Cianidanol and its metabolites bind tightly to red cells and are responsible for the production of auto- and/or drug-dependent antibodies against these cells.

Cianidanol ((+)-2-(3,4-dihydroxyphenyl)-3, 5, 7-chromantriol) is a flavonoid which has been associated with severe immune haemolysis by as yet unclear mechanisms. We report six patients who developed haemolysis while receiving the drug. The disorder was episodic in all patients and resolved after discontinuing the drug. The causative antibodies could be demonstrated in all six cases, even when the haemolytic episode was more than 1 year prior to this study. One patient had developed drug-independent IgG autoantibodies, another simultaneously developed autoantibodies and drug-dependent antibodies (ddab) of the IgG class, while the remaining four patients had only ddab of the IgM and/or the IgG classes. All ddab were reactive with red blood cells (RBC) in the presence of the drug and/or its metabolites (ex vivo antigens), and, quite unexpectedly, also with RBC coated with the drug (metabolites) in vitro or in vivo. This reactivity did not change either by preincubating the antibodies with the drug or by adding large amounts of the drug to the mixture of drug-coated cells plus antibody. It seems that the stable association of cianidanol with RBC generates antigenic sites against which a heterogeneous immune response is elicited giving rise to long-lasting drug-dependent antibodies as well as autoantibodies.