**Core Concept**
Phenothiazine-induced dystonia is a type of extrapyramidal side effect characterized by involuntary muscle contractions. This occurs due to the blockade of dopamine D2 receptors in the basal ganglia, specifically in the nigrostriatal pathway, which disrupts normal motor control.

**Why the Correct Answer is Right**
The drug of choice for treating phenothiazine-induced dystonia is an anticholinergic agent, specifically benztropine mesylate. This is because anticholinergics can counteract the cholinergic imbalance caused by dopamine receptor blockade, thereby reducing muscle spasms and dystonic posturing. Benztropine works by blocking the action of acetylcholine at muscarinic receptors in the striatum, which helps to restore balance to the dopaminergic-cholinergic system.

**Why Each Wrong Option is Incorrect**
**Option A:** Haloperidol - This is a typical antipsychotic medication, similar to phenothiazines, which would exacerbate the dystonic reaction by further blocking dopamine receptors.
**Option B:** Amantadine - While amantadine has some anticholinergic effects, it is primarily an NMDA receptor antagonist and is not the first-line treatment for phenothiazine-induced dystonia.
**Option C:** Baclofen - Baclofen is a GABA_B receptor agonist that can be used to treat spasticity, but it is not the preferred treatment for acute dystonic reactions.

**Clinical Pearl / High-Yield Fact**
When treating phenothiazine-induced dystonia, it's essential to act quickly, as the condition can progress rapidly. Administering an anticholinergic agent like benztropine intramuscularly can provide rapid relief from dystonia.

**Correct Answer:** C. Benztropine mesylate