Antipsychotic drug with least extrapyramidal effects is :
**Core Concept**
The question is testing the understanding of antipsychotic medications, specifically their propensity to cause extrapyramidal side effects (EPS). EPS are a group of movement disorders associated with the blockade of dopamine D2 receptors in the nigrostriatal pathway. Antipsychotics that preferentially block serotonin (5-HT2A) receptors over dopamine D2 receptors tend to have lower EPS rates.
**Why the Correct Answer is Right**
The correct answer is an atypical antipsychotic that has a lower affinity for dopamine D2 receptors compared to serotonin 5-HT2A receptors. This property allows it to have a lower incidence of EPS. **Clozapine** and **quetiapine** are examples of atypical antipsychotics with this profile. However, since **quetiapine** is not among the options, we'll assume the correct answer is **clozapine**. Clozapine's unique pharmacology, which includes a high affinity for serotonin 5-HT2A receptors and a lower affinity for dopamine D2 receptors, contributes to its lower EPS rate.
**Why Each Wrong Option is Incorrect**
* **Option A:** Haloperidol is a typical antipsychotic with high affinity for dopamine D2 receptors, making it more likely to cause EPS.
* **Option B:** Risperidone is an atypical antipsychotic, but it has a higher affinity for dopamine D2 receptors compared to serotonin 5-HT2A receptors, leading to a higher EPS rate.
* **Option D:** Olanzapine is another atypical antipsychotic, but its EPS profile is not as favorable as clozapine's.
**Clinical Pearl / High-Yield Fact**
When choosing an antipsychotic, consider the patient's risk factors for EPS, such as age, comorbid Parkinson's disease, or a history of EPS. Atypical antipsychotics like clozapine may be a better option in these cases.
**Correct Answer:** A. Clozapine