Safety of a Fixed-Dose Coformulation of Sodium Phenylbutyrate and Taurursodiol in Amyotrophic Lateral Sclerosis and Alzheimer’s Disease: Integrated Clinical Trials Experience
Steven E. Arnold1, Sabrina Paganoni2,3, Suzanne Hendrix4, Jessie Nicodemus-Johnson4, Samuel P. Dickson4, Newman Knowlton4, Jay Mason5, Jamie Timmons6, Machelle Manuel6, Shide Badri6, Patrick D. Yeramian6, Merit Cudkowicz2
1Department of Neurology, Massachusetts General Hospital, 2Sean M. Healey and AMG Center for ALS & the Neurological Clinical Research Institute, Massachusetts General Hospital, Harvard Medical School, 3Spaulding Rehabilitation Hospital, Harvard Medical School, 4Pentara Corporation, 5University of Utah Department of Medicine, 6Amylyx Pharmaceuticals, Inc.
Safety and tolerability of an oral, fixed-dose sodium phenylbutyrate/taurursodiol (PB/TURSO) coformulation were assessed in phase 2 trials in amyotrophic lateral sclerosis (ALS) and Alzheimer’s disease (AD). 

PB/TURSO was designed to reduce neurodegeneration by targeting endoplasmic reticulum and mitochondrial stress, both implicated in the pathophysiology of ALS and AD.

In the AMX-3500 Study (CENTAUR) in ALS, participants (PB/TURSO, n=89; placebo, n=48) completing the 24-week randomized phase (NCT03127514) were eligible to enroll in an open-label extension (OLE) phase (NCT03488524) and receive PB/TURSO (≤132 weeks, week 24 reported). Study AMX-8000 (PEGASUS; NCT03533257) was a 24-week randomized trial in adults with AD or mild cognitive impairment (PB/TURSO, n=51; placebo, n=44). PB/TURSO safety and tolerability was the primary objective of both trials. 
Mean (SD) ages were 57.7 (9.6) and 70.7 (7.5) years in CENTAUR and PEGASUS, respectively. Treatment-emergent adverse event (TEAE) incidence was similar between groups in the CENTAUR randomized phase (PB/TURSO, 97%; placebo, 96%); 77% reported ≥1 TEAEs in the OLE phase. In PEGASUS, TEAEs occurred in 67% and 59% of the PB/TURSO and placebo groups, respectively. Gastrointestinal TEAEs were more frequent during initial PB/TURSO exposure (week ≤3) in CENTAUR and accounted for the predominance of PB/TURSO-related TEAEs in PEGASUS. Incidence of cardiac events with PB/TURSO was low (CENTAUR, 8%; PEGASUS, 4%), and in both studies, electrocardiographic findings were similar between groups at baseline, with no clinically meaningful changes observed over the course of treatment.
These findings support the PB/TURSO safety profile in ALS and AD. TEAE incidence was generally similar between PB/TURSO and placebo in both trials. PB/TURSO-associated TEAEs were mostly gastrointestinal, consistent with the known profiles for PB and TURSO. Findings in AD further elucidate the PB/TURSO safety profile, as TEAEs in CENTAUR appear to have been largely disease driven. An updated safety analysis (pooled and OLE data) will be presented.