Ketamine: teaching an old drug new tricks

Ketamine has a special position among anesthetic drugs. It was introduced into clinical practice >30 yr ago with the hope that it would function as a “monoanesthetic” drug: inducing analgesia, amnesia, loss of consciousness, and immobility. This dream was not fulfilled because significant side effects were soon reported. With the introduction of other IV anesthetic drugs, ketamine’s role diminished rapidly. However, it is still used clinically for indications such as induction of anesthesia in patients in hemodynamic shock; induction of anesthesia in patients with active asthmatic disease; IM sedation of uncooperative patients, particularly children; supplementation of incomplete regional or local anesthesia; sedation in the intensive care setting; and short, painful procedures, such as dressing changes in burn patients. However, recent insights into ketamine’s anesthetic mechanism of action and its neuronal effects, as well as a reevaluation of its profound analgesic properties, offer the potential of expanding this range of indications. In addition, studies with the S(+) ketamine isomer suggest that its use may be associated with fewer side effects than the racemic mixture. In this article, we review the mechanism of action of ketamine anesthesia, the pharmacologic properties of its stereoisomers, and the potential uses of ketamine for preemptive analgesia and neuroprotection. Several aspects discussed herein have been reviewed previously [1-4].