GW Pharmaceuticals plc (AIM: GWP) announces preliminary results of a Phase III double-blind randomised placebo-controlled study of Sativex® in 339 patients with central neuropathic pain due to Multiple Sclerosis (MS), who have achieved inadequate pain relief with existing therapies.
- Very high patient response rate to Sativex but statistical significance narrowly missed
due to large, unexpected placebo response
- Ongoing Phase III trial in MS Spasticity on track and due to report in Q4
- MS Spasticity trial has specific features designed to address placebo response
This study is one of three Phase III trials for Sativex underway in 2008, each of which targets a distinct indication. The other European Phase III study in MS Spasticity, requested last year by the UK regulator in order to gain approval in this indication and which involves a different trial design, is on track to report later this year.
The primary efficacy endpoint in the study reported today was the proportion of patients whose pain reduced by at least 30% as measured on a 0-10 numerical rating scale (“responder analysis”). In this study, 50% of Sativex patients experienced a pain reduction of at least 30%, the second largest response rate seen in any Sativex study and amongst the largest seen for any pain treatment in the published literature. However, although the difference between the Sativex and placebo groups was clearly in favour of Sativex, it narrowly failed to reach statistical significance in this trial due to an unexpectedly large placebo response. Key secondary endpoints followed the same trend – in favour of Sativex versus placebo but not at a statistically significant level due to the very high placebo response.
The placebo response in the study reported today appears related to dosing design, whereby patients were able to self-administer the oral spray at will. This was intended to reflect as far as possible the “real world” use of Sativex whereby patients initially experiment with dosing of Sativex to find their optimum dose level and which, once established, is usually maintained thereafter. Analysis of the efficacy data at fixed dose levels demonstrates a highly significant difference between Sativex and placebo. However, a consequence of allowing patients to determine their own dose was that patients on placebo took significantly more doses than patients on Sativex, thus confounding the overall comparison. This validates the decision by GW last year to adopt a fixed target dose approach in both the ongoing studies of Sativex in MS Spasticity and Cancer Pain.
The safety profile of Sativex in this study is superior to that seen in previous studies. The withdrawal rate due to adverse events was 9% on Sativex vs 6% on placebo, the lowest seen in long duration Sativex studies. As in previous studies, the most common adverse event was dizziness. The rate of this adverse event was less than in previous studies (20% on Sativex vs 8% on placebo as compared with 32% vs 9%).
GW’s regulatory strategy is to file Sativex for approval in MS Spasticity in Europe and Cancer Pain in the United States. In Europe, regulatory discussions with the Medicines and Healthcare products Regulatory Agency (MHRA) have exclusively focused on MS Spasticity, a distinct indication supported by different clinical trials. Last year, the MHRA provided clear guidance on the additional clinical trial required for approval. As indicated above, this trial is on track and due to report later this year.
Dr Stephen Wright, R&D Director, said: “It is clear from the size of the response seen in this study that Sativex provides important improvements for these high need patients, even those that have failed to respond to all other pain treatments. It is frustrating that the extent of the placebo response has narrowly prevented the benefits seen on Sativex translating into a statistically significant outcome. The design of the MS Spasticity study due to report later this year is specifically focused on limiting the potential for placebo response and we expect the outcome of this trial and our other studies to confirm the benefits of Sativex.”
“MS Spasticity is a distinct indication supported by different clinical trials and the route to regulatory approval for Sativex as a treatment for this indication remains clear and unaffected by the data announced today.”
Dr Stuart Ratcliffe, Principal Investigator of the study and most recently Director, Pain Research Group, St Bartholomew’s and The Royal London Hospitals NHS Trust, added: “In seeking to replicate the real world usage of Sativex, where each patient finds his or her own optimum dose level, the design of this trial appears to have encouraged an abnormally high placebo response. However, this in no way should detract from the beneficial effects of Sativex seen in the study. Patients saw a marked improvement in their symptoms, a highly impressive effect since they are treatment resistant, and the study recorded the lowest drop-out rate, demonstrating the mild side effect profile of Sativex. My experience with Sativex continues to show that it is an extremely helpful medicine for these high need patients and I am confident that the ongoing trials which seek to address the placebo issue will demonstrate its value.”
Following a comprehensive review of this data, GW intends to carry out a further study in this patient population.
As at 31 March 2008, GW’s cash position stood at £18.5m.
There will be a conference call for analysts today at 8.30am BST. Analysts should contact Gemma Cross Brown at Financial Dynamics on +44 (0) 20 7831 3113 for details. There will be a live audio web cast of this call, which will be accessible on the press releases page in the investor relations section of the GW website (www.gwpharm.com). A recording of this call will be available on the GW website later today.