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 past that has ruled out a progressive cause of epilepsy.
* Participant must have been receiving stable doses of allowable ASMs (a minimum of 1 and a maximum of 3 ASMs).
* Participant and/or caregiver (if applicable) self-reports at least 2 countable focal onset seizures per month for focal onset patients, or 1 countable generalized tonic-clonic seizure per month in the 3 months immediately prior to the Screening/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 be counted, or an episode of convulsive status epilepticus requiring hospitalization and 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 \<2 years prior to enrollment.
* Schizophrenia and obsessive-compulsive disorder, or other serious mental health disorders.
* Active suicidal plan/intent in the past 6 months, or a history of suicide attempt in the last 2 years, or more than 1 lifetime suicide attempt.
* Participants with a history of malignancy, myeloproliferative or lymphoproliferative disorders within the past 5 years are excluded.
* History of cardiac disease(s)/cardiac conduction disorders/or cardiac structural abnormality(ies).
* Is pregnant or breastfeeding at the time of Screening, or has a positive serum pregnancy test at Screening or is planning to become pregnant during the clinical trial or within 14 days of the last study drug dose.
* Has received any other experimental or investigational drug, device or other therapy within 30 days or 5 half-lives (whichever is longer) prior to Screening, or any prior use of gene therapy.
* Vigabatrin: Use in the last 5 years without stable visual fields tested twice over the 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 received felbamate in the past, it must have been discontinued 2 months prior to Screening.