Cross-Tapering from Thorazine 50mg BID to Olanzapine
The recommended protocol for cross-tapering from Thorazine (chlorpromazine) 50mg BID to olanzapine is to start with olanzapine 5-10mg daily while gradually reducing Thorazine by 25% every 2 weeks until discontinuation.
Initial Considerations
Before beginning the cross-taper:
- Olanzapine's typical effective dose range is 7.5-20 mg/day 1
- Starting dose should be lower (5mg) for elderly patients or those with hepatic impairment
- Standard starting dose is 10mg for most adult patients 1
- Avoid concurrent use of other dopamine antagonists during the transition to prevent excessive dopamine blockade 2
Cross-Tapering Protocol
Week 1-2:
- Start olanzapine 5-10mg at bedtime
- Continue Thorazine 50mg BID unchanged
- Monitor for sedation, orthostatic hypotension, and extrapyramidal symptoms
Week 3-4:
- Continue olanzapine at established dose
- Reduce Thorazine to 37.5mg BID (25% reduction)
- Monitor for withdrawal symptoms or symptom recurrence
Week 5-6:
- Continue olanzapine (adjust dose if needed based on response)
- Reduce Thorazine to 25mg BID (50% of original dose)
- Monitor for withdrawal symptoms or symptom recurrence
Week 7-8:
- Continue olanzapine (adjust dose if needed based on response)
- Reduce Thorazine to 12.5mg BID (75% reduction)
- Monitor for withdrawal symptoms or symptom recurrence
Week 9-10:
- Continue olanzapine at therapeutic dose
- Discontinue Thorazine
- Monitor closely for withdrawal symptoms or symptom recurrence
Rationale for This Approach
This gradual cross-tapering approach is based on several principles:
- Slow tapering is preferred to minimize withdrawal symptoms and reduce relapse risk 2, 3
- The hyperbolic tapering method (reducing by percentage of most recent dose) is supported by evidence showing it may reduce relapse risk 3
- Adding the new medication before tapering the old one ensures continuous symptom control 4
Monitoring and Adjustments
During the cross-taper period, monitor for:
- Excessive sedation (common with both medications)
- Orthostatic hypotension
- Extrapyramidal symptoms
- Metabolic effects (weight gain, hyperglycemia)
- Signs of withdrawal from Thorazine
- Symptom recurrence or exacerbation
If withdrawal symptoms occur, slow the taper by extending the time between dose reductions to 3-4 weeks instead of 2 weeks 2.
Special Considerations
- Elderly patients: Start with lower olanzapine dose (2.5-5mg) and taper Thorazine more slowly 1
- Hepatic impairment: Use lower olanzapine doses and monitor more closely 1
- Previous adverse reactions: If the patient has had previous adverse reactions to antipsychotics, consider an even more gradual taper
Potential Complications
- Drug interactions: Avoid combining olanzapine with other dopamine antagonists, metoclopramide, phenothiazines, or haloperidol 2
- Sedation risk: Both medications can cause sedation; monitor carefully during the overlap period 1, 5
- Metabolic effects: Monitor for weight gain, hyperglycemia, and dyslipidemia 1
Alternative Approaches
A randomized trial comparing two switching strategies to aripiprazole found that both immediate cross-tapering and delayed tapering (4-week overlap before tapering) were equally effective and well-tolerated 4. This suggests some flexibility in the timing of the taper based on individual patient response.
If the patient experiences difficulty with the taper, extending the tapering schedule to 3-6 months may be necessary, particularly for patients who have been on Thorazine for a long time 3.