Emerging concepts on the use of ketamine for chronic pain

Introduction: The use of ketamine infusions for chronic pain has surged, with utilization exceeding the proliferation of knowledge. A proposed mechanism for the long-term benefit in chronic pain is that ketamine may alter the affective-motivational component of pain. Areas covered: In this review, we discuss the classification and various dimensions of pain, and explore the effects of ketamine on different pain categories and components. The relationship between ketamine's action at the NMDA receptor, the development of chronic pain, and the its possible role in preventing the persistence of pain are examined. We also summarize animal models evaluating the antinociceptive effects of ketamine and risk mitigation strategies of ketamine-associated side effects. Expert opinion: Although ketamine exerts most of its analgesic effects via the NMDA receptor, recent evidence suggests that other receptors such as AMPA, and active metabolites such as nor-ketamine, may also play a role in pain relief and alleviation of depression. Data from clinical studies performed in patients with chronic pain and depression, and the observation that ketamine's analgesic benefits outlast its effects on quantitative sensory testing, suggest that the enduring effects on chronic pain may be predominantly due ketamine's ability to modulate the affective-motivational dimension of pain.