Bacterial Lipopolysaccharide Retention by a Positively Charged Filter

We read with interest the recent paper by Bononi and colleagues (2) concerning the capacity of positively charged membranes to remove endotoxins from solutions intended for intravenous administration. This study raises two issues of concern that should be made known to your readership.

First, the abstract of the article was incorrect in stating that “to date no filters have retained bacterial endotoxins.” Pall Corporation has manufactured positively charged, membrane-based intravenous filter products with a claim for the removal of bacteria and associated endotoxins for the health care community for over two decades. Evidence corroborating this fact is readily available in the peer-reviewed literature (1, 3, 4). We are pleased to see that the results demonstrated by Bononi and colleagues further substantiate the findings in these published works.

Second, there are historical data to suggest that filter performance is influenced by the ionic strength of a salt solution, with filtration efficacy decreasing as ionic strength increases (5). Although the filters evaluated in the referenced studies show performance in the presence of physiologic levels of salt, Bononi and colleagues did not challenge their test filters with saline-based solutions. This leaves open the question of whether or not, in a clinical setting, the new-generation positively charged filters tested will reduce the risk associated with infusing salt-containing intravenous solutions inadvertently contaminated with gram-negative bacteria and associated endotoxins.

We encourage the authors to further characterize this filter, and we look forward to the results of such studies employing more clinically relevant salt-containing intravenous solutions.