[Ketamine for treatment of chronic pain: meta-analysis]

The idea of using Ketamine to treat chronic pain is mainly based on the central antinoceptive effect of the substance acting as a noncompetitive antagonist at the NMDA-receptor. In the present meta analysis over a period from 1/1981 up to 6/1996 twelve publications (1994-1996), which have dealt the use of Ketamine for patients with chronic pain, are evaluated and discussed. The entire positive evaluation of the drug is based on the results of the studies under consideration. The studies investigating 88 cases are classified, i.e. seven studies are assigned to level 3, two studies to level 4, and three studies to level 5. A significant reduction of pain has been proven for patients with neuropathic pain by four cross-over-studies comparing the drug with placebo. However, observations have been restricted to a few hours after the administration of the drug. A positive effect of Ketamine as compared with opioids has been demonstrated by three studies, one of them with statistical significance. Positive long term results have been observed by two studies considering the subcutaneous and intravenous application of Ketamine (72-480 mg, daily) to 14 cancer pain patients, to whom opioids have been administered with insufficient effects before. A successful five-week-application (oral) of Ketamine has been described convincingly in a case report of a patient with postherpetic neuralgia. Two studies interpret the additional intrathecal administration of Ketamine to cancer patients as a possibility of either impeding the development of tolerance of the local anesthetic or reducing morphine requirements. Only one paper has dealt with the known side effects of Ketamine. Here, the therapy had to break off in two cases. In nine cases the side effects could be suppressed by Droperidol. For the future, research with more study power is necessary to establish Ketamine in the therapy of chronic pain.