Which of the following drugs is a dissociative agent?

• A. Diazepam
• B. Tricaine methanesulfonate
• C. Ketamine
• D. Xylazine

Answer: (C)

Dissociative anesthesia is defined by analgesia and a trance-like state where the patient is detached from the environment, often with preserved reflexes and airway control. Ketamine achieves this by antagonizing NMDA receptors, producing a dissociation between the thalamocortical and limbic systems. This gives analgesia and amnesia with a characteristic detachment, while many patients continue to breathe on their own and may have preserved reflexes.

Diazepam is a benzodiazepine that enhances GABA A activity, leading to sedation and anxiolysis rather than dissociation. Tricaine methanesulfonate (MS-222) is used mainly in fish anesthesia and acts differently (blocking nerve conduction and providing general anesthesia without the dissociative state). Xylazine is an alpha-2 adrenergic agonist used as a sedative and analgesic with muscle relaxation, not a dissociative agent. Ketamine is the one that fits the dissociative profile.