Response to Letter

W e thank Dr. Rasmussen for his recent letter expressing concerns about statements made in our article with regard to the efficacy of sodium zirconium cyclosilicate (ZS-9) in patients with serum potassium (K ) concentrations 6.5 mEq/L. Although ZS-9 is certainly one of the potential agents for the treatment of acute hyperkalemia in the future, the HARMONIZE trial (1) was conducted in an outpatient setting and did not include hospitalized patients. Moreover as mentioned in our article (2), the mean K level in the HARMONIZE trial was 5.6 mEq/L with only nine patients with baseline serum K 6.5 mEq/L. While the substudy (3) quoted by the authors showed a significant decline in the mean serum potassium level (0.4 and 0.6 mmol per liter at 1 and 2 hours, respectively), it had a mean baseline serum K of 6.3 mEq/L (95% CI 6.2 6.4). We do agree that due to the significant limitations of the existing treatment options, it is highly likely that ZS-9 with its low side-effect profile in the trials seems to be aviable alternative. However, large-scale randomized control trials looking at ZS-9 in the acute setting with severe hyperkalemia will be needed to implement it in clinical practice.