**Question:** Which of the following antipsychotic drugs causes QT interval prolongation?

**Core Concept:**
Antipsychotic drugs are a class of medications primarily used to treat psychotic disorders such as schizophrenia and bipolar disorder. QT interval prolongation is a side effect that can lead to life-threatening arrhythmias like torsades de pointes. QT prolongation occurs when the duration of the QT interval on an electrocardiogram (ECG) is extended.

**Why the Correct Answer is Right:**
The correct answer is D: Olanzapine, also known as Zyprexa, is a second-generation (atypical) antipsychotic drug that can cause QT interval prolongation. This is due to its interaction with the cardiac ion channels, specifically the hERG potassium channel, which results in an increased risk of arrhythmias.

**Why Each Wrong Option is Incorrect:**
A. Haloperidol (Haldol) is a first-generation (typical) antipsychotic drug that can cause extrapyramidal symptoms (EPS) like Parkinsonism but does not typically cause QT interval prolongation.
B. Quetiapine (Seroquel) is another second-generation antipsychotic drug that can cause EPS but is less likely to cause QT prolongation compared to other antipsychotic drugs.
C. Risperidone (Risperdal) is another second-generation antipsychotic drug that can cause EPS but is not as potent as Olanzapine in causing QT prolongation.

**Clinical Pearl:**
Understanding the side effects of antipsychotic drugs is crucial for clinicians to identify patients at risk and monitor them accordingly. QT interval prolongation is an important parameter to assess in patients on antipsychotic therapy, especially those with a pre-existing risk factor for arrhythmias, such as congenital long QT syndrome or electrolyte imbalances (low potassium or magnesium).

**Correct Answer:** D: Olanzapine (Zyprexa)

---

**Core Concept:**
Olanzapine is a second-generation antipsychotic drug that belongs to the atypical antipsychotic class. It is a dopamine D2 receptor antagonist, which means it blocks dopamine receptors in the brain, thereby treating psychotic symptoms in patients with schizophrenia and bipolar disorder.

**Why the Correct Answer is Right:**
Olanzapine is known to affect the cardiac action potential by blocking the hERG potassium channel, leading to a reduction in the repolarization phase of the cardiac action potential and hence prolonging the QT interval. This is distinct from the typical antipsychotics, which primarily affect dopamine D2 receptors without affecting the cardiac ion channels.

**Why Each Wrong Option is Incorrect:**
- A: Haloperidol (Haldol) is a typical antipsychotic drug that does not affect the cardiac ion channels and is less likely to cause QT prolongation compared to Olanzapine.
- B: Quetiapine (Seroquel) is another atypical antipsychotic