The Preventive Antibiotics in Stroke Study (PASS) is an ongoing, phase III, multicenter, prospective, randomized, open-label, blinded end-point (PROBE) trial of preventive antibiotic therapy in acute stroke that started in 2010 (ISRCTN-number: 66140176). Patients presenting with stroke (symptoms less than 24 h) are randomly assigned to either ceftriaxone at a dose of 2 g, given every 24 h intravenously for four-days, in addition to stroke-unit care, or standard stroke unit care without preventive antibiotic therapy. The aim of the study is to assess whether preventive antibiotic treatment improves functional outcome at three-months at the modified Rankin Scale (mRS). Currently, more than 2400 patients have been enrolled. In the initial trial protocol we presented a dichotomized analysis of on the mRS (0–2 vs. 3–6) as primary outcome, requiring a sample size of 3200 patients, and a proportional odds model in a secondary analysis of the primary end-point . Blinded for any of the outcomes, we have changed the primary analysis in PASS from dichotomization to ordinal regression on the mRS, enhancing statistical power . A new power analysis showed that with identical assumptions on the clinical effect, using a 0·05 two-sided significance level and 80% study power, 2550 patients are needed. The dichotomized analysis will be the secondary analysis of the primary end-point. We expect to complete our trial in June 2014.