Time course of DDAB titer development and platelet count.

Patients with a negative DDAB prescreen using citrated plasma were treated with roxifiban for 5 days (qualification period), followed by a drug holiday for 10 days. During the drug holiday, antibody development was monitored on days 7 and 14. (A) The prescreen citrated plasma for patient 99016 was negative for DDABs to roxifiban. Antibody binding, denoted as delta, is determined by the difference in IgG bound to purified GP IIb/IIIa in the presence of roxifiban to that in the absence of roxifiban. The patient was treated with roxifiban for 5 days and developed severe thrombocytopenia on day 14. The time course of DDAB reactivity (●) and decrease in platelet count (♦) is indicated. (B) Prescreen citrated plasma samples of patient 99016, as well as peak DDAB samples, were reanalyzed by the DDAB ELISA. The washing steps with an automated plate washer were replaced by gentle “hand washing” using a multichannel pipettor. Note that the prescreen of patient 99016 is clearly positive using these assay modifications. (C) An increase in antibody concentration was observed in 5 additional patients (identified by ID numbers). Patients were excluded from the study based on a confirmed positive test result and participated in follow-up antibody testing. The antibody development (Delta ELISA) as a function of time is indicated (day 1 equals start of qualification period). The platelet counts did not change significantly from baseline values.