Low-dose ketamine as an adjunct to morphine: A randomized controlled trial among patients with and without current opioid use.

Background: Pain is a common complaint among patients presenting to the emergency department (ED), yet pain treatment is frequently suboptimal. The aim of this study was to determine the effectiveness of low-dose ketamine (LDK) as an adjunct to morphine versus morphine alone for treatment of acute pain among ED patients with and without current opioid use.

Methods: Adult patients presenting with acute pain of ≥5 on a numeric rating scale (0-10) who were deemed by their treating ED physician to require intravenous opioids were randomized to receive either 0.1 mg/kg ketamine (treatment group) or isotonic saline (placebo) as an adjunct to morphine. Patients with and without current opioid use were randomized separately. Pain was measured at baseline (T0) and 10, 20, 30, 45, 60, and 120 min after randomization. The primary outcome was pain reduction from T0 to T10. Secondary outcomes included pain intensity over 120 min, need of rescue opioids, side effects, and patient and provider satisfaction.

Results: A total of 116 patients were included from May 2022 to August 2023. Median (IQR) age was 51 (36.5-67) years; 58% were male and 36% had current opioid use. Pain reduction from T0 to T10 was greater in the LDK group (4 [IQR 3-6]) compared to the placebo group (1 [IQR 0-2]; p = 0.001). Pain intensity was lower in the LDK group at T10, T20, and T30, compared to the placebo group. There was a higher risk of nausea, vomiting, and dissociation in the LDK group during the first 10 min.

Conclusions: LDK may be effective as an adjunct analgesic to morphine for short-term pain relief in treatment of acute pain in the ED for both patients with and without current opioid use.