Analysis of sodium phenylbutyrate and taurursodiol survival effect in ALS using external controls

Abstract

Objective: Sodium phenylbutyrate and taurursodiol (PB and TURSO) was evaluated in amyotrophic lateral sclerosis (ALS) in the CENTAUR trial encompassing randomized placebo-controlled and open-label extension phases. On intent-to-treat (ITT) survival analysis, median overall survival (OS) was 4.8 months longer and risk of death 36% lower in those originally randomized to an initial 6-month double-blind period of PB and TURSO versus placebo. To estimate PB and TURSO treatment effect without placebo-to-active crossover, we performed a post hoc survival analysis comparing PB and TURSO-randomized participants from CENTAUR and a propensity score-matched, PB and TURSO-naïve external control cohort from the Pooled Resource Open-Access ALS Clinical Trials (PRO-ACT) database.

Methods: Clinical trial control participants from the PRO-ACT database who met prespecified eligibility criteria were propensity score matched 1:1 with PB and TURSO-randomized CENTAUR participants using prognostically significant covariates in ALS.

Results: Baseline characteristics including propensity score-matched covariates were generally well balanced between CENTAUR PB and TURSO (n = 89) and PRO-ACT external control (n = 85) groups. Estimated median (IQR) OS was 23.54 (14.56-39.32) months in the CENTAUR PB and TURSO group and 13.15 (9.83-19.20) months in the PRO-ACT external control group; hazard of death was 52% lower in the former group (hazard ratio, 0.48; 95% CI, 0.31-0.72; p = 0.00048).

Interpretation: This analysis suggests potentially greater survival benefit with PB and TURSO in ALS without placebo-to-active crossover than seen on ITT analysis in CENTAUR. Analyses using well-matched external controls may provide additional context for evaluating survival effects in future ALS trials.

Figure 1

Summarized process for constructing the PRO‐ACT external control group. ALSFRS‐R, Amyotrophic Lateral Sclerosis Functional Rating Scale‐Revised; PRO‐ACT, Pooled Resource Open‐Access ALS Clinical Trials; PSM, propensity score matching.

Figure 2

Kaplan–Meier analyses: CENTAUR PB and TURSO group and PRO‐ACT external control group. Kaplan–Meier plot for the CENTAUR PB and TURSO group is from the ITT analysis previously conducted at a cutoff date coinciding with the final participant visit in CENTAUR. ITT, intent‐to‐treat; OS, overall survival; PB and TURSO, sodium phenylbutyrate and taurursodiol; PRO‐ACT, Pooled Resource Open‐Access ALS Clinical Trials database.