The 5-HT3-receptor antagonist tropisetron has a favourable effect on the pain, not only of primary but also of secondary fibromyalgia. In an open study, ten women with clinical and serological evidence of secondary fibromyalgia were treated with tropisetron. Treatment comprised a single daily injection of 5 mg tropisetron on five consecutive days. Prior to, and 7 and 14 days after, treatment, the patients rated their pain on the visual analog pain (VAP) scale.
Nine patients experienced a substantial reduction in pain, with the mean VAP score decreasing from 64.3 initially, to 31.9 on the 7th day. After 14 days, the average score was 33.3, that is, roughly the same as that recorded after 7 days; however, 3 patients indicated the reappearance of substantially greater pain.
On the basis of these preliminary results, it would appear to be worth initiating a double-blind study to investigate the effects of short-term i.v. treatment with tropisetron in a large, clearly defined patient population with secondary fibromyalgia.