivacaine larger than 300 mg for peripheral nerve block in man, although in clinical practice higher doses are frequently used. The purpose of the present study was to describe the pharmacokinetic profile in serum of 450 mg ropivacaine with and without epinephrine in patients undergoing anterior cruciate ligament reconstruction. Twelve patients were randomly allocated to receive a single shot combined sciatic/femoral nerve block with 60 ml of either ropivacaine 0.75% alone (group R, n = 6) or ropivacaine 0.75% plus epinephrine 5 μg ml(-1) (group RE, n = 6). Venous blood samples for total and free ropivacaine serum concentrations were obtained during 48 h following block placement. Pharmacokinetic parameters were calculated using a non-compartmental approach. Results are given as mean (SD) for group R vs. group RE (95% CI of the difference). Total Cmax was 2.81 (0.94) μg ml(-1) vs. 2.16 (0.21) μg ml(-1) (95% CI -0.23, 1.53). tmax was 1.17 (0.30) h vs. 1.67 (0.94) h (95% CI -1.40, 0.40). The highest free ropivacaine concentration per patient was 0.16 (0.08) μg ml(-1) vs. 0.12 (0.04) μg ml(-1) (95% CI -0.04, 0.12). t(1/2) was 6.82 (2.26) h vs. 5.48 (1.69) h (95% CI -1.23, 3.91). AUC was 28.35 (5.92) μg ml(-1) h vs. 29.12 (7.34) μg ml(-1) h (95% CI -9.35, 7.81). Free serum concentrations of ropivacaine with and without epinephrine remained well below the assumed threshold of 0.56 μg ml(-1) for systemic toxicity. Changes in pharmacokinetics with epinephrine co-administration did not reach statistical significance.