The investigators are planning a large clinical trial to assess the efficacy of ceftriaxone and metronidazole on mortality, nutritional recovery and antimicrobial resistance in sick, severely malnourished children. This preparatory work aims to determine the pharmacokinetics of ceftriaxone and metronidazole in 80 severely malnourished children who are admitted to three hospitals in Kenya in order to ensure dosing for the main trial is safe and in the therapeutic range. The study will also determine the frequency of faecal carriage of antimicrobial resistant enteric bacteria at presentation to hospital and at discharge following exposure to antibiotics and the hospital environment, comparing 360 children with, and 360 children without severe malnutrition at three different hospitals. Clear data on the benefits, risks and pharmacokinetics of these antimicrobials will influence policy on case management and antimicrobial stewardship in this vulnerable population.