Myotoxicity of local anesthetics and regeneration of the damaged muscle fibers.

In view of the documented myotoxic effects of the local anesthetic, bupivacaine, a survey of myotoxic effects of seven local anesthetics was conducted. In 70 rats, 200 microliters of an anesthetic solution was injected into one tibialis anterior muscle and a control solution was injected into the contralateral muscle. The anesthetics fell into two groups in their effects upon muscle. One group, including 1% procaine, 0.2% tetracaine, 0.5% lidocaine, and 0.75% bupivacaine, produced effects that were confined principally to the muscle fiber. The other group (2% chloroprocaine, 0.25% dibucaine, 0.5% lidocaine with 1:200,000 epinephrine and 2% piperocaine) produced toxic effects on other tissue components of the muscles in addition to affecting muscle fibers. With all anesthetics, the initial damage to and breakdown on muscle fibers was restored by regeneration and 30-day muscles showed relatively few long-term effects of the damage.