Safety and Tolerability Study of SPN-817 in Adult Patients With Treatment Resistant Epilepsy

Inclusion Criteria: 1. A diagnosis of treatment resistant epilepsy as adjudicated by the Epilepsy Study Consortium. 2. Is male or female, aged 18 to ≤ 70 years at screening. 3. Is able to read, understand, and sign the Informed Consent Form (ICF). If the participant is unable to sign informed consent, a Legally Authorized Representative (LAR) will complete the ICF. 4. Ability to keep accurate seizure diaries (with the aid of a caregiver as needed). 5. Weight within the normal or overweight ranges according to accepted values of the Body Mass Index Chart (18.0 to 40 kg/m2). 6. Is able to swallow capsules whole without crushing, chewing, or cutting. 7. Is willing to adhere to all study procedures and able to attend study visits within the specified time windows. 8. Failure of at least 2 tolerated, appropriately chosen and adequately dosed ASM drug schedules to achieve sustained seizure freedom. 9. Taking at least 1 ASM at Screening and Baseline. If following a diet plan along with the ASM, the participant should have been on a stable diet plan for at least 1 month prior to screening (Visit 1). The diet plan should be maintained throughout the duration of the study. Participants on a ketogenic diet will not be permitted to participate in the intense PK group. 10. At least 4 seizures accepted by the Epilepsy Study Consortium for the secondary outcome (adjudicated as "probable seizures" that are countable) during the 42-day baseline seizure diary period, and no more than a 21-day period that was seizure-free. 11. A clinical diagnosis of Focal Cortical Dysplasia (FCD) Type I or Type II (approximately n=10) confirmed by: 1. Likely FCD supported by neuroimaging that has been performed in the last 5 years, or 2. History of surgical resection of the cortical dysplasia that is histopathologically confirmed in patients who continue to have uncontrolled seizures without a compelling alternate explanation for ongoing seizures. Note: The Epilepsy Study Consortium will review to confirm FCD/probable FCD diagnosis. 12. Be in good general health as per PI's judgment based upon medical history, physical exams, standard 12-lead ECG, and clinical laboratory evaluations obtained during the Screening Period 13. Be able to comply with and complete all study-specified procedures; enrollment for participants with limited ability to complete self-reported questionnaires or cognitive assessments may be permitted on a case-by-case basis after approval by the MM and Sponsor 14. Non-pregnant females of childbearing potential (FOCP) who are either in an exclusive same-sex relationship or sexually inactive (abstinent), or if sexually active with a male partner who is biologically capable of having children, must agree to use one of the following acceptable birth control methods beginning 30 days prior to the first dose of SPN-817, throughout the study, and for 30 days following the last dose: 1. Simultaneous use of male condom and intra-uterine contraceptive device (IUD) placed at least 4 weeks prior to first SPN-817 administration 2. Surgically sterile male partner (6 months minimum) 3. Simultaneous use of any male barrier (condom) combined with any female barrier 4. Established hormonal contraceptive Female participants are considered not to be of childbearing potential if they are either postmenopausal (amenorrhea for at least 2 years and serum follicle-stimulating hormone \[FSH\] level of \>40 IU/L) or permanently sterilized (eg, bilateral tubal ligation, hysterectomy, bilateral oophorectomy) for 6 months minimum. 15. Males must: 1. Use 2 methods of contraception in combination if his female partner is of childbearing potential; this combination of contraceptive methods must be used from the screening visit to 90 days after the last dose of SPN-817, or 2. Have been surgically sterilized (6 months minimum) prior to the screening visit 3. Refrain from donating any sperm from the first administration of SPN-817 until 90 days after the last dose of SPN-817 4. Males who are in same-sex partner relationships or with those who are not biologically capable of having children are required to use a condom from the first dose through 7 days after the last dose of the SM. Exclusion Criteria: 1. Has taken huperzine A within the past year 2. Is planning to become pregnant or impregnate spouse, not using an acceptable method of birth control (defined as use of double-barrier birth control methods, use of oral contraceptives, or surgical sterilization), pregnant, or nursing. 3. Participants with Lennox-Gastaut syndrome. Participants should also be excluded in case of nondiagnostic information. 4. Has non-epileptic events that could be confused by the patient and/or study staff as epileptic seizures. 5. Has only seizures that are difficult to count; for example, has seizures that are not clinically observable. 6. Has a history of only seizure clusters, for example, seizure clusters defined as multiple seizures with at least one seizure within 30 minutes of the previous seizure. 7. Has a history of status epilepticus in the 6 months prior to Screening. 8. Change in ASM regimen in the last 28 days prior to screening. No changes in ASMs are allowed during the Screening, Titration/Optimization, or Maintenance Period. Changes in ASM regimen (including any diet plan used as an ASM) are allowed during the OLE Period only. 9. Vagus nerve stimulation (VNS), deep brain stimulation (DBS), responsive neurostimulator system (RNS), or other neurostimulation for epilepsy device implanted or activated \<1 year prior to screening; stimulation parameters that have been stable for \<3 months; or epilepsy surgery \<1 year prior to screening. 10. Any suicidal behavior or suicidal ideation of type 4 (active suicidal ideation with some intent to act without specific plan) or type 5 (active suicidal ideation with specific plan and intent) based on the C-SSRS in the 2 years before screening; a history