This was a multi-centre, pan-European, randomised double-blind placebo-controlled clinical trial in acute stroke to evaluate the effect of ancrod, a natural defribrinogenating agent (Hennerici et al. (2006)). The primary endpoint was based on the Barthel Index; a favourable score of 95 or 100 or a return to the pre-stroke level at three months was viewed as a success. The primary method of statistical analysis was based on a logistic model including terms for treatment, age category, baseline Scandinavian Stroke Scale and centre.
The proposed sample size was 600 patients and two interims were planned after 200 and 400 patients (completing 3 months follow-up) using the O'Brien and Fleming scheme with adjusted two-sided significance levels of 0.00052, 0.014 and 0.045. A futility rule was also introduced, based on conditional power (under the current trend) being below 30 per cent for the trial to be stopped.
Safety was a concern and a formal rule was implemented (Bolland and Whitehead (2000)) with an overall one-sided type I error of 0.025 and 90 per cent power to detect an excess death rate in the ancrod group of 29 per cent compared to 18 per cent on placebo. This sequential plan was updated following the recruitment of every 20 patients.
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