Comparison of tegaserod (HTF 919) and its main human metabolite with cisapride and erythromycin on cardiac repolarization in the isolated rabbit heart

Tegaserod (HTF 919) is a new drug being developed for gastrointestinal moti lity disorders. Because other gastrointestinal prokinetic agents, such as c isapride and erythromycin, cause slowing of cardiac repolarization and have been implicated in the development of the potentially fatal ventricular ar rhythmia, torsades de pointes, a study was initiated to determine whether t egaserod and its main human metabolite adversely influence cardiac repolari zation. By using isolated Langendorff-perfused rabbit hearts, we show that QT intervals remain unchanged at concentrations of tegaserod from 0.5 to 10 mu M. It was not until the tegaserod concentration was increased to 50 mu M (roughly 500-5,000 times mon concentrated than those typically found in h uman plasma after administration of recommended clinical dosages), that a s mall, but significant increase in the QT interval (12 +/- 4%; p < 0.05; n = 4) was observed. No significant changes in QT occurred in the presence of the tegaserod metabolite at any of the concentrations tested (0.5-50 mu M). In contrast, cisapride caused QT lengthening at concentrations as low as 0 .1 mu M, with significant QT increases occurring when 5-50 mu M cisapride w as used (22 +/- 4% to > 70%, respectively; p < 0.01; n = 4). Erythromycin a lso caused significant lengthening of QT intervals (11 +/- 2%; p < 0.001; n = 4), although 100 mu M concentrations of this drug were required to achie ve this effect. These results demonstrate that both cisapride and erythromy cin can slow cardiac repolarization at therapeutic doses and that tegaserod 's lack of QT prolongation at therapeutic doses suggests that it has the po tential to be a safer alternative to cisapride as a gastrointestinal prokin etic agent.