An elderly woman suffering from schizophrenia is on antipsychotic medication. She developed purposeless involuntary facial and limb movements, constant chewing and puffing of cheeks. Which of the following drugs is least likely to be involved in this side effect:

**Core Concept**
Antipsychotic medications, particularly first-generation (typical) antipsychotics, can cause extrapyramidal side effects (EPS) due to their blockade of dopamine D2 receptors in the nigrostriatal pathway. This blockade disrupts the normal balance between dopamine and acetylcholine, leading to increased muscle tone and rigidity.

**Why the Correct Answer is Right**
The elderly woman's symptoms, such as purposeless involuntary facial and limb movements, constant chewing, and puffing of cheeks, are characteristic of Tardive Dyskinesia (TD). TD is a type of EPS that is more likely to occur with long-term use of first-generation antipsychotics. The correct answer is likely to be a second-generation (atypical) antipsychotic, which has a lower risk of causing TD due to its partial agonist activity at dopamine D2 receptors.

**Why Each Wrong Option is Incorrect**
**Option A:** First-generation antipsychotics, such as Haloperidol, are well-known to cause EPS, including TD. They block dopamine D2 receptors, leading to increased muscle tone and rigidity.
**Option C:** Typical antipsychotics, such as Chlorpromazine, also block dopamine D2 receptors and can cause EPS, making them less likely to be the correct answer.

**Clinical Pearl / High-Yield Fact**
Atypical antipsychotics, such as Aripiprazole, have a lower risk of causing EPS due to their partial agonist activity at dopamine D2 receptors. This makes them a better choice for long-term treatment of schizophrenia, especially in elderly patients.

**Correct Answer:** D.

✓ Correct Answer: B. Clozapine