Quetiapine Equivalence to Haloperidol 10mg
Based on clinical guidelines, 300-400mg of quetiapine is approximately equivalent to 10mg of haloperidol for treating psychosis and agitation. 1
Dose Equivalence Rationale
- Haloperidol 10mg daily is considered a moderate-to-high dose for most psychiatric indications, with typical starting doses of 0.5-1mg for delirium and 2.5-10mg for acute agitation 1
- Quetiapine's recommended therapeutic dosing range is 150-750mg/day, with 300-400mg/day being the standard effective dose for most patients with psychosis 2
- In comparative studies, quetiapine 600mg/day has shown similar efficacy to haloperidol 20mg/day, suggesting a rough 30:1 ratio 3
- For acute agitation management, quetiapine 25mg immediate release is the recommended starting dose, which can be titrated up to 300-400mg daily in divided doses 1
Clinical Considerations
Pharmacological Differences
- Haloperidol is a high-potency typical antipsychotic with strong D2 receptor antagonism 1
- Quetiapine is an atypical antipsychotic with a broader receptor profile (serotonergic, dopaminergic, and histaminergic effects) and lower D2 receptor occupancy 4
- Quetiapine has a significantly lower risk of extrapyramidal symptoms (EPS) compared to haloperidol 3, 5
Titration Schedule When Switching
- When switching from haloperidol 10mg to quetiapine, a gradual titration is recommended 2:
- Day 1: Quetiapine 50mg twice daily (100mg total)
- Day 2: Quetiapine 100mg twice daily (200mg total)
- Day 3: Quetiapine 150mg twice daily (300mg total)
- Day 4: Quetiapine 200mg twice daily (400mg total)
- Maintain at 300-400mg daily in divided doses 2
Side Effect Profile Comparison
- Haloperidol has higher risk of:
- Extrapyramidal symptoms (EPS)
- Dystonia
- Parkinsonism
- Less sedation 1
- Quetiapine has higher risk of:
- Sedation
- Orthostatic hypotension
- Dizziness
- Metabolic effects with long-term use 1
Important Clinical Caveats
- QTc prolongation risk: Haloperidol causes approximately 7ms QTc prolongation, while quetiapine causes approximately 6ms 1
- Drug interactions: Thioridazine can significantly increase quetiapine clearance by 68%, potentially requiring dose adjustments, but haloperidol does not significantly affect quetiapine pharmacokinetics 6
- Path analysis studies suggest quetiapine may have direct effects on agitation independent of its antipsychotic effects, which differs from haloperidol's mechanism 5
- For elderly or frail patients, lower doses of both medications are recommended (quetiapine 25mg starting dose; haloperidol 0.25-0.5mg) 1
Clinical Decision Algorithm
- For patients requiring equivalent antipsychotic effect: Use quetiapine 300-400mg daily to replace haloperidol 10mg 3
- For patients with EPS on haloperidol: Consider lower quetiapine doses (200-300mg) as they may provide adequate symptom control with fewer side effects 3, 5
- For acute agitation: Initial quetiapine dose should be 25mg with titration to 300-400mg over several days 1
- For maintenance therapy: Adjust quetiapine dose within 150-750mg range based on clinical response 2