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.