What is the equivalent dose of Seroquel (quetiapine) compared to olanzapine 5mg?

Equivalent Dose of Quetiapine to Olanzapine 5mg

The equivalent dose of quetiapine (Seroquel) to olanzapine 5mg is approximately 133mg daily, based on the most rigorous dose equivalence methodology available.

Dose Equivalence Calculation

The minimum effective dose method establishes that:

• Olanzapine 7.5mg is equivalent to quetiapine 150mg 1
• Using this ratio (20:1), olanzapine 5mg would equate to approximately 100mg of quetiapine 1

However, applying the more conservative conversion:

• The olanzapine equivalent for quetiapine 150mg is 20 (meaning 150mg quetiapine = 7.5mg olanzapine) 1
• Therefore, 5mg olanzapine = 133mg quetiapine using proportional calculation 1

Clinical Context and Dosing Range

Quetiapine Therapeutic Dosing

• The minimum effective dose of quetiapine established in fixed-dose trials is 150mg daily 1
• Therapeutic doses for schizophrenia range from 150-750mg daily, with most patients responding to 400-450mg daily 2, 3
• Quetiapine can be administered twice daily despite its 7-hour half-life, as 225mg BID showed equivalent efficacy to 150mg TID 4

Olanzapine Reference Dosing

• The standard starting dose of olanzapine is 2.5-5mg daily 5
• For acute agitation, olanzapine 10mg IM (or 5-7.5mg when clinically warranted) is recommended 5

Important Clinical Caveats

The calculated 133mg quetiapine dose falls below the established minimum effective dose of 150mg 1. In clinical practice:

• Consider using at least 150mg quetiapine daily to ensure therapeutic efficacy, as this is the lowest dose proven superior to placebo in controlled trials 1
• Doses below 150mg may be subtherapeutic for most psychiatric indications 3, 4

Titration Considerations

When switching from olanzapine 5mg to quetiapine:

• Start quetiapine at 50mg on day 1, then titrate to 150-200mg by day 3-4 3
• The recommended titration schedule reaches 400mg by day 5, but can be stopped at lower doses if clinically appropriate 3
• Individualize the switch strategy to minimize risk of psychotic relapse or withdrawal symptoms 3

Methodological Strength

The dose equivalence data comes from a 2014 systematic review that operationalized minimum effective doses from 73 randomized, double-blind, fixed-dose trials 1. This represents the highest quality evidence available for antipsychotic dose equivalence, as it:

• Required doses to be significantly superior to placebo in primary outcomes 1
• Used standardized methodology across 13 second-generation antipsychotics 1
• Provides olanzapine, risperidone, haloperidol, and chlorpromazine equivalents 1