Myotoxic effects of levobupivacaine, bupivacaine and ropivacaine in a rat model

Aim: The aim of this study is to histopathalogically compare the myotoxic effects of a single injection of levobupivacaine, bupivacaine and ropivacaine in rat skeletal muscle. Materials and Methods: Rats received intramuscular injections of 0.5% bupivacaine (Group B), 0.5% ropivacaine (Group R), 0.5% levobupivacaine (Group L), or 0.9% normal saline (Group SF) (30 rats/group). At two, 10 and 20 days, 10 rats from each group were sacrificed and muscle samples were examined for myotoxic effects using hematoxylin-eosin staining under a light microscope. Results: Muscle damage in Groups B, L and R was similar qualitatively. In samples taken two days after injection, the muscle damage in Group B was maximal [Damage score: 3.0 (2.0-3.0)], Group R had less damage than Group B [damage score: 2.0 (2.0-3.0)] and the damage in Group L was minimal [Damage score: 1.0 (1.0-2.0)]. In muscle samples taken 10 days after injection, there was no significant difference in muscle damage scores among Groups B, R and L. In muscle samples taken 20 days after injection, regeneration was complete, and muscle mass was histologically normal for each of the three groups (B, L and R). Conclusion: Levobupivacaine's myotoxic effect is qualitatively similar to that seen (and previously reported) with bupivacaine and ropivacaine. Levobupivacaine was found to be quantitatively less myotoxic than bupivacaine and ropivacaine after a single intramuscular injection, only two days after injection. Myonecrosis developed after a single intramuscular injection of local anesthetic but was completely regenerated by the 20th day after injection.