Dose matters: Dose of antibiotics in the critically ill patient depends on the dose of renal replacement therapy:

How can we ensure effective antibiotic dosing in critically ill patients receiving different types of renal replacement therapy?

Determining appropriate antibiotic dosing for critically ill patients receiving renal replacement therapy (RRT) is complex. Worldwide unstandardized and heterogeneous prescribing of RRT as well as altered patient physiology and pathogen susceptibility all cause drug disposition to be much different to that seen in non-critically ill patients. Significant changes to pharmacokinetic parameters, including volume of distribution and clearance, could be expected, in particular, for antibiotics that are hydrophilic with low plasma protein binding and that are usually primarily eliminated by the renal system. Antibiotic clearance is likely to be significantly increased when higher RRT intensities are used. The combined effect of these factors that alter antibiotic disposition is that non-standard dosing strategies should be considered to achieve therapeutic exposure. In particular, an aggressive early approach to dosing should be considered and this may include administration of a 'loading dose', to rapidly achieve therapeutic concentrations and maximally reduce the inoculum of the pathogen. This approach is particularly important given the pharmacokinetic changes in the critically ill as well as the increased likelihood of less susceptible pathogens. Dose individualization that applies knowledge of the RRT and patient factors causing altered pharmacokinetics remains the key approach for ensuring effective antibiotic therapy for these patients. Where possible, therapeutic drug monitoring should also be used to ensure more accurate therapy. A lack of pharmacokinetic data for antibiotics during the prolonged intermittent RRT and intermittent hemodialysis currently limits evidence-based antibiotic dose recommendations for these patients.