Digoxin Pharmacodynamics in Infants with Heart Failure due to Single Ventricle Congenital Heart Disease

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In infants with single ventricle congenital heart disease (SVD), heart failure is deadly. Each year 30% of infants hospitalized with heart failure due to SVD die, and 25% require cardiac transplant. This unacceptable morbidity and mortality is due to both the anatomic abnormalities of SVD unfavorably loading the infant myocardium, and the lack of drugs proven efficacious in this population. The absence heart failure therapeutics in infants with SVD is a public health crisis, necessitating an urgent and systematic response to address drug development challenges in this population. Recently, the Na+/K+-ATPase inhibitor digoxin was the first ever drug found in retrospective studies to improve survival in infants with SVD. Despite this promising finding, therapeutic failures occurred. While the cause of failures may be multifactorial, the experience with digoxin in heart failure due to SVD illustrates the knowledge gaps and limitations of current pediatric heart failure drug development. Digoxin is a narrow therapeutic index drug renally eliminated via glomerular filtration. While pharmacokinetics (PK) and exposure targets are known in adults, the PK and pharmacodynamics (PD) of digoxin have not been studied in infants with SVD. In this population, growth and maturation dynamically interact with disease pathophysiologic changes to affect drug disposition and response. For digoxin, renal maturation and kidney injury oppositely affect drug exposure, while the infantile cardiomyocyte, the digoxin target, is structurally, metabolically, and functionally altered by immaturity and SVD. Though incompletely understood, these interactions likely affect digoxin efficacy through differing exposure, response, or both. Understanding how ontogeny and disease interact to alter drug exposure and response is essential to reducing treatment failures and inform development of new heart failure drugs for infants with SVD. Despite the high