Pentazocine is a good drug as non-narcotics for pain control, but repeated intramuscular injection can cause the disorders of skin and muscles as side effect.

13 cases who has been treated by injection chronically for pain control, were evaluated clinically, laboratory and electrodiagnostically.

The obtained results are as follows:

1) The most injured muscles were deltoids, gluteus, biceps brachii, and quadriceps.

2) There were swelling, induration, inflammatory nodule and abscess formation in skin, and fibrous contracture in muscle (especially, hip and shoulder is abducted), which showed fixed posture.

3) There increment of the serum CPK (creatine phosphokinase), serum LDH (lactate dehydrogenase) in 2 cases, and urine myoglogbin in 5 cases were observed, but there were no significance statiscally.

4) Electrodiagnostic study revealed myopathic pattern, i.e. short amplitude polypohasic motor unit and normal conduction velocity with low amplitude of motor action potential.

As indicated above, since the repetitive injection of pentazocine on the same site causes a serious skin and muscle disorders, it is considered that pain control by means of other non-narcotic analgesics is proper in the future.