Previous studies evaluating the efficacy and tolerance of tropisetron for the treatment of fibromyalgia (FM) used the drug either intravenously or orally, and at different dosage levels ranging from 2 mg to 15 mg daily. The shortest treatment was a single dose and the longest treatment period covered 28 days.
A significant reduction of the pain intensity was achieved by using tropisetron 5 mg per day. Apart from the fact that treatment periods were different, the efficacy of oral and intravenous administration did not differ significantly. Tropisetron was well tolerated; but in the 15 mg group in one of the studies, the decrease in pain was less than in the placebo group, however, the frequency of constipation and other gastrointestinal symptoms increased. Furthermore, it was hypothesized that due to the impacts of CYP2D6 activities, a daily dose of tropisetron 2 mg may be efficacious in slow metabolizers only.
Although tropisetron proved to be efficacious in a group of fibromyalgia patients, the dose-response curves cannot yet be explained in a fully satisfactory manner, which may encourage research focusing on possible subgroups of FM.