Fluoxetine vs Escitalopram

Overview

Escitalopram is the S-enantiomer of citalopram and represents one of the most selective SERT inhibitors available. It is generally considered to have a superior efficacy-tolerability balance among SSRIs, as established by the Cipriani 2018 network meta-analysis.

Mechanism of Action

Both block SERT. Escitalopram's SERT affinity is approximately twice that of racemic citalopram per unit dose because the inactive R-enantiomer of citalopram is absent. Escitalopram also allosterically modulates SERT via a secondary binding site, potentially enhancing its antidepressant effect.

Pharmacokinetics

Escitalopram: bioavailability ~80%, half-life 27–32 h, primarily metabolized by CYP2C19 (and partially CYP2D6, 3A4). Minimal CYP inhibition. Fluoxetine: bioavailability ~72%, half-life 1–4 days (norfluoxetine 4–16 days), potent CYP2D6 inhibitor. Escitalopram is subject to the same 20 mg/day dose limitation and QTc monitoring requirement as citalopram (from same R-enantiomer reasoning is not applicable here, but the class effect is considered relevant).

Clinical Evidence

Cipriani et al. 2018 (Lancet) ranked escitalopram highest for combined efficacy and acceptability among 21 antidepressants. Multiple head-to-head trials have shown escitalopram non-inferior or superior to other SSRIs with fewer side effects. Fluoxetine shows equivalent efficacy.

Key Takeaways

• Escitalopram ranked best for efficacy + acceptability in major network meta-analysis
• Both have minimal non-SERT activity (escitalopram more selective)
• Fluoxetine's ultra-long half-life protects against missed doses; escitalopram has mild discontinuation syndrome
• Escitalopram mild QTc risk; fluoxetine none