Using PK/PD to optimize antibiotic dosing for critically ill patients.

Antibiotic prescription for critically ill patients is a complicated process because of the pharmacokinetic differences of this patient population with non-critically ill patients and the lack of robust informative studies. This article seeks to review the available literature describing dosing requirements for optimized treatment of critically ill patients and to discuss a framework to rationally address complex cases by outlining the suggested processes for optimal achievement of pharmacokinetic/ pharmacodynamic targets. A variety of papers exist describing the effect of pathophysiology on antibiotic kinetics. In the critically ill patient, dysfunction of almost any organ system can result in significant changes to drug volume of distribution and clearance. Dysfunction of the cardiovascular and renal systems in particular is problematic and can lead to potentially sub-therapeutic antibiotic concentrations in blood and in interstitial fluid. In response to altered pharmacokinetics, dose regimens that adhere to the pharmacodynamics of the antibiotic are essential. In the absence of validated dosing algorithms, therapeutic drug monitoring data and susceptibility data of the infecting pathogen should be inputted into a Bayesian software program that include population pharmacokinetic models to calculate dosing regimens that are personalized for the critically ill patient.