Shares in GW Pharmaceuticals have shot up almost 7% this morning after the firm presented data from a late study of its cannabis-based product Sativex which confirm the long-term efficacy of the drug in patients with neuropathic pain due to multiple sclerosis.

The study evaluated 42 MS patients with central neuropathic pain who had previously been in a Sativex (delta-9-tetrahydrocannabinol and cannabidiol)) Phase III MS neuropathic pain study and who continued to take the product for 12 weeks. They were then randomised to receive Sativex or placebo for a further four weeks. During the randomised period, patients were not permitted to adjust their dose. The purpose of this study was to assess the maintenance of pain control in patients who remain on Sativex versus those who switch to placebo.

GW says that the primary endpoint of the study - the time to treatment failure - was statistically significantly in favour of Sativex, which also performed better for mean pain score and sleep quality. The importance of the study lies in the fact that until now, all the evidence for long-term maintenance of efficacy of Sativex has come from long-term open-label exposure and the latest “confirm in the context of a placebo-controlled double-blind study that efficacy is indeed maintained in long-term use”, the firm said.

Stephen Wright, GW’s R&D director, said that the results “support the design of the ongoing Phase III trial in MS spasticity”. He added that it is encouraging to note that “if the difference between Sativex and placebo achieved in the results today are replicated in the ongoing Phase III MS spasticity study”, the latter will meet its objectives.

That study, which was requested by the UK regulator prior to granting approval for Sativex, is due to report in the first quarter of 2009 and a regulatory submission is planned for the first half of next year.