The clinical and pharmacokinetic properties of ropivacaine and bupivacaine, both 5 mg/mL, used in axillary plexus block were compared in 60 patients in this randomized, double-blind, parallel-group study. The axillary plexus was identified with a nerve stimulator and 30, 35, or 40 mL of drug, depending on body weight, was injected into the perivascular sheath. In 20 patients, venous blood samples for the pharmacokinetic measurement were obtained over 24 h. The median onset times for anesthesia and complete motor block were in the range of 12-48 min and 5-20 min, respectively. Thirty-eight percent of patients in the ropivacaine group and 29% in the bupivacaine group needed additional nerve block(s) or supplementary analgesia and 7% in the bupivacaine group needed general anesthesia for surgery. Anesthesia was achieved in 52%-86% of the evaluated six nerves in the ropivacaine group and in 36%-87% in the bupivacaine group; the lowest figures were seen in the musculocutaneous nerve. In the pharmacokinetic study the mean peak plasma concentrations (Cmax) were 1.28 +/- 0.21 mg/L in the ropivacaine group and 1.28 +/- 0.47 mg/L in the bupivacaine group and the median times to peak plasma concentration (tmax) were 0.86 h and 0.96 h, respectively. The median terminal half-lives (t1/2) were 7.1 h and 11.5 h in the ropivacaine group and the bupivacaine group, respectively (P = 0.07). No statistically significant differences were found between ropivacaine and bupivacaine in either the clinical or the pharmacokinetic comparisons.

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In an open study we have investigated the efficacy of 20 ml of 0.75% ropivacaine (7.5 mg ml-1) to provide extradural anaesthesia for elective Caesarean section. Plasma concentrations (total and free) were estimated in the mother and neonate. Anaesthesia was effective and safe. Plasma concentrations of ropivacaine in the mother and neonate were within safe limits and consistent with previous studies. Two mothers received accidental i.v. injections of ropivacaine 75 mg and 150 mg, respectively, without serious adverse effects.