GW Pharmaceuticals of the UK has presented impressive preliminary results for two late-stage trials looking at Sativex, its cannabinoid spray medicine, for peripheral neuropathic pain and the data will “contribute significantly to a future regulatory filing.”

The first of the Phase III studies examined the effect of Sativex (tetrahydrocannabinol plus cannabidiol) in 246 patients with neuropathic pain characterised by allodynia, which is the occurrence of pain in response to a normally non-painful stimulus, such as clothes touching the skin). The results showed that patients taking Sativex obtain clinically important improvements in their management of pain and quality of sleep and GW noted that in comparison with placebo, statistically significant improvements were seen for key outcome measures, including a positive result in the primary analysis of patient response, “the outcome measure recommended by regulatory authorities.”

The second Phase III study examined the effect of Sativex in 297 patients with painful diabetic neuropathy who were being treated with currently available analgesics. Here, patients taking the GW drug showed a 30% mean improvement in pain scores, “among the highest level of response seen in the published literature” and one-third of Sativex patients achieved over a 50% improvement in pain. However, the company noted that the results are difficult to interpret due to an abnormally large response in the placebo group and do not reach statistical significance.

Stephen Wright, GW’s R&D director, said the studies focused on particularly high-need patients, who were already taking the best available pain treatments, and yet still suffered severe pain.” Even in this most-difficult-to-treat population, Sativex has produced improvements over and above current treatments,” he added.

Sativex has only been launched in one market, Canada (by partner Bayer), and that is for the relief of neuropathic pain in adult multiple sclerosis patients. GW noted that the two aforementioned studies “are part of a programme to generate data for the future expansion of the use of Sativex in Europe beyond MS into other pain conditions.”

The company recently filed for approval of Sativex to relieve spasticity in people with MS under the European Union's decentralised procedure, whereby the UK will act as reference member state for a green light in Spain, Denmark and the Netherlands. Once approved, Sativex will be marketed in the UK by Bayer and in the rest of Europe by Spain's Almirall. It is also the subject of an ongoing regulatory submission in Canada for the relief of cancer pain.

Regulators allow only one submission at a time for a single drug, no application for Sativex in neuropathic pain can take place any time soon. This may explain why GW’s shares barely moved on the news though it could be that investors are mindful of the string of setbacks the company has had to bear in order to get Sativex on the market. One such problem came just over 18 months ago when the UK’s Committee on the Safety of Medicines said that a further clinical study would be required before it could win approval for MS spasticity.