Azetukalner NDA Filed for Focal Seizures, But Psychiatry Safety Pause Clouds the Approval Story

Xenon Submits Azetukalner NDA for Focal Seizures, Pauses Psychiatry Enrollment

Xenon Pharmaceuticals has submitted a New Drug Application (NDA) to the U.S. FDA for azetukalner, targeting focal seizures (FS). This submission is supported by positive clinical data from the Phase 2b X-TOLE and Phase 3 X-TOLE2 studies, which demonstrated a statistically significant reduction in monthly seizure frequency and a consistent, well-tolerated safety profile across over 1,500 patient-years of data. Concurrently, Xenon announced a temporary, voluntary pause on new patient enrollment in its major depressive disorder (MDD) and bipolar depression (BPD) psychiatry studies due to neuropsychiatric adverse events, while existing patients continue treatment. Topline data for the MDD study, X-NOVA2, is now expected in Q1 2027.

• Xenon Pharmaceuticals has successfully submitted a New Drug Application (NDA) to the U.S. FDA for azetukalner for the treatment of focal seizures. This significant regulatory milestone is based on robust efficacy and safety data from the global, randomized, double-blind, placebo-controlled Phase 2b X-TOLE and Phase 3 X-TOLE2 studies, which consistently showed a statistically significant reduction in monthly seizure frequency and a favorable safety profile.
• Across the pivotal X-TOLE and X-TOLE2 studies, azetukalner demonstrated a statistically significant reduction from baseline in monthly seizure frequency compared to placebo. The drug was generally well-tolerated, exhibiting a consistent safety profile comparable to long-term observations in the X-TOLE open-label extension study, with the entire epilepsy program accumulating over 1,500 patient-years of safety and exposure data.
• Xenon has initiated a voluntary, temporary pause on new patient enrollment in its ongoing major depressive disorder (MDD) and bipolar depression (BPD) clinical studies. This decision follows an analysis of neuropsychiatric adverse events, which, while consistent with azetukalner's known profile, had not been observed in the Phase 2 X-NOVA MDD study. The company is evaluating potential dosing modifications to mitigate these events, with currently enrolled patients continuing treatment.
• Enrollment for the Phase 3 X-NOVA2 study in major depressive disorder has been completed with approximately 360 patients, representing about 80% of the initial target. Despite the enrollment pause in other psychiatry studies, Xenon plans to complete the six-week dosing period for current X-NOVA2 participants and unblind the data, with topline results now anticipated in Q1 2027.

Why New Options for Focal Seizures Remain Critically Needed

Despite advances in antiseizure medication (ASM) development, a substantial proportion of patients with focal seizures continue to face inadequate seizure control. The persistence of drug-resistant epilepsy — defined as failure of adequate trials of two tolerated, appropriately chosen, and used ASM schedules to achieve sustained seizure freedom — underscores the unmet need that remains across both pharmacological and non-pharmacological treatment strategies.

• Drug resistance affects a significant patient population. Up to 40% of patients are refractory to pharmacological management. The ILAE consensus definition establishes failure of two adequate ASM trials as the threshold for drug-resistant epilepsy, yet even this operationally agreed-upon benchmark reflects ongoing variability in how intractability is defined across clinical and research settings, with factors such as seizure frequency, duration of unresponsiveness, etiology, and epilepsy syndrome all contributing to definitional complexity.

• Third-generation ASMs carry serious, potentially preventable adverse effects. Lacosamide, eslicarbazepine acetate, perampanel, brivaracetam, and cenobamate — agents used specifically for focal seizures — are associated with psychiatric side effects (including psychosis and depression), cardiac rhythm and conduction disturbances (lacosamide), hyponatremia and hyperammonemia (eslicarbazepine, perampanel), and Drug Rash with Eosinophilia and Systemic Symptoms (DRESS) syndrome (eslicarbazepine, cenobamate, lacosamide). Managing these risks requires intensive monitoring and careful patient selection based on psychiatric and cardiac history.

• Polypharmacy in drug-resistant focal epilepsy introduces complex drug interaction challenges. When adding agents such as cenobamate, concomitant ASM load must be actively managed. Spanish consensus guidance specifies that clobazam, phenytoin, phenobarbital, and sodium channel blockers at high dosages — or combinations of two or more sodium channel blockers — require proactive dose reduction during cenobamate titration to preserve tolerability without compromising efficacy.

• Neuromodulation, while effective, is not universally accessible or definitive. For patients who are not surgical resection candidates, devices such as responsive neurostimulation (RNS), vagus nerve stimulation (VNS), and deep brain stimulation (DBS) reduce seizures but render only a small percentage of patients seizure-free. Dual-device neurostimulation has received limited study, and the ability to localize the seizure onset zone remains the primary determinant of device selection — a capability that is not uniformly available across centers. Prospective multicenter data on dual-device approaches remain absent.

Azetukalner's Efficacy and Safety Profile in Focal Seizures Trials

Several key trials have evaluated antiseizure drugs as adjunctive therapy in patients with focal (partial-onset) seizures, spanning phase II/III randomized controlled designs through open-label long-term follow-up studies. The trials below represent a cross-section of study architectures, patient populations, and endpoint frameworks used in this indication.

Azetukalner's Broader Pipeline and Psychiatry Program Update

Beyond focal seizures, azetukalner is being investigated for two additional indications: generalized tonic-clonic seizures (GTCS) and major depressive disorder (MDD). In epilepsy, its development spans both focal-onset and primary generalized tonic-clonic seizures, with Phase 3 clinical trials underway to further characterize efficacy and tolerability across these seizure types. The mechanistic basis for this breadth lies in azetukalner's potent, selective opening of Kv7.2/7.3 potassium channels — a target distinct from all currently marketed antiseizure medications — which modulates intrinsic neuronal excitability rather than broadly suppressing synaptic transmission.

In psychiatry, azetukalner has been evaluated for MDD through the X-NOVA trial, a multicenter, proof-of-concept, Phase 2, randomized, double-blind, parallel-group, placebo-controlled clinical trial. Participants were adults aged ≥18 to ≤65 years with moderate to severe MDD in a current depressive episode, randomized 1:1:1 to 10 mg of azetukalner, 20 mg of azetukalner, or placebo orally once daily with food for 6 weeks, with a 4-week follow-up. Concomitant antidepressant medications were not permitted. The primary efficacy endpoint was change in Montgomery-Åsberg Depression Rating Scale (MADRS) score at week 6, with secondary endpoints including change from baseline in the Snaith-Hamilton Pleasure Scale (SHAPS) and Beck Anxiety Inventory, and exploratory endpoints encompassing change in the Hamilton Depression Rating Scale, 17-Item (HAM-D17) score and change in MADRS at week 1.

The X-NOVA trial enrolled 168 participants and yielded preliminary findings that supported further clinical development of azetukalner for MDD and anhedonia. While the mean reduction in MADRS scores with 20 mg of azetukalner versus placebo was clinically meaningful but not statistically significant at week 6 (−3.04 points; 95% CI, −7.04 to 0.96 points; P = .14), it reached statistical significance at week 1 (−2.66 points; 95% CI, −5.30 to −0.03 points; P = .047). The mean reduction in HAM-D17 from baseline to week 6 was significantly greater with 20 mg of azetukalner versus placebo (−13.3 [1.1] vs −10.2 [1.0] points; P = .04), as was the reduction in SHAPS scores (−7.77 [0.87] vs −5.30 [0.85] points; P = .046), suggesting a particular signal in anhedonia. Rates of discontinuation due to treatment-emergent adverse events were similar across all groups.

Azetukalner: Epilepsy Momentum Meets Psychiatry Pause

The recent news from Xenon Pharmaceuticals presents a compelling, albeit complex, narrative for the future of central nervous system therapeutics. On one hand, the submission of a New Drug Application for azetukalner in focal seizures marks a significant step forward. Research indicates that azetukalner, a novel Kv7 potassium channel opener, has demonstrated sustained efficacy in reducing seizure frequency and achieving seizure freedom in a difficult-to-treat population, with a safety profile that appears well-tolerated and notably free from the pigmentation issues that led to the withdrawal of the first-generation Kv7 activator, ezogabine. This positions azetukalner as a potentially valuable new option, offering a mechanistically elegant approach to restoring neuronal stability and improving patient-centered outcomes, which are crucial for long-term market success.

However, the simultaneous announcement of a voluntary pause in new patient enrollment for azetukalner's major depressive disorder and bipolar depression studies due to neuropsychiatric adverse events introduces a layer of caution. While the epilepsy data is robust, this development underscores the inherent challenges in developing drugs that modulate fundamental neuronal excitability across diverse indications. Studies in major depressive disorder have shown mixed efficacy signals, with some endpoints not reaching statistical significance, further complicating its psychiatric development path. This divergence highlights the need for a deeper understanding of Kv7 channel subtype selectivity and tissue-specific effects to mitigate potential off-target or dose-limiting adverse events. For the company, this necessitates a strategic re-evaluation, likely prioritizing the epilepsy program where the risk-benefit profile appears more favorable. The broader implication for the field is a renewed focus on precision medicine strategies for Kv7 activators, ensuring that the promise of this innovative mechanism is realized safely and effectively across its intended therapeutic applications.