PROJECT SUMMARY/ABSTRACT Amoxicillin is recommended by the World Health Organization (WHO) as adjunctive therapy for the treatment of uncomplicated severe acute malnutrition (SAM). Because children with uncomplicated SAM may have asymptomatic infection due to immune suppression, presumptive treatment with a broad-spectrum antibiotic may be beneficial by clearing any existing infection and improving outcomes. Two randomized placebo- controlled randomized trials have evaluated amoxicillin for uncomplicated SAM and have found conflicting results. These results may indicate either that antibiotics are not helpful for the management of uncomplicated SAM, or that a better antibiotic is needed. Recently, we demonstrated that biannual mass azithromycin distribution as a single oral dose reduces all-cause child mortality in sub-Saharan Africa. Children with uncomplicated SAM, who have an elevated risk of mortality relative to their well-nourished peers, may particularly benefit from presumptive azithromycin treatment. Our pilot data demonstrated feasibility in rapid enrollment of children with uncomplicated SAM in our study area, and showed no significant difference between azithromycin and amoxicillin, demonstrating equipoise for a full-scale trial. Here, we propose an individually randomized trial in which children will be randomized to a) azithromycin, b) amoxicillin, or c) placebo, and evaluated for differences in weight gain, nutritional recovery, and the gut microbiome. The results of this study will strengthen the evidence base for policy related to the use of antibiotics as part of the management of uncomplicated SAM, including additional evidence of amoxicillin versus placebo as well as evaluation of an antibiotic class that has not been considered for uncomplicated SAM, which may lead to changes in guidelines for treatment.