UK company GW Pharmaceuticals stuttered on Friday after it revealed plans to withdraw the regulatory dossier for its cannabinoid-based drug Sativex (tetrahydrocannabinol plus cannabidiol) to treat spasticity in multiple sclerosis in Europe, after what it termed “constructive and detailed discussions with regulatory authorities”. It now plans to re-file in 2008 after being provided with a “clear path to approval” of the drug in this indication.

GW sought approval for Sativex in September last year in four European countries – the UK, Spain, Denmark and the Netherlands – and says it has satisfied questions raised by all regulators bar the UK. At a meeting last week, GW says it became clear that one outstanding issue “requires the generation of additional data”. However, the current European regulatory process does not permit new data being added into the dossier, therefore the UK firm says it has chosen instead to withdraw its application and seek a re-filing next year.

Identifying responders

The issue relates to the benefit obtained by “responders” in clinical trials, which UK regulators said could be masked by looking at the mean improvement across the whole studied patient population. There are no issues as regards safety or efficacy, according to the company, so the new trial will look solely at identifying Sativex responders in the first four weeks of treatment and whether any improvements are significantly greater than placebo over an additional 12-week period.

The study, which differs from a conventional Phase III design and has been guided by the regulators, is expected to start recruiting patients in the next few months, with the results due in the second half of 2008. GW notes that it had previously planned an additional trial for muscle spasticity in MS, so there will be no impact on its R&D budget projections.

But while GW was taking the news on the chin, Professor Mike Barnes, President of the World Federation of Neuro-rehabilitation, Professor of Neurological Rehabilitation and Consultant Neurologist, University of Newcastle, said: “It is regrettable and unnecessary in my view, and in the view of other prominent members of the MS treatment community, that the regulators require GW to generate further data to show what we already know – that Sativex is a safe and efficacious treatment for people with MS.”

The MS Trust, of which Prof Barnes is a trustee, also said it is gravely disappointed with what it terms the "continued reluctance by the medicines regulator to license and cannabis medicine for people with MS in the UK." It added that around one half of people with MS who took Sativex gained some benefit with no safety concerns.

Meanwhile, the firm may also seek approval next year for Sativex in MS neuropathic pain following completion of a second pivotal trial in this separate indication early next year. It is also looking forward to a final nod in Canada in the coming weeks and hopes to begin US clinical trials in late summer.

But it wasn't enough to stop GW's shares taking a 29% nosedive on the London Stock Exchange on Friday.