Triamterene-induced immune haemolytic anaemia with acute intravascular haemolysis and acute renal failure.

Acute intravascular haemolysis and renal failure developed while a patient was taking triamterene. A direct antiglobulin test with a polyvalent reagent was positive. Serum caused agglutination of normal red cells in the presence of triamterene and caused an increase of partial haemolysis of both trypsin-treated erythrocytes and red cells from a patient with paroxysmal nocturnal haemoglobinuria (PNH) in the presence of complement. From the results of antibody-neutralization test and treatment with 2-mercaptoethanol, the presence of IgM antibody with lambda light chain could be demonstrated. The triamterene seemed to bind strongly to the red cells in vitro but in vivo there was no detectable adsorption to red cells. Haptenic inhibition was not demonstrated. From these results, it was assumed that this antibody was found to cross-react with methotrexate which has a structure similar to that of triamterene.