Subanesthetic, Subcutaneous Ketamine Infusion Therapy in the Treatment of Chronic Nonmalignant Pain.

This study was designed to describe the efficacy and toxicity of subcutaneous ketamine infusions and sublingual ketamine lozenges for the treatment of chronic nonmalignant pain. Data were collected prospectively on 70 subjects managed in an academic, tertiary care hospital between 2007 and 2012 who received between 3 and 7 days of subanesthetic, subcutaneous ketamine infusion. Data were analyzed for efficacy, adverse effects, and reduction in use of opioid medication. We also analyzed whether subsequent treatment with sublingual ketamine lozenges resulted in longer-term efficacy of the beneficial effects of the initial ketamine infusion. There was a significant reduction in pain intensity measured by numerical rating scale (NRS) from mean of 6.38 before ketamine to 4.60 after ketamine (P < .005) that was sustained for between 3 months and 6 years. In subjects on opioids, there was a significant reduction in opioid use at the end of the ketamine infusion from a mean morphine equivalent dose (MMED) of 216 mg/day before ketamine to 89 mg/day after ketamine (P < .005). The overall reduction in opioid use after ketamine infusion was 59%. No subjects increased their use of opioids during their hospitalization for the ketamine infusion. A small proportion of subjects who responded to the infusion were continued on ketamine lozenges. This group was followed for between 3 months and 2 years. The use of ketamine lozenges after the infusion resulted in 31% of these subjects being able to cease their use of opioids compared with only 6% who did not receive ketamine lozenges. Eleven percent of subjects who received lozenges subsequently increased their opioid usage. Adverse effects were fairly common, but only mild, with 46% of patients experiencing light-headedness and dizziness, 25% tiredness and sedation, 12% headaches, 12% hallucinations, and 8% vivid dreams. Adverse effects were easily managed by reducing the rate of the ketamine infusion. The administration of subanesthetic, subcutaneous ketamine infusion was well tolerated, with mostly mild adverse effects and no serious adverse effects. The infusion provided significant pain relief in subjects who had failed a wide range of pharmacological and cognitive behavioral therapies. In addition, the results indicate that sublingual ketamine lozenges offer a promising therapeutic option for longer-term relief of chronic nonmalignant pain. The ketamine lozenges have been shown to have acceptable storage stability, and the sublingual bioavailability is sufficiently high and reproducible to support its use in this context.