January 13th, 2011
Merck’s Thrombin Receptor Antagonist Suffers Major Setback
Larry Husten, PHD
Merck’s thrombin receptor antagonist, vorapaxar, has suffered a major setback in its clinical trial program. In one trial, TRACER, the study drug is being discontinued and the trial will be closed out. The second trial, TRA-2P TIMI 50, is being curtailed but not stopped. The actions were based on recommendations from the combined Data and Safety Monitoring Board for the trials. In a letter to investigators from the study chairs, no explanations were offered about the reasons for the changes. Vorapaxar is a selective protease activated receptor 1 (PAR-1) thrombin receptor antagonist intended to fight clot formation.
In TRACER, 13,000 hospitalized ACS patients were randomized to placebo or vorapaxar in addition to standard care. Merck announced that TRACER had accumulated the predefined number of primary and major secondary endpoints, but not all patients had received the drug for the prespecified one-year followup.
In TRA-2P TIMI 50, more than 25,000 patients with MI, ischemic stroke, or peripheral vascular disease were randomized to either vorapaxar or placebo in addition to standard care for the secondary prevention of MI and stroke. Merck said that vorapaxar would be discontinued in patients who experienced a stroke prior to entry or during the trial. The study drug will be continued in patients with previous MI or peripheral disease, representing approximately three-quarters of the study population.
In the letter to investigators from the study chairmen at the Duke Clinical Research Institute and the TIMI group, no explanations for the actions were presented.
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