Interim analyses will be conducted every 25% of the maximum planned enrollment using a groups sequential design to test for efficacy and futility. We will use a gamma spending function (gamma = -4 for efficacy and -2 for futility) to maintain the significance level for the primary outcome at 2.5% and the power at 90% across the interim analyses. Significance criteria for all tests will be adjusted for interim analyses based on the above-mentioned gamma spending function and the corresponding z-statistic at teach interim look.