Parenteral ketamine as an analgesic adjuvant for severe pain: development and retrospective audit of a protocol for a palliative care unit.

BACKGROUND: Ketamine is an effective analgesic agent for treating a variety of neuropathic and cancer pain syndromes. Recent studies indicate that ketamine may have a particular role in the management of patients with neuropathic and/or pain syndromes that are poorly responsive to opioids. OBJECTIVE: To develop, implement, and subsequently assess a protocol designed to maximize the analgesic effect of ketamine while minimizing its side effects. DESIGN: A retrospective chart audit of 16 patients who had used the ketamine protocol over a 12-month period. Criteria for assessing the effectiveness of ketamine were defined. RESULTS: Ketamine was an effective, well-tolerated analgesic adjuvant for 11 of 16 patients with previously uncontrolled pain. Pain scores were reduced by at least 4 of 10 in 15 of the 16 patients. Median opioid dose reduction on starting ketamine was 25%. CONCLUSION: The audit confirmed the safety and effectiveness of ketamine as an analgesic adjuvant for patients with severe pain. Baseline opioid dose reduction and prophylactic use of haloperidol or benzodiazepine were effective in minimizing psychotomimetic side effects.

Low dose ketamine as an analgesic adjuvant in difficult pain syndromes: a strategy for conversion from parenteral to oral ketamine.

Ketamine is a non-competitive N-methyl D-aspartate (NMDA) receptor antagonist with analgesic and dissociative anesthetic properties. Low dose or sub-anesthetic doses of ketamine have been used effectively as either a primary analgesic or analgesic adjuvant in a variety of pain syndromes. In this paper, three patients with difficult to treat, predominantly neuropathic pain syndromes will be described. Their pain syndromes were initially managed successfully with the addition of low dose parenteral ketamine as an analgesic adjuvant. The strategy of concurrently starting ketamine at a low dose, i.e., 40-60 mg over 24 hours, with a benzodiazepine proved effective in preventing psychotomimetic side effects. An unavoidable shortage of ketamine prompted a literature search, which suggested that the equianalgesic dose of oral ketamine could be lower than the parenteral dose. Subsequently the patients were converted to oral ketamine at doses 30 to 40% of the previous parenteral dose. Their pain syndromes remained controlled on the lower dose of oral ketamine with remarkably few side effects. The implications of this warrant further discussion and study.