What are extrapyramidal side effects and which drugs cause them?

What Are Extrapyramidal Side Effects and Which Drugs Cause Them?

Extrapyramidal side effects (EPS) are drug-induced movement disorders caused by dopamine receptor blockade in the basal ganglia, most commonly from antipsychotic medications, with high-potency typical antipsychotics like haloperidol carrying the highest risk. 1

Definition and Types of EPS

Extrapyramidal symptoms manifest as four distinct clinical syndromes, each with different timing and characteristics:

Acute Dystonia

• Sudden spastic contractions of muscle groups affecting the neck, eyes (oculogyric crisis), or torso, typically occurring within the first few days of treatment 2, 3
• Young males represent the highest-risk group for acute dystonia 2, 1
• Can be life-threatening when laryngospasm occurs 2

Drug-Induced Parkinsonism

• Bradykinesia, tremors, and rigidity that mimic idiopathic Parkinson's disease, resulting directly from dopamine D2 receptor blockade 2, 1
• Generally appears within the first three months of treatment 4

Akathisia

• Subjective feeling of severe restlessness manifesting as pacing or physical agitation 2, 3
• Frequently misinterpreted as psychotic agitation or anxiety, leading to inappropriate dose escalation rather than recognition as a medication side effect 2, 1
• The most difficult EPS to treat 2

Tardive Dyskinesia

• Involuntary choreiform or athetoid movements, typically in the orofacial region but potentially affecting any body part 3, 1
• Associated with long-term antipsychotic use, occurring in approximately 5% of young patients per year 2, 1

Medications That Cause EPS

Antipsychotic Medications (Primary Culprits)

High-Potency Typical Antipsychotics (Highest Risk):

• Haloperidol produces significantly more EPS due to strong dopamine D2 receptor blockade 2, 1
• These agents carry the greatest risk of acute dystonia, particularly in young males 1

Low-Potency Typical Antipsychotics (Lower EPS Risk, More Sedation):

• Chlorpromazine causes more sedation with fewer EPS compared to high-potency agents 3

Atypical Antipsychotics (Variable Risk):

• Risperidone has dose-dependent EPS risk that increases significantly above 2 mg/day in elderly/dementia patients and above 4-6 mg/day in general populations 2, 3
• Olanzapine, quetiapine, and clozapine have the lowest EPS risk among all antipsychotics 2, 1
• Clozapine has minimal EPS risk but requires intensive blood monitoring for agranulocytosis (approximately 1% risk) 5, 1

Non-Antipsychotic Medications

Antiemetics:

• Metoclopramide can cause EPS, with approximately 20% of patients using it longer than 12 weeks developing tardive dyskinesia 1
• Prochlorperazine also carries EPS risk 1

Other Medications (Less Common):

• Certain antidepressants can cause EPS 6, 7
• Lithium may produce extrapyramidal symptoms 6, 7
• Various anticonvulsants rarely cause EPS 6, 7
• Oral contraceptive agents very rarely associated with EPS 6, 7

Risk Factors for Developing EPS

Patient-Specific Factors:

• Age: Children, adolescents, and elderly patients are at higher risk 1
• Gender: Male gender, particularly for dystonic reactions 1

Medication-Related Factors:

• High-potency typical antipsychotics carry greater risk than atypical agents 1
• Higher doses and rapid dose escalation increase EPS risk 1
• Concurrent use of multiple dopamine-blocking agents 1

Management Principles

Acute Dystonia (Immediate Treatment Required)

• Administer benztropine 1-2 mg IM/IV immediately for rapid relief, with improvement often noticeable within minutes 2, 1
• Alternative: diphenhydramine 12.5-25 mg IM/IV provides equivalent rapid relief 2, 1

Drug-Induced Parkinsonism (Hierarchical Approach)

• First strategy: Reduce the antipsychotic dose if clinically feasible 2, 1
• Second strategy: Switch to olanzapine, quetiapine, or clozapine, which have substantially lower EPS risk 2, 1
• Only add anticholinergics after dose reduction and medication switching have failed 2, 1

Akathisia (Most Difficult to Treat)

• Lower the antipsychotic dose as the primary intervention 2
• Lipophilic beta-blockers (propranolol or metoprolol) are the most effective pharmacological treatments 2, 4
• Anticholinergics are less consistently effective for akathisia than for other EPS 2

Critical Clinical Pitfalls

Avoid routine prophylactic anticholinergics – regular monitoring for early EPS signs is the preferred prevention strategy rather than prophylactic anticholinergic use 2, 1

Anticholinergic medications carry significant risks:

• Can cause delirium, drowsiness, and paradoxical agitation, particularly in older adults 2, 1
• Exercise extreme caution in elderly patients due to oversedation and confusion risk 2
• Avoid diphenhydramine in patients with glaucoma, benign prostatic hypertrophy, ischemic heart disease, or hypertension 2

Akathisia misdiagnosis leads to inappropriate treatment escalation – when akathisia is mistaken for psychotic agitation or anxiety, clinicians may increase the antipsychotic dose, worsening the problem 2, 1

Monitoring Requirements

• Regular monitoring for early EPS signs during antipsychotic therapy 1
• Monitor for tardive dyskinesia every 3-6 months using a standardized scale during long-term antipsychotic therapy 2, 1
• For clozapine: weekly blood cell counts during the first 6 months, then every 2 weeks thereafter 5