Ketamine is formulated as an acidic solution, pH 3.5 to 5.5, available with or without 0.1 mg/mL benzethonium chloride preservative. Ketamine is marketed as the racemic mixture and some properties of the individual isomers have been elucidated.50 Ketamine is a rapid-acting agent that can be used for induction, used as the sole agent for general anesthesia or combined with other agents. Unlike the proposed mechanism of action for most anesthetics, ketamine does not act at the GABAA receptor. Ketamine acts as a noncom-petitive antagonist at the glutamate, NMDA receptor, a nonspecific ion channel receptor. The NMDA receptor is located throughout the brain and contains four well-studied binding sites. The primary binding site binds l-glutamate, NMDA, and aspartate. The allosteric site binds glycine, which facilitates primary ligand binding. There is also a magnesium binding site that blocks ion flow through the channel and a phencyclidine (PCP) binding site that blocks the ion channel when occupied. Ketamine is believed to bind to the PCP site in a stereoselective manner and block the ion flow in the channel.51 By blocking the flow of calcium ions into the cell, ketamine prevents the calcium
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