Efficacy and tolerability of tropisetron in primary fibromyalgia - a highly selective and competitive 5-HT3 receptor antagonist

Objective: Based on a potential role for serotonin receptors in fibromyalgi a, we investigated the efficacy and tolerability of treatment with tropiset ron, a highly selective, competitive inhibitor of the 5-HT3 receptor. Methods: In this prospective, multicenter, double-blind, parallel-group, do se-finding study, 418 patients suffering from primary fibromyalgia (ACR cri teria) were randomly assigned to receive either placebo, 5 mg, 10 mg or 15 mg tropisetron once daily, respectively. The duration of treatment was 10 d ays. The clinical response was measured by changes in pain-score, visual an alog scale (VAS), and the number of painful tender-points. Results: Treatment with 5 mg tropisetron resulted in a significantly higher response rate (39.2%) when compared with placebo (26.2%) (p=0.033). The ab solute reduction in pain-score was -13.5% for 5 mg tropisetron, -13.0% for 10 mg tropisetron, and -6.3% for placebo (p<0.05). The effects of 15 mg tro pisetron were similar to placebo, thus suggesting a bell-shaped dose-respon se curve. Compared with placebo, treatment with 5 mg tropisetron led to a s ignificant improvement (p<0.05) in VAS, while a clear trend in terms of cli nical benefit was seen with 10 mg tropisetron. The number of painful tender -points was also reduced significantly (p=0.002) in the 5 mg tropisetron gr oup. Of interest, during the 12-month follow-up period, pain intensity of r esponders on 5 mg and 10 mg tropisetron was still markedly below baseline. The treatment was well tolerated, with gastro-intestinal complaints being t he most frequently reported side effects, in keeping with the known safety profile for 5-HT3 receptor antagonists. Conclusions: This study demonstrates the efficacy of short-term treatment w ith 5 mg tropisetron once daily in primary fibromyalgia. Treatment was well tolerated and prolonged clinical benefits were seen.