Efficacy of oral ketamine against opioid-refractory cancer pain due to bone metastases: Four case reports.

161 Background: The use of oral ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, is reported to be effective against opioid-refractory cancer pain. Only a few studies have been performed worldwide so far, and in Japan we have more difficulty evaluating it, as the insurance doesn’t cover the application of ketamine to the tumor pain unlike in some other countries. Here we present the successful treatment of four patients with severe cancer-related pain due to bone metastases, by oral administration of ketamine. Methods: Inclusion criteria were cancer pain refractory to standard opiates. After institutional approval and informed patient consent were obtained, the treatment started with 40mg/day of oral ketamine. The ketamine regimen was adjusted individually based on analgesia and any adverse effects. Results: Self-reported pain significantly improved. In addition, serious adverse effects such as nightmares were not observed. In one case, epidural anesthesia became unnecessary. In another case,...