The goal of this study is to compare two different ways of dosing cefepime, an antibiotic for very sick patients - the usual approach to dosing or a new dosing method. The new dosing method uses only doses that are available in normal care, but choosing between the different doses is based on more information about the patient's body including their kidney function. The primary purpose of this study is to test how easy it is for healthcare professionals to use the new dosing method and how best to conduct the trial. The study will also assess if the new dosing method helps patients recover faster and reduces side effects.