A phase 2a trial of Rapport Therapeutics’ focal onset seizure drug candidate has hit its primary endpoint, sending shares in the biotech​​ up more than 170% in morning trading.

The study enrolled 30 people with drug-resistant seizures who were taking a median of three antiseizure medicines such as lamotrigine, levetiracetam and cenobamate. Participants received daily oral doses of RAP-219, Rapport’s TARPγ8-specific AMPA receptor negative allosteric modulator, for eight weeks. The receptor is expressed in parts of the brain associated with seizures but not areas linked to side effects.

After eight weeks, 23 of the 27 patients in the primary endpoint analysis had experienced at least a 30% decline in long episodes from baseline. The episodes are an electrographic biomarker for clinical seizure reduction. Rapport reported a 71% median reduction in episode frequency from baseline. Shares in the company jumped 140% to $34.50 at one point in premarket trading.

The biotech also reported reductions in clinical seizures, a key secondary endpoint. In an analysis of 25 patients, Rapport found 72% of participants experienced a 50% or greater reduction in clinical seizures from baseline. Almost one-quarter of patients achieved seizure freedom. Rapport tracked a 77.8% median reduction in clinical seizure frequency from baseline.

Three patients discontinued treatment because of treatment-emergent adverse events (TEAEs). Almost 80% of TEAEs were grade 1 cases, indicating that they were mild cases. The remaining TEAEs were grade 2. Dizziness, headache and fatigue were the most common TEAEs.

Based on the data, Rapport plans to start two phase 3 trials of RAP-219 in the third quarter of 2026. The next steps are to hold an end-of-phase 2 meeting with the FDA, share data from the ongoing eight-week follow-up period and start an open-label long-term safety trial. Those events are all scheduled for this year. Rapport expects to share follow-up data and preliminary long-term results next year.

The biotech has predicted that a multibillion-dollar commercial opportunity is open to RAP-219. The forecast reflects an analysis that suggests 30% to 40% of the 3 million epilepsy patients in the U.S. have drug-resistant focal onset seizures.

If approved, RAP-219 could compete with SK Life Science’s Xcopri and Catalyst Pharmaceuticals’ Fycompa and potentially against other assets that are currently in development. The pipeline of potential rivals in focal onset seizures includes Biohaven’s BHV-7000, Praxis Precision Medicines’ vormatrigine and Xenon Pharmaceuticals’ azetukalner.