Which drug is known for its ability to inhibit NMDA receptors?

Ketamine is well-known for its ability to inhibit NMDA (N-methyl-D-aspartate) receptors. It is a dissociative anesthetic that works primarily by blocking these receptors, which are involved in excitatory neurotransmission in the central nervous system. By inhibiting NMDA receptors, ketamine reduces the effects of glutamate, one of the most significant neurotransmitters in the brain responsible for cognition, memory, and learning. This mechanism contributes not only to its anesthetic properties but also to its unique effects on mood and perception, making it useful in both general anesthesia and for the treatment of depression in certain cases.

This action differentiates ketamine from the other drugs listed. For instance, propofol is primarily known for its sedative-hypnotic properties and does not specifically target NMDA receptors. Isoflurane, an inhalational anesthetic, acts mainly through enhancing GABA-A receptor activity and does not inhibit NMDA receptors in the significant way that ketamine does. Fentanyl, an opioid analgesic, primarily acts on mu-opioid receptors and does not have a direct inhibitory effect on NMDA receptors. Thus, ketamine stands out for its unique role in NMDA receptor inhibition.