Fluoxetine Dosing in Adults
The recommended initial dose of fluoxetine for adults with depression is 20 mg once daily in the morning, with a maximum recommended dose of 80 mg/day. 1
Standard Dosing for Different Indications
Major Depressive Disorder
- Initial dose: 20 mg once daily in the morning
- Maintenance dose: 20 mg/day
- Maximum dose: 80 mg/day (although doses above 20 mg/day are rarely needed for depression)
- Duration: Several months or longer of sustained therapy is generally recommended following remission 1
Obsessive-Compulsive Disorder
- Initial dose: 20 mg/day in the morning
- Titration: Dose increases may be considered after several weeks if insufficient clinical improvement is observed
- Therapeutic range: 20-60 mg/day
- Maximum dose: 80 mg/day
- Full therapeutic effect: May be delayed until 5 weeks of treatment or longer 1
Bulimia Nervosa
- Recommended dose: 60 mg/day (administered in the morning)
- Titration: For some patients, titrate up to target dose over several days
- Maximum dose: 60 mg/day (doses above this have not been systematically studied) 1
Dosing Considerations
Special Populations
- Hepatic impairment: Lower or less frequent dosage should be used
- Elderly patients: Lower or less frequent dosage should be considered
- Patients with concurrent disease or on multiple medications: Consider lower or less frequent dosage 1
Alternative Dosing Regimens
- Weekly dosing: Prozac Weekly (90 mg) can be initiated 7 days after the last daily dose of fluoxetine 20 mg for maintenance treatment of depression 1
- Low-dose option: Some patients, particularly those with panic disorder, may benefit from starting at 5 mg/day and gradually increasing to 20 mg/day over a 1-week period 2
Efficacy and Safety
- Fluoxetine at 20 mg/day has demonstrated significantly greater remission and response rates compared to placebo in patients with major depression 3
- The most common adverse events at 20 mg/day include:
Clinical Pearls
- Allow 4-8 weeks at therapeutic dose to evaluate efficacy for depression 5
- The long half-life of fluoxetine and its active metabolite (norfluoxetine) essentially precludes withdrawal phenomena, making it easier to discontinue than other SSRIs 4
- For OCD treatment, higher doses (40-60 mg/day) are often required for optimal efficacy 6
- Fluoxetine is an inhibitor of CYP2D6 and other CYP enzymes, which increases potential for drug interactions 4
Monitoring
- Assess for improvement in symptoms after 2 weeks of treatment
- Monitor for common side effects including insomnia, headache, nausea, and sexual dysfunction
- Consider discontinuing gradually over 10-14 days to limit withdrawal symptoms, although this is less critical with fluoxetine due to its long half-life 7
Fluoxetine's unique pharmacokinetic profile with its long half-life allows for flexible dosing options, including daily, every third day (in some cases), or weekly administration (for maintenance), which can be advantageous for patients with adherence concerns or those sensitive to medication changes.