Harmony's Dravet Trial Hits Year Seven With Completion Pushed to 2027
EPX-100's Phase 3 primary completion date has slipped 66 months since 2021 as enrollment grew fivefold, raising the bar for what a 2026 readout can actually show.
Executive Summary
- Harmony Biosciences has repeated 2026 topline guidance for EPX-100 across nine disclosures since April 2024, but the trial's own primary completion date moved from April 2026 to April 2027 as recently as May 2026, a gap between sponsor messaging and registry fact that investors should track closely NCT04462770+1A Study of EPX-100 (Clemizole Hydrochloride) in Participants With Dravet SyndromeNCT04462770Press ReleaseApr 30, 2024.
- Enrollment target grew from 24 to 150 participants, a 525% increase spread across four separate revisions since 2021, which extended the trial's operational runway even as completion dates slipped seven times NCT04462770A Study of EPX-100 (Clemizole Hydrochloride) in Participants With Dravet SyndromeNCT04462770.
- No primary endpoint threshold, effect size, or safety data has been disclosed for the ongoing readout, and ClinicalTrials.gov shows no posted results, so no endpoint-met probability can be computed and none should be inferred.
- No other trial targets HRH1 in Dravet syndrome, meaning a result here carries limited direct mechanistic readthrough to competitors like fenfluramine, soticlestat, or the SCN1A-targeted gene and oligonucleotide programs from Stoke, Ionis, and Encoded.
- Until an actual endpoint result posts, the setup remains an operational-timing story rather than a decision-grade efficacy story; the trial's protocol-stability record is the most concrete signal available today.
The catalyst
Harmony Biosciences has guided investors to a 2026 topline data readout for EPX-100 (clemizole hydrochloride), a Phase 3 registrational trial in Dravet syndrome running under NCT04462770 NCT04462770A Study of EPX-100 (Clemizole Hydrochloride) in Participants With Dravet SyndromeNCT04462770. The company's April 2024 announcement of its Epygenix Therapeutics acquisition called the resulting rare epilepsy portfolio a potential "Billion Dollar Plus Rare Epilepsy Franchise," with EPX-100 as its lead asset Press ReleasePress ReleaseApr 30, 2024. Harmony's guidance for the 2026 window has repeated across nine separate disclosures from April 2024 through February 2026, according to the guidance-history record tied to this catalyst Press ReleasePress ReleaseApr 30, 2024. The trial itself remains actively recruiting as of its most recent registry update on June 30, 2026 NCT04462770A Study of EPX-100 (Clemizole Hydrochloride) in Participants With Dravet SyndromeNCT04462770.
The timeline gap
The trial's primary completion date has moved seven times since the study started in July 2020: from October 2021 to October 2022, then September 2022, then December 2024, then December 2024 again, then April 2026, and most recently to April 2027 as of a May 14, 2026 registry update NCT04462770A Study of EPX-100 (Clemizole Hydrochloride) in Participants With Dravet SyndromeNCT04462770. That is a cumulative delay of more than five years against the original target. The trial was briefly marked "Completed" in January 2024 before reverting to "Recruiting" two weeks later, alongside another completion-date revision. AppliedXL's protocol stability tool labels the overall record "Moderate," with 10 total registry change events and 2.01 changes per year.
The enrollment expansion
Alongside the timeline slippage, the trial's enrollment target grew from 24 participants at first posting to 150 participants as of a May 2025 update, a 525% increase spread across four separate revisions NCT04462770A Study of EPX-100 (Clemizole Hydrochloride) in Participants With Dravet SyndromeNCT04462770. Growing the enrollment target while repeatedly pushing the completion date can reflect a sponsor's effort to build a more decision-grade dataset, or it can reflect operational strain in recruiting a rare pediatric epilepsy population; the dossier does not disclose which explanation the sponsor has offered.
What the readout can and cannot show
No primary endpoint threshold, effect size, p-value, or safety profile has been disclosed for this ongoing readout, and ClinicalTrials.gov shows no posted results for the trial. The registry's only disclosed outcome measure is the European Union primary endpoint, percent change in countable motor seizures per 28 days during the maintenance period relative to baseline; whether this matches the endpoint FDA will review for a US filing is not established in the dossier. Until topline data post, the readout remains a timing and operational story, not an efficacy story that can be graded against a known bar.
Competitive frame
No other trial in the dossier targets HRH1 in Dravet syndrome, so EPX-100 sits without a direct same-target comparator. The nearest precedents are other small-molecule Dravet syndrome therapies working through different mechanisms: fenfluramine and lorcaserin act on the 5-HT2C receptor, soticlestat on CYP46A1, and stiripentol on the GABAA receptor. AppliedXL's landscape data also show HRH1 as a declining research target broadly, with zero recent trials against 81 older ones, which limits how much this readout would inform investors' view of the target class even if the result shows a seizure-frequency reduction.
Regulatory standing
EPX-100 holds FDA Orphan Drug Designation and Rare Pediatric Disease Designation for Dravet syndrome, though the dossier does not specify grant dates. Neither designation predicts approval; they signal an unmet need in a rare disease rather than confirmed efficacy. No FDA approval history exists yet for clemizole hydrochloride in any indication.
This analysis was produced using AI-assisted reporting systems, AppliedXL data, and official public records. These systems undergo editorial review, quality checks, and regular audits by human experts. Errors may still occur, as with any automated system. Always consult the linked primary sources. Read our AI Editorial Policy.