## Core Concept
The question tests understanding of the mechanism of action of certain drugs, specifically their interaction with N-methyl-D-aspartate (NMDA) receptors. NMDA receptors are a subtype of glutamate receptors, which play a critical role in synaptic plasticity, memory formation, and are involved in the pathophysiology of various neurological conditions.

## Why the Correct Answer is Right
Ketamine and similar compounds act by blocking NMDA receptors, which are critical for the regulation of synaptic plasticity and memory. By blocking these receptors, they can induce dissociative anesthesia and have effects on pain perception and cognition. Understanding which drugs do not act through this mechanism is essential for their clinical application and managing potential side effects.

## Why Each Wrong Option is Incorrect
- **Option A:** Ketamine is known to act by blocking NMDA receptors, which makes it an incorrect choice for an answer that does not act by this mechanism.
- **Option B:** Similarly, another drug that blocks NMDA receptors would also be incorrect as an answer.
- **Option C:** If another drug acts through NMDA receptor blockade, it would not be the correct answer to this question.

## Why Option D is Correct
- **Option D:** should be a drug that does not act by blocking NMDA receptors. For example, if is a drug with a different mechanism of action, such as affecting GABA receptors, opioid receptors, or other neurotransmitter systems, it would be the correct answer.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that ketamine's use in anesthesia and its potential for abuse are closely related to its NMDA receptor antagonism. Clinicians must be aware of the implications of NMDA receptor blockade, including dissociative effects and potential for cognitive impairment.

## Correct Answer: D.