In a preliminary, placebo-controlled, 1-month trial, the marijuana-based synthetic drug nabilone (Cesamet, Valeant Pharmaceuticals) showed promise for temporary pain relief for fibromyalgia patients.

The study, by Ryan Quinlan Skrabek, MD, and colleagues at the University of Manitoba, in Winnipeg, is published in the February issue of the Journal of Pain.

"The results are interesting and provocative, and there may very well be a place for this kind of treatment eventually, but I think it would have to be [tested] in a much larger study with a more rigorous methodology," John Kissel, MD, from Ohio State University, in Columbus, who was not involved in the study, speaking on behalf of the American Academy of Neurology, told Medscape Psychiatry.

Fibromyalgia, which is characterized by diffuse musculoskeletal pain, affects 2% to 4% of the general population and is up to 7 times more common in women, the group writes. The pathophysiology of fibromyalgia is not clearly understood, and only recently pregabalin (Lyrica, Pfizer) was the first drug approved by the US Food and Drug Administration for this disease.

Nabilone is one of 2 orally administered synthetic cannabinoid drugs available in Canada and approved for management of nausea during chemotherapy, and research into its use to manage neuropathic pain has been encouraging, they add.

The investigators hypothesized that nabilone would significantly improve pain and quality of life in fibromyalgia patients.

They recruited 40 outpatients with fibromyalgia, who were randomized to receive nabilone (n = 20) or placebo (n = 20) for 4 weeks. Patients were seen at baseline, after 2 and 4 weeks of treatment, and at 8 weeks (after 4 weeks of washout).

Patients in the treatment group received nabilone 0.5 mg/day for week 1, 1 mg/day for week 2, and if they tolerated this, 1.5 mg/day for week 3, and 2 mg/day for week 4. The study drug was provided by Valeant Canada (Montreal, Quebec).

The primary outcome was pain intensity at 2 and 4 weeks, measured by visual analog scale (VAS; from 0 = no pain to 10 = worst pain imaginable). Secondary outcomes included the number of positive tender points, the average tender-point pain threshold, and quality of life as measured by the Fibromyalgia Impact Questionnaire (FIQ). The FIQ evaluates, among other things, physical function, depression, anxiety, and well-being, using a scale of 0 to 100 where higher scores indicate worse quality of life.

At baseline, patients had an average VAS score of 6 and an average FIQ score of 66.

A total of 5 subjects in the treatment group (25%) and 2 subjects in the placebo group (10%) dropped out of the study before or at 2 weeks. Reasons for dropout in the treated group included dizziness, nausea, and fatigue.

Compared with baseline, at week 4, at a nabilone dose of 1 mg twice a day, patients in the nabilone-treatment group had significantly improved VAS, FIQ, and anxiety scores (all P < .02). The nabilone-treated patients had significantly greater improvements in these measures than did the placebo-treated patients.

The patients did not have significant improvements in the remaining outcomes, including depression, fatigue, and tender points.

Adverse effects — most commonly drowsiness, dry mouth, vertigo, and ataxia — were more common in the nabilone-treated patients but were generally mild.

None of the patients achieved remission, and the effects of nabilone were not lasting; at 8 weeks, after the 4-week washout, the outcome measures in both groups were not significantly different from baseline.

Still Early Days

"The significant reductions in VAS, FIQ, and anxiety seen in the treatment group, coupled with minimal side effects, suggest that nabilone may be a beneficial, well-tolerated treatment option for patients with fibromyalgia," the researchers conclude.

Future studies with a longer duration of treatment and a stable dose are still needed, they add. The medication's costs — $4000 a year in Canada — may be prohibitive to some patients, they observe.

When interpreting the study results, it is important to note that the study drug was costly, the study was done in a small number of patients, and there was a high dropout rate, Dr. Kissel said. In addition, the dropout patients were not included in an intention-to-treat analysis, which would have resulted in a lower improvement rate. Also, patients in the nabilone group had more adverse effects and likely knew they were taking the study drug.

"I don't think this should change at all the way physicians practice right now . . . without this being replicated in a bigger study," he said.

The study was supported by an unrestricted research grant from Valeant Canada and a Health Sciences Center Medical Staff Council Fellowship fund.

J Pain. 2008;9:164-173. Abstract