A rare case presentation of rifampin induced idiopathic thrombocytopenia purpura The most common cause of acute onset of thrombocytopenia in an otherwise well child is (autoimmune) idiopathic thrombocytopenic purpura (ITP). In a small number of children, estimated at 1 in 20,000, 1-4 wk after exposure to a common viral infection, an autoantibody directed against the platelet surface develops with resultant sudden onset of thrombocytopenia. A recent history of viral illness is described in 50–65% of children with ITP. The peak age is 1-4 yr, although the age ranges from early in infancy to elderly. In childhood, males and females are equally affected. ITP seems to occur more often in late winter and spring after the peak season of viral respiratory illness. The exact antigenic target for most such antibodies in most cases of childhood acute ITP remains undetermined, although in chronic ITP many patients demonstrate antibodies against αIIb-β3 and GPIb. After binding of the antibody to the platelet surface, circulating antibodycoated platelets are recognized by the Fc receptor on splenic macrophages, ingested, and destroyed. Most common viruses have been described in association with ITP, including Epstein-Barr virus (EBV; see Chapter 281) and HIV (see Chapter 302). EBV-related ITP is usually of short duration and follows the course of infectious mononucleosis. HIV-associated ITP is usually chronic. In some patients, ITP appears to arise in children infected with Helicobacter pylori or rarely following vaccines and after some drugs include valproic acid, phenytoin, carbamazepine, sulfonamides, vancomycin, and trimethoprim-sulfamethoxazole and in rare cases rifampicin.