Background and Objectives Ropivacaine and levobupivacaine, both single S(−) enantiomers, are being promoted as safer alternatives to racemic bupivacaine. To determine whether levobupivacaine produces a more potent and longer lasting peripheral nerve block than ropivacaine, we compared functional blockade of sciatic nerve in the rat at several doses with these 2 agents.

Methods Percutaneous sciatic nerve blocks were performed in 6 groups of rats (n = 8) with 0.1 mL of 0.0625%, 0.125%, and 0.25% of levobupivacaine or ropivacaine, with and without 1:200,000 epinephrine. In the 2 different hindlegs of the same 8 rats, we measured the degree and duration of deficit of 3 functions of peripheral nerve (proprioception, motor function, nociception) effected by the 2 respective drugs at the same concentration, using a blinded cross-over design.

Results In general, both degree and duration of functional deficits produced by levobupivacaine were slightly greater than those from ropivacaine at the same dose. At the lowest concentration (0.0625%), no functions were completely blocked and the only significant difference was a longer motor impairment by levobupivacaine. At the highest concentration (0.25%), all formulations completely blocked the 3 functions, all of which lasted longer with levobupivacaine than ropivacaine. There were no significant differences in degree and duration of deficits between the 2 drugs at midconcentration (0.125%). The actions of both drugs were generally potentiated by epinephrine, but the rank order of potency was not altered.

Conclusions At the lowest concentration (0.0625%), levobupivacaine produces a greater degree of motor impairment and a longer duration of proprioceptive impairment relative to ropivacaine. At the middle concentration (0.125%), there no differences between the 2 drugs. At the higher concentration (0.25%), which is within the range used clinically for peripheral nerve block (0.25%-0.5%), levobupivacaine produces approximately a 30% longer duration of complete block in each modality compared with that by ropivacaine.