Key Highlights
- Xenon Pharmaceuticals shares climbed 40% following positive Phase 3 X-TOLE2 results showing azetukalner achieved its primary endpoint across both dosing cohorts.
- Patients receiving the 25 mg dose experienced a 53.2% reduction in monthly focal onset seizure frequency from baseline, compared with 10.4% for placebo.
- The data surpassed outcomes from the earlier Phase 2b X-TOLE trial, where the placebo-adjusted median percent change reached 34.6%.
- More than half of participants on 25 mg (54.8%) achieved at least 50% fewer seizures monthly.
- The company intends to submit a New Drug Application (NDA) to the FDA during Q3 2026.
Xenon Pharmaceuticals (XENE) shares soared 40% during Monday’s session following the company’s announcement that azetukalner achieved its primary endpoint in the Phase 3 X-TOLE2 trial for focal onset seizures. The strength of the data exceeded analyst expectations, triggering sharp gains at market open.
Xenon Pharmaceuticals Inc., XENE
The study recruited 380 adults living with severe treatment-resistant epilepsy. These individuals had attempted a median of five previous antiseizure medications and continued to experience approximately 12.75 seizures monthly at the study’s start.
Patients taking the 25 mg dose of azetukalner achieved a median reduction of -53.2% in monthly focal onset seizure frequency from baseline. The placebo cohort experienced only -10.4% reduction. This creates a placebo-adjusted difference of -42.7%.
This figure carries significant weight. The previous Phase 2b X-TOLE trial demonstrated a placebo-adjusted median percent change of -34.6% in the 25 mg cohort. X-TOLE2 substantially exceeded this benchmark.
The 15 mg dose also delivered solid results, achieving -34.5% median percent change versus placebo, although the 25 mg outcomes garnered primary focus.
Key Secondary Measures Achieved
The study successfully met its key secondary endpoint. Within the 25 mg cohort, 54.8% of participants experienced at least a 50% reduction in monthly seizure frequency — the Responder Rate 50 metric. This compared with only 20.8% in the placebo cohort. The 15 mg group recorded 37.6%.
Among the 332 participants who finished the double-blind phase, 322 continued into the open-label extension study.
The safety data remained consistent with expectations. The most frequently reported side effects included dizziness, headache, somnolence, and fatigue. Treatment discontinuation rates due to adverse events were 14.5% in the 25 mg cohort, 4.8% in the 15 mg cohort, and 3.2% in the placebo cohort.
Xenon CEO Ian Mortimer characterized the findings as demonstrating “the highest placebo-adjusted efficacy ever observed in a pivotal epilepsy study,” according to the company’s press release.
Regulatory Timeline and Market Entry
Xenon will submit an NDA to the FDA for azetukalner in focal onset seizures during Q3 2026. Upon approval, this would become the first KV7 potassium channel opener authorized for epilepsy treatment.
Stifel analysts suggested the results may prompt investors to increase their peak sales and market penetration forecasts for the drug candidate.
Azetukalner offers several practical benefits compared with current treatment options — once-daily dosing, no titration requirements, and minimal drug-drug interactions.
The X-TOLE2 findings will be shared during an oral presentation at the American Academy of Neurology (AAN) Annual Meeting in April.
Xenon is simultaneously advancing azetukalner for depression treatment, though this program was separate from Monday’s announcement.
Shares traded up approximately 40% by Monday morning, with the rally driven exclusively by the Phase 3 data disclosure.
