To investigate the skeletal muscle changes, intramuscular injections of local anesthetics were performed using animal, Sprague-Dawley rat.

The experiments were composed of two procedures, experiment I and II. In experi ment I, single injection was performed using 0.4 cc of 1 and 2% of procaine and lidocaine.

In experiment II, repeated injection of 0.4 cc of 2% lidocaine on weekly bases 3 times were performed.

The experimental rats were divided into five groups in experiment I: Four experimental groups 40(10 rats for each local anesthetics) and Control 10 and were divided into two groups in experiment II: Experimental group 8 and Control 4. The muscle biopsies were performed in 15 minutes, 2, 4, 8 and 16 days after injection in two experiments.

No muscle fiber changes were shown in control group, and 1~2 % procaine, and 2% lidocaine injected groups of experiment I and control group of experiment II. In the groups of single and repeated injections of 2% lidocaine, muscular inflammatory changes were shown on 2 and 4 days after injection. The changes were more extensive in the group of repeated injections. The inflammatory reaction was usually abated on 8 days after injection and the muscles appeared to be normal in quality and quantity on 16 days after injection. These histopathologic results indicated reversible muscular changes.

Although the muscular changes are reversible after local anesthetics injection, the concentration of local anesthetics and injection interval should be considered to minimize the muscle fiber changes in the repeated injections.