Distinct in vitro Complement Activation by Various Intravenous Iron Preparations

Intravenous (IV) iron preparations are widely used in the treatment of anemia in patients undergoing hemodialysis (HD). All IV iron preparations carry a risk of causing hypersensitivity reactions. However, the pathophysiological mechanism is poorly understood. We hypothesize that a relevant number of these reactions are mediated by complement activation, resulting in a pseudo-anaphylactic clinical picture known as complement activation-related pseudo allergy (CARPA).

First, the in-vitro complement-activating capacity was determined for 5 commonly used IV iron preparations using functional complement assays for the 3 pathways. Additionally, the preparations were tested in an ex-vivo model using the whole blood of healthy volunteers and HD patients. Lastly, in-vivo complement activation was tested for one preparation in HD patients.

In the in-vitro assays, iron dextran, and ferric carboxymaltose caused complement activation, which was only possible under alternative pathway conditions. Iron sucrose may interact with complement proteins, but did not activate complement in-vitro. In the ex-vivo assay, iron dextran significantly induced complement activation in the blood of healthy volunteers and HD patients. Furthermore, in the ex-vivo assay, ferric carboxymaltose and iron sucrose only caused significant complement activation in the blood of HD patients. No in-vitro or ex-vivo complement activation was found for ferumoxytol and iron isomaltoside. IV iron therapy with ferric carboxymaltose in HD patients did not lead to significant in-vivo complement activation.

This study provides evidence that iron dextran and ferric carboxymaltose have complement-activating capacities in-vitro, and hypersensitivity reactions to these drugs could be CARPA-mediated.