A Response to: “Letter to the Editor regarding ‘Impact of Continuous Renal Replacement Therapy with Polyacrylonitrile-Derived Filter on Caspofungin Concentration: A Retrospective Study'”

discussion.We also highlighted that studies specifically designed to explore early pharmacokinetics after filter change are mandatory to complement our findings.Massol et al. noted that our samples were obtained after several doses of caspofungin and not immediately after filter replacement.While we acknowledge the latter point, we would like to indicate that the median time from filter change to sampling was 31.5 h (21.5-63.5 h).This implies that one quarter of samples were collected after only one caspofungin dose with the new filter, and half after only two doses, given the once-daily regimen.In such a context, filter saturation may have been limited.To further investigate this phenomenon, the elegant in vitro model used by Baud et al. [3], could be applied with repeated caspofungin dosing to better characterize adsorption and saturation kinetics.Such data might help guide specific dosing regimens of caspofungin in patients undergoing CRRT with polyacrylonitrile (PAN) filters.Regarding the second point, Massol et al. suggested that our comparative arm was not completely free from sequestration, and founded their argumentation on unpublished in vitro findings that polysulfone membranes may also adsorb caspofungin.While these data are of great interest, we would like to clarify that the non-PAN group in our study included a majority of patients without any form of kidney