What is the typical dosing regimen for Prozac (fluoxetine)?

Fluoxetine (Prozac) Dosing Regimen

For adults with depression, the standard initial dose of fluoxetine is 20 mg once daily in the morning, which is sufficient to obtain a satisfactory response in most cases. 1

Adult Dosing for Major Depressive Disorder

• Initial dose: 20 mg once daily in the morning 1
• Due to fluoxetine's very long half-life (1-3 days for fluoxetine, 4-16 days for its active metabolite norfluoxetine), side effects may not manifest for several weeks 2
• For patients who may be sensitive to side effects, starting with 10 mg daily or even 10 mg every other morning may be appropriate 2, 3
• Dose increases may be considered after several weeks if insufficient clinical improvement is observed 1
• Maximum recommended dose: 80 mg/day 1
• Full therapeutic effect may be delayed until 4 weeks of treatment or longer 1

Special Populations

• Lower or less frequent dosing should be used in:
  • Patients with hepatic impairment 1
  • Elderly patients 1
  • Patients with concurrent disease or on multiple medications 1
• Dosage adjustments for renal impairment are not routinely necessary 1

Administration Considerations

• Morning dosing is preferred as fluoxetine is activating and may cause insomnia if taken later in the day 4, 2
• After initial daily dosing, some patients may be switched to Prozac Weekly (once weekly dosing) for maintenance treatment 1
• Weekly dosing should be initiated 7 days after the last daily dose of fluoxetine 20 mg 1

Titration and Duration

• Dose increases should use increments of initial dose every 5-7 days until therapeutic benefits or significant side effects become apparent 4
• Common early side effects (nausea, insomnia, nervousness, somnolence) typically resolve with continued treatment over a 6-month period 5
• Maintenance treatment is generally recommended for several months or longer for acute episodes of major depressive disorder 1
• After 9 months, dosage reduction can be used to reassess the need for medication 4

Alternative Dosing Strategies

• Some patients who cannot tolerate 20 mg daily may benefit from lower doses (5-10 mg daily) 3
• Patients with panic disorder and depression may be particularly sensitive to standard doses and may benefit from starting at lower doses (5 mg daily) with gradual titration 3
• In some cases of non-response, paradoxically, lowering the dose may improve response if serotonergic overstimulation is occurring 6

Common Pitfalls and Caveats

• Due to the very long half-life of fluoxetine and its active metabolite, side effects may take weeks to manifest 2
• Steady-state plasma levels are not reached for nearly 4 weeks, which means clinical effects and side effects may continue to evolve during this time 7
• When switching to or from a monoamine oxidase inhibitor (MAOI), at least 14 days should elapse between discontinuation of an MAOI and initiation of fluoxetine, and 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 TCA may need to be reduced and plasma TCA concentrations may need to be monitored temporarily 1