Abstract Body (Do not enter title and authors here): Background
The Etanercept as Adjunctive Treatment for Acute Kawasaki Disease study, a phase 3 randomized placebo-controlled clinical trial, evaluated etanercept, a TNF-alpha inhibitor, as an adjunct to IVIg for Kawasaki Disease (KD). In children presenting with coronary artery (CA) aneurysm, etanercept resulted in reduction in progression of CA dilation and earlier aneurysm regression compared to placebo. Following study conclusion, our institution implemented etanercept as a first line IVIg adjunctive treatment for patients presenting with early CA aneurysm formation.

Hypothesis
Real world use with etanercept as adjunct to IVIg in children with KD and CA aneurysm shows high patient compliance, is safe and results in early CA regression.

Methods
We reviewed charts and echocardiograms for all children admitted to Seattle Children’s Hospital from 5/2019 to 4/2024 and treated with etanercept for KD with CA aneurysms at presentation (Z-score ≥2.5 per AHA aneurysm definition). Etanercept is injected subcutaneously at 0.8 mg/kg with IVIg at diagnosis and then with 2 repeat weekly doses at outpatient visits.

Results
Thirty-six patients with KD and CA aneurysms received at least one dose of etanercept. Sixteen (44%) were <1 year of age, 17 (47%) were diagnosed with incomplete KD and 5 (14%) were ‘IVIg refractory.’ Four patients responded to a second IVIg dose and two patients received additional biologic agents. Thirty-two patients completed the 3-dose course of etanercept, with outpatient doses administered 6.6±1.5 days (mean±SD) and 13.5±2.3 days after the first. Seven patients had giant CA aneurysms (Z-score ≥10) requiring anticoagulation. In patients with giant aneurysms and at least 6-month follow-up, all aneurysms regressed to below the threshold for requiring anticoagulation beyond aspirin. Of 31 children with long-term follow-up echocardiograms available, 19 had complete resolution (Z-score <2.5) of CA dilation by 6 months, 22 by 1 year, and 29 by 2-year follow-up. No severe or serious adverse events were attributed to etanercept.

Conclusions
Etanercept for KD with early CA aneurysms was delivered safely and with high compliance. CA aneurysm regression occurred in most patients with marked reduction in giant CA aneurysms by 6 months. These real-world data support the use of etanercept as an intensification therapy for preventing persistence of CA aneurysms in KD.