La d A patient was prescribed an antipsychotic drug following which he developed parkinsonism. Which of the following drugs can be given?

Explanation

## Correct Answer: B. Trihexyphenidyl Antipsychotic-induced parkinsonism is an **extrapyramidal side effect (EPS)** caused by dopamine blockade in the basal ganglia, leading to relative cholinergic predominance. The gold standard treatment is an **anticholinergic agent**, which restores the balance between dopamine and acetylcholine in the basal ganglia. **Trihexyphenidyl** is a centrally acting anticholinergic drug that crosses the blood-brain barrier and effectively reverses antipsychotic-induced parkinsonism by blocking muscarinic receptors in the striatum. It is the most commonly prescribed anticholinergic in Indian clinical practice for this indication and is listed in the NLEM as a first-line agent for drug-induced parkinsonism. The typical dose is 1–2 mg thrice daily, titrated based on response. Anticholinergics are preferred over dopamine agonists in acute antipsychotic-induced EPS because they work faster and have a more predictable effect in this specific context. Other anticholinergics like benztropine are also effective but trihexyphenidyl is the most widely used in India due to cost and availability. ## Why the other options are wrong **A. Pramipexole** — Pramipexole is a dopamine agonist used primarily for idiopathic Parkinson's disease and restless leg syndrome. While dopamine agonists can theoretically help parkinsonism, they are NOT the first-line choice for antipsychotic-induced EPS because: (1) they may worsen the underlying psychotic condition by increasing dopamine activity, and (2) anticholinergics work faster and more reliably in this acute drug-induced setting. NBE trap: confusing dopamine agonists (for primary PD) with anticholinergics (for drug-induced parkinsonism). **C. Rasagiline** — Rasagiline is a selective MAO-B inhibitor used as monotherapy or adjunct in idiopathic Parkinson's disease to slow disease progression. It has NO role in acute antipsychotic-induced parkinsonism because: (1) it does not provide immediate symptomatic relief, (2) it is not indicated for drug-induced EPS, and (3) it carries risk of serotonin syndrome if combined with certain antipsychotics. NBE trap: grouping all Parkinson's drugs together without distinguishing between primary PD treatment and acute EPS management. **D. Entacapone** — Entacapone is a COMT inhibitor used as an adjunct to levodopa in idiopathic Parkinson's disease to extend dopamine availability. It is NOT indicated for antipsychotic-induced parkinsonism because: (1) it requires concurrent levodopa therapy (not used in drug-induced EPS), (2) it has no anticholinergic properties, and (3) it is used for chronic PD management, not acute EPS. NBE trap: listing multiple Parkinson's medications to confuse students about which class treats drug-induced versus primary parkinsonism. ## High-Yield Facts - **Anticholinergics** (trihexyphenidyl, benztropine) are first-line for antipsychotic-induced parkinsonism by restoring dopamine-acetylcholine balance in the basal ganglia. - **Dopamine agonists** (pramipexole, bromocriptine) are avoided in antipsychotic-induced EPS because they may exacerbate psychosis. - **Trihexyphenidyl** typical dose: 1–2 mg three times daily; onset of action within hours (faster than dopamine agonists). - **MAO-B inhibitors** (rasagiline) and **COMT inhibitors** (entacapone) are used only in idiopathic Parkinson's disease, not drug-induced EPS. - Anticholinergic side effects (dry mouth, urinary retention, constipation, tachycardia) must be monitored; contraindicated in glaucoma and urinary obstruction. ## Mnemonics **ACNE for Antipsychotic-induced EPS management** **A**nticholinergics (first-line) → **C**entral dopamine agonists (second-line, risky) → **N**ot MAO-B or COMT inhibitors → **E**xtrapyramidal symptoms resolve. Use this to remember that anticholinergics come first, dopamine agonists are risky, and other PD drugs don't apply. **Memory hook: 'ANTI-psychotic → ANTI-cholinergic'** Antipsychotics block dopamine (cause parkinsonism) → Anticholinergics restore balance. This 'opposite' pairing helps recall that the antidote to dopamine blockade is cholinergic blockade, not dopamine replacement. ## NBE Trap NBE pairs all Parkinson's-related drugs (dopamine agonists, MAO-B inhibitors, COMT inhibitors) in the options to trap students who know 'Parkinson's drugs' but don't distinguish between **idiopathic PD treatment** (where dopamine agonists, rasagiline, entacapone apply) and **acute antipsychotic-induced EPS** (where only anticholinergics are first-line). The key discriminator is the clinical context: drug-induced EPS requires anticholinergics, not dopaminergic agents.</trap> <parameter name="textbookRef">KD Tripathi Pharmacology Ch. 9 (Antipsychotics and EPS management); Harrison Ch. 476 (Drug-induced movement disorders)</textbookRef> <parameter name="clinicalPearl">In Indian psychiatric practice, when a patient on chlorpromazine, haloperidol, or risperidone develops acute parkinsonism (rigidity, bradykinesia, tremor), trihexyphenidyl 1 mg BD–TDS is prescribed immediately and often continued for the duration of antipsychotic therapy. This is far more practical and cost-effective than switching antipsychotics or adding dopamine agonists, which risk psychotic relapse.</clinicalPearl> </invoke>