Amantadine, a N-Methyl-d-Aspartate Receptor Antagonist, Does Not Enhance Postoperative Analgesia in Women Undergoing Abdominal Hysterectomy

N-methyl-d-aspartate (NMDA) antagonists administered before surgery will improve postoperative analgesia, presumably by inhibiting spinal sensitization processes. However, current clinical formulations of NMDA antagonists either enable only an oral application (i.e., dextromethorphan) or are associated with psychotropic side effects, as with the IV delivery of ketamine. Because of its noncompetitive NMDA receptor antagonist characteristics, amantadine may improve postoperative analgesia when administered before surgically induced trauma. In this prospective, randomized clinical study, we examined whether female patients undergoing elective abdominal hysterectomy experienced less postoperative pain when IV amantadine was applied in comparison with placebo before the start of surgery. Thirty patients were randomly assigned to receive 500 mL saline IV before the induction of standardized general anesthesia in Group 1 (Control group) or, in a double-blinded manner, 200 mg amantadine IV in 500 mL saline in Group 2 (Treatment group). Postoperative pain control was provided via IV patient-controlled analgesia with piritramide. During the first 48 h after tracheal extubation, pain perception was assessed by visual analog scales, and all analgesic requirements were documented. There were no significant differences between the two groups with respect to pain scores, postoperative analgesic requirements, and the incidence of side effects. Because of no differences in postoperative pain or opioid consumption, we conclude that a preoperative dose of 200 mg amantadine IV fails to enhance postoperative analgesia in patients undergoing elective abdominal hysterectomy.