Results of the preplanned interim analysis ( n = 15 in each group ) of the primary endpoint showed that futility criteria had been met , and the trial was stopped ( the mean rate of change [ slope analysis ] of UMSARS I score was 0.62 points [ SD 0.85 ] per month in the rifampicin group vs 0.47 points [ 0.48 ] per month in the placebo group ; futility p = 0.032 ; efficacy p = 0.76 ) .