A Study of Possible Drug-drug Interactions Between Stiripentol or Valproate and Cannabidiol in Patients With Epilepsy

This trial consists of 2 parts: a double-blinded phase and an open-label extension phase. The blinded phase only will be described in this record. Participants will be randomized in a 4:1 ratio to receive GWP42003-P or matching placebo. The hypothesis is that levels of stiripentol (STP) or valproate (VPA) may be altered (increased or decreased) as a result of using GWP42003-P.


Eligibility Criteria:
Note: Participants who enroll in Sweden must be aged 18-55 years.

Key Inclusion Criteria:

* Participant must be taking STP (for the STP arm) or VPA (for the VPA arm) and no more than 2 other antiepileptic drugs (AEDs) during the blinded period of the trial.

  * In the VPA arm only, the participant must not be receiving STP (VPA allowed in STP arm).
* AED doses, including STP or VPA, must be stable for 4 weeks prior to screening and regimen must remain stable throughout the duration of the blinded period of the trial.
* Participant must have a documented magnetic resonance imaging/computerized tomography of the brain that ruled out a progressive neurologic condition.
* Participant must have experienced at least 1 countable uncontrolled seizure of any type (i.e., tonic-clonic, tonic, clonic, atonic, partial onset or focal: focal seizures with retained consciousness and a motor component, focal seizures with impaired consciousness, focal seizures evolving to bilateral secondary generalization) within 2 months prior to randomization.
* Intervention with vagus nerve stimulation and/or ketogenic diet must be stable for 4 weeks prior to baseline and the participant must be willing to maintain a stable regimen during the blinded period of the trial.
* Participant must abstain from alcohol during the blinded period of the trial.

Key Exclusion Criteria:

* Participant has clinically significant unstable medical conditions other than epilepsy.
* Participant has a history of symptoms related to a drop in blood pressure due to postural changes (e.g., dizziness, light-headedness, blurred vision, palpitations, weakness, syncope).
* Participant has a QT interval, corrected for heart rate with Bazett's formula (QTcB), greater than:

  * 450 msec for males.
  * 470 msec for females.
  * 480 msec if right bundle branch block is present.
* Participant has any history of suicidal behavior or any suicidal ideation of type 4 or 5 on the C-SSRS in the last month or at screening.
* Participant has had clinically relevant symptoms or a clinically significant illness in the 4 weeks prior to screening or enrollment, other than epilepsy.
* Participant is currently using felbamate and has been taking it for less than 12 months prior to screening.
* Participant has consumed alcohol during the 7 days prior to enrollment and is unwilling to abstain during the blinded phase of the trail.
* Participant is currently using or has in the past used recreational or medicinal cannabis, or synthetic cannabinoid-based medications (including Sativex®) within the 3 months prior to trial entry.
* Participant has any known or suspected history of any drug abuse or addiction.
* Participant is unwilling to abstain from recreational or medicinal cannabis, or synthetic cannabinoid based medications (including Sativex) for the duration for the study.
* Participant has consumed grapefruit or grapefruit juice 7 days prior to enrollment and is unwilling to abstain from drinking grapefruit juice within 7 days of pharmacokinetic visits.
* Participant has any known or suspected hypersensitivity to cannabinoids or any of the excipients of the Investigational Medicinal Product (IMP), e.g., sesame oil.
* Participant has received an IMP within the 12 weeks prior to the screening visit.
* Participant has significantly impaired hepatic function at the screening or randomization visit, defined as any of the following:

  * Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \> 5 × upper limit of normal (ULN).
  * ALT or AST \> 3 × ULN and total bilirubin (TBL) \> 2 × ULN or international normalized ratio (INR) \> 1.5.
  * ALT or AST \> 3 × ULN with the presence of fatigue, nausea, vomiting, right upper quadrant pain or tenderness, fever, rash, and/or eosinophilia (\> 5%).