D2 occupancy of 78% is associated with which adverse effect?

D2 occupancy of 78% is associated with which adverse effect?

• A. Efficacy correlation
• B. Hyperprolactinemia
• C. Clozapine monitoring
• D. EPS

Answer: (D)

High D2 receptor occupancy in the nigrostriatal pathway drives extrapyramidal symptoms. When occupancy reaches the high 70s to around 80%, the risk of EPS rises significantly, and an occupancy of 78% sits squarely in that range. Extrapyramidal symptoms include dystonia, akathisia, and drug-induced parkinsonism, which is why EPS is the best answer for this occupancy level. Hyperprolactinemia results from D2 blockade in the tuberoinfundibular pathway and can occur with substantial occupancy, but the 78% figure is more characteristically linked to movement-related adverse effects. Efficacy correlation and clozapine monitoring address different aspects (therapeutic effect and a separate safety monitoring issue, respectively) and do not specifically explain the adverse effect most associated with this high D2 occupancy.

High D2 receptor occupancy in the nigrostriatal pathway drives extrapyramidal symptoms. When occupancy reaches the high 70s to around 80%, the risk of EPS rises significantly, and an occupancy of 78% sits squarely in that range. Extrapyramidal symptoms include dystonia, akathisia, and drug-induced parkinsonism, which is why EPS is the best answer for this occupancy level. Hyperprolactinemia results from D2 blockade in the tuberoinfundibular pathway and can occur with substantial occupancy, but the 78% figure is more characteristically linked to movement-related adverse effects. Efficacy correlation and clozapine monitoring address different aspects (therapeutic effect and a separate safety monitoring issue, respectively) and do not specifically explain the adverse effect most associated with this high D2 occupancy.