How to switch from fluoxetine (Prozac) to citalopram (Celexa)?

Switching from Fluoxetine to Citalopram

Start citalopram 20 mg/day immediately while continuing fluoxetine, then taper fluoxetine by 50% after 3-7 days, and discontinue fluoxetine completely after another 3-7 days of overlap. This cross-taper approach minimizes both withdrawal symptoms and treatment gaps while accounting for fluoxetine's exceptionally long half-life 1, 2.

Switching Protocol

Week 1: Initiation Phase

• Begin citalopram 20 mg/day while maintaining current fluoxetine dose 3, 4
• Continue both medications for 3-7 days to allow citalopram to reach therapeutic levels 5
• This overlap period is safe because both are SSRIs with similar mechanisms, though monitoring for serotonin syndrome remains important 1

Week 2: Fluoxetine Taper

• Reduce fluoxetine by 50% (e.g., from 20 mg to 10 mg, or from 40 mg to 20 mg) while maintaining citalopram 20 mg/day 5
• Continue this reduced fluoxetine dose for 3-7 days 5
• The gradual taper reduces risk of discontinuation syndrome, though fluoxetine's long half-life (and active metabolite norfluoxetine) provides inherent protection against withdrawal 1, 2

Week 3: Complete Transition

• Discontinue fluoxetine completely after the taper period 5
• Continue citalopram 20 mg/day 3
• Fluoxetine's active metabolites will continue to wash out over several weeks, providing a natural buffer against discontinuation symptoms 1, 6

Dose Titration of Citalopram

• Maintain citalopram 20 mg/day for at least 3-4 weeks before considering dose adjustments, as fluoxetine's long half-life means therapeutic overlap continues 1
• If needed, titrate citalopram up to 40 mg/day maximum (do not exceed this dose due to QT prolongation risk) 1, 3
• Increase in 10-20 mg increments at 1-2 week intervals as tolerated 1

Monitoring Schedule

First Week Contact (Days 3-7)

• Assess for early adverse effects from citalopram: nausea, headache, insomnia, nervousness, tremors 5, 3
• Monitor for any signs of serotonin syndrome during the overlap period: confusion, agitation, tremors, hyperreflexia, tachycardia, diaphoresis 1
• Evaluate adherence to the switching protocol 7

Week 2-3 Monitoring

• Check for fluoxetine discontinuation symptoms (though rare given its long half-life): dizziness, fatigue, sensory disturbances, irritability 1, 2
• Continue monitoring citalopram tolerability 3

Week 4-6 Assessment

• Evaluate therapeutic response using standardized measures (e.g., PHQ-9, clinical assessment) 5, 3
• Determine if dose adjustment is needed based on efficacy and tolerability 3

Critical Safety Considerations

Absolute Contraindications During Switch

• Never combine with MAOIs - both fluoxetine and citalopram are contraindicated with monoamine oxidase inhibitors due to severe serotonin syndrome risk 1, 7
• Avoid other serotonergic agents during the overlap period (tramadol, meperidine, dextromethorphan, St. John's wort) 1

QT Prolongation Risk

• Do not exceed citalopram 40 mg/day - higher doses associated with QT prolongation, Torsade de Pointes, and sudden death 1
• Avoid citalopram in patients with long QT syndrome 1
• Use caution with other QT-prolonging medications 1

Bleeding Risk

• Monitor for abnormal bleeding, especially if patient takes aspirin or NSAIDs concurrently, as both SSRIs increase bleeding risk 1

Suicide Risk Monitoring

• Increased behavioral activation and suicide-related events possible, particularly in younger patients during any antidepressant switch 5, 7
• Maintain close contact during the first 4 weeks 7

Advantages of This Specific Switch

• Direct switching from fluoxetine is well-tolerated - research demonstrates 95% completion rate when switching fluoxetine-intolerant patients directly to citalopram 3
• Citalopram has minimal CYP450 interactions compared to fluoxetine, which strongly inhibits CYP2D6 - this reduces drug-drug interaction concerns 1, 5
• Lower recurrence of fluoxetine-associated side effects - only 18-27% of patients experienced recurrence of previous adverse events when switched to citalopram 3
• Fluoxetine's long half-life provides natural protection against discontinuation syndrome, making this one of the easier SSRI switches 1, 6

Expected Outcomes

• Response rate of 63-65% among fluoxetine nonresponders who switch to citalopram 4
• Significant improvement typically seen within 1 week of starting citalopram 3, 4
• 81% completion rate in clinical trials of this switch 4

Common Pitfalls to Avoid

• Do not abruptly stop fluoxetine without overlap - while fluoxetine's long half-life protects against withdrawal, starting citalopram simultaneously prevents treatment gaps 2
• Do not rush citalopram dose escalation - allow 3-4 weeks at initial dose given ongoing fluoxetine activity 1
• Do not exceed citalopram 40 mg/day regardless of previous fluoxetine dose 1
• Do not assume lack of response before 4-6 weeks at therapeutic citalopram dose 5, 3