Repeated and escalating preoperative subanesthetic doses of ketamine for postoperative pain control in patients undergoing tumor resection: a randomized, placebo-controlled, double-blind trial.

Background: Ketamine induces a short-term effect on postoperative pain when administered intravenously immediately before or during acute pain. Repeated administration of low-dose ketamine may induce long-term pain relief in chronic pain syndromes.

Objective: The aim of our study was to determine whether ketamine's effect on acute postoperative pain could be enhanced and prolonged and analgesia consumption reduced if it was administered intramuscularly in repeated and escalating subanesthetic doses many hours before surgery.