The relevance of drug volume of distribution in antibiotic dosing

Despite the importance of early an appropriate therapy for the outcomes of severe infections in critically ill patients, there is still little understanding of dose optimization during the most important phase of the treatment, the initial phase. Disease-driven variations in pharmacokinetics and pharmacokinetics/ pharmacodynamics may compromise the therapeutic success of antibiotic therapy. Therefore, dose adjustments that account for these variations are paramount for improving antibiotic use in critically ill patients. Compelling evidence shows significant increases in the Vd of both hydrophilic and lipophilic drugs in critically ill patients as a consequence of patient pathology and from clinical interventions. These increases in the Vd can lead to lower than expected plasma concentrations during the first day of therapy, which may result in sub-optimal achievement of antibiotic pharmacokinetics/pharmacodynamic targets, resulting in inappropriate treatment. Therefore, loading doses of antibiotic during the first day of therapy that account for the predicted increase in the Vd are required. Further research towards the establishment of new dosing regimens that use loading doses to satisfy such increased volumes of distribution is recommended.