Recovery of jaw muscle function following injection of a myotoxic agent (lidocaine-epinephrine).

Intramuscular injection of 2% lidocaine hydrochloride with epinephrine (1:100,000) bilaterally into the masseter muscles of growing rats resulted in a 30% to 40% decrease in maximal stimulated bite force at 3 days following injection. By 6 days postinjection, bite force had begun to increase, but significant differences from control bite force levels were still present 15 days postinjection. By 25 days postinjection, recovery to control values was complete. These data are consistent with previously documented fiber destruction and subsequent regeneration following exposure to this and other local anesthetic agents. It is suggested that local myotoxic effects produced by the administration of such drugs may result in a transient functional deficit in the injected muscle(s) that may persist for up to 2 weeks.