What is the safest way to switch a patient from Celexa (citalopram) to Lexapro (escitalopram), including appropriate dosing schedule and monitoring?

How to Switch from Celexa to Lexapro

Direct Cross-Titration Without Washout Period

You can switch directly from citalopram (Celexa) to escitalopram (Lexapro) without a washout period, using a simple dose conversion of approximately 2:1 (citalopram to escitalopram). 1, 2

Dose Conversion Strategy

• Convert citalopram 20 mg to escitalopram 10 mg, or citalopram 40 mg to escitalopram 20 mg 1
• The therapeutic activity of citalopram resides primarily in the S-enantiomer (escitalopram), making this a pharmacologically rational switch 3
• Escitalopram demonstrates dose-proportional pharmacokinetics in the 10-30 mg/day range, with steady-state achieved within 7-10 days 2

Switching Methods

Option 1: Immediate Switch (Preferred for Most Patients)

• Stop citalopram and start escitalopram at the equivalent dose the next day 1
• This approach is safe because both medications share the same mechanism (SSRI) and escitalopram has minimal drug interaction potential 2, 3
• No washout period is required due to overlapping pharmacology 1

Option 2: Brief Cross-Taper (For Anxious or Sensitive Patients)

• Day 1-3: Reduce citalopram by 50% while starting escitalopram at target dose
• Day 4 onward: Discontinue citalopram completely, continue escitalopram
• This minimizes any theoretical discontinuation symptoms, though they are uncommon with this switch 1

Clinical Advantages of This Switch

• Escitalopram separates from placebo as early as week 1, while citalopram requires 4-6 weeks, suggesting faster onset of therapeutic effect 4
• Escitalopram demonstrates superior efficacy compared to citalopram in severe depression (MADRS ≥30), with significantly greater mean improvement (-17.3 vs -13.8, p=0.003) 5
• Response rates are higher with escitalopram (56% vs 41%, p=0.007) in severely depressed patients 5
• Both medications have similar safety profiles, with escitalopram showing no clinically significant differences in discontinuation rates due to adverse events compared to placebo at 10 mg/day 3

Monitoring Requirements

• Assess response at week 1-2 to capture early improvement that may occur with escitalopram 4
• Monitor for common SSRI side effects: nausea (most common), insomnia, diarrhea, dry mouth 3
• Full therapeutic assessment should occur at 6-8 weeks after the switch 1
• Watch for any emergence of suicidality, particularly in patients ≤24 years old, during the first weeks after switching 6

Important Pharmacokinetic Considerations

• Escitalopram has a half-life of 27-33 hours, consistent with once-daily dosing 2
• It has low protein binding (56%) and negligible effects on CYP450 enzymes, minimizing drug-drug interaction risk 2, 3
• The medication can be taken with or without food, as absorption is not affected 2
• Morning dosing is preferred if activation or insomnia occurs 6

Critical Safety Points

• No MAOI contraindication concerns during this switch, as you're moving between two SSRIs 7
• Escitalopram and citalopram can be safely combined with methadone or buprenorphine in patients on opioid substitution therapy 1
• If the patient is a CYP2D6 poor metabolizer (rare but important), this switch is actually advantageous because escitalopram has less CYP2D6 involvement than many other antidepressants 6

When to Expect Improvement

• Initial response may be evident within 1 week with escitalopram 4
• Maximal benefit typically occurs by 6-8 weeks 1
• If switching due to non-response to citalopram, studies show significant improvement is achievable (β = -0.34,95% CI -0.41 to -0.26, P<0.001) 8