Thrombocytopenic purpura following iopanoic acid ingestion.

A 48-year-old woman had severe symptomatic thrombocytopenia three times in 13 months. Each episode followed ingestion of iopanoic acid. The interval between drug ingestion and onset of symptoms was 40, 12, and 8 hours. Resolution to normal platelet counts occurred in 6, 5, and 8 days. The third thrombocytopenic crisis occurred while the patient was receiving maintenance steroid therapy, given because the initial diagnosis was idiopathic thrombocytopenic purpura. Incubation of platelet-rich plasma with the patient's serum caused platelet lysis if either the patient or the donor serum obtained after ingestion of iopanoic acid was present in the mixture.