Background: Inpatient subanaesthetic ketamine infusion for 5 days may improve pain and reduce oral opioid usage in patients with chronic pain. Objective: This study aims to investigate pain and psychological outcomes of ketamine parenteral infusion (0.1 - 0.35 mg/kg/h or maximum 24 mg/hour) for 5 days in patients with chronic refractory pain. The secondary objective is to explore any prognostic pain and psychological factors associated with the successful response to the ketamine treatment. Methodology: A prospective longitudinal study of a small cohort (N = 35) of patients with heterogenous chronic refractory pain conditions was conducted from one week to two months follow-up. Results: Pain Severity was significantly improved from mean 6.5 to 5.1 (t = 3.77, p < 0.001, d = 0.6) at 1-week and 5.9 (t = 2.14, p = 0.042, d = 0.4) at 2-month; Pain Interference from mean 7.0 to 5.1 (t = 4.99, p < 0.001, d = 0.9) at 1-week and 6.1 (t = 2.16, p = 0.041, d = 0.4) at 2-month; Pain Self-Efficacy Questionnaire (PSEQ) from mean 17 to 24 (t = −3.37, p = 0.002, d = −0.6) at 1-week and 23 (t =−2.60, p = 0.016, d =−0.5) at 2-month; Pain Catastrophizing (PCS) from 28 to 23 (t = 3.4, p = 0.002; d = 0.6) at 1-week and 21 (t = 2.45, p = 0.022, d = 0.5) at 2-month; Depression from mean 21 to 16 (t = 2.16, p = 0.038, d = 0.4) at 1-week and 16 (t = 3.53, p = 0.002, d = 0.7) at 2-month; and oral Morphine Equivalent Daily Dose (oMEDD) reduced from mean 191 mg/day on admission to 122 mg/day at 1-week (t = 2.38, p = 0.023; d = 0.4) and 93 mg/day at 2-month (t = 2.59, p = 0.016; d = 0.5). There was no significant difference between responders and non-responders on baseline psychological measures (t33 < 1.19, p > 0.244) and pain classifications ( = 0.610, p = 0.894). Conclusion: Ketamine subanaesthetic dose infusion for 5 days was found to be effective in managing chronic refractory pain with significant opioid reduction and small improvements in all chronic pain outcomes, except anxiety, at 1-week and 2-month follow-up and with
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= 0.610, p = 0.894). Conclusion: Ketamine subanaesthetic dose infusion for 5 days was found to be effective in managing chronic refractory pain with significant opioid reduction and small improvements in all chronic pain outcomes, except anxiety, at 1-week and 2-month follow-up and with
