Abstract Body (Do not enter title and authors here): Introduction: There are limited data on the medications taken by patients with Fontan circulation in adult congenital heart disease (ACHD) clinics.

Research Questions/Hypothesis: We aim to describe the type and frequency of medications prescribed to adults with Fontan circulation and hypothesize that patients with higher medication burden have worse outcomes.

Methods: We conducted a retrospective cohort study of adults with Fontan circulation followed in an outpatient ACHD clinic between 2009 and 2023. Demographics, clinical variables, and all prescribed outpatient cardiac medications were abstracted. The outcome of interest was transplant-free survival. Survival analysis was performed to evaluate the impact of medication type and burden on survival.

Results: There were 429 patients (55.2% male, 72.5% White, 49.7% systemic left ventricle) with median age 29 years (IQR 25-35) at last visit. The commonly prescribed medication classes were antiplatelet agents (74.6%) followed by angiotensin converting enzyme inhibitors or angiotensin receptor blockers (59.0%), beta blockers (44.8%), anticoagulants (44.0%), loop diuretics (39.6%), mineralocorticoid receptor antagonists (MRA) (31.5%), antiarrhythmics (19.6%), and pulmonary vasodilators (16.1%). There were a smaller number of patients prescribed sacubitril-valsartan (0.9%) and sodium glucose cotransporter 2 inhibitors (1.9%). Being prescribed loop diuretics, antiarrhythmics, pulmonary vasodilators, or MRA was associated with decreased transplant-free survival (Table). There is a stepwise decrease in transplant-free survival with increasing number of cardiac medication classes prescribed (Figure).

Conclusions: We report one of the first large-scale studies of prescription patterns in adult patients with Fontan circulation in a single ACHD clinic. We demonstrate an association between increasing number of medications with transplant-free survival.