GW Pharmaceuticals has kicked off a Phase III trial of Sativex in multiple sclerosis spasticity, data from which should form the basis of the drug’s planned resubmission in Europe in 2008.

Earlier this year, the company announced that it had pulled back the file seeking permission to market the cannabinoid-based therapy Sativex (tetrahydrocannabinol plus cannabidiol) in Europe for MS spasticity, after regulators insisted on additional data clarifying the amount of patients responding to the drug. The move saw its shares plummet nearly 30% at the time.

Previous clinical trials “masked” the responder rate to some degree because they looked at the mean improvement across the whole study population, ie both responders and non-responders, the company explained. And although “post-hoc” analysis demonstrated that, after 12 weeks of therapy, the difference in responder rate between the Sativex and placebo group was statistically significant, regulators requested that “this analysis be replicated in a prospectively planned study”, it added.

The new study, which has been designed in close association with the regulators, plans to first sift out those patients responding to treatment over a four-week period, and then analyse the effect of Sativex compared to placebo in the responders over a 12 weeks. The company says it hopes to recruit around 244 patients into the second stage of the trial in five different European countries, and that results should be available by the end of next year.

Near-term opportunities
Currently, Canada is the only market in which Sativex is available. The drug was first launched there in 2005 for the relief of neuropathic pain in adult MS patients, and received an additional nod for cancer pain in August. In Europe, there are two potential short-term opportunities to re-submit Sativex for regulatory approval – one for MS neuropathic pain, which is currently being tested in a second pivotal Phase III trial and could be submitted in the first half of next year, or the planned resubmission of MS spasticity following completion of the new study towards the end of next year, the group said.

In addition, the company also plans to seek approval to market Sativex in Europe for the treatment of cancer pain and peripheral neuropathic pain. Just a couple of weeks ago, The International Association of the Study of Pain published the results of a study showing that the drug is effective and well-tolerated in the patients with the latter condition, but GW previously said it plans to get the green light in MS first before further pursuing this indication.