Ketamine Is an Effective Adjunct to Morphine for Pain, Even at Low Doses

Authors: Beaudoin FL et al., Acad Emerg Med 2014 Nov 21:1193

Patients receiving ketamine (at either 0.3 mg/kg or 0.15mg/kg) in addition to morphine reported better pain relief, but the higher ketamine dose was associated with more side effects.

Although the use of ketamine as an adjunct to opioid treatment for pain has been previously described (NEJM JW Emerg Med Oct 15 2003), it is not widely used for this purpose in the emergency department (ED). Researchers compared morphine plus saline placebo versus morphine plus ketamine at two doses (0.3 mg/kg and 0.15 mg/kg) in a randomized, double-blind trial of 60 adult ED patients who required intravenous opioids for moderate to severe pain.

Patients in each of the ketamine groups achieved significantly greater pain relief over 2 hours (the primary outcome) than those in the placebo group. However, by 2 hours after drug administration, patients in the lower-dose ketamine group had comparable improvement in pain relief to those in the placebo group. Patients in the higher-dose ketamine group were more likely to have dizziness, lightheadedness, and vomiting than those in the other groups. Dysphoria or confusion occurred in 10% to 15% of the ketamine patients. The need for rescue medication was similar among the three groups (20% to 35%).

Comment
The three study groups were small and heterogeneous with respect to the cause of their pain, so intergroup differences are difficult to interpret. Frequent dosing of opioid analgesic titrated to a predetermined pain-reduction goal is the best approach to moderate to severe pain in the ED, and most patients can be treated effectively with opioids alone. For patients whose pain is refractory to opioid therapy alone, low-dose ketamine may be a reasonable adjunctive therapy, although its side effects make it inappropriate for routine use.