A whole blood assay of inhibition of platelet aggregation by glycoprotein IIb/IIIa antagonists: Comparison with other aggregation methodologies

We have used a whole blood single-platelet counting assay (WB SPC) that is sensitive to microaggregation for monitoring GPIIb/IIIa antagonists and hav e compared this with other methodologies. In vitro effects of the GPIIb/III a antagonist fradafiban on ADP-induced platelet aggregation were determined using WBSPC and PRP turbidimetry, comparing citrate and hirudin anticoagul ation. Fradafiban was a more potent inhibitor of aggregation assessed by PR P turbidimetry compared to WBSPC. Citrate showed only a trend towards enhan cing fradafiban potency (p = 0.087). Citrated blood from 8 patients with un stable angina, randomised to receive oral lefradafiban (the oral prodrug of fradafiban) or placebo, was studied before and during treatment using WBSP C, PRP turbidimetry, impedance aggregometry and Rapid Platelet Function Ass ay (RPFA, Accumetrics). RPFA, PRP turbidimetry and WBSPC measurements corre lated well. Impedance aggregometry responses were oversensitive to GPIIb/II Ia blockade. WBSPC was most discriminating at high levels of inhibition and offered a rapid means of monitoring GPIIb/IIIa antagonist effect within th e therapeutic range of inhibition.