GW Pharmaceuticals saw its stock hit a 12-month high this week after unveiling encouraging safety and efficacy data for its investigational cannabidiol Epidiolex in difficult-to-treat epilepsy patients.

The company said physician reports from 27 children and young adults with treatment-resistant epilepsy showed that, following a 12-week course with Epidiolex, 48% obtained at least a 50% reduction in seizure frequency as compared to baseline, while 41% experienced at least a 70% reduction.

When looking specifically at patients with a severe form of epilepsy called Dravet syndrome the figures were even higher, with 56% obtaining at least a 50% cut in seizure frequency and 44% at least a 70% reduction.

On the safety side, the drug seemed well tolerated overall. Eighty percent of side effects reported were mild or moderate, while none of those that were deemed serious were found to be related to Epidiolex by independent investigators, the firm noted.

PhII/III trial later this year

Justin Gover, GW's Chief Executive Officer, said the safety and efficacy signals from this data support the company's decision to advance Epidiolex into a formal development programme, and that a Phase II/III clinical trial of the drug in Dravet syndrome is expected to kick off in the second half of this year.

"There remains an enormous unmet need in a range of paediatric and adult treatment-resistant epilepsy syndromes, which affect approximately 750,000 Americans," said Orrin Devinsky, Director, NYU Comprehensive Epilepsy Center. "Some of the greatest needs are in children with severe epilepsy syndromes such as Dravet and Lennox-Gastaut, where frequent seizures often persist despite high doses of multiple anti-epileptic drugs," he noted.

Epidiolex has received both orphan drug designation and Fast Track designation from the US Food and Drug Administration.

Shares closed up 15% last night on the London Stock Exchange at 429 pence.