Four-week therapy with the 5-HT3 receptor antagonist tropisetron in fibromyalgia

The optimum duration of therapy for fibromyalgia with 5-HT3 receptor antagonists is not yet clear. Up to now treatments with these substances have only been implemented over 10-day periods, which resulted in significant reduction of the pain in a multi-centre, double-blind, placebo-controlled study which we carried out on approx. 400 fibromyalgia patients. The question arose whether the results of the treatment could be improved by increasing the duration of therapy. In an open pilot study 30 patients aged between 36 and 66 with fibromyalgia established according to the ACR-criteria were treated for 28 days with daily 5 mg Tropisetron p. o., a dose that had proved more effective then higher doses in the double-blind study. The effects of the therapy were recorded together with the pain score, the visual analog scale, dolorimetric investigations of the "tender points", the paracetamol consumption, the alteration in vegetative and functional symptoms, collection of data through psychometric questionnaires (MPI-D, BDI, STAI, Bf-S) as well as the general verdict of patients and testers on effectiveness, compatibility, and the change in intensity of the illness. Undesirable pharmacological effects of Tropisetron were also recorded. During these investigations it was observed that pain improved rapidly in the first 10 days, and an additional but slower reduction in pain followed in the subsequent period up to the 28th day of treatment. A significant improvement in various functional and vegetative symptoms was also observed during the therapy and also measured via various psychometric scales such as the Beck Depression Inventory (BDI) and the v. Zerssen State of Health Scale (SH-S), as well as the scales based on pain (but not the psychosocial consequences) of the multidimensional pain inventory MPI-D. It was also possible to reduce the consumption of paracetamol. However, no significant change could be seen in pressure sensitivity of the tender points. In 70% of cases, according to the testing physician, and in 60% according to the patient, the general verdict on the effectiveness of Tropisetron was good or very good. Undesirable pharmacological effects manifested themselves primarily as headache, constipation, and stomach pains. These led to an early termination of the therapy in only 2 cases where the therapy was also insufficiently effective. According to the present study, a four-week therapy with Tropisetron appears to produce better results in fibromyalgia than a ten-day treatment but the conclusions are limited by the open test systems and the small number of cases. The findings need verfication by placebo-controlled studies.