MT-1186 oral edaravone in ALS: a Phase 3b extension follows its parent into futility

What was tried

Tanabe Pharma America ran NCT05151471, a Phase 3b multicenter, randomized, double-blind extension of MT-1186-A02. Subjects who completed the parent 48-week study were eligible to continue oral edaravone (MT-1186) or placebo for an additional 48 weeks under the same on-off cycle approved for intravenous edaravone (Radicava): 14 days of daily dosing followed by 14 days off. The primary endpoint was time from the original MT-1186-A02 randomization date to a 12-point or larger decrease on the revised ALS Functional Rating Scale (ALSFRS-R) or death, whichever happened first. Actual enrollment reached 202 participants. The study was terminated when the prespecified futility analysis of the parent MT-1186-A02 trial was met. Tanabe Pharma America posted results before termination, and the extension was closed without completing the planned 48-week follow-up window.

The biological hypothesis

Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one, ChEMBL290916) is a low-molecular-weight pyrazolone that scavenges peroxynitrite and hydroxyl radicals. Oxidative stress is one of the most reproducible histopathological signatures across SOD1-linked and sporadic ALS, and a free-radical sink was the mechanistic justification for the original Japanese MCI-186-19 Phase 3 (Writing Group on Behalf of the Edaravone ALS 19 Study Group, Lancet Neurology 2017, doi:10.1016/S1474-4422(17)30115-1). That study, restricted to early disease and predicted vital capacity above 80 percent, showed a 2.49 point smaller ALSFRS-R decline at 24 weeks versus placebo. Open Targets v25.06 places the SOD1 to amyotrophic lateral sclerosis association score at 0.87, the strongest genetic anchor in the disease. MT-1186 was Tanabe Pharma America's oral suspension formulation, which the FDA approved in 2022 on the basis of a pharmacokinetic bridging package, not a new efficacy trial. MT-1186-A02 was the post-marketing confirmatory study Mitsubishi Tanabe had committed to delivering.

What actually happened

MT-1186-A02 randomized 380 adults with ALS to oral edaravone 105 mg or placebo on the approved on-off cycle for 48 weeks, with a primary endpoint of time to a 12-point decrease in ALSFRS-R or death. The Data and Safety Monitoring Board called futility, and Tanabe Pharma America terminated both the parent study and this extension. The 96-week safety extension publication and the once-daily versus on-off dosing analysis in Muscle and Nerve in September 2025 (and) describe a population whose ALSFRS-R trajectory tracked the placebo group closely, with no statistical separation. The 202 subjects who rolled into NCT05151471 were a survivor cohort selected for being able to complete 48 weeks of either arm, and the extension was unable to recover the parent trial's lost effect once futility was declared. OpenFDA FAERS records 1,247 edaravone case reports through April 2026, with cerebral infarction (105), ALS progression (66), death (40), and aspiration pneumonia (31) leading the reaction list, consistent with the underlying disease trajectory more than a drug toxicity signal.

Failure mechanism, best guess

The parent population was broader than the MCI-186-19 cohort that produced the 2017 positive result. MCI-186-19 enrolled patients within two years of symptom onset, with forced vital capacity at or above 80 percent, an ALSFRS-R score of at least 2 on every item, and an estimated decline of one to four points over the 12-week run-in. MT-1186-A02 used looser eligibility consistent with real-world Radicava use. The most parsimonious explanation for futility is that the original benefit was confined to a narrow window of early, relatively preserved patients where the peroxynitrite contribution to motor neuron death is rate-limiting, and that effect dilutes to zero once the eligibility window opens. The drug exposure data in the Clinical Therapeutics PK paper (doi:10.1016/j.clinthera.2023.09.025) showed oral suspension bioequivalence to the IV product, so under-dosing is not a credible mechanism.

How to prevent this next time

Future confirmatory studies for symptomatic ALS therapies should require Bayesian sequential monitoring tied to the original enrichment criteria of the positive subgroup, not the broader label population. With a prior on 24-week ALSFRS-R decline centred at minus 7.5 points on placebo and minus 5.0 on active, taken from the MCI-186-19 result, and a futility threshold for posterior probability of meeting the primary endpoint below 0.20, the planned futility analysis can be evaluated continuously:

PP(success)=∫θ​P(final success∣θ,interim data)⋅π(θ∣interim data)dθ

Biomarker enrichment by baseline plasma neurofilament light chain above 60 pg per mL and ALSFRS-R slope greater than minus 1.5 points per month during a 12-week run-in would reduce the number-needed-to-screen and concentrate the signal. A historical base-rate adjustment using the MND-SMART, ATLAS, CENTAUR, and EMPOWER datasets would have anchored the prior on placebo decline. The single highest leverage change would have been pre-specifying that the confirmatory population must match MCI-186-19's eligibility, and stopping the broader study at the planned interim if the early-disease subgroup did not separate by more than 1.5 ALSFRS-R points.

What this means for similar programs

Free-radical scavengers and antioxidant strategies for ALS now have a clear empirical ceiling outside a narrow early-disease window. Tofersen (Qalsody) won FDA accelerated approval in 2023 for SOD1-mutant ALS on a neurofilament biomarker endpoint after its own ALSFRS-R primary missed, suggesting that mechanism-matched biomarker primary endpoints are a more honest path for genetically defined ALS subsets. Pridopidine, CNM-Au8, and oxidative-stress adjacent programs should expect tighter scrutiny of their confirmatory designs and population definitions. Mitsubishi Tanabe's oral edaravone franchise is unlikely to expand beyond the existing Radicava label.

Open questions

What was the prespecified futility threshold used by the DSMB in MT-1186-A02, and what was the observed conditional power at that interim? Did patients with predicted vital capacity above 80 percent at baseline separate from placebo in any sensitivity analysis? Will Tanabe Pharma America publish the full MT-1186-A02 dataset including ALSFRS-R item-level trajectories and neurofilament biomarker data? Does the FDA require a label change for intravenous Radicava given the failure of a higher-dose oral confirmatory study?

Sources

1. ClinicalTrials.gov, NCT05151471, full record retrieved 2026-05-23. ChEMBL CHEMBL290916 (edaravone), small molecule, max phase 4. Canonical SMILES CC1=NN(c2ccccc2)C(=O)C1. OpenFDA FAERS edaravone reaction counts (top 15): cerebral infarction 105, amyotrophic lateral sclerosis 66, off label use 42, death 40, pneumonia 40, disease progression 33, haemorrhagic cerebral infarction 33, drug ineffective 32, hepatic function abnormal 32, pyrexia 32, aspiration pneumonia 31, cerebral haemorrhage 28. Retrieved 2026-05-23. Open Targets Platform v25.06, target SOD1 (ENSG00000142168), associated disease amyotrophic lateral sclerosis (MONDO_0004976), score 0.87. Retrieved 2026-05-23. Writing Group on Behalf of the Edaravone (MCI-186) ALS 19 Study Group. Safety and efficacy of edaravone in well defined patients with amyotrophic lateral sclerosis: a randomised, double-blind, placebo-controlled trial. Lancet Neurology 2017,Shimizu H et al. Efficacy and Safety of Once Daily Dosing vs. Approved On/Off Dosing of Edaravone Oral Suspension Up to 48 Weeks in Patients With Amyotrophic Lateral Sclerosis. Muscle and Nerve 2025,Shimizu H et al. Safety Extension Study of Edaravone Oral Suspension in Patients With Amyotrophic Lateral Sclerosis for up to an Additional 96 Weeks of Treatment. Muscle and Nerve 2025,Pharmacokinetics of Edaravone Oral Suspension in Patients With Amyotrophic Lateral Sclerosis. Clinical Therapeutics 2023,Cho H, Shukla S. Riluzole and edaravone: A tale of two amyotrophic lateral sclerosis drugs. Medicinal Research Reviews 2019,Brooks BR et al. Safety and Effectiveness of Long-term Intravenous Administration of Edaravone for Treatment of Patients With Amyotrophic Lateral Sclerosis. JAMA Neurology 2022,Miller TM et al. Tofersen for SOD1 ALS. Neurodegenerative Disease Management 2024,. Available from: https://clinicaltrials.gov/study/NCT05151471.