Anti-drug-related antibodies in nonthrombocytopenic cardiac patients

Drug-related antibodies (quinidine, hydrochlorothiazide, and digoxin) were studied using the 51Cr platelet lysis test and a recently introduced simplified platelet factor 3 assay in a total of 109 patients admitted to a coronary care unit. Quinidine antibodies were found in 16 (14.7%), hydrochlorothiazide antibodies in six (5.5%) and digoxin antibodies in two (1.8%) of 109 patients. All patients had normal hematologic data, including platelet counts. There was a significantly high incidence of quinidine antibodies in male patients (p less than 0.02), despite the previous report that quinidine-induced purpura was seen predominantly in female patients. Ten patients (9.2%) had antiplatelet antibodies. The simplified platelet factor 3 assay can easily be done in most laboratories and appears as sensitive as the 51Cr platelet lysis test. The high incidence of drug-related or antiplatelet antibodies in hematologically asymptomatic patients may indicate the presence of an insidious, compensated thrombolytic state in many patients.