Background and Objectives. Local anesthetics including bupivacaine have been known to be myotoxic. Continuous brachial plexus blocks with bupivacaine provide good postoperative pain relief, but their effects on the surrounding muscles have not been studied.

Methods. Eight rabbits were given continuous bilateral brachial plexus blocks with 0.25% bupivacaine (BUPI) and another eight (SALINE) equivalent volumes of saline infused into the plexus region under pentobarbital-ketamine sedation. At the end of the 24-hour blocks, muscle biopsies were taken from one side of the neck in both groups. A week later, the biopsy procedure was repeated on the other side. Plasma concentrations of bupivacaine were measured before and at the end of the 24-hour blocks.

Results. Inflammatory cell infiltration and muscle fiber necrosis were significantly more common in the BUPI than in the SALINE group ( p < 0.001). At the end of the continuous block, predominantly neutrophils were found, but in the BUPI group large amounts of eosinophilic granulocytes also were found. A week later lymphocytes, plasma cells, macrophages, and fibroblasts were seen as a sign of beginning scar formation. Plasma concentrations of bupivacaine at 24 hours were at a nontoxic level (0.28-0.71 μg/ml).

Conclusions. Brachial plexus blocks with bupivacaine caused reversible myotoxicity and inflammation in the rabbit. A week after the continuous blocks, muscle fiber regeneration had already started.