Pharmacokinetics and Pharmacodynamics of Inorganic Nitrate in Heart Failure With Preserved Ejection Fraction

Rationale: Nitrate-rich beetroot juice has been shown to improve exercise capacity in heart failure with preserved ejection fraction, but studies using pharmacological preparations of inorganic nitrate are lacking. Objectives: To determine (1) the dose–response effect of potassium nitrate (KNO 3 ) on exercise capacity; (2) the population-specific pharmacokinetic and safety profile of KNO 3 in heart failure with preserved ejection fraction. Methods and Results: We randomized 12 subjects with heart failure with preserved ejection fraction to oral KNO 3 (n=9) or potassium chloride (n=3). Subjects received 6 mmol twice daily during week 1, followed by 6 mmol thrice daily during week 2. Supine cycle ergometry was performed at baseline (visit 1) and after each week (visits 2 and 3). Quality of life was assessed with the Kansas City Cardiomyopathy Questionnaire. The primary efficacy outcome, peak O 2 -uptake, did not significantly improve ( P =0.13). Exploratory outcomes included exercise duration and quality of life. Exercise duration increased significantly with KNO 3 (visit 1: 9.87, 95% confidence interval [CI] 9.31–10.43 minutes; visit 2: 10.73, 95% CI 10.13–11.33 minute; visit 3: 11.61, 95% CI 11.05–12.17 minutes; P =0.002). Improvements in the Kansas City Cardiomyopathy Questionnaire total symptom (visit 1: 58.0, 95% CI 52.5–63.5; visit 2: 66.8, 95% CI 61.3–72.3; visit 3: 70.8, 95% CI 65.3–76.3; P =0.016) and functional status scores (visit 1: 62.2, 95% CI 58.5–66.0; visit 2: 68.6, 95% CI 64.9–72.3; visit 3: 71.1, 95% CI 67.3–74.8; P =0.01) were seen after KNO 3 . Pronounced elevations in trough levels of nitric oxide metabolites occurred with KNO 3 (visit 2: 199.5, 95% CI 98.7–300.2 μmol/L; visit 3: 471.8, 95% CI 377.8–565.8 μmol/L) versus baseline (visit 1: 38.0, 95% CI 0.00–132.0 μmol/L; P <0.001). KNO 3 did not lead to clinically significant hypotension or methemoglobinemia. After 6 mmol of KNO 3 , systolic blood pressure was reduced by a maximum of 17.9 (95% CI −28.3 to −7.6) mm Hg 3.75 hours later. Peak nitric oxide metabolites concentrations were 259.3 (95% CI 176.2–342.4) μmol/L 3.5 hours after ingestion, and the median half-life was 73.0 (interquartile range 33.4–232.0) minutes. Conclusions: KNO 3 is potentially well tolerated and improves exercise duration and quality of life in heart failure with preserved ejection fraction. This study reinforces the efficacy of KNO 3 and suggests that larger randomized trials are warranted. Clinical Trial Registration : URL: http://www.clinicaltrials.gov . Unique identifier: NCT02256345