Intravenous Ketamine for Cancer Pain: A Single-Center Retrospective Analysis Comparing Fixed-Rate Versus Weight-Based Dosing

Although weak evidence exists to support subanesthetic ketamine for cancer pain treatment, successful use may be hindered in the absence of standardized dosing guidance. We aimed to compare the success rates of intravenous ketamine fixed-rate versus weight-based dosing strategies for cancer pain treatment, and to assess patient characteristics that correlate with treatment success. We conducted a single-center retrospective review including non-critically ill adults with cancer pain who received subanesthetic ketamine for at least 24-h. All patients received fixed-rate ketamine; weight-based doses were retrospectively determined using total body weight. Treatment was considered successful if after reaching the maximum prescribed ketamine dose the patient had a 30% reduction in: baseline pain score, as-needed opioid use, or total morphine equivalent daily dose over a standardized 24-h. Of 105 included patients, 51 (48.6%) successfully responded to ketamine. Responders had lower fixed-rate ketamine doses compared to non-responders (median[IQR] 15 mg/hr[10-15] vs. 15 mg/hr[15-20],  = 0.043), but no difference in retrospectively calculated weight-based doses (0.201 ± 0.09 mg/kg/hr vs. 0.209 ± 0.08 mg/kg/hr,  = 0.59). Responders had higher daily opioid requirements at baseline compared to non-responders ( = 0.04). Though underpowered, our findings suggest that weight-based ketamine dosing may not convey additional benefit over fixed-rate dosing.