Eligible patients at the end of week @ ( those with a baseline potassium level of @ to < @ mmol per liter in whom the level decreased to @ to < @ mmol per liter ) entered an @-week randomized withdrawal phase in which they were randomly assigned to continue patiromer or switch to placebo ; the primary efficacy end point was the between-group difference in the median change in the serum potassium level over the first @ weeks of that phase .