P2.247: One-Two Punch: Successful Synergistic Use of Cefazolin and Ertapenem in Methicillin Susceptible Staphylococcus Aureus Endocarditis

Introduction: Staphylococcus aureus is the leading cause of endocarditis in pediatrics. Methicillin susceptible (MSSA) isolates respond well to intravenous (IV) cefazolin. Prolonged bacteremia is associated with increased morbidity and mortality. In adults, dual therapy with cefazolin and ertapenem has been utilized synergistically to clear MSSA bacteremia. We describe a case of MSSA endocarditis with successful blood clearance using cefazolin and ertapenem synergistic therapy previously only reported in the adult population.

Case Description: A previously healthy 9-year-old female presented to the emergency department after her pediatrician found bilateral pulmonary nodules with central cavitation on computed tomography of the chest following four weeks of productive cough associated with sternal pain, post-tussive emesis, and tactile fevers. On presentation, she was in shock with fever, tachycardia, hypoxia, and hypotension prompting treatment with broad-spectrum antibiotics, fluid, and norepinephrine. A harsh systolic murmur prompted an echocardiogram revealing severe tricuspid regurgitation with an echogenic mobile mass attached to the septal and anterior leaflets of the tricuspid valve, flail segment, and a mobile echogenic mass in RV attached to interventricular septum, consistent with a ruptured papillary muscle. Blood cultures grew MSSA within 16 hours. She was placed on IV cefazolin, 150mg/kg/day divided every 8 hours. Four subsequent blood cultures obtained at six and 24 hours were positive within 16 hours of collection. The final positive blood culture, obtained 36 hours after cefazolin, was positive at 22 hours. Ertapenem, 30 mg/kg/day divided every 12 hours was added to her regimen at 36 hours and blood cultures sterilized within 24 hours of initiation. She underwent surgical resection of the vegetation and tricuspid valve repair. Surgical tissue was positive for MSSA. Ertapenem was discontinued two days post-operatively. She remained inpatient for two weeks. Her course was complicated by pleural effusion requiring a chest tube, pericardial effusion w/o tamponade responded to steroids and ibuprofen, and a 1-day CICU stay for fluid overload. She has since completed a 6-week course of cefazolin with excellent recovery.

Discussion: Infective endocarditis is rare in pediatrics. Bacteremia lasting over 3 days is a high predictor of mortality. Mortality and morbidity remain high despite improvements in identification and treatment. Ertapenem has been utilized as salvage therapy alongside cefazolin in MSSA bacteremia in adults; however, we do not know of reports as a synergistic choice in pediatrics. Notably, blood cultures sterilized immediately after starting ertapenem in this patient with a large burden of valvular disease. Additional studies are needed to clarify the effect of synergistic therapy with cefazolin and ertapenem.

Conclusion: This case highlights the potential utility of ertapenem in pediatric MSSA bacteremia and endocarditis. Additionally, it demonstrates the potential benefits of research into antibiotic synergy in pediatrics to reduce morbidity and mortality from infection.