Rapid dissociation from the D2 receptor allows periodic accommodation of endogenous dopamine, causing less EPS. This theory is called what?

Rapid dissociation from the D2 receptor allows periodic accommodation of endogenous dopamine, causing less EPS. This theory is called what?

• A. Fast-off D2 theory
• B. D2 bounce theory
• C. Dopamine partial agonism
• D. Serotonin-Dopamine antagonism

Answer: (A)

Fast-off D2 theory explains why some antipsychotics cause fewer movement side effects. The idea is that the drug binds to the D2 receptor but dissociates from it rapidly. Because of this quick unbinding, endogenous dopamine can periodically occupy the receptor when its levels rise, so the blockade isn’t sustained. In the nigrostriatal pathway, this transient blockade reduces the risk of extrapyramidal symptoms, while in the mesolimbic pathway you still get enough receptor occupancy to help treat psychosis. Clozapine and quetiapine are classic examples described as having fast dissociation from D2 receptors, which accounts for their low EPS despite antipsychotic effects. Other concepts, like partial agonism or serotonin–dopamine antagonism, describe different mechanisms and don’t specifically rely on rapid D2 dissociation.

Fast-off D2 theory explains why some antipsychotics cause fewer movement side effects. The idea is that the drug binds to the D2 receptor but dissociates from it rapidly. Because of this quick unbinding, endogenous dopamine can periodically occupy the receptor when its levels rise, so the blockade isn’t sustained. In the nigrostriatal pathway, this transient blockade reduces the risk of extrapyramidal symptoms, while in the mesolimbic pathway you still get enough receptor occupancy to help treat psychosis. Clozapine and quetiapine are classic examples described as having fast dissociation from D2 receptors, which accounts for their low EPS despite antipsychotic effects. Other concepts, like partial agonism or serotonin–dopamine antagonism, describe different mechanisms and don’t specifically rely on rapid D2 dissociation.