An Ex Vivo Study to Evaluate the Effect of Tegaserod on Platelet Activation and Aggregation

Tegaserod, an orally active, potent 5-hydroxytryptamine-4 serotonin receptor agonist, was previously indicated for irritable bowel syndrome but was voluntarily withdrawn due to potential cardiovascular side effects. In vitro studies suggested that tegaserod increased platelet aggregation, but these results were not reproduced or were inconclusive. We sought to assess ex vivo effects of tegaserod on platelet aggregation.

In this double-blind, placebo-controlled, crossover study, we randomized a majority of healthy patients with no history of cardiovascular risk factors (n = 21) to receive tegaserod or matching placebo for 7 + 2 days followed by a 7- to 10-day washout period, and then patients were crossed over to the other study drug for the next 7 + 2 days. Unstimulated and agonist-stimulated platelet aggregation; P-selectin expression; serum thromboxane (Tx)B₂ and urinary 11-dehydro (11-dh) TxB₂; and tegaserod and M29.0 concentrations were serially assessed.

There was no significant difference in percentage change in unstimulated or adenosine diphosphate (ADP)- and ADP + serotonin-, collagen- and thrombin receptor activating peptide-induced maximum platelet aggregation and in platelet P-selectin expression in the presence of tegaserod at any time point when compared to placebo. Similarly, there was no significant difference in percentage change in serum TxB₂ or urinary 11-dhTxB₂ levels between placebo and tegaserod. No new or unexpected findings were observed in evaluations of safety or pharmacokinetic parameters.

This comprehensive pharmacodynamic study, by employing established markers used in prior investigations, which have been considered by the Food and Drug Administration to indicate drug-related platelet effects, does not demonstrate any influence of tegaserod treatment on platelet function.