**Core Concept**
Fluphenazine is a first-generation antipsychotic that belongs to the phenothiazine class. It has a unique property of prolonged action due to its high lipophilicity, which allows it to remain in the brain for an extended period.

**Why the Correct Answer is Right**
Fluphenazine's prolonged action is attributed to its high affinity for dopamine D2 receptors in the brain. When fluphenazine binds to these receptors, it blocks the action of dopamine, leading to a decrease in psychotic symptoms. The high lipophilicity of fluphenazine enables it to cross the blood-brain barrier easily, resulting in a prolonged duration of action. This property makes fluphenazine an effective treatment option for schizophrenia and other psychotic disorders.

**Why Each Wrong Option is Incorrect**
**Option A:** Trifluperazine is another first-generation antipsychotic, but it does not have the same level of lipophilicity as fluphenazine and therefore does not have prolonged action.
**Option B:** Thioridazine is also a first-generation antipsychotic, but it has a higher risk of side effects, such as orthostatic hypotension, and does not have the same prolonged action as fluphenazine.
**Option C:** Penfluridol is a second-generation antipsychotic, but it is not known for its prolonged action. Instead, it is used to treat schizophrenia and other psychotic disorders due to its rapid onset of action.

**Clinical Pearl / High-Yield Fact**
When choosing an antipsychotic medication, it's essential to consider the patient's individual needs and medical history. Fluphenazine's prolonged action makes it a suitable option for patients who require long-term treatment, but it may not be the best choice for patients who are prone to side effects or require rapid symptom relief.

**✓ Correct Answer: D. Fluphenazine**