Polypharmacy and Drug Interaction Risk in Children and Adolescents with Congenital Heart Defects: Insights from a Nationwide Survey

Background: Congenital heart defects (CHD) are the most common congenital malformations and often require complex, lifelong pharmacotherapy. In pediatric CHD populations, multidrug regimens targeting cardiac function and comorbidities predispose patients to polypharmacy. At the molecular level, concomitant drug use increases the risk of pharmacokinetic and pharmacodynamic interactions. Methods: This study aimed to characterize medication patterns and assess polypharmacy and potential drug–drug interactions in patients with CHD. A cross-sectional online survey was conducted in collaboration with the German National Register for Congenital Heart Defects (NRCHD) between November and December 2021. Patients aged 6–17 years with CHD were eligible for inclusion. Participants reported their current medications in open-ended questions. Drugs were categorized into pharmacological classes, and common drug combinations were evaluated for potential interactions. Results: Of 894 participants included in the analysis, 372 reported current medication use. Among these, 179 (48.1%) met criteria for polypharmacy (≥2 drugs). Polypharmacy was more frequent in patients with higher disease severity and comorbidity burden. Several drug combinations showed potential for clinically relevant pharmacokinetic and pharmacodynamic interactions, including mechanisms involving renal electrolyte handling, altered protein binding, cytochrome P450-mediated metabolism, and additive pharmacodynamic effects. Conclusions: Children with CHD are exposed to complex multidrug regimens with a considerable interaction risk, underscoring the need for systematic medication review and mechanistically informed pharmacological management in pediatric CHD care.