Which drug exerts its main central nervous system action by inhibiting NMDA receptors?

Which drug exerts its main central nervous system action by inhibiting NMDA receptors?

• A. Thiopental
• B. Midazolam
• C. Etomidate
• D. Ketamine

Answer: (D)

Ketamine works mainly by blocking NMDA receptors, a type of glutamate receptor that mediates excitatory signaling in the brain. By blocking this channel, ketamine reduces excitatory transmission, producing anesthesia, analgesia, and dissociation. This NMDA antagonism gives ketamine its distinctive dissociative anesthetic profile and analgesic effects, while often preserving airway reflexes. The other agents listed act primarily through GABA-A receptor modulation—thiopental and etomidate are barbiturate-like and nonbarbiturate drugs that enhance GABAergic inhibition, and midazolam is a benzodiazepine that also potentiates GABA-A. Because the question asks for the drug whose main CNS action is NMDA receptor inhibition, ketamine is the best choice.

Ketamine works mainly by blocking NMDA receptors, a type of glutamate receptor that mediates excitatory signaling in the brain. By blocking this channel, ketamine reduces excitatory transmission, producing anesthesia, analgesia, and dissociation. This NMDA antagonism gives ketamine its distinctive dissociative anesthetic profile and analgesic effects, while often preserving airway reflexes. The other agents listed act primarily through GABA-A receptor modulation—thiopental and etomidate are barbiturate-like and nonbarbiturate drugs that enhance GABAergic inhibition, and midazolam is a benzodiazepine that also potentiates GABA-A. Because the question asks for the drug whose main CNS action is NMDA receptor inhibition, ketamine is the best choice.