Successful use of ketamine for intractable cancer pain

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Abstract
Despite medical awareness, intractable pain is a serious problem in cancer and occurs in up to 2% of advanced cancer patients. However, few data are available concerning the optimal treatment of such patients. The emergence of intractable pain may notably be due to the activation of N-methyl-D-aspartate (NMDA) receptors located in the central nervous system. NMDA antagonists might thus be an interesting approach in such pain syndromes. Twelve patients with intractable cancer pain received a test dose of 5–10 mg of ketamine, a strong NMDA antagonist, in order to determine their response and tolerance to the drug. Continuous intravenous infusions of ketamine associated with morphine were then administered. The acute test dose was successful in all cases (VAS <3/10 after 5 min). The prolonged use of ketamine allowed us to reduce the total daily dose of morphine required (range: 200–1,200 mg) by 50% and allowed eight patients to go home with a portable pump with morphine and ketamine during a relatively long period of time (range: 7–350 days, median: 58 days). Side effects were moderate (dizziness) and they were limited to the test phase. Our data suggest the importance of NMDA receptors in the genesis of chronic cancer pain and indicate that NMDA antagonists should be further studied for the management of cancer pain and, in particular, intractable pain.