Authors: Gabriela A. Calhoun, M.D. et al
George Washington University, Washington, Dist. of Columbia, United States
Background: Ketamine has been in clinical practice since the 1960s, used for its analgesic properties as a N-methyl-d-aspartic acid receptor antagonist (1). The role of ketamine at lower, sub-anesthetic doses has recently gained interest in chronic pain management, a condition affecting over 100 million Americans (2). Although ketamine is not FDA approved for chronic pain treatment, the current literature provides adequate evidence for acute relief of chronic pain (1). However, information supporting the long-term efficacy of Ketamine in patients with chronic pain is limited.
Objectives: Our previous study found that pain, sleep, and enjoyment of life improved following 3-day infusions. This study aims to: (1)reevaluate the impact of ketamine infusions on pain level and quality of life (QOL) outcomes with a larger sample size; (2)determine if there is a difference in results in patients receiving 1-day or 3-day infusions; and, (3) examine whether repeated infusions have an influence on outcomes.
Methods: Patients completed the basic pain inventory (BPI) to rate, on a scale from 0 (no impact) to 10 (severe impact), their pain score and the degree their pain interfered with QOL (general activity, walking, work, relationships, mood, sleep, and enjoyment of life). The BPI was completed prior to 1-day or 3-day outpatient ketamine infusions and was repeated two to four weeks after the infusions. Paired two tailed t-tests were used to compare post and pre-infusion scores. Random effect mixed models were used to determine whether the change of outcome (post vs. pre) is different for 1-day versus 3-day infusions and to examine the association between pain score or other BPI indicators and repeat number of infusions among repeaters (patients who received greater than one 1-day or 3-day infusions) only. Repeaters were grouped into 2-3, 4-6, and 7+ infusions and results were compared to the 1st infusion. Results were adjusted for age, gender and race.
Results: There were 252 3-day infusions and 34 1-day infusions. 118 of these patients completed pre/post infusion BPI’s. 48 patients, termed repeaters, had more than one infusion (1-day or 3-day). The analysis produced statistically significant improvement in post versus pre-infusion outcomes in pain level (p= 0.0124), enjoyment of life (p= 0.0052), general activity (p= 0.0015), mood (p= 0.0023), work (p= 0.0041), relationships (p= 0.0001), and sleep (p< 0.0001). The mean walk score did not have significant improvement (p= 0.2419). The statistical model predicting 1-day versus 3-day infusions revealed no significant difference in pain level or QOL outcome measurements. The statistical model for repeaters revealed significant cumulative improvement in enjoyment of life (p= 0.0132) and relationships (F= 3.90, p= 0.0092) with increased number of repeated infusions. However, the change in pre-post scores for later infusions was not different from the pre-post infusion change of the first infusion.
Conclusion: Outpatient ketamine infusions for treating chronic neuropathic pain improved pain levels and QOL measurements including enjoyment of life, general activity, mood, work, relationships, and sleep, but walking was not improved. There was no significant difference in improvement between patients who received 1-day versus 3-day infusions. However, there was a positive correlation between improvement in enjoyment of life and number of repeated infusions. Importantly, this conclusion may be overstated, as there was a small sample of 1-day infusions, We plan to continue this study to look at a larger sample size to determine if duration of infusion affects outcome measurements.