A new local anesthetic, ropivacaine. Its epidural effects in humans

The current study was initiated to evaluate the epidural anesthetic properties of 0.5%, 0.75%, and 1.0% ropivacaine, a new local anesthetic agent structurally similar to bupivacaine. Fifteen patients scheduled for lower limb orthopedic surgery were enrolled in the study. As the concentration of ropivacaine increased from 0.5% to 1.0%, the time to onset of sensory anesthesia decreased from 6.4 +/- 1.7 (SD) min to 2.4 +/- 0.6 min and the maximum level of sensory anesthesia increased from T6 to T1. These changes were not statistically significant. Time to regression of anesthesia to T12 increased from 255 +/- 73 min with the 0.5% solution to 356 +/- 75 min with 1.0% ropivacaine (P less than 0.05). The degree of motor blockade using the Bromage scale varied with the concentration. When the 0.5% concentration was used, only one patient (20%) had greater than 1+ motor blockade. However, all of the patients receiving the 0.75% or 1.0% solution had at least 2+ motor blockade. Sensory anesthesia was adequate for surgery in 14 of the 15 patients. The mean peak plasma concentration of ropivacaine (Cmax) increased from 0.65 +/- 0.15 micrograms/mL with the 100-mg dose to 1.30 +/- 0.43 microgram/mL with the 200-mg dose. No adverse effects were noted in any patient in the study. These initial studies in humans suggest that ropivacaine provides satisfactory sensory anesthesia with minimal motor blockade at a concentration of 0.5%. An increase in concentration resulted in a more profound motor blockade. The Cmax of ropivacaine in this study was below levels associated with toxicity in animal studies.