In patients who received 5 g of ZS-9 and those who received 10 g of ZS-9 , serum potassium levels were maintained at 4.7 mmol per liter and 4.5 mmol per liter , respectively , during the maintenance phase , as compared with a level of more than 5.0 mmol per liter in the placebo group ( P < 0.01 for all comparisons ) .