ENHANCE: Phase 3, Randomized, Double-Blind, Placebo-Controlled Study of Adjunctive Pimavanserin for Schizophrenia in Patients With an Inadequate Response to Antipsychotic Treatment.

Inadequate response to antipsychotic treatment is common in patients with schizophrenia. This study evaluated pimavanserin, a 5-HT _2A receptor inverse agonist/antagonist, as adjunctive treatment in patients with inadequate response. This was a 6-week, randomized, double-blind, placebo-controlled, study conducted in North America and Europe. Adult outpatients with schizophrenia and inadequate response to current antipsychotic were enrolled. Inclusion criteria included Positive and Negative Syndrome Scale (PANSS) total score ≥65 and ≤110 and retrospective antipsychotic treatment stability of 8 weeks. Pimavanserin 20 mg/day or placebo added to ongoing antipsychotic was tested in a flexible-dose paradigm with dose adjustments allowed during the first 3 weeks. The primary efficacy endpoint, PANSS total score change from baseline to week 6, was not met, although improvement was greater with pimavanserin than placebo (LS mean difference: -2.1, [95% CI: -4.5, 0.4]; P = .094). As a hierarchical testing procedure was used, additional efficacy analyses were exploratory. Clear separation from placebo was observed with pimavanserin at week 6 for the PANSS Negative Symptoms subscale (LS mean difference: -0.7, [95% CI: -1.5, 0.0]) and Marder Negative Symptom Factor score (-0.9, [-1.7, -0.1]). Analysis of European sites (81.5% of patients) revealed a difference for pimavanserin versus placebo on PANSS total score (LS mean difference: -3.1, [95% CI: -5.8, -0.4]) and Clinical Global Impressions-Severity score (-0.2, [-0.4, -0.0]). Treatment-emergent adverse events occurred in 39.9% with pimavanserin and 36.4% with placebo. Although statistical significance for the primary endpoint was not met, a trend toward improvement in negative symptoms was observed with pimavanserin, warranting further study.