Background: Patients with dementia due to neurodegenerative disease can have dementia-related psychosis. The effects of the oral 5-HT(2A) inverse agonist and antagonist pimavanserin on psychosis related to various causes of dementia are not clear.

Methods: We conducted a phase 3, double-blind, randomized, placebo-controlled discontinuation trial involving patients with psychosis related to Alzheimer's disease, Parkinson's disease dementia, dementia with Lewy bodies, frontotemporal dementia, or vascular dementia. Patients received open-label pimavanserin for 12 weeks. Those who had a reduction from baseline of at least 30% in the score on the Scale for the Assessment of Positive Symptoms-Hallucinations and Delusions (SAPS-H+D, with higher scores indicating greater psychosis) and a Clinical Global Impression-Improvement (CGI-I) score of 1 (very much improved) or 2 (much improved) at weeks 8 and 12 were randomly assigned in a 1:1 ratio to continue receiving pimavanserin or to receive placebo for up to 26 weeks. The primary end point, assessed in a time-to-event analysis, was a relapse of psychosis as defined by any of the following: an increase of at least 30% in the SAPS-H+D score and a CGI-I score of 6 (much worse) or 7 (very much worse), hospitalization for dementia-related psychosis, stopping of the trial regimen or withdrawal from the trial for lack of efficacy, or use of antipsychotic agents for dementia-related psychosis.

Results: Of the 392 patients in the open-label phase, 41 were withdrawn for administrative reasons because the trial was stopped for efficacy; of the remaining 351 patients, 217 (61.8%) had a sustained response, of whom 105 were assigned to receive pimavanserin and 112 to receive placebo. A relapse occurred in 12 of 95 patients (13%) in the pimavanserin group and in 28 of 99 (28%) in the placebo group (hazard ratio, 0.35; 95% confidence interval, 0.17 to 0.73; P = 0.005). During the double-blind phase, adverse events occurred in 43 of 105 patients (41.0%) in the pimavanserin group and in 41 of 112 (36.6%) in the placebo group. Headache, constipation, urinary tract infection, and asymptomatic QT prolongation occurred with pimavanserin.

Conclusions: In a trial that was stopped early for efficacy, patients with dementia-related psychosis who had a response to pimavanserin had a lower risk of relapse with continuation of the drug than with discontinuation. Longer and larger trials are required to determine the effects of pimavanserin in dementia-related psychosis. (Funded by Acadia Pharmaceuticals; HARMONY ClinicalTrials.gov number, NCT03325556.).