Bexicaserin Advances to Phase III DEEp SEA Trial With Completion of Randomization

The final patient has been randomized in DEEp SEA (NCT06660394), a Phase III study evaluating the efficacy, safety and tolerability of oral bexicaserin in participants aged 2 to 65 years with Dravet syndrome.

DEEp OCEAN (NCT06719141), the second pivotal trial in the program, completed randomization first in July 2026. The study evaluates bexicaserin in children and adults with developmental and epileptic encephalopathies (DEEs), including Lennox-Gastaut syndrome (LGS), but excluding Dravet syndrome.

With DEEp SEA now fully randomized, both pivotal Phase III trials in the global DEEp program have reached this development milestone.

Bexicaserin Targets the 5-HT2C Receptor

Dravet syndrome is a rare, severe childhood-onset epilepsy classified as a developmental and epileptic encephalopathy. Patients can experience treatment-resistant seizures as well as developmental stagnation or regression, underscoring the need for additional treatment options.

Bexicaserin is an investigational oral, highly selective superagonist of the serotonin 5-HT2C receptor. The compound increases inhibitory neuronal activity while reducing excitatory neuronal function, providing a dual mechanism that may contribute to seizure reduction across DEEs with different underlying causes.

Its pharmacological selectivity is intended to limit activity at other serotonin receptor subtypes, including 5-HT2A and 5-HT2B, potentially reducing off-target receptor effects. However, whether this translates into a clinically meaningful safety advantage remains to be established in clinical trials.

DEEp SEA Focuses on Motor Seizure Reduction

DEEp SEA is a randomized, double-blind, placebo-controlled, multicenter Phase III trial that enrolled more than 100 participants with Dravet syndrome.

The study includes a screening period of up to 35 days followed by a 15-week treatment period, comprising a three-week titration phase and a 12-week maintenance phase. Participants receive bexicaserin or placebo three times daily, with weight-based dosing for pediatric participants.

The primary efficacy assessment evaluates changes in countable motor seizure frequency. After the treatment period, participants enter a taper and safety follow-up or may transition to a 52-week open-label extension (OLE), providing an opportunity to collect longer-term safety and treatment data.

DEEp OCEAN follows the same broad treatment structure and also allows eligible participants to enter a 52-week open-label extension.

Regulatory Designations Support Development

The U.S. Food and Drug Administration has granted Breakthrough Therapy designation to bexicaserin for the treatment of seizures associated with DEEs in patients aged two years and older. Bexicaserin has also received Breakthrough Therapy designation in China for seizures associated with DEEs.

Tarek Samad, Lundbeck’s Executive Vice President and Head of Research & Development, described completion of DEEp SEA randomization as an important milestone in evaluating bexicaserin in people living with Dravet syndrome and advancing the broader Phase III DEEp program.

Phase III Readouts Will Determine Next Steps

The completion of randomization moves DEEp SEA into the treatment and follow-up stages, while DEEp OCEAN continues through its clinical evaluation.

The key upcoming milestone will be the Phase III efficacy and safety results from the two pivotal studies. These data will determine whether bexicaserin can demonstrate a clinically meaningful reduction in seizures while maintaining an acceptable safety and tolerability profile in patients with DEEs.

Bexicaserin remains investigational and is not approved for marketing by any regulatory authority worldwide. Its efficacy and safety have not yet been established.

Reference

Lundbeck announces last patient randomized in DEEp SEA, a Phase III trial of bexicaserin in Dravet syndrome, Lundbeck, 15 September 2026