Double-blind, Randomized Controlled Study to Assess the Analgesic Effect of 2 g of Magnesium Dipyrone (Metamizol) and Changes in Plasma Beta-endorphin Immunoreactivity Values in Patients Undergoing Elective Inguinal Herniorrhaphy Under Epidural Anesthesia.

A double-blind, randomized controlled study is designed to assess the analgesic effect of a single intravenous dose of 2 g of magnesium dipyrone (metamizol) and whether the administration of the active drug will be associated with changes in plasma beta-endorphin immunoreactivity values in patients undergoing elective inguinal herniorrhaphy (Bassini operation) under epidural anesthesia. Participants, care givers, and those assessing the outcomes will be blinded to group assignment. Participants will be randomized to receive dipyrone or a placebo. The active drug or placebo will be administered as an intravenous infusion over 10 min. Pain will be evaluated by the patient according to a 100-mm visual analogue scale. Assessments will be carried out the day before surgery, immediately after operation, at the time of drug administration, and 60 and 180 min after treatment. At the same time as pain will be evaluated, blood samples will be drawn for plasma beta-endorphin immunoreactivity measurement (immunoradiometric assay).