Bupivacaine injection leads to muscle force reduction and histologic changes in a murine model

Objective: To evaluate the effect of bupivacaine on muscle force and histology. We hypothesize that bupivacaine will worsen the muscle's physiological activity.

Setting: Controlled laboratory experiment.

Methods: Bupivacaine (0.5 mL, 0.5%) was injected into the mid belly and distal portions of the right gastrocnemius in 32 Wistar male rats (the left gastrocnemius was used as a control). After 5, 14, 21, and 28 days, in groups of 4, muscle force was evaluated and the animals were euthanized by an overdose of anesthetic for histologic evaluation. One-way analysis of variance was used to analyze data from force and weight measurements. Only the values of P < .05 were considered to be statistically significant.

Results: Bupivacaine causes a process of degeneration-regeneration of the muscle fibers and it also causes a reduction in muscle force, which is significant at 2 and 3 weeks and does not normalize at 4 weeks. The muscle injury is obvious after 5 days, and the degenerative process is predominant at 2 and 3 weeks. We found an increase in muscle mass in the acute phase and a decrease in muscle force.

Conclusion: Although our results do not allow a direct clinical application, we believe that caution should be warranted when intramuscular bupivacaine is used.