Pentazocine-induced fibrous myopathy.

Fibrous myopathy was found in three patients who had taken pentazocine intramuscularly for years. Fibrotic induration in the quadriceps and deltoid muscles, the considerable limitation of motion due to the fibrotic muscle contracture, and the minimal weakness of involved muscles are the most characteristic findings in this condition. Results of animal experiments support the close relationship between myopathy and pentazocine. This serious complication emphasizes more judicious use of pentazocine