Introduction: A previous phase 2b study supported the use of the 5-HT6 receptor antagonist intepirdine as adjunctive therapy to donepezil for Alzheimer's disease (AD) dementia. A phase 3 study, MINDSET, was performed to test this hypothesis.

Methods: MINDSET was a global, double-blind, randomized, placebo-controlled trial in 1315 mild-to-moderate AD dementia patients on stable donepezil. Patients received 35 mg/day intepirdine or placebo for 24 weeks. The co-primary endpoints were change from baseline to week 24 on the Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog) and Alzheimer's Disease Cooperative Study-Activities of Daily Living (ADCS-ADL).

Results: There were no statistically significant differences between intepirdine and placebo groups (adjusted mean [95% confidence interval]) on the co-primary endpoints ADAS-Cog (-0.36 [-0.95, 0.22],P = 0.2249) and ADCS-ADL (-0.09 [-0.90, 0.72],P = 0.8260). Intepirdine demonstrated a favorable safety profile similar to placebo.

Discussion: Intepirdine as adjunctive therapy to donepezil did not produce statistical improvement over placebo on cognition or activities of daily living in mild-to-moderate AD dementia patients.