TO THE EDITOR
It is with interest that we read the study by Rojas et al on colistin resistance in carbapenem-resistant Klebsiella pneumoniae(CRKp), which occurred in 13% (n = 31) of their isolates . The authors found that colistin exposure was uncommon in the cohort as a whole and occurred in only 6/27 (22%) patients with colistin-resistant isolates, for whom treatment data was available beyond 14 days prior to infection. This finding is surprising given that colistin exposure has been associated with colistin resistance in multiple studies, mainly from outbreak settings in southern Europe [2–6]. One important question that arises from these findings is how far back clinical records were available and the length of time for colistin administration....
One important question that arises from these findings is how far back clinical records were available and the length of time for colistin administration.
In order to e ectively prioritize future interventions, we must accurately understand the relative importance of de novo resistance to polymyxins vs resistance due to previous drug exposure.
We retrospectively evaluated cases of polymyxin-resistant CRKp (PR-CRKp) infections in our institution from 2011 to 2016, where polymyxin B is the preferred agent.
We identied 88 patients with PR-CRKp, 81 of whom had been admitted to our institution during the 6 months prior to isolation of PR-CRKp.
Of those, 40/81 (49%) received polymyxin prior to detection of PR-CRKp (median 21.4 days before detection; interquartile range [IQR], 12.1–36.0 days).
Polymyxin was given for a median cumulative duration of 12.0 days prior to PR-CRKp detection IQR, 8.2–21.4 days).
Nebulized colistin was given concurrently to 11 patients (median cumulative duration, 16.4 days; IQR, 10.0–20.3 days).
None of the patients had received nebulized colistin alone prior to PR-CRKp.
Previous exposure to polymyxins appears to be an important risk factor for future resistance to these agents and underlines the need for their rational use.
While antimicrobial stewardship remains of the utmost importance, recent evidence regarding the pharmacology of polymyxins may assist in optimizing dosing to prevent the emergence of resistance.
Future studies will need to assess whether therapeutic drug monitoring may have a role in improving outcomes and preventing emergence of resistance to polymyxins.