Fluoxetine: Typical Use and Dosage
Fluoxetine is typically prescribed at an initial dose of 20 mg/day for adults with major depressive disorder, administered in the morning, with dose increases considered after several weeks if insufficient clinical improvement is observed. 1
FDA-Approved Indications
- Fluoxetine is FDA approved for major depressive disorder, obsessive-compulsive disorder (OCD), bulimia nervosa, premenstrual dysphoric disorder, panic disorder, and bipolar disorder (in combination with olanzapine) 2
- It is the only SSRI FDA approved for major depression in children/adolescents aged 8 years or older 2
- For pediatric patients, treatment should be initiated with 10-20 mg/day, with lower weight children typically starting at 10 mg/day 1
Dosage Guidelines
- For adults with major depression, the recommended initial dose is 20 mg/day in the morning 1
- Doses above 20 mg/day may be administered once daily (morning) or twice daily (morning and noon) 1
- Maximum dose should not exceed 80 mg/day 1
- For children and adolescents, starting dose is 10-20 mg/day (10 mg/day for lower weight children) 1
- For OCD, higher dosing (60-80 mg) has shown superior efficacy compared to lower dosing 2
Pharmacokinetics and Special Considerations
- Fluoxetine has a very long half-life compared to other SSRIs 3
- Full therapeutic effect may be delayed until 4 weeks of treatment or longer 1
- Lower or less frequent dosing should be used in patients with hepatic impairment 1
- Elderly patients and those with concurrent disease or on multiple medications may require lower or less frequent dosing 1
- Fluoxetine is metabolized through cytochrome P450 (CYP) 2D6, which is subject to genetic variation 2
- CYP2D6 poor metabolizers may require dose adjustments due to higher plasma concentrations 4
Maintenance Treatment
- For major depressive disorder, efficacy is maintained for periods up to 38 weeks following 12 weeks of acute treatment at 20 mg/day 1
- Weekly dosing with Fluoxetine Weekly capsules can be initiated 7 days after the last daily dose of Fluoxetine 20 mg 1
- Maintenance treatment is generally recommended for several months or longer following remission of acute episodes 1
Adverse Effects and Monitoring
- Fluoxetine has a more favorable side effect profile compared to tricyclic antidepressants, with fewer anticholinergic effects 5
- Most common adverse effects include nausea, nervousness, and insomnia 6
- Black box warnings have been issued for treatment-emergent suicidality, particularly in adolescents and young adults 2
- Nervousness or insomnia at the start of therapy may be predictors of a good response to fluoxetine 7
- Monitor for emergence or worsening of adverse effects within 24-48 hours after dose increases 4
Special Populations
- Genetic testing for CYP2D6 status may be beneficial before significant dose increases in patients with poor initial tolerance 4
- Fluoxetine has been shown to be effective and well-tolerated in geriatric patients 6
- For pediatric patients, efficacy has been demonstrated at doses of 10-20 mg/day 1
- Patients with medical comorbidities may benefit from fluoxetine's favorable side effect profile 5
Clinical Pearls
- Unlike some other SSRIs, fluoxetine's long half-life helps prevent withdrawal symptoms upon discontinuation or missed doses 5
- Fluoxetine requires no titration and can be dosed once daily, improving compliance compared to medications requiring multiple daily doses 8
- Fluoxetine is remarkably safe in overdose compared to tricyclic antidepressants 5
- Fluoxetine is particularly effective in anxious, agitated depressed patients 5