Reply to Dr Hatipoglu et al and to Dr Mancini et al

First, we would like to remark that our study aim was uniquely to investigate the renal toxicity of a pharmacokinetics-pharmacodynamics (PK/PD)-driven colistin dosing approach for critically ill patients [2, 4] and was not to assess colistin efficacy. Accordingly, it was not a “resistance study”: because sequential samples for cultures were not routinely performed, and therapeutic drug monitoring was not available, the study was not aimed to relate colistin minimal inhibitory concentration (MIC) with individual drug exposure. Moreover, a colistin unexposed group was lacking and control for confounders in the spread of colistin resistance (eg, cross-transmission) was not allowed.