Recommended Dosage and Treatment Regimen for Prozac (Fluoxetine)
For adults with major depressive disorder, the recommended initial dose is 20 mg once daily in the morning, with potential increases up to a maximum of 80 mg/day if needed after several weeks of insufficient clinical improvement. 1
Dosing Guidelines by Condition
Major Depressive Disorder
Adults:
- Initial dose: 20 mg once daily in the morning
- Dose range: 20-80 mg/day
- Maximum dose: 80 mg/day
- Doses above 20 mg may be administered once daily or divided (morning and noon) 1
Children and Adolescents (8 years and older):
- Initial dose: 10-20 mg/day
- For lower weight children: Start with 10 mg/day
- Target dose: 20 mg/day after 1 week at 10 mg/day 1
Obsessive-Compulsive Disorder (OCD)
Adults:
- Initial dose: 20 mg/day in the morning
- Dose range: 20-60 mg/day (recommended)
- Maximum dose: 80 mg/day 1
Children and Adolescents:
- Adolescents/higher weight children: Start with 10 mg/day, increase to 20 mg/day after 2 weeks
- Lower weight children: Start with 10 mg/day
- Dose range: 20-30 mg/day for lower weight children; 20-60 mg/day for adolescents 1
Bulimia Nervosa
- Recommended dose: 60 mg/day in the morning
- Consider titrating to target dose over several days 1
Panic Disorder
- Initial dose: 10 mg/day
- After 1 week, increase to 20 mg/day
- Most common effective dose: 20 mg/day
- Maximum dose: 60 mg/day 1
Special Populations
Elderly Patients
- Lower or less frequent dosing recommended due to risk of higher concentrations and more side effects 2, 1
Hepatic Impairment
- Lower or less frequent dosing recommended 1
Renal Impairment
- Routine dose adjustments not necessary 1
Treatment Duration and Monitoring
Acute Treatment
- Full therapeutic effect may be delayed until 4 weeks of treatment or longer 1
- Regular follow-up within 2-4 weeks of starting therapy 2
Maintenance Treatment
- For major depression: Efficacy maintained for up to 38 weeks following 12 weeks of acute treatment 1
- Weekly dosing option: Prozac Weekly can be initiated 7 days after the last daily dose of 20 mg 1
- For OCD and panic disorder: Periodic reassessment recommended to determine need for continued treatment 1
Side Effect Management
Common Side Effects
- At 20 mg/day: Primarily nausea and insomnia 3
- At higher doses (60 mg/day): Nausea, anxiety, dizziness, and insomnia 3
- Gastrointestinal disturbances: Take medication with food 2
- Sleep disturbances: Adjust dosing time 2
Behavioral Activation
- Can manifest as restlessness, insomnia, impulsiveness, irritability, and anxiety
- Manage with slow dose titration and close monitoring 2
- Particularly important in children and adolescents 2
Important Considerations
Drug Interactions
- CYP2D6 inhibitor: Use caution with other medications metabolized by CYP2D6 4
- Allow at least 14 days between discontinuing an MAOI and starting fluoxetine 1
- Allow at least 5 weeks between stopping fluoxetine and starting an MAOI 1
Discontinuation
- Gradual dose reduction recommended rather than abrupt cessation 1
- Long half-life of fluoxetine and its active metabolite (norfluoxetine) essentially precludes withdrawal phenomenon 5
QT Prolongation Risk
- Use with caution in patients with congenital long QT syndrome, history of QT prolongation, family history of long QT syndrome or sudden cardiac death 4
- CYP2D6 poor metabolizers may be at higher risk 4
Alternative Dosing Strategies
For patients who cannot tolerate standard doses, starting at lower doses may be beneficial:
- Starting at 5 mg/day and gradually increasing to 20 mg/day over 1 week may be useful, particularly for patients with panic disorder 6
- Approximately 28% of patients may be unable to tolerate the full 20 mg dose but may benefit from lower doses 6
The long half-life of fluoxetine (1-3 days) and its active metabolite norfluoxetine (7 days) allows for flexible dosing schedules in some patients 7, 8.