The use of ketamine in the management of refractory cancer pain in a palliative care unit

Background: Ketamine has been used as an adjuvant to opioid therapy for the management of refractory cancer pain but the current evidence is insufficient to draw any conclusions regarding its efficacy. We aimed to assess the response to ketamine in patients with refractory cancer pain treated in an oncology palliative care unit. Methods: Patients with refractory cancer pain despite opioid dose escalation were selected for a trial of parenteral ketamine infusion according to a local protocol. The medical records of those patients treated between January 2004 and December 2018 were retrospectively reviewed. The primary endpoint of the study was a favorable response to ketamine, defined as a reduction in regular opioid dose with no increase in pain intensity or a reduction in pain intensity by >= 2 points on the numerical rating scale (NRS) with a stable regular opioid dose. The secondary endpoint was adverse events associated with ketamine. Results: Among the 70 patients, mean pain score on NRS improved from 7.0 to 4.0 after ketamine (P<0.001). Forty-nine patients had a reduction of pain score by >= 2 points on NRS, 33 had >= 50% reduction in pain intensity. The median decrease in regular opioid dose was 25.5%, and the mean difference was -133.2 mg (P=0.002). A favorable response to ketamine was observed in 52 patients (74.3%). The use of more than one coanalgesic (odds ratio 3.451; 95% CI: 1.087-10.960; P=0.036) was associated with a favorable response to ketamine on multivariate analysis. Adverse events were mostly mild, with the commonest being drowsiness (45.7%), hypertension (34.3%) and nightmares (25.7%). Only five and three patients required temporary suspension and early termination of ketamine infusion respectively. Conclusions: These data demonstrated the efficacy and safety of ketamine in a population of patients with refractory cancer pain. The use of more than one coanalgesic was associated with a favorable response to ketamine. Further large and multicentered studies are warranted to confirm these data.