Ketamine for cancer pain: what is the evidence?

PURPOSE OF REVIEW: In this review, we assess the benefit of ketamine in the treatment of terminal cancer pain that is refractory to opioid treatment and/or complicated by neuropathy.

RECENT FINDINGS: While randomized controlled trials consistently show lack of clinical efficacy of ketamine in treating cancer pain, a large number of open-label studies and case series show benefit.

SUMMARY: Ketamine is an N-methyl-D-aspartate receptor antagonist that at low-dose has effective analgesic properties. In cancer pain, ketamine is usually prescribed as adjuvant to opioid therapy when pain becomes opioid resistant or when neuropathic pain symptoms dominate the clinical picture. A literature search revealed four randomized controlled trials that examined the benefit of oral, subcutaneous or intravenous ketamine in opioid refractory cancer pain. None showed clinically relevant benefit in relieving pain or reducing opioid consumption. This suggests absence of evidence of benefit for ketamine as adjuvant analgesic in cancer pain. These findings contrast the benefit from ketamine observed in a large number of open-label studies and (retrospective) case series. We relate the opposite outcomes to methodological issues. The complete picture is such that there is still insufficient evidence to state with certainty that ketamine is not effective in cancer pain.