GW Pharmaceuticals is on the brink of filing its cannabis-derived therapy Epidiolex in the US as another late-stage study highlights the drug’s efficacy in treating Dravet Syndrome, a rare and severe type of epilepsy.

The New England Journal of Medicine has published results from a Phase III study showing that Epidiolex (cannabidiol) significantly reduced monthly convulsive seizure frequency compared to placebo in highly treatment-resistant children when added to existing treatment.

Five percent of children became seizure free while taking the treatment compared to none in the placebo arm, while patients also had a significantly greater median reduction in convulsive seizures (39 percent) compared to placebo (13 percent).

The proportion of patients who had a 50 percent or better reduction in convulsive seizure frequency was 43 percent with Epidiolex versus 27 percent with placebo.

On the safety side, Epidiolex was generally well tolerated in the trial, the the most common adverse events (AEs) found to be somnolence, diarrhoea, decreased appetite, fatigue, vomiting, pyrexia, lethargy, convulsion, upper respiratory tract infection. Of the 93 percent that experienced an AE, 84 percent reported it to be mild or moderate, the firm noted.

Ten patients taking the drug experienced a serious adverse event compared with three patients on placebo, while eight discontinued treatment due to adverse events compared with one patient in the control group.

"Dravet syndrome is one of the most difficult types of epilepsy to treat and many of the children in this study were experiencing dozens, even hundreds, of seizures per month despite taking multiple concurrent anti-epileptic medications," said Orrin Devinsky, of NYU Langone Medical Center's Comprehensive Epilepsy Center and lead author of the study.

“These results suggest that Epidiolex can provide clinically meaningful benefits and I look forward to the prospect of an appropriately standardised and tested pharmaceutical formulation of cannabidiol available as a treatment option for these patients.”

The New Drug Application for Epidiolex remains on track for submission to the US Food and Drug Administration in the middle of 2017. If the drug makes it to market, analysts are expecting annual sales to hit $1.6 billion in 2023, according to Thomson Reuters data, as reported by Reuters.