The use of 5-HT3 receptor antagonists in various rheumatic diseases - a clue to the mechanism of action of these agents in fibromyalgia?

In a pilot study, the action of the 5-HT3 receptor antagonist, tropisetron, on different types of local rheumatic pain and inflammatory effects was st udied. With intra-articular injection of tropisetron, an improvement in inf lammation and pain was obtained in inflammatory rheumatic diseases and acti vated osteoarthrosis. Also, the majority of patients with localized soft-ti ssue rheumatic diseases (periarthritis) demonstrated an obvious decrease in their pain following local infiltration of tropisetron. Chronic low back p ain and cervical pain responded somewhat to i.v. treatment with tropisetron . The effect of the 5-HT3 receptor antagonists is probable primarily to lim it the release of substance P, which acts as a pain and inflammatory mediat or, and is itself released by the neurogenic inflammation that occurs after the binding of serotonin to its corresponding receptor. These results shou ld be backed up with placebo controlled studies, which if confirmed, might imply that 5-HT3 receptor antagonists could supplement or replace the local administration of corticosteroids.