120mg is a high dose of Cymbalta

Duloxetine effective in women with fibromyalgia

Fibromyalgia is a chronic disease with pain in the muscles and joints, associated with increased muscle tone and associated with fatigue, muscle stiffness, anxiety, sleep disorders and depression. The prevalence in the general population is estimated at 2%, with women about five times more likely to be affected than men. Previous studies have shown that duloxetine (Cymbalta®), a selective serotonin-norepinephrine reuptake inhibitor, is able to positively influence pain in fibromyalgia. However, the smaller phase II studies indicated that this effect may be more pronounced in women than in men.

It was therefore decided to conduct a study exclusively in women with two different doses of duloxetine. It was a multicenter, randomized, double-blind, placebo-controlled study. Women over 18 years of age who met the American College of Rheumatology's criteria for primary fibromyalgia and had a score of at least 4 (between 0 and 10) on a pain scale were included. The patients were divided into three therapy groups:

  • Duloxetine 60 mg twice a day
  • Duloxetine 30 mg twice a day
  • Placebo

The randomization was carried out in a stratified manner, depending on whether depression was present or not. The treatment extended over 12 weeks.

The primary endpoint was the intensity of the pain on a scale of 0 to 10. Secondary endpoints included the highest pain intensity within 24 hours and the influence of the pain on everyday activities. Treatment response was defined as a more than 30% reduction in pain intensity over 24 hours in the patients. Other endpoints were a special scale for recording the symptoms of fibromyalgia, a global impression scale and the Hamilton depression scale. Quality of life and side effects were also recorded.

354 women could be randomized, 68 of whom completed the study in the placebo group, 76 in the low-dose and 71 in the high-dose group of duloxetine. The mean age was 49.6 years, and a quarter of the women were depressed at the time of randomization.

For the primary endpoint, both duloxetine doses were significantly more effective than placebo. The first significant difference was already apparent after a week. The difference in the pain scale was 0.8 points on average for placebo and 2.0 to 2.5 points on average when duloxetine was administered. There was no difference between the two duloxetine doses.

There were also significant differences in favor of duloxetine for most of the secondary endpoints. This also applied to the quality of life measured with the SF-36.

79% of the women complained of side effects when given placebo and 92.4 and 90.5% respectively when treated with 60 and 120 mg duloxetine. The most frequently reported side effects of duloxetine therapy were nausea, dry mouth, constipation, diarrhea, fatigue, loss of appetite, sweating and a feeling of restlessness. Patients treated with duloxetine were also more likely to drop out of the study because of side effects.