WEDNESDAY, Dec. 12, 2012 (HealthDay News) -- A cannabis-based prescription drug called Sativex, used to treat debilitating muscle spasms in multiple sclerosis (MS) patients, is the subject of a large new evidence review. Whether the drug -- licensed for use in the United Kingdom -- actually gets the job done remains uncertain.
Cannabinoids are active ingredients in marijuana. Sativex is not currently approved by the U.S. Food and Drug Administration, which considers it an investigational drug as clinical trials are under way.
In Britain, Sativex mouth spray is prescribed for patients only as an alternative treatment when standard therapies fail to provide adequate symptom relief.
And now a British team's review of previous studies upon which its initial U.K. approval had been granted suggests that although Sativex appeared to offer some benefit, the studies themselves contain design flaws or insufficiencies that may make the conclusions unreliable.
"Our findings were that the medicine has a small beneficial effect," said David Phizackerley, the London-based deputy editor of the journal Drug and Therapeutics Bulletin, which published the study Dec. 12.
"However, we identified problems with the clinical trials of the drug," he added. "The trials compared the drug against placebo rather than against another drug, some of the trials were short, some included small numbers of patients; some trials didn't show a benefit from using the drug and some trials used a dose greater than the recommended dose," Phizackerley said.
"[So] at the moment there is limited evidence that this particular formulation of cannabis extract has a small beneficial effect in relieving the symptoms of spasticity in patients with MS," he explained.
The authors stressed that their review focused solely on investigations of the Sativex formulation. None of the studies explored the use of marijuana in its recreational or homegrown form for the treatment of spasticity, which afflicts about 60 percent of MS patients.
That said, the review team noted that many studies were of limited clinical usefulness, given that patients only took Sativex for between six weeks and four months. No study set out to compare Sativex against other standard spasm-control medications, whereas others had patients routinely take Sativex beyond the maximum use (12 sprays daily) approved by U.K. authorities.
However, the British research team did cite one study that was well designed. And the result of that investigation: Sativex patients fared no better than patients not given the drug.
Sativex is by no means a cheap therapy, Phizackerley noted. At roughly $2.25 per spray, it costs upwards of 10 times more than standard spasm-control drugs.
So while acknowledging that additional research is now exploring a range of cannabis extract formulations, including tablets and capsules, he and his colleagues concluded that for the moment there is not yet enough evidence to warrant recommending that doctors and MS patients turn to this medication as a proven approach for the relief of spasms.
In a statement. GW Pharmaceuticals plc, the makers of Sativex, said the company was "disappointed with the conclusions drawn" by the study.
"The article contradicts the opinion of 22 separate national authorities in Europe and around the world that have granted approval for Sativex and recognize the important benefits it provides to MS patients with spasticity," said Dr. Stephen Wright, director of research and development at GW Pharmaceuticals.
The company statement also cites Dr. David Shakespeare, lead author of a Cochrane review of anti-spasticity treatments and a consultant in neurological rehabilitation medicine at the Royal Preston Hospital, England. He said that, "I have over six years prescribing experience of Sativex, and in my opinion it provides a valuable addition to multiple sclerosis patients whose spasticity does not respond to other drugs and who would otherwise have no other effective treatment option."
In the U.S., Nicholas LaRocca, vice president of health care delivery and policy research with the National Multiple Sclerosis Society, said that although the Sativex option is not an approved drug intervention in the United States, "there is obviously a need for additional therapies for the many symptoms of MS."
LaRocca said: "I think this analysis speaks for itself. Clearly, right now there's insufficient data available to recommend Sativex for targeting spasticity. And because it's not available here, we mostly just have anecdotal reporting from patients who go ahead and use marijuana on their own. And there's an inability to verify these reports, which just raises questions about uncontrolled long-term use and safety."
So, LaRocca added, "for now it remains an open question. And certainly there needs to be more research to look into this issue more deeply, because the larger issue is that there are treatments available, but they don't necessarily work as well for everyone, because everyone with MS is a little bit different."
For more on multiple sclerosis, visit the U.S. National Institute of Neurological Disorders and Stroke.