Citalopram is effective in treating agitation in Alzheimer's dementia (AD), but it is associated with cognitive and cardiac risks, likely due to its R-enantiomer. Escitalopram, the S-enantiomer, may be an alternative. In this double-masked randomized (1:1) placebo-controlled trial, we assessed the efficacy and safety of escitalopram in treating agitation in AD after failure of a psychosocial intervention (PSI). Assessments occurred at enrollment, post-PSI (baseline) and at 3, 6, 9 and 12 weeks post-baseline. Settings were 27 community-based centers. The target randomization sample was 392 participants. Participants were adults with AD, a Mini-Mental State Examination Telephone score of 3-20 and significant agitation. PSI non-responders received escitalopram (up to 15 mg per day) or placebo for 12 weeks while continuing PSI. The outcome was the proportion of participants with clinically significant improvement in agitation from baseline at 12 weeks. In total, 173 participants were randomized (84 escitalopram versus 89 placebo; mean ± s.d. age = 78.4 ± 8.7 years; 90 men (52.0%); 127 White (73.4%)). The unadjusted risk difference at 12 weeks was 0.08 (95% confidence interval: -0.21, 0.06). Drug-related QT interval prolongation was observed. Although the randomized sample was smaller than planned, escitalopram was not effective in treating agitation in AD and was associated with cardiac conduction delays. Clinicians need to be cautious in recommending escitalopram as an alternative to citalopram for this condition. ClincialTrials.gov identifier: NCT03108846 .

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