BACKGROUND: Infants under 6 months (U6M) contribute a significant proportion of the burden and mortality of severe malnutrition globally. Evidence of underlying aetiology in this population is sparse, but it is known that the group includes ex-preterm and low birthweight (LBW) infants. They represent a unique population given their dependence on breastmilk or a safe, secure alternative. Nutrition agencies and health providers struggle to make programming decisions on which interventions should be provided to this group based upon the 2013 WHO Guidelines for the 'Management of Severe Acute Malnutrition in Infants and Young Children' since there are no published interventional trial data focussed on this population. Interim guidance for this group might be informed by evidence of safety and efficacy in adjacent population groups. METHODOLOGY: A narrative literature review was performed of systematic reviews, meta-analyses and randomised controlled trials of antimicrobial and micronutrient interventions (antibiotics, deworming, vitamin A, vitamin D, iron, zinc, folic acid and oral rehydration solution (ORS) for malnutrition) across the population groups of low birthweight/preterm infants, infants under 6 months, infants and children over 6 months with acute malnutrition or through supplementation to breastfeeding mothers. Outcomes of interest were safety and efficacy, in terms of mortality and morbidity. RESULTS: Ninety-four articles were identified for inclusion within this review. None of these studied interventions exclusively in severely malnourished infants U6M. 64% reported on the safety of studied interventions. Significant heterogeneity was identified in definitions of study populations, interventions provided, and outcomes studied. The evidence for efficacy and safety across population groups is reviewed and presented for the interventions listed. CONCLUSIONS: The direct evidence base for medical interventions for severely malnourished infants U6M is sparse. Our review identifies a specific need for accurate micronutrient profiling and interventional studies of micronutrients and oral fluid management of diarrhoea amongst infants U6M meeting anthropometric criteria for severe malnutrition. Indirect evidence presented in this review may help shape interim policy and programming decisions as well as the future research agenda for the management of infants U6M identified as malnourished.