Intravenous alteplase (rtPA) remains the only approved treatment for acute ischemic stroke, but its use remains limited. In a previous pilot dose-escalation study, intravenous tenecteplase showed promise as a potentially safer alternative. Therefore, a Phase IIB clinical trial was begun to (1) choose a best dose of tenecteplase to carry forward; and (2) to provide evidence for either promise or futility of further testing of tenecteplase versus rtPA. If promise was established, then the trial would continue as a Phase III efficacy trial comparing the selected tenecteplase dose to standard rtPA. The trial began as a small, multicenter, randomized, double-blind, controlled clinical trial comparing 0.1, 0.25, and 0.4 mg/kg tenecteplase with standard 0.9 mg/kg rtPA in patients with acute stroke within 3 hours of onset. An adaptive sequential design used an early (24-hour) assessment of major neurological improvement balanced against occurrence of symptomatic intracranial hemorrhage to choose a "best" dose of tenecteplase to carry forward. Once a "best" dose was established, the trial was to continue until at least 100 pairs of the selected tenecteplase dose versus standard rtPA could be compared by 3-month outcome using the modified Rankin Scale in an interim analysis. Decision rules were devised to yield a clear recommendation to either stop for futility or to continue into Phase III. The trial was prematurely terminated for slow enrollment after only 112 patients had been randomized at 8 clinical centers between 2006 and 2008. The 0.4-mg/kg dose was discarded as inferior after only 73 patients were randomized, but the selection procedure was still unable to distinguish between 0.1 mg/kg and 0.25 mg/kg as a propitious dose at the time the trial was stopped. There were no statistically persuasive differences in 3-month outcomes between the remaining tenecteplase groups and rtPA. Symptomatic intracranial hemorrhage rates were highest in the discarded 0.4-mg/kg tenecteplase group and lowest (0 of 31) in the 0.1-mg/kg tenecteplase group. Neither promise nor futility could be established. This prematurely terminated trial has demonstrated the potential efficiency of a novel design in selecting a propitious dose for future study of a new thrombolytic agent for acute stroke. Given the truncation of the trial, no convincing conclusions can be made about the promise of future study of tenecteplase in acute stroke.
