Analgesic Effectiveness of Dipyrone (Metamizol) for Postoperative Pain after Herniorrhaphy: A Randomized, Double-Blind, Dose-Response Study

Background: The efficacy of non-narcotic analgesics is mostly supported by randomized, placebo-controlled trials with no comparison with ordinary practice. Additionally, systematic reviews of these placebo-controlled trials have failed to determine clinically meaningful doseresponse effect. Methods: In this double-blind, randomized trial, patients undergoing elective inguinal, umbilical or epigastric herniorrhaphy under general anesthesia were assigned to receive 15 mg/kg (D15 group) vs. 40 mg/kg (D40 group) of dipyrone intravenously during surgery. The primary outcome was the incidence of moderate to severe pain with movement during the recovery room phase. The secondary outcomes were morphine consumption, incidence of vomiting, and Ramsay score (sedation scale). Results: One hundred sixty-two patients were enrolled and analyzed for the primary and secondary outcomes. Relative to the D15 group, the D40 group showed a lower incidence of moderate to severe pain in the first 30 minutes (61% and 40%; P value < 0.05); lower cumulative morphine consumption during the recovery period (3.85 vs. 2.55 mg, P value < 0.006) as well as a lower incidence of vomiting (15.8% vs. 2.5%, P value < 0.005). In addition, more cases of sedation were recorded in the D15 group than in the D40 group (17 vs. 10 cases). There were no serious adverse effects attributed to dipyrone in either group. Conclusion: This trial shows a dose-response effect of 40 mg/kg over 15 mg/kg of intravenous dipyrone based on better movement-induced pain control, lower morphine consumption and fewer opioid-related side effects.