Fluoxetine Dosing Recommendations
For major depressive disorder in adults, initiate fluoxetine at 20 mg once daily in the morning, which is sufficient for most patients, with a maximum dose of 80 mg/day if needed after several weeks of inadequate response. 1
Adult Dosing by Indication
Major Depressive Disorder
- Starting dose: 20 mg once daily in the morning 1
- Dose adjustment: May increase after several weeks if insufficient clinical improvement, though 20 mg/day is adequate for most patients 1
- Maximum dose: 80 mg/day 1
- Dosing schedule: Doses above 20 mg/day can be given once daily (morning) or twice daily (morning and noon) 1
- Time to full effect: May require 4 weeks or longer 1
Obsessive-Compulsive Disorder
- Starting dose: 20 mg once daily in the morning 1
- Dose range: 20-60 mg/day recommended 1
- Maximum dose: 80 mg/day (well-tolerated in open studies) 1
- Time to full effect: May be delayed until 5 weeks or longer 1
Bulimia Nervosa
- Recommended dose: 60 mg/day administered in the morning 1
- Titration: May titrate up to 60 mg over several days for some patients 1
- Rationale: Only the 60 mg dose was statistically superior to placebo in reducing binge-eating and vomiting frequency 1
Panic Disorder
- Starting dose: 10 mg/day 1
- Target dose: Increase to 20 mg/day after 1 week (most frequently administered dose in clinical trials) 1
- Dose range: 10-60 mg/day studied 1
- Maximum evaluated: Doses above 60 mg/day have not been systematically evaluated 1
Pediatric Dosing
Major Depressive Disorder (Children and Adolescents)
- Lower weight children: Start 10 mg/day, may increase to 20 mg/day after several weeks if needed 1
- Higher weight children/adolescents: Start 10-20 mg/day, increase to 20 mg/day after 1 week at 10 mg/day 1
- Maximum dose: 60 mg/day 2
Obsessive-Compulsive Disorder (Children and Adolescents)
- Higher weight children/adolescents: Start 10 mg/day, increase to 20 mg/day after 2 weeks 1
- Lower weight children: Start 10 mg/day, recommended range 20-30 mg/day 1
- Maximum studied: 60 mg/day (minimal experience with doses >20 mg in lower weight children) 1
Special Population Considerations
Elderly Patients
- Maximum recommended: 20 mg every morning 3
- Rationale: Lower or less frequent dosing should be considered due to age-related pharmacokinetic changes 1
Hepatic Impairment
- Recommendation: Use lower or less frequent dosage 1
Renal Impairment
- Recommendation: Dosage adjustments not routinely necessary 1
Maintenance Treatment
Daily Dosing
- Major depression: Efficacy maintained for up to 38 weeks following acute treatment at 20 mg/day 1
- Bulimia nervosa: Systematic evaluation supports continuing 60 mg/day for up to 52 weeks in responders 1
Weekly Dosing (Adults with Major Depression)
- Prozac Weekly: Initiate 7 days after last daily 20 mg dose 1
- Duration studied: Efficacy maintained for up to 25 weeks with once-weekly dosing 1
- Important caveat: Therapeutic equivalence with daily dosing for delaying relapse has not been established; consider reestablishing daily dosing if response not maintained 1
Important Safety Considerations
Drug Interactions
- CYP2D6 inhibition: Fluoxetine inhibits CYP2D6 and other cytochrome P450 enzymes, increasing potential for drug interactions particularly at higher doses 2
- Specific concern: Concomitant use with paroxetine may decrease plasma levels of endoxifen (active tamoxifen metabolite) in breast cancer patients 3
MAOI Interactions
- Before starting fluoxetine: Allow at least 14 days after discontinuing an MAOI 1
- Before starting MAOI: Allow at least 5 weeks (perhaps longer) after stopping fluoxetine 1
Common Adverse Events
- Most frequent at 20 mg/day: Insomnia, asthenia, somnolence, gastroenteritis, decreased libido 4
- Time course: Common adverse events (nausea, insomnia, nervousness, somnolence) resolve in the majority of patients and become significantly less frequent with continued treatment over 6 months 5
- Discontinuation rate: Adverse events leading to discontinuation similar to placebo (6.1% vs 5.8%) at 20 mg/day 4
Dosing Frequency Considerations
- Alternative regimen: Research suggests fluoxetine 20 mg once every third day (after initial 4 weeks of daily dosing) may be effective due to long half-life, though higher daily doses show reduced relapse rates 6
- Clinical recommendation: Maintain standard daily dosing for optimal outcomes, as 40 mg daily showed significantly delayed time to relapse compared to lower doses 6