It was good news for GW Pharmaceuticals yesterday, after The International Association of the Study of Pain published the results of a study showing that its cannabinoid-based drug Sativex is effective in treating patients with peripheral neuropathic pain.

The five-week, late-stage trial, published online in the journal Pain, was conducted in 125 patients with peripheral neuropathic pain characterised by allodynia (the occurrence of pain in response to a normally non-painful stimulus), and hit its primary endpoint of showing significant superiority to placebo in reducing pain.

Furthermore, Sativex (tetrahydrocannabinol plus cannabidiol) was found to be well-tolerated in the study, and also induced significant improvements in several other markers such as the Neuropathic Pain Scale composite score, sleep disturbance, Pain Disability Index and Patients Global Impression of Change, the group said.

Patients taking part in the investigation were not getting adequate pain relief from analgesics on the market, but continued to take their therapies throughout the trial. Therefore, any improvement in pain obtained through Sativex “were over and above those obtained on currently available treatments”, the researchers concluded.

Encouraging improvements
“Peripheral neuropathic pain can be extremely disabling and is one of the most difficult types of chronic pain to treat,” explained Professor Turo Nurmikko, Principal Investigator, Professor of Pain Science and Consultant Pain Physician at the Walton Centre for Neurology and Neurosurgery in Liverpool. “This study demonstrates that Sativex is effective in the relief of peripheral neuropathic pain…the improvements seen…are very encouraging,” he said.

The company is working towards getting a European green light for Sativex in neuropathic pain, and this study is part of a clinical trial programme designed to help secure regulatory approval. Further clinical trials testing its utility in this indication will be carried out as soon as clearance for the initial multiple sclerosis indication, which the company is pursuing first, is obtained in Europe, it said.

Earlier this year, GW Pharmaceuticals’ stock dropped 29% after it pulled back the European filing for Sativex as a treatment for spasticity in MS to undertake a further trial to identify drug responders in the first four weeks of treatment and whether any improvements are significantly greater than placebo over an additional 12-week period. The group says it plans to refile for this indication in 2008.

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.