What is the mechanism of action of ketamine?

• A. Serotonin receptor agonist
• B. Dopamine receptor antagonist
• C. NMDA antagonist
• D. Gamma-aminobutyric acid (GABA) agonist

Answer: (C)

Ketamine primarily acts as an NMDA antagonist, which is a key aspect of its pharmacological profile. NMDA (N-methyl-D-aspartate) receptors are a subtype of glutamate receptors that play a critical role in excitatory neurotransmission in the central nervous system. By blocking these receptors, ketamine inhibits the action of glutamate, leading to decreased excitatory signaling. This mechanism is responsible for its anesthetic and analgesic effects, as well as its distinctive dissociative anesthesia properties.

Additionally, the NMDA antagonism is thought to contribute to ketamine's rapid antidepressant effects, which have garnered significant attention in recent years. By disrupting the normal excitatory neurotransmission mediated by glutamate, ketamine induces a unique state of anesthesia that allows for a different therapeutic approach in both surgical and psychological contexts.

The other mechanisms listed do not accurately represent ketamine's primary action. Serotonin receptor agonism and GABA agonism relate to other classes of drugs, while dopamine receptor antagonism is also linked to different pharmacological effects not characteristic of ketamine. Thus, understanding ketamine’s action as an NMDA antagonist is critical for recognizing its diverse applications in medicine, from anesthesia to psychiatric treatment.