Water-diluted local anesthetic for trigger-point injection in chronic myofascial pain syndrome: Evaluation of types of local anesthetic and concentrations in water

Background and objectives: We have recently demonstrated that a mixture of 1% lidocaine with water in a 1:3 ratio has less injection pain and is more effective than unaltered 1% lidocaine in treating chronic myofascial pain s yndromes. Yet, the most suitable local anesthetic and the most effective di lution in water have not been evaluated. Methods: Various mixtures of local anesthetics and water or saline were inj ected intramuscularly into the shoulder of 40 female volunteers, and pain s cores on injection were evaluated in a randomized and double-blinded manner . In another portion of the study, 0.25% or 0.2% lidocaine in water were in jected randomly into 1 side of 21 outpatients with chronic neck, shoulder, or lumbar myofascial pain to the same degree in both sides. The other solut ion was injected into the other side of the same patients. Results: Less injection pain was experienced with the water-diluted 0.25% l idocaine and water-diluted 0.25% mepivacaine than the saline-diluted 0.25% lidocaine and water-diluted 0.0625% bupivacaine. Also,less injection pain w as experienced with the water-diluted 0.25% and 0.2% lidocaine than the wat er-diluted 0.3% and 0.15% lidocaine. In the other study, there were no diff erences in either the effectiveness or duration of analgesia between the 0. 25% and 0.2% water-diluted lidocaine. Conclusions: The suitable type of local anesthetic may be lidocaine or mepi vacaine, and the most effective water-diluted concentration is considered t o be 0.2% to 0.25%.