Opioid-sparing effect of intravenous outpatient ketamine infusions appears short-lived in chronic-pain patients with high opioid requirements.

BACKGROUND AND OBJECTIVES: Ketamine is opioid-sparing. It attenuates the onset of opioid tolerance, and suppresses opioid-induced hyperalgesia. This study evaluated whether or not repeated outpatient infusions of intravenous ketamine reduced the amount of pain and the amount of opioid requirements for patients suffering with chronic, non-cancerous pain.

STUDY DESIGN: Retrospective study

SETTING: Outpatient pain clinic

METHODS: We reviewed the records of 18 patients taking high doses of opioids chronically and nonetheless reporting poorly controlled pain. A comparison control group of 18 similar patients with high opioid requirements who were not given ketamine were selected from our clinic population.

INTERVENTION: Intravenous ketamine infusions

MEASUREMENT: VAS pain scores and opioid use

RESULTS: Morphometric and demographic characteristics, baseline opioid use, and pain scores were similar in the ketamine and comparison groups. Five patients given ketamine experienced no benefit and discontinued treatment after 1-2 infusions. One patient developed a supraventricular arrhythmia which immediately resolved upon cessation of the infusion. And another, despite pain relief, felt overly-anxious and opted out. Eleven patients thus completed 3-6 weekly ketamine infusions. At 6 months, 5 patients maintained less than 50% of their baseline opioid use, while the remaining patients returned to the baseline opioid use or increased their requirements. There was no significant difference in pain scores at 6 months in patients who received ketamine infusions and control group patients.

LIMITATIONS: Retrospective nature of the study

CONCLUSIONS: Outpatient intravenous ketamine infusions did not improve long-term pain scores in patients with high opioid requirements and only a few were able to substantially reduce opioid use. Considering infusion risks and cost of such outpatient treatment, ketamine infusions do not appear to be a feasible option for improving pain relief and decreasing opioid use in high-opioid requirement patients.