Fluoxetine Dosing Recommendations
For adults with depression, the recommended starting dose of fluoxetine is 20 mg once daily in the morning, with potential dose increases up to a maximum of 80 mg/day if needed. 1
Initial Dosing for Different Conditions
Major Depressive Disorder
- For adults: Start with 20 mg/day administered in the morning 1
- For children and adolescents: Start with 10 mg/day (especially for lower weight children) or 20 mg/day; after 1 week at 10 mg/day, the dose can be increased to 20 mg/day 1
- Dose increases above 20 mg/day may be considered after several weeks if insufficient clinical improvement is observed 1
- Maximum recommended dose is 80 mg/day 1
Obsessive-Compulsive Disorder (OCD)
- For adults: Start with 20 mg/day in the morning 1
- For adolescents and higher weight children: Start with 10 mg/day, increase to 20 mg/day after 2 weeks 1
- For lower weight children: Start with 10 mg/day, with a recommended dose range of 20-30 mg/day 1
- Dose range for adults and higher weight children: 20-60 mg/day 1
- Maximum dose should not exceed 80 mg/day 1
Bulimia Nervosa
- Recommended dose is 60 mg/day, administered in the morning 1
- For some patients, it may be advisable to titrate up to this target dose over several days 1
Panic Disorder
- Start with 10 mg/day 1
- After 1 week, increase to 20 mg/day 1
- Most frequently used dose in clinical trials was 20 mg/day 1
- Maximum studied dose is 60 mg/day 1
Special Considerations
Pharmacokinetics and Administration Timing
- Fluoxetine has a very long half-life (1-3 days for fluoxetine, 4-16 days for its active metabolite norfluoxetine) 2
- Due to its activating properties, morning dosing is preferred to avoid insomnia 2
- Side effects may not appear immediately but can develop over several weeks of treatment due to the long half-life 2
Dose Adjustments for Special Populations
- Lower or less frequent dosing should be used in patients with hepatic impairment 1
- Lower or less frequent dosing should be considered for elderly patients 1
- Dosage adjustments for renal impairment are not routinely necessary 1
Maintenance Treatment
- For major depressive disorder, efficacy is maintained for periods up to 38 weeks following 12 weeks of open-label acute treatment at 20 mg/day 1
- Weekly dosing with Prozac Weekly (once weekly) can be initiated 7 days after the last daily dose of Prozac 20 mg for maintenance treatment 1
Managing Treatment Failure
- If a patient relapses on 20 mg/day, increasing the dose to 40 mg/day can be effective, with studies showing 67% of patients achieving full response after dose increase 3
- Higher daily doses of fluoxetine (40 mg) have shown reduced relapse rates compared to lower doses (20 mg) 4
Potential Adverse Effects
- Common side effects include insomnia, asthenia, somnolence, decreased libido, and gastrointestinal disturbances 5
- Fluoxetine should be used with caution in patients with congenital long QT syndrome, previous history of QT prolongation, or family history of long QT syndrome 6
- CYP2D6 poor metabolizers may experience higher plasma concentrations and potentially more side effects 6
Drug Interactions and Precautions
- At least 14 days should elapse between discontinuation of an MAOI and initiation of therapy with fluoxetine 1
- At least 5 weeks should be allowed after stopping fluoxetine before starting an MAOI 1
- When switching to a tricyclic antidepressant (TCA), the dosage of the TCA may need to be reduced and plasma TCA concentrations may need to be monitored 1
By following these dosing recommendations and considering individual patient factors, clinicians can optimize the therapeutic benefits of fluoxetine while minimizing potential adverse effects.