Antipsychotics & Extrapyramidal Side Effects

Antipsychotics (neuroleptics) are the cornerstone of treating schizophrenia and other psychotic states. The most heavily tested NEET PG material is not their efficacy but their adverse-effect profile — the four faces of extrapyramidal side effects (EPS) with their characteristic timelines, neuroleptic malignant syndrome (NMS), clozapine monitoring, and the metabolic burden of the atypicals.

Definition & classification

Antipsychotics control the positive symptoms of psychosis (delusions, hallucinations, disorganised thought) primarily by blocking dopamine D2 receptors in the mesolimbic pathway. They are classified into two broad generations.

Feature	Typical (first-generation, FGA)	Atypical (second-generation, SGA)
Prototype	Haloperidol, chlorpromazine	Clozapine, olanzapine, risperidone
Main mechanism	Strong D2 blockade	D2 + 5-HT2A blockade
Positive symptoms	Good	Good
Negative symptoms	Poor	Better
EPS risk	High	Low (dose-dependent)
Tardive dyskinesia	High	Low
Prolactin rise	High	Low (except risperidone, which raises it most)
Metabolic syndrome	Low–moderate	High (esp. clozapine, olanzapine)
Seizure threshold	Lowered (chlorpromazine)	Lowered most by clozapine

Typicals are further split by potency:

• High potency (haloperidol, fluphenazine, trifluoperazine, pimozide) → more EPS, less sedation/anticholinergic/hypotension.
• Low potency (chlorpromazine, thioridazine) → less EPS, more sedation, anticholinergic, postural hypotension, weight gain.

High-yield: High-potency typicals cause more EPS; low-potency typicals cause more sedation, hypotension and anticholinergic effects. The trade-off is driven by relative D2 vs histaminic/muscarinic/alpha blockade.

Receptor pharmacology

The clinical picture of any antipsychotic is read straight off its receptor-binding fingerprint:

• D2 (mesolimbic) → antipsychotic effect (positive symptoms).
• D2 (nigrostriatal) → EPS.
• D2 (tuberoinfundibular) → hyperprolactinaemia (galactorrhoea, amenorrhoea, gynaecomastia, sexual dysfunction).
• D2 (chemoreceptor trigger zone) → antiemetic effect.
• 5-HT2A blockade → reduces EPS, helps negative symptoms (the basis of "atypicality").
• H1 → sedation, weight gain.
• M1 (muscarinic) → dry mouth, constipation, blurred vision, urinary retention; also self-protects against EPS.
• alpha-1 → postural hypotension, reflex tachycardia.

High-yield: The Meltzer ratio — a high 5-HT2A : D2 affinity ratio defines an "atypical" antipsychotic and explains its low EPS.

The four classic dopamine pathways are best memorised as a flow:

Mesolimbic (positive symptoms) → Mesocortical (negative/cognitive symptoms) → Nigrostriatal (EPS) → Tuberoinfundibular (prolactin)

Extrapyramidal side effects (EPS)

EPS result from D2 blockade in the nigrostriatal pathway. The single most examined concept is the timeline — which EPS appears when. Match the syndrome to its onset and you answer most questions correctly.

EPS subtype	Typical onset	Clinical picture	Treatment
Acute dystonia	Hours to days (4 hrs–4 days)	Sustained muscle spasm: torticollis, oculogyric crisis, trismus, opisthotonus, laryngospasm	Anticholinergics (IM/IV benztropine, promethazine) or IV diphenhydramine
Akathisia	Days to weeks	Subjective inner restlessness, inability to sit still, pacing	Propranolol (beta-blocker); benzodiazepines; reduce dose
Parkinsonism	Weeks to months	Bradykinesia, rigidity, resting tremor, masked facies	Anticholinergics (trihexyphenidyl, benztropine); reduce dose; amantadine
Tardive dyskinesia (TD)	Months to years (≥3 months)	Choreoathetoid movements — orofacial/lingual ("bon-bon sign"), lip-smacking	Stop/reduce drug; switch to clozapine; VMAT2 inhibitors (valbenazine, deutetrabenazine, tetrabenazine)

High-yield: Mnemonic for the EPS timeline — "4 hours, 4 days, 4 weeks, 4 months" maps roughly to dystonia → akathisia → parkinsonism → tardive dyskinesia. (Onset gets progressively later.)

Acute dystonia

A frightening, sometimes life-threatening (laryngospasm) muscle spasm appearing within the first few days. Young males receiving high-potency typicals are most at risk. Oculogyric crisis (forced sustained upward deviation of the eyes) is the classic exam image. Treat with parenteral anticholinergics / antihistaminics — response is dramatic and within minutes.

High-yield: Acute dystonia is the earliest EPS and the most common reason for an emergency-room visit after starting an antipsychotic. First-line treatment is IM/IV anticholinergic (or promethazine/diphenhydramine), NOT dose reduction alone.

Akathisia

The most commonly missed EPS — patients are mislabelled as "anxious" or "agitated" and given more antipsychotic, worsening it. The hallmark is a subjective sense of restlessness with objective fidgeting. Beta-blockers (propranolol) are first-line; benzodiazepines are adjuncts. Distinguish from psychotic agitation (more antipsychotic helps the latter, harms akathisia).

High-yield: Drug of choice for akathisia is propranolol — not anticholinergics. Anticholinergics work for dystonia and drug-induced parkinsonism, not akathisia.

Drug-induced parkinsonism

Indistinguishable from idiopathic Parkinson's disease except by drug history and (often) symmetry. Bradykinesia and rigidity predominate; the tremor may be the coarse "rabbit syndrome" (perioral tremor). Manage with anticholinergics (trihexyphenidyl/benzhexol), amantadine, or dose reduction. Crucially, never give levodopa — it worsens psychosis.

Tardive dyskinesia (TD)

A late, potentially irreversible complication of prolonged D2 blockade, attributed to dopamine-receptor up-regulation / supersensitivity. Risk factors: long duration, high cumulative dose, elderly women, diabetics, mood disorders, typical antipsychotics. Classic signs: orofacial-lingual dyskinesia, lip-smacking, tongue protrusion ("fly-catcher tongue"), choreoathetoid limb movements.

High-yield: Anticholinergics WORSEN tardive dyskinesia (whereas they treat dystonia/parkinsonism). The management is to stop or switch the offending drug — preferably to clozapine, the antipsychotic with the lowest TD risk — and add a VMAT2 inhibitor (valbenazine/deutetrabenazine).

TD treatment flow: Recognise early (AIMS scale) → stop anticholinergics → reduce/withdraw causative antipsychotic → switch to clozapine → add VMAT2 inhibitor if persistent.

Neuroleptic malignant syndrome (NMS)

A rare but life-threatening idiosyncratic reaction caused by central D2 blockade, classically with high-potency typicals (haloperidol) but possible with any antipsychotic, and even with abrupt withdrawal of dopaminergic drugs in Parkinson's.

The diagnostic tetrad — FEVER:

1. Fever (hyperthermia, often >38°C)
2. Encephalopathy / altered mental status
3. Vitals unstable (autonomic dysfunction — labile BP, tachycardia, diaphoresis)
4. Elevated enzymes (raised CK, often >1000; leucocytosis)
5. Rigidity ("lead-pipe" rigidity)

High-yield: NMS = lead-pipe rigidity + hyperthermia + autonomic instability + altered sensorium + raised CK. It develops over days (not minutes). The most useful lab marker is a markedly elevated creatine kinase (CK).

Management flow: Stop the antipsychotic immediately → supportive care (cooling, IV fluids, ICU monitoring) → dantrolene (muscle relaxant) and/or bromocriptine/amantadine (dopamine agonists) → benzodiazepines (lorazepam) for agitation/catatonia. Complications include rhabdomyolysis → acute kidney injury, DIC, and aspiration pneumonia.

Feature	NMS	Serotonin syndrome	Malignant hyperthermia
Trigger	Dopamine antagonist	Serotonergic drugs (SSRI, MAOI, tramadol)	Volatile anaesthetics, succinylcholine
Onset	Days	Hours (rapid)	Minutes (intra-op)
Neuromuscular	Lead-pipe rigidity, hyporeflexia	Hyperreflexia, clonus, myoclonus	Rigidity, masseter spasm
Pupils	Normal	Mydriasis	Normal
GI	Absent	Diarrhoea	Absent
Specific Rx	Dantrolene, bromocriptine	Cyproheptadine	Dantrolene

High-yield: Clonus + hyperreflexia = serotonin syndrome; lead-pipe rigidity + bradyreflexia = NMS. Serotonin syndrome is treated with cyproheptadine; NMS with dantrolene/bromocriptine.

Clozapine — the special atypical

Clozapine is the most effective antipsychotic but is reserved for treatment-resistant schizophrenia because of its toxicity. It has negligible EPS and the lowest risk of tardive dyskinesia, and is the only agent shown to reduce suicidality in schizophrenia.

Indications: (1) treatment-resistant schizophrenia (failure of ≥2 adequate antipsychotic trials), (2) schizophrenia with persistent suicidality/self-harm, (3) severe tardive dyskinesia.

Major adverse effects:

• Agranulocytosis (~1%) — the reason for mandatory monitoring.
• Myocarditis and cardiomyopathy.
• Seizures (dose-dependent; greatest seizure-threshold lowering of all antipsychotics).
• Metabolic syndrome — most weight gain and diabetes risk of any antipsychotic.
• Hypersalivation (paradoxical, despite anticholinergic action — classic exam fact).
• Constipation → ileus; myocarditis; sedation.

High-yield: Clozapine requires regular absolute neutrophil count (ANC) monitoring — weekly for the first 6 months, then fortnightly to month 12, then monthly. Stop clozapine if ANC < 1500/µL (or < 1000 in benign ethnic neutropenia protocols).

High-yield: Clozapine causes paradoxical hypersalivation/sialorrhoea and has the highest seizure risk and highest metabolic risk — yet the lowest EPS/TD risk. It does not raise prolactin significantly.

Metabolic syndrome & other adverse effects

SGAs (especially clozapine and olanzapine) cause significant weight gain, dyslipidaemia, insulin resistance and type-2 diabetes. Monitor weight/BMI, waist circumference, fasting glucose/HbA1c and lipid profile at baseline and periodically.

Relative metabolic risk: Clozapine ≈ Olanzapine > Quetiapine > Risperidone > Aripiprazole ≈ Ziprasidone (lowest).

Other notable effects:

• QT prolongation → ziprasidone, thioridazine, pimozide, haloperidol (IV). Risk of torsades.
• Hyperprolactinaemia → highest with risperidone and typicals; aripiprazole (a partial D2 agonist) can lower prolactin.
• Retinal pigmentation (retinitis pigmentosa) → thioridazine (dose-dependent, irreversible).
• Corneal/lens deposits & photosensitivity, cholestatic jaundice → chlorpromazine.
• Cataracts → quetiapine (monitoring advised).
• Agranulocytosis → clozapine (and rarely chlorpromazine).

High-yield: Quick eponym-style associations: Thioridazine → retinal pigmentation + QT prolongation; Risperidone → highest prolactin among atypicals; Aripiprazole → D2 partial agonist (lowers prolactin); Ziprasidone → QT prolongation; Clozapine → agranulocytosis + myocarditis.

Aripiprazole — the "dopamine system stabiliser"

Aripiprazole is a partial agonist at D2 and 5-HT1A and an antagonist at 5-HT2A. Because of partial agonism it produces less EPS, minimal prolactin elevation (may even lower it), and a favourable metabolic profile. It can paradoxically cause akathisia. This mechanism is a recurrent single-best-answer favourite.

Diagnosis / monitoring of choice

There is no "diagnostic test" for choosing an antipsychotic, but the investigations of choice for monitoring are heavily tested:

• Clozapine → serial ANC/CBC (agranulocytosis); ECG and troponin/CRP if myocarditis suspected.
• NMS → serum CK (markedly raised) + leucocytosis; rule out infection.
• QT-prolonging agents (thioridazine, ziprasidone, pimozide) → baseline and periodic ECG.
• All SGAs → metabolic panel (fasting glucose/HbA1c, lipids, weight).
• Tardive dyskinesia → AIMS (Abnormal Involuntary Movement Scale) for screening/quantification.

Recently asked / exam angle

NEET PG and INI-CET have repeatedly tested:

• EPS timelines — "A patient develops sustained upward eye deviation 2 days after starting haloperidol" → acute dystonia → treat with anticholinergic/promethazine. "Restlessness, can't sit still after a week" → akathisia → propranolol.
• Tardive dyskinesia management — recognising that anticholinergics worsen TD, and that clozapine/VMAT2 inhibitors are preferred.
• Clozapine — the ANC cut-off for stopping (<1500/µL), agranulocytosis, paradoxical hypersalivation, indication of treatment resistance and suicidality.
• NMS vs serotonin syndrome — distinguishing rigidity/bradyreflexia (NMS, dantrolene) from clonus/hyperreflexia (serotonin syndrome, cyproheptadine), and the raised CK.
• Receptor-based MCQs — Meltzer's 5-HT2A:D2 ratio defining atypicality; aripiprazole as a partial D2 agonist.
• Drug-specific toxicities — thioridazine (retinal pigmentation + QT), risperidone (hyperprolactinaemia), olanzapine/clozapine (metabolic syndrome), ziprasidone (QT).
• Image-based items showing oculogyric crisis or orofacial dyskinesia.

High-yield: A two-step trap question — patient on antipsychotic develops orofacial movements; the wrong answer is "give an anticholinergic." Correct approach is to reduce/switch the drug because these are tardive dyskinesia, which anticholinergics aggravate.

Key differentials

• Acute dystonia vs tetanus vs strychnine poisoning vs focal seizure — dystonia responds within minutes to IV anticholinergic; drug history is key.
• Akathisia vs psychotic agitation vs anxiety — akathisia is relieved by reducing antipsychotic / propranolol, worsened by increasing the drug.
• Drug-induced parkinsonism vs idiopathic Parkinson's — drug history, symmetry, reversibility on stopping.
• NMS vs serotonin syndrome vs malignant hyperthermia vs heat stroke vs lethal/malignant catatonia — use onset speed, neuromuscular signs (rigidity vs clonus), pupils and trigger drug.
• Tardive dyskinesia vs Huntington chorea vs Sydenham chorea vs Wilson disease — TD has a clear antipsychotic exposure history and orofacial predominance.

Rapid revision

1. Atypicality = high 5-HT2A : D2 ratio (Meltzer ratio) → low EPS, better negative symptoms.
2. EPS timeline mnemonic: dystonia (hours–days) → akathisia (days–weeks) → parkinsonism (weeks–months) → tardive dyskinesia (months–years).
3. Acute dystonia (oculogyric crisis) → IM/IV anticholinergic / promethazine / diphenhydramine.
4. Akathisia drug of choice → propranolol (not anticholinergics).
5. Tardive dyskinesia → anticholinergics worsen it; switch to clozapine + VMAT2 inhibitor (valbenazine/deutetrabenazine).
6. NMS = lead-pipe rigidity + hyperthermia + autonomic instability + altered sensorium + raised CK; treat with dantrolene / bromocriptine after stopping the drug.
7. NMS vs serotonin syndrome: rigidity/bradyreflexia (dantrolene) vs clonus/hyperreflexia/mydriasis (cyproheptadine).
8. Clozapine → reserved for treatment-resistant schizophrenia & suicidality; causes agranulocytosis — stop if ANC < 1500/µL; lowest EPS/TD, highest seizure & metabolic risk; paradoxical hypersalivation.
9. Metabolic risk: clozapine ≈ olanzapine (highest) → aripiprazole/ziprasidone (lowest).
10. Risperidone → highest prolactin among atypicals; aripiprazole is a D2 partial agonist that lowers prolactin.
11. Thioridazine → retinal pigmentation + QT prolongation; chlorpromazine → corneal/lens deposits, cholestatic jaundice, photosensitivity.
12. Screen tardive dyskinesia with the AIMS scale; never give levodopa for drug-induced parkinsonism (worsens psychosis).