GW Pharmaceuticals has started a Phase 3 clinical trial of Epidiolex as an adjunctive therapy for treatment of seizures related to tuberous sclerosis complex (TSC), a rare genetic disorder where the most common symptom is epilepsy.

Epilepsy happens in nearly 80%-90% of TSC patients and is a major cause of morbidity and mortality.

With the trial, GW aims to support its Epidiolex clinical development programme that covers four Phase 3 trials in Dravet syndrome and Lennox-Gastaut syndrome, both rare and disastrous forms of childhood-onset epilepsy.

Last month, GW announced positive results from the first of these trials in Dravet syndrome.

"GW’s Epidiolex development programme now encompasses three rare epilepsy indications with pivotal trials fully underway."

The new single Phase 3 dose-ranging trial is a 16-week comparison of Epidiolex versus placebo in a total of around 200 patients, aged one to 65, to measure its safety and efficacy as an adjunctive antiepileptic treatment.

The trial’s primary measure is the percentage change from baseline in seizure frequency during the treatment period, while the primary endpoint seizures include focal motor seizures with or without impairment of consciousness or awareness and generalised convulsive seizures.

Various other efficacy and safety secondary outcome measures will also be analysed during the study.

Once completed, patients may be considered eligible to receive Epidiolex through a long-term open-label extension study.

GW Pharmaceuticals chief executive officer Justin Gover said: "Our decision to evaluate Epidiolex in TSC is based on findings from the physician-led Epidiolex expanded access programme, which found that TSC patients reported reductions in seizure activity.

"With the commencement of this trial, GW’s Epidiolex development programme now encompasses three rare epilepsy indications with pivotal trials fully underway.

"GW is committed to establishing Epidiolex as a new therapy to address the significant unmet need among patients who have few treatment options."

Epidiolex is a liquid formulation of pure plant-derived CBD, and is GW’s main cannabinoid product candidate.

The product is currently in development for the treatment of several rare pediatric epilepsy disorders.

GW has been conducting pre-clinical research of CBD in epilepsy since 2007.