To study the efficacy of 5-hydroxytryptamine type 3 receptor (5-HT-3R) antagonist (ondansetron) vs paracetamol in primary fibromyalgia (FM) syndrome.
A double blind, crossover, latin square study of 21 patients with FM. Visual analog scale (VAS) and body drawings were used to record pain intensity. Functional symptoms were determined for using a Likert-type self-developed protocol. Quantitative dolorimetry was applied to assess the number of painful tender points and the average pain threshold. Serum serotonin levels were measured by a commercial ELISA.
A marked improvement in pain intensity measured by VAS (p < 0.005), pain score (p < 0.05), tender points (p < 0.05), and average pain threshold (p < 0.01) was obtained with ondansetron, whereas no improvement was seen with paracetamol. After ondansetron treatment, there was also significant reduction in both functional symptoms (p < 0.01) and headache intensity (p < 0.05). In patients who did not respond to ondansetron there was higher baseline pain intensity measured by VAS (p < 0.05) and pain score (p < 0.01), and a lower pain threshold (p < 0.05) compared to those who did respond well. In the responsive group, no significant differences were seen in the serotonin level before and after therapy. Whereas a significant increase in serum serotonin concentration (p < 0.01) was observed in nonresponders after ondansetron treatment.
Ondansetron appears to be an effective drug in about 50% of patients with FM. There may be 2 subsets of patients with FM that differ clinically and pathogenetically with regard to the disturbance in the 5-HT-3R system.