Zeta potential and vancomycin-red blood cell interactions.

Vancomycin hydrochloride is a polycationic antibiotic that we have previously reported to cause spontaneous aggregation of red blood cells (RBCs) in vitro at concentrations of more than 3.0 mg/mL, and false-positive direct antiglobulin tests at concentrations of 2.0 and 2.5 mg/mL. These latter reactions were abolished when the RBCs were pretreated with the proteolytic enzyme ficin suggesting an interaction with sialoglycoproteins. In this study we show that prior addition of vancomycin did not block binding of antibodies to several blood group antigens, nor does vancomycin precipitate in an Ouchterlony assay with any of several sialic acid moieties. Finally, we show that vancomycin possesses fluorescent properties but fails to be detected on the RBC surface by flow cytometry. These data indicate that vancomycin may be acting through its polycationic properties. Our findings do not support protein binding of vancomycin to the RBC surface, but underline the importance of the zeta potential in RBC serologic reactions.