An Open Label Trial to Evaluate the Efficacy and Safety of PRAX-628 in Adults With Focal Onset or Tonic-Clonic Seizures

Inclusion Criteria:

• A diagnosis of focal onset seizures or idiopathic generalized tonic clonic seizures.

• Evidence by computed tomography (CT) or magnetic resonance imaging (MRI) in the pastthat has ruled out a progressive cause of epilepsy.

• Participant must have been receiving stable doses of allowable ASMs (a minimum of 1and a maximum of 3 ASMs).

• Participant and/or caregiver (if applicable) self-reports at least 2 countable focalonset seizures per month for focal onset patients, or 1 countable generalizedtonic-clonic seizure per month in the 3 months immediately prior to theScreening/Observation Period for PGTCS patients.

Exclusion Criteria:

• History of pseudo or psychogenic seizures, or cluster seizures only, within the 12-month period preceding study entry where the individual seizures cannot becounted, or an episode of convulsive status epilepticus requiring hospitalizationand intubation in the 12 months prior to Screening.

• Planned epilepsy surgery during the course of the clinical trial.

• History of neurosurgery for seizures <1 year prior to enrollment, or radiosurgery <2years prior to enrollment.

• Schizophrenia and obsessive-compulsive disorder, or other serious mental healthdisorders.

• Active suicidal plan/intent in the past 6 months, or a history of suicide attempt inthe last 2 years, or more than 1 lifetime suicide attempt.

• Participants with a history of malignancy, myeloproliferative or lymphoproliferativedisorders within the past 5 years are excluded.

• History of cardiac disease(s)/cardiac conduction disorders/or cardiac structuralabnormality(ies).

• Is pregnant or breastfeeding at the time of Screening, or has a positive serumpregnancy test at Screening or is planning to become pregnant during the clinicaltrial or within 14 days of the last study drug dose.

• Has received any other experimental or investigational drug, device or other therapywithin 30 days or 5 half-lives (whichever is longer) prior to Screening, or anyprior use of gene therapy.

• Vigabatrin: Use in the last 5 years without stable visual fields tested twice overthe 12 months after the last dose of vigabatrin.

• Felbamate: If used as a concomitant ASM, patients must be on felbamate for at least 2 years, with a stable dose for 2 months prior to Screening. If a patient receivedfelbamate in the past, it must have been discontinued 2 months prior to Screening.