Arbaclofen: Phase II data

In the per protocol (PP) population (n=54) of a double-blind, crossover, U.S. Phase II trial, STX209 missed the primary endpoint of significantly improving irritability subscale scores on the ABC-I from baseline to week 4 vs. placebo. Seaside also said that STX209 showed clinically meaningful, but not statistically significant, improvements in global and specific neurobehavioral outcomes vs. placebo, including investigators' assessments of Clinical Global Impressions of Improvement (CGI-I) (p=0.18) and Severity (CGI-S) (p<0.1) and investigator and caregiver treatment preference (p<0.1 for both). The company said that because there are no validated approval endpoints in fragile X syndrome, a major goal of the study was to explore a list of potential indicators of efficacy to identify the most appropriate endpoints for use in future trials for the indication. Seaside believes it has identified potential endpoints to discuss with FDA and plans to start "late-stage" clinical trials of STX209 later this year after meeting with the agency.

In a subset of 15 pediatric patients with severe impairments in sociability at baseline, STX209 significantly improved all global outcomes, including CGI-I (p<0.01), CGI-S (p<0.05) and clinician and parent/caregiver preference vs. placebo (p<0.01 for both). STX209 also significantly improved Aberrant Behavior Checklist-Social Withdrawal (ABC-SW) scores from baseline vs. placebo (p=0.05), but non-significantly improved Vineland Play and Leisure scores (p<0.1). ...