Inclusion Criteria:

• Participant must be ≥ 34 weeks of corrected gestational age (CGA), < 46 weeks of CGA, and < 28 days of postnatal age (PNA), at the time of signing the informed consent.
• Participants who have confirmation on video-EEG of ≥ 2 minutes of cumulative ENS or ≥ 3 identifiable ENS prior to entering the Treatment Period (ENS is defined as a seizure lasting for at least 10 seconds on video-EEG), despite receiving previous AED treatment for the treatment of electroencephalographic seizures. The occurrence of ENS during an up to 1-hour period must be confirmed by the local video-EEG reader prior to randomized study drug administration. Video-EEG recording can be shortened per clinical need (e.g., if status epilepticus is detected). If possible, an attempt should be made to record at least 30 minutes of Baseline video-EEG.
• Participants must have received either PB, LEV, or MDZ (in any combination) before entering the study.
• Participants with or without concomitant hypothermia treatment.
• Participant weighs at least 2.3kg at the time of enrollment.
• An Independent Ethics Committee (IEC)-approved written ICF is signed and dated by the participant’s parent(s) or legal representative(s).

Exclusion Criteria:

• Participant with seizures responding to correction of metabolic disturbances (hypoglycemia, hypomagnesemia, or hypocalcemia) or with seizures for which a targeted, known treatment is available.
• Participant has seizures related to prenatal maternal drug use or drug withdrawal.
• Participant has known severe disturbance of hemostasis, as assessed by the investigator.
• Participant has a poor prognosis for survival, as judged by the investigator.
• Participant has a medical condition that could be expected, in the opinion of the investigator, to interfere with study medication absorption, distribution, metabolism, or excretion.
• Participant has a clinically relevant ECG abnormality, in the opinion of the investigator (eg, second or third degree heart block at rest or a corrected QT interval [QTc] ≥ 450ms).
• Participant has a hemodynamically significant congenital heart disease.
• Participant has any clinically relevant cardiac arrhythmia.
• If participant is in the first 24 hours of life, urine output is < 1 mL/kg/hour.  If older than 24 hours, participant urine output is < 1 mL/kg/hour or serum creatinine is > 1.7 mg/dL.
• Participant receiving treatment with PHT, LDC, or other sodium channel blockers at any time.
• Participant requires extracorporeal membrane oxygenation.
• Participant requires or is expected to require phototherapy or exchange transfusion due to elevated bilirubin.
• Participant has 2 x upper limit of normal (ULN) of any of the following: aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP), with the following exception:
  • For participants with perinatal asphyxia, elevation of AST, ALT, or ALP 2mg/dL.

Eligibility last updated 4/14/22. Questions regarding updates should be directed to the study team contact.