Comparative pharmacokinetics of bupivacaine and ropivacaine, a new amide local anesthetic.

The pharmacokinetics of ropivacaine, a new amide local anesthetic, and bupivacaine were determined in dogs after IV and epidural administration. After 15-minute IV infusions of 3.0 mg/kg ropivacaine (n = 6) and 3.4 mg/kg bupivacaine (n = 4), the maximum arterial concentrations (Cmax) of ropivacaine averaged 2.41 +/- 0.52 micrograms/ml compared with 3.35 +/- 0.16 micrograms/ml of bupivacaine. The elimination half life (t 1/2 beta) of ropivacaine (25.9 +/- 1.7 min) was significantly shorter than for bupivacaine (39.1 +/- 13.3 min) after IV infusion. This was reflected by mean clearance values (Cl) for ropivacaine of 41.1 +/- 8.2 ml.min-1.kg-1 compared with 32.3 +/- 4.8 ml.min-1.kg-1 for bupivacaine, although the difference was not statistically significant. After epidural injections (ropivacaine n = 6; bupivacaine n = 5), a dose-related increase in Cmax was observed with both drugs. Although Cmax tended to be higher for ropivacaine, a significant difference was only attained when comparing Cmax after administration of 0.25% plain solutions of both agents. The addition of epinephrine did not consistently decrease the Cmax of either agent. The apparent t 1/2 beta of both agents was significantly longer after epidural administration than after IV infusion. No differences existed between t 1/2 beta values for ropivacaine and bupivacaine after epidural administration. Total body clearance of both agents tended to be lower after epidural administration, particularly when epinephrine-containing solutions were employed. Little difference existed between the two drugs when equivalent solutions were administered.(ABSTRACT TRUNCATED AT 250 WORDS)