The overarching hypothesis of the ARRC trial is that administration of Azithromycin (AZM) during acute, Respiratory Syncytial Virus (RSV)-induced respiratory failure will be beneficial, mediated through the matrix metalloproteinase (MMP)-9 pathway.

The proposed study will be a randomized, double-blinded, placebo-controlled Phase III trial to examine the efficacy of AZM therapy relative to placebo in reducing RSV-related morbidity. Patients will be recruited during acute hospitalization and admission to the ICU at 10 pediatric hospitals. The target population selected is pediatric patients with severe RSV lung disease as defined by need for ICU management and intensive respiratory support.

Inclusion criteria:

• Admission to the pediatric ICU with a confirmed diagnosis of RSV infection. RSV infection is based on a positive nasal swab for RSV fluorescent antibody or via multiplex assay or culture;
• Requiring intensive respiratory support defined as either mechanical ventilation or NIV (BiPAP or CPAP) or HFNC (at >1 L/kg/min of flow
• Enrollment into the study within 48 hours of ICU admission and placement on intensive respiratory support;
• Onset of RSV-related symptoms must be less than 5 days
• Age: Neonates-2 years. For those less than 1 week of age, they must have been discharged home from the hospital after their birth.

Exclusion criteria:

• AZM use within 7 days of ICU admission;
• Contraindication to AZM use including known hypersensitivity to AZM, erythromycin, any macrolide, or ketolide drug, patients with significant hepatic impairment (direct bilirubin >1.5 mg/dL or ALT ≥ 10 times the upper limits of normal);
• Patients with known cardiac disease, cardiac arrhythmia or with electrocardiogram QT interval corrected for heart rate (QTc) ≥ 450 milisecond (ms);
• Intensive respiratory support greater than 48 hours prior to ICU admission;
• Chronic ventilation or supplemental oxygen need at home;
• Immunosuppressive conditions such as those post heart or hematopoietic stem cell transplant or receiving chemotherapy and chronic steroids;
• History of pyloric stenosis;
• AZM is deemed necessary for clinical treatment (for instance, if patient has pertussis).

To be determined.