At 48 hours , the mean serum potassium level had decreased from 5.3 mmol per liter at baseline to 4.9 mmol per liter in the group of patients who received 2.5 g of ZS-9 , 4.8 mmol per liter in the 5-g group , and 4.6 mmol per liter in the 10-g group , for mean reductions of 0.5 , 0.5 , and 0.7 mmol per liter , respectively ( P < 0.001 for all comparisons ) and to 5.1 mmol per liter in the 1.25-g group and the placebo group ( mean reduction , 0.3 mmol per liter ) .