Exposure-response Modeling From the CLARITY Trial of Pimavanserin for Adjunctive Treatment of Major Depressive Disorder.

In the 10-week, phase 2 CLARITY study of patients with major depressive disorder, adjunctive therapy to antidepressants with pimavanserin 34 mg once daily statistically significantly improved the Hamilton Depression Rating Scale (HAMD-17) total score (primary endpoint) and Sheehan Disability Scale (SDS) score (secondary endpoint) versus placebo. This analysis characterized the exposure-response (E-R) relationships of pimavanserin in this CLARITY patient population. Exposure measures were estimated for each patient based on population-pharmacokinetic empirical Bayesian estimates. E-R models were developed to describe exposure-efficacy (HAMD-17, SDS, and Clinical Global Impression-Improvement [CGI-I] scale) and exposure-safety relationships (Karolinska Sleepiness Scale [KSS], Massachusetts General Hospital Sexual Functioning Inventory [MGH-SFI], and adverse events [AEs] of headache, sedation, and somnolence) relationships. For the primary efficacy endpoint (HAMD-17 scores), a sigmoid maximum-effect model described the time course of response, and a linear function of pimavanserin exposure was statistically significant. HAMD-17 scores decreased steadily over time following placebo and pimavanserin treatment; separation from placebo increased as peak pimavanserin plasma concentration (Cmax ) increased. At median pimavanserin Cmax (34-mg dose), the reduction from baseline in HAMD-17 scores was -11.1 and -13.5 at weeks 5 and 10, respectively. Relative to placebo, the model predicted comparable reductions in HAMD-17 scores at weeks 5 and 10. Similar improvements in favor of pimavanserin were detected with SDS, CGI-I, MGH-SFI, and KSS scores. No E-R relationship was found for AEs. E-R modeling predicted a relationship between higher pimavanserin exposure and improvement in HAMD-17 score and improvement across multiple secondary efficacy endpoints.

Adjunctive Pimavanserin in Patients with Major Depressive Disorder: Combined Results from Two Randomized, Double-Blind, Placebo-Controlled Phase 3 Studies.

Objective: In a phase 2 study, pimavanserin demonstrated efficacy as adjunctive treatment for major depressive disorder (MDD). Subsequently, two phase 3 studies (NCT03968159 in the US; NCT03999918 in Europe) were initiated to examine the efficacy and safety of adjunctive pimavanserin in subjects with MDD and inadequate response to antidepressant treatment. Studies were combined with a prespecified statistical analysis plan owing to recruitment challenges related to the COVID-19 pandemic. Experimental design: The randomized, double-blind studies enrolled 298 patients with MDD and inadequate response to current antidepressants. Patients were randomly assigned 1:1 to pimavanserin or placebo added to current antidepressant for 6 weeks. Primary endpoint was change from baseline to week 5 in the Hamilton Rating Scale for Depression, 17-item version (HAM-D-17). Principal observations: There was no effect of pimavanserin in change from baseline to week 5 in the HAM-D-17 (pimavanserin [n = 138]: least-squares mean [LSM] [standard error {SE}], -9.0 [0.58]; placebo [n = 135]: -8.1 [0.58]; mixed-effects model for repeated measures LSM [SE] difference, -0.9 [0.82], P = 0.2956). Nominal improvement with pimavanserin was observed on 2 secondary endpoints: Clinical Global Impressions-Severity scale, Karolinska Sleepiness Scale. Treatment-emergent adverse events occurred in 58.1% of pimavanserin-treated and 54.7% of placebo-treated patients. Conclusions: Adjunctive pimavanserin did not significantly improve depressive symptoms, although pimavanserin was well tolerated.