What is the appropriate citalopram dose when converting a patient from escitalopram 5 mg?

Escitalopram 5 mg to Citalopram Conversion

Convert escitalopram 5 mg to citalopram 10 mg using a 1:2 dose ratio, as escitalopram is the therapeutically active S-enantiomer and requires half the dose of the racemic citalopram to achieve equivalent serotonergic activity. 1

Pharmacological Basis for Conversion

• Escitalopram is the isolated S-enantiomer of citalopram, which is the component responsible for antidepressant activity in the racemic mixture 2, 3
• Pharmacokinetic studies demonstrate that escitalopram 10 mg produces plasma concentrations of S-citalopram equivalent to citalopram 20 mg, establishing the 1:2 conversion ratio 3
• At steady state, citalopram 40 mg produces mean plasma concentrations of 86±38 ng/mL for the parent compound and 35±11 ng/mL for demethylcitalopram, while escitalopram 10 mg (equivalent to 20 mg citalopram) produces 27±14 ng/mL and 14±5 ng/mL respectively 4

Direct Switch Protocol

• Perform a direct switch without tapering or cross-titration, stopping escitalopram 5 mg and immediately starting citalopram 10 mg the following day 1
• The similar half-lives (27-33 hours for escitalopram vs approximately 33 hours for citalopram) and shared mechanism of action minimize discontinuation risk with direct switching 2
• Assess clinical response at 2-4 weeks after the switch to evaluate tolerability and efficacy 1

Critical Safety Monitoring

• Monitor for behavioral activation or increased anxiety during the first 1-2 weeks, particularly in adolescents or young adults, though this risk is equivalent to initiating any SSRI 1
• Assess for suicidality during the first months after the medication change, as this represents the highest-risk period following any antidepressant modification 1
• Obtain baseline ECG if cardiac risk factors are present, as citalopram carries a maximum dose of 40 mg daily (20 mg in elderly or hepatic impairment) due to QT prolongation risk at higher doses 1, 5

Common Pitfalls to Avoid

• Do not use a 1:1 conversion ratio (escitalopram 5 mg to citalopram 5 mg), as this provides only half the required serotonergic activity and will result in treatment failure 1, 3
• Do not exceed citalopram 40 mg daily in adults or 20 mg daily in elderly patients (>60 years) or those with hepatic impairment, as dose-dependent QT prolongation occurs above these thresholds 1, 5
• Do not perform gradual cross-titration when switching between these medications, as their similar pharmacokinetic profiles and mechanisms make direct switching both safe and more practical 1, 3

Efficacy Expectations

• Pooled analyses demonstrate that citalopram 20-40 mg/day produces equivalent efficacy to escitalopram 10-20 mg/day, with similar response rates (72.4% vs 73.5%) and remission rates (52.6% vs 54.5%) at 6 weeks 6
• Individual studies show comparable mean MADRS score reductions between equivalent doses, confirming the 1:2 conversion maintains therapeutic effect 7, 8