Marijuana Derivative Called Effective in Fibromyalgia

[Herb Fellow]

Winnipeg, Manitoba, - Pain, anxiety, and disability were significantly reduced with the marijuana derivative nabilone (Cesamet) used for fibromyalgia, researchers here said. In a small trial, four weeks of off-label nabilone reduced mean scores on the 10-point Visual Analog Scale of pain by 2.0 points from baseline (P=0.02), reported Ryan Q. Skrabek, M.D., and colleagues at the University of Manitoba in the February issue of the Journal of Pain.

Nabilone is a synthetic analog of tetrahydrocannabinol, a key component of marijuana. It is FDA-approved for chemotherapy-induced nausea and vomiting. Forty patients were enrolled in the randomized, double-blind, placebo-controlled trial, the first such trial of nabilone in fibromyalgia, according to the investigators.

The 20 patients given nabilone also showed improvement of 12.0 points from baseline (P=0.02) on the 100-point Fibromyalgia Impact Questionnaire. The instrument evaluates physical function, work status, depression, anxiety, sleep, pain, stiffness, fatigue, and well-being in fibromyalgia patients. On the Fibromyalgia Impact Questionnaire's 10-point anxiety component, mean scores declined 2.2 points from baseline (P<0.01) with nabilone.

No significant improvements from baseline were seen with the 20 placebo controls in any outcome measure at any time point in the study, Dr. Skrabek and colleagues reported.

At four weeks, there were statistically significant differences between nabilone and placebo in Visual Analog Scale pain scores (-1.43, P<0.05), Fibromyalgia Impact Questionnaire scores (-10.76, P<0.01), and the latter's anxiety scale (-2.20, P<0.01).

Nabilone treatment began at 0.5 mg orally at bedtime during the first week of treatment and was increased by 0.5 mg/day each week until patients were receiving 1 mg twice daily during the fourth week of treatment. A four-week washout period followed.

Patients were included in the trial if they met American College of Rheumatology criteria for fibromyalgia and had continued pain despite other oral medications. They could continue on other medications during the study.

The mean baseline score on the Fibromyalgia Impact Questionnaire was 66.5 in both treatment arms. On the pain scale, mean scores were 6.9 in the nabilone group and 6.2 in the placebo group. Patients were evaluated at weeks two and four, and again at week eight after patients had been off treatment for four weeks. After the washout period, pain and fibromyalgia impact scores returned to near baseline values in the nabilone group.

The assessments included tender point counts and the average pain threshold associated with tender points. These did not change significantly with nabilone treatment, with respect either to baseline or to placebo, Dr. Skrabek and colleagues said.

Side effects were more common in the nabilone group. Many of these were consistent with what is reported with smoked marijuana, Dr. Skrabek said. They included drowsiness, dry mouth, vertigo, confusion, and disassociation.
On the other hand, only one patient reported feeling euphoria, and no one said they felt "stoned," he said.

Five patients assigned to nabilone dropped out within the study's first two weeks, compared with two discontinuations in the placebo group. However, Dr. Skrabek pointed out that two of the nabilone patients gave no reason for withdrawing. He added that fibromyalgia patients are sensitive to side effects of medications and that the investigators were concerned that the dropout rate might be even higher.

Nevertheless, he said nabilone was well-tolerated. Taken with the evidence for efficacy, he said, the drug deserves additional study for treating fibromyalgia.

The investigators pointed out that "subjects were only trialed on nabilone for a total of four weeks, of which only the last week of treatment was at 1mg twice a day. The long-term effect of nabilone in alleviating pain and improving quality of life in patients with fibromyalgia cannot be determined based on the short duration of the study."

"Future studies are still necessary to assess the long-term benefit of nabilone on pain and quality of life, and secondary outcome measures such as anxiety, depression, and fatigue should be further explored with validated assessment tools," the researchers concluded.

Nabilone is regulated as a Class II controlled substance, and its label includes warnings about potential psychotropic effects and a precaution referring to abuse potential.

Dr. Skrabek characterized nabilone's price for chronic use as "prohibitive." He said a year of treatment at the dosage studied in the trial would cost $4,000.
In the United States, the average wholesale cost of a single 1-mg capsule is about $20, according to the University of Utah Hospital in Salt Lake City.

The study was supported by Valeant Canada Ltd. and the HSC Medical Staff Council Fellowship Fund. No potential conflicts of interest were disclosed.

Source: Medpage Today
Copyright: 2008, Medpage Today
Contact: John Gever, Staff Writer
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