Escitalopram 10 mg is the equivalent dose to fluoxetine (Prozac) 10 mg
Based on the most rigorous dose-equivalence methodology using randomized controlled trial data, fluoxetine 40 mg/day is equivalent to escitalopram 18 mg/day 1. Using this ratio, fluoxetine 10 mg corresponds to approximately escitalopram 4.5 mg, though in clinical practice you would round to the nearest available dose of 5 mg escitalopram.
However, the standard therapeutic starting dose of escitalopram is 10 mg/day 2, 1, which is also the FDA-approved starting dose for adolescents aged 12 years and older 2. This 10 mg dose represents the most commonly prescribed and studied dose in clinical trials 3.
Practical Dosing Algorithm
For a direct switch from fluoxetine 10 mg:
- Start escitalopram at 10 mg once daily 2, 1—this is the standard therapeutic dose and requires no washout period since neither drug is an MAOI 4
- The 10 mg escitalopram dose will provide slightly greater serotonergic activity than fluoxetine 10 mg based on dose-equivalence ratios, but this difference is clinically insignificant and well-tolerated 1, 3
- Assess response at 6–8 weeks before considering dose adjustment 4
If the patient is highly sensitive to medication or elderly:
- Consider starting at 5 mg escitalopram daily for 1 week, then increase to 10 mg 2
- Elderly patients do not require routine dose reduction based on pharmacokinetics alone, but lower starting doses may improve tolerability 5, 6
Key Pharmacokinetic Considerations
- Escitalopram reaches steady-state in 7–10 days 5, compared to fluoxetine's 4–6 week steady-state due to its long half-life 4
- No washout period is required when switching from fluoxetine to escitalopram 4
- Escitalopram has minimal drug interactions due to negligible CYP enzyme inhibition 5, unlike fluoxetine which is a potent CYP2D6 inhibitor 4
Critical Safety Screening
Before initiating escitalopram, verify the patient:
- Has not taken an MAOI within 14 days 4—concurrent use can precipitate serotonin syndrome within 24–48 hours
- Is not taking other serotonergic agents (tramadol, meperidine, methadone, fentanyl, dextromethorphan, St. John's wort) 4
- Does not have risk factors for QT prolongation 4—escitalopram can prolong QT at higher doses
Monitoring During Transition
- Watch for serotonin syndrome signs in the first 1–2 weeks: confusion, agitation, tremor, clonus, hypertension, tachycardia, diaphoresis 4
- Monitor for suicidal ideation, especially in patients younger than 24 years 2, 4—risk is highest in the first 1–2 months of any antidepressant therapy
Common Pitfall to Avoid
Do not underdose escitalopram at 5 mg thinking it is equivalent to fluoxetine 10 mg 1. While the mathematical ratio suggests 4.5 mg, the 10 mg dose is the evidence-based therapeutic starting dose that has demonstrated efficacy in clinical trials 2, 3. Starting at 5 mg may delay therapeutic response and is only appropriate for highly sensitive patients or as a brief titration step 2.