Platelet glycoprotein IIb/IIIa blockade with tirofiban: effect on aggregation caused by P256, an antibody to human IIb/IIIa receptors

Aims P256 is a divalent antibody which aggregates human platelets by interaction with glycoprotein (GP) IIb/IIIa receptors. We investigated the effect of tirofiban, an antagonist of the GP IIb/IIIa receptor, on P256‐mediated platelet aggregation.

Methods Responses to agonists were measured turbidometrically at 37° C in stirred citrated platelet‐rich plasma from venous blood samples from healthy human volunteers. Inhibitory effects were determined by comparison with aggregation to the same concentration of agonist in a vehicle treated sample.

Results Tirofiban inhibited a near maximally effective dose of P256 (10⁻⁷ mol l⁻¹ ) with an IC₅₀ of 9.3×10⁻⁸ mol l⁻¹. Tirofiban (10⁻⁷ mol l⁻¹ ) inhibited responses to arachidonic acid, U46619 and P256 similarly, whereas aspirin (1.1×10⁻⁴ mol l⁻¹ ) inhibited arachidonic acid more effectively than P256 (P<0.007 by anova ).

Conclusions Tirofiban potently and selectively inhibits P256‐stimulated aggregation of human platelets.

DOI: 10.1046/j.1365-2125.1999.00990.x

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