Ketamine for acute and subacute pain in opioid-tolerant patients.

Prolonged acute pain, especially that of oncologic neurological origin, is at times difficult to control; it is seldom entirely alleviated by opioids. We report eight patients with severe pain, three of whom suffered from new onset oncologic metastatic bone pain, others had previous pain syndromes and presented with exacerbation of pain. Pain was associated with hyperalgesia and allodynia phenomena in two patients and with phantom pain in a third one. Tolerance to opioids had developed, and high IV doses of morphine, meperidine or fentanyl, and patient-controlled intravenous and epidural analgesia were insufficient. Several patients became dependent on opioids and could not be weaned from assisted ventilation. Pain was controlled with decreasing adjunct doses of ketamine. Within 5-10 days of ketamine and opioid protocols, pain was controlled and after an additional 5-7 days, ketamine could be stopped and pain controlled on oral regimens compatible with outpatient care. Ketamine is an efficient adjuvant analgesic for intractable severe pain, caused by metastasis, trauma, chronic ischemia, or central neuropathic pain. It is effective even when mega doses of IV, epidural, or oral opioids prove ineffective and when signs of tolerance have developed.