Which statement best describes the relationship between D2 dissociation rates and extrapyramidal symptoms?

Which statement best describes the relationship between D2 dissociation rates and extrapyramidal symptoms?

• A. Faster dissociation (fast-off) is associated with fewer EPS
• B. Faster dissociation increases EPS
• C. Dissociation rates do not affect EPS
• D. EPS are only determined by D1 receptors

Answer: (A)

The key idea is that extrapyramidal symptoms come from how long a drug blocks D2 receptors in the nigrostriatal (motor) pathway. If a drug dissociates quickly from D2 receptors (fast-off), the receptor blockade is shorter on average, so dopaminergic signaling can resume sooner in motor circuits. This reduced effective D2 blockade lowers the risk of EPS, even if the drug has antipsychotic effects elsewhere. So faster dissociation is associated with fewer EPS. D2 receptor activity in the striatum is the main driver of EPS, not D1 receptors alone, and many antipsychotics reduce EPS risk by having rapid off-rate or by balancing receptor effects (e.g., via serotonin modulation). This is why the statement about fast-off leading to fewer EPS best fits the pharmacology and clinical observations.

The key idea is that extrapyramidal symptoms come from how long a drug blocks D2 receptors in the nigrostriatal (motor) pathway. If a drug dissociates quickly from D2 receptors (fast-off), the receptor blockade is shorter on average, so dopaminergic signaling can resume sooner in motor circuits. This reduced effective D2 blockade lowers the risk of EPS, even if the drug has antipsychotic effects elsewhere. So faster dissociation is associated with fewer EPS.

D2 receptor activity in the striatum is the main driver of EPS, not D1 receptors alone, and many antipsychotics reduce EPS risk by having rapid off-rate or by balancing receptor effects (e.g., via serotonin modulation). This is why the statement about fast-off leading to fewer EPS best fits the pharmacology and clinical observations.