Treatment of chronic fatigue syndrome with 5-HT3 receptor antagonists--preliminary results.

Objective: The serotonin system presumably is involved in the pathogenesis of chronic fatigue syndrome (CFS). Results from a few studies led to the hypothesis of a "postsynaptic hyperresponsiveness" in CFS. Therefore we intended to evaluate the efficacy of 5-HT3 receptor antagonists in the treatment of CFS.

Patients and methods: 2 patient groups (10 patients each; CFS according to the CDC classification criteria) received either oral tropisetron (5 mg once daily) or oral ondansetron (2 x 8 mg daily), open-labelled. Treatment duration was 15 days. Treatment response was evaluated by visual analog scales (VAS) for fatigue and capability.

Results: 19 patients finished their respective study. In the tropisetron group 6/9 (VAS fatigue) and 7/9 (VAS capability) patients documented benefit, 8/10 rsp. 8/10 patients in the ondansetron group. The score changes (VAS before and after treatment) in case of response were more pronounced in the tropisetron group. The frequency of concomitant symptoms did not differ significantly in the treatment groups. The overall analysis of both studies showed a remarkable improvement (> or = 35%) of approximately one third of the patients in both VAS. Treatment was well tolerated.

Conclusion: Our preliminary results encourage to perform placebo-controlled, double-blind studies to further evaluate the efficacy of 5-HT3 receptor antagonists in the treatment of CFS.