Immune thrombocytopenia due to Tranilast (Rizaben): detection of drug-dependent platelet-associated IgG.

Tranilast (Rizaben)-induced thrombocytopenia occurring in a 17-year-old man was reported. After withdrawal of the drug, he recovered within a week with oral prednisolone administration. Serological examination revealed no anti-platelet antibody, but platelet-associated IgG (PAIgG) was found. After incubation of peripheral blood of the patient with the drug in vitro, the level of PAIgG was significantly increased. These findings suggest the presence of a drug-dependent anti-platelet IgG in the patient's serum. This is the first report of immune thrombocytopenia caused by Tranilast. Our method for detecting drug-dependent platelet antibody in vitro is safe and useful for diagnosing drug-induced thrombocytopenia.