Which antidepressant is often used to treat major depressive disorder and has a unique mechanism of action involving NMDA receptor antagonism?

The antidepressant that is known for its unique mechanism of action involving NMDA receptor antagonism is ketamine. Unlike traditional antidepressants such as SSRIs and SNRIs, which primarily work by inhibiting the reuptake of neurotransmitters like serotonin and norepinephrine, ketamine functions by blocking the NMDA (N-methyl-D-aspartate) receptor. This action is thought to result in increased levels of glutamate, a neurotransmitter that enhances synaptic plasticity and potentially leads to rapid antidepressant effects. This mechanism sets ketamine apart as it offers a different treatment avenue for major depressive disorder, especially in cases where standard therapies may not be effective.

Other medications listed, like escitalopram and fluoxetine, are well-established SSRIs that primarily increase serotonin levels, while duloxetine is an SNRI that affects both serotonin and norepinephrine. Although these drugs are effective for many patients, they do not share the same rapid-acting profile or the NMDA receptor antagonism characteristic of ketamine. Thus, ketamine's unique approach makes it a notable option in the treatment landscape for major depressive disorder.