Epidiolex (GWP42003-P) is an oral cannabidiol solution developed by GW Pharmaceuticals and approved by the U.S. Food and Drug Administration (FDA) for patients with Dravet syndrome and Lennox-Gastaut syndrome.

How Epidiolex works

Epidiolex is a plant-derived cannabidiol, a non-psychoactive marijuana extract, meaning that it does not have the mind-altering effects that are characteristic of delta (9)-tetrahydrocannabinol (THC), the main psychoactive component of marijuana that gets people “high.”

While marijuana derivatives have been used to treat epilepsy since the late 19th century, modern-day researchers still do not fully understand how cannabidiol works to treat epilepsy. They hypothesize that it may be due to its ability to interact with many other non-cannabinoid receptors in the brain. (The brain has a natural endocannabinoid system with cannabinoid receptors that can respond to CBD and THC.)

Epidiolex in clinical trials

An open-label, Phase 1 clinical trial (NCT02286986) compared the safety and tolerability of increasing doses of Epidiolex given to patients, ages 2 to 19 with a diagnosis of drug-resistant epilepsy. Researchers also aimed to determine changes in the number of seizures experienced during a year. The trial was completed, but the results have not been published.

Results from a Phase 3 clinical trial (NCT02091375) conducted at 23 centers in the U.S. and Europe found that 120 children and young adults, ages 2 to 19 who were given 20 mg per kilogram body weight of Epidiolex for three-and-a-half months had half the average number of convulsive seizures in a month compared to the number they experienced before treatment (5.9 versus 12.4).

Five percent of those receiving Epidiolex were seizure-free for the duration of the study. However, Epidiolex did not reduce the number of non-convulsive seizures. Sixty-two percent of caregivers of those who received Epidiolex noticed an improvement of at least one category in the Caregiver Global Impression (CGI) scale, compared to the 34 percent of caregivers of those in the placebo group.

The most common side effects of the treatment were fatigue, fever, vomiting, diarrhea, sleepiness, and abnormal liver enzyme test results, recorded in 93 percent of patients taking Epidiolex. A majority of these (89 percent) were of mild-to-moderate severity. The findings from this trial were published in The New England Journal of Medicine.  

Another Phase 3 clinical trial (NCT02224703) began in 2015 and is assessing the safety and effectiveness of Epidiolex in children and young adults with Dravet syndrome. The trial aims to compare a high and low dose of Epidiolex to placebo in terms of their abilities to reduce the number of seizures within a three-and-a-half month treatment period. The trial is taking place at clinical sites in the U.S. and in the Netherlands.

An open-label, Phase 3 extension trial (NCT02224573) is currently underway. It aims to record side effects, improvements in seizure symptoms, and overall improvements in quality of life in patients who were in the previous Phase 1, 2 and 3 clinical trials of Epidiolex. The trial is enrolling by invitation only and is expected to end in June 2019.

Additional information

In February 2018, the European Medicine Agency (EMA) accepted for review a marketing authorization application for Epidiolex, a process that would allow the treatment to be approved and marketed in all E.U. member states. The outcome of this review is expected in early 2019.

Epidiolex also has the largest expanded access program (also known as a compassionate use program) in epilepsy, a program that allows patients with potentially life-threatening conditions to gain access to treatments not available outside of clinical trials. Through this program, more than 1,100 patients were able to receive Epidiolex treatment. The medication is provided free of charge by Greenwich Biosciences, a subsidiary of GW Pharmaceuticals

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