Switching from Prozac (Fluoxetine) to Luvox (Fluvoxamine)
When switching from fluoxetine to fluvoxamine, use a conservative cross-tapering approach: reduce fluoxetine by 25% weekly while starting fluvoxamine at a low dose (25-50 mg daily) after 1-2 weeks, given fluoxetine's exceptionally long half-life (4-6 days) compared to fluvoxamine's short half-life (15-20 hours). 1
Critical Pharmacological Differences
The key challenge in this switch is the dramatic difference in half-lives between these two SSRIs:
- Fluoxetine has an extended half-life of 4-6 days (including its active metabolite norfluoxetine, which extends to 7-15 days), meaning it naturally tapers itself over weeks after discontinuation 2, 3
- Fluvoxamine has a short half-life of 15-20 hours, making it prone to causing discontinuation symptoms if stopped abruptly 2, 4
This pharmacokinetic mismatch actually works in your favor when switching FROM fluoxetine TO fluvoxamine, as fluoxetine's long half-life provides a built-in buffer against abrupt serotonin withdrawal 3.
Recommended Switching Protocol
Week 1-2: Begin Fluoxetine Taper
- Reduce fluoxetine dose by 25-50% of the original dose 1
- Do not start fluvoxamine yet—allow fluoxetine levels to begin declining 4
- Monitor for early withdrawal symptoms (dizziness, fatigue, headaches, nausea, anxiety) 1, 2
Week 2-3: Initiate Fluvoxamine
- Start fluvoxamine at 25-50 mg daily while continuing reduced fluoxetine dose 1
- This low starting dose minimizes the risk of serotonin syndrome from overlapping serotonergic activity 1, 4
- Continue reducing fluoxetine by another 25% if not already discontinued 1
Week 3-4: Complete Fluoxetine Discontinuation
- Discontinue fluoxetine entirely 4
- Increase fluvoxamine to 50-100 mg daily based on tolerability 1
- The typical therapeutic dose range for fluvoxamine is 100-150 mg daily for depression 1
Week 4-8: Titrate to Therapeutic Dose
- Gradually increase fluvoxamine to 100-150 mg daily in divided doses (typically 50 mg BID or 100 mg at bedtime) 1
- Fluvoxamine can be sedating, so evening dosing may be preferred over fluoxetine's more activating profile 1
Critical Drug Interaction Considerations
Fluvoxamine has significantly greater potential for drug-drug interactions than fluoxetine due to its inhibition of multiple CYP450 enzymes (CYP1A2, CYP2C19, CYP2C9, CYP3A4, CYP2D6), while fluoxetine primarily inhibits CYP2D6 1.
Before initiating the switch:
- Review all concomitant medications for potential interactions, particularly theophylline, warfarin, clozapine, olanzapine, and benzodiazepines metabolized via CYP1A2 1
- Dose adjustments of other medications may be necessary as fluvoxamine reaches therapeutic levels 1
Monitoring During the Switch
First 2 Weeks
- Monitor closely for serotonin syndrome during the overlap period, particularly in the first 24-48 hours after each dose change 1, 4
- Watch for symptoms: agitation, confusion, tremor, hyperthermia, hyperreflexia, diaphoresis, diarrhea 4
Weeks 2-6
- Assess for withdrawal symptoms from fluoxetine discontinuation, though these are less common due to its long half-life 2, 3
- Monitor for fluvoxamine side effects: nausea (less common than with fluoxetine), sedation, sexual dysfunction 5
- Follow up within 1-2 weeks after completing the switch to assess therapeutic response and adverse effects 1
Weeks 6-12
- Continue monitoring for 4-6 weeks to ensure stabilization on fluvoxamine, as full therapeutic effects may take this long 1
- Assess efficacy using standardized measures, as both medications show equivalent antidepressant efficacy 6, 5
Common Pitfalls and How to Avoid Them
Never abruptly switch between SSRIs without cross-tapering, as this can precipitate serotonin syndrome or severe withdrawal symptoms 1, 4. The conservative approach is always safer than rapid switching 4.
Do not assume fluoxetine needs aggressive tapering—its long half-life means it self-tapers over 4-6 weeks after discontinuation, reducing withdrawal risk compared to shorter-acting SSRIs 2, 3. However, some patients may still experience discontinuation symptoms, so gradual reduction is still recommended 2.
Be aware that fluvoxamine may cause more sedation than the activating effects of fluoxetine, which can be therapeutic for patients with insomnia but may require dose timing adjustments 1.
Do not overlook the drug interaction profile change—fluvoxamine's broad CYP450 inhibition requires careful medication review that wasn't necessary with fluoxetine 1.
Alternative Approach for Severe Cases
If the patient has severe depression or cannot tolerate any gap in therapeutic coverage, consider a more rapid cross-taper over 1-2 weeks with closer monitoring, though this increases the theoretical risk of serotonin syndrome 4. This should only be done with frequent clinical contact and clear patient education about warning signs 4.
For patients who experience severe withdrawal symptoms despite gradual tapering, reinstitute the previous fluoxetine dose and taper more slowly over several additional weeks 2, 3.