Comparative motor-blocking effects of bupivacaine and ropivacaine, a new amino amide local anesthetic, in the rat and dog

Ropivacaine (S-(-)-1-propyl-2',6'-pipecoloxylidide) is a new local anesthetic that is structurally related to mepivacaine and bupivacaine. The comparative effects of ropivacaine and bupivacaine on motor function were assessed in the laboratory rat and dog. (It was not possible to accurately evaluate sensory blockade in these models.) Several concentrations of both agents were injected in the region of the sciatic nerve of the rat and into the lumbar epidural or subarachoid space in the dog. Epidural blockade was also performed utilizing solutions of ropivacaine and bupivacaine which contained epinephrine (1:200,000). The rat sciatic block studies indicate that at concentrations of 0.5 and 0.75%, ropivacaine had a slightly shorter time of onset and duration of motor blockade than did bupivacaine. In the epidural and spinal studies in the dog, ropivacaine was less potent and had a shorter duration of motor blockade than did bupivacaine at equal drug concentrations. A 1.0% solution of ropivacaine produced epidural motor blockade similar in onset and duration to that achieved with a 0.75% solution of bupivacaine. Epinephrine did not significantly prolong the duration of motor blockade of either agent after epidural administration.