Prozac (Fluoxetine) Starting Dose
The recommended starting dose of Prozac (fluoxetine) for adults with major depressive disorder is 20 mg once daily, administered in the morning. 1
Standard Adult Dosing for Depression
- Start with 20 mg/day in the morning for most adult patients with major depressive disorder 1
- This 20 mg dose is sufficient to obtain a satisfactory response in most cases, as demonstrated in controlled trials 1
- Dose increases may be considered after several weeks if insufficient clinical improvement is observed, with a maximum of 80 mg/day 1
- The full therapeutic effect may be delayed until 4 weeks of treatment or longer 1
Pediatric Dosing (Children and Adolescents)
- Start with 10 mg/day for pediatric patients with depression 1
- After 1 week at 10 mg/day, increase to 20 mg/day 1
- For lower weight children, the starting and target dose may remain at 10 mg/day due to higher plasma levels 1
Special Population Considerations
Elderly Patients
- Use 10 mg every other morning as the initial dose for elderly patients with dementia and depression 2
- Maximum dose is 20 mg every morning in this population 2, 3
- Fluoxetine should generally be avoided in older adults due to greater risk of agitation and overstimulation 2, 3
- The drug is activating with a very long half-life, making it particularly problematic in geriatric populations 2
Hepatic Impairment
- A lower or less frequent dosage should be used in patients with hepatic impairment 1
Renal Impairment
- Dosage adjustments for renal impairment are not routinely necessary 1
Other Indications with Different Starting Doses
Obsessive-Compulsive Disorder (OCD)
- Adults: Start with 20 mg/day in the morning 1
- Adolescents and higher weight children: Start with 10 mg/day, increase to 20 mg/day after 2 weeks 1
- Lower weight children: Start with 10 mg/day, with a target range of 20-30 mg/day 1
Bulimia Nervosa
- Start with 60 mg/day administered in the morning 1
- For some patients, titrate up to this target dose over several days 1
- Only the 60 mg dose was statistically superior to placebo in controlled trials 1
Panic Disorder
- Start with 10 mg/day 1
- After 1 week, increase to 20 mg/day 1
- The most frequently administered dose in clinical trials was 20 mg/day 1
Important Clinical Considerations
Activation and Side Effects
- Fluoxetine tends to be activating and may cause initial anxiety or agitation 2
- Common adverse events at the 20 mg/day dose include nausea, nervousness, insomnia, and headache 4, 5
- These side effects are dose-related and more common at higher doses 4
Long Half-Life
- Fluoxetine has a half-life of 1-3 days, with its active metabolite (norfluoxetine) having a half-life of 7-15 days 5
- This long half-life essentially precludes withdrawal phenomena 4
- At least 5 weeks should be allowed after stopping fluoxetine before starting an MAOI 1