Tirofiban

Tirofiban is a selective platelet GPIIb/IIIa receptor antagonist with IC50 value of 9 nM, it inhibits platelet aggregation of gel-filtered platelets induced by 10 μM ADP. ^[1] 

The GPIIb/IIIa receptor is a heterodimer composed of alpha and beta subunits. Each subunit consists of a larger extracellular region, a transmembrane domain, and a short intracellular cytoplasmic tail. There are over 80,000 GPIIb/IIIa receptors present on the plasma membrane of platelets. These receptors are relatively quiescent in the dormant platelet. ^[2] 

In vitro, Tirofiban selectively inhibits the GP-IIb/IIIa receptor and have minimal effects on the ɑvβ3 vitronectin receptor.  It inhibits platelet aggregation of gel-filtered platelets induced by 10 μM ADP with IC50 of 9 nM, but the IC50 for inhibition of human umbilical vein adhesion to vitronectin, which depends on ɑvβ3 vitronectin receptors, is 62 μmol/L. ^[1] 

In vivo, Tirofiban inhibits platelet aggregation responses to ADP and collagen in canine models. When administered to humans at 0.15μg/kg/min for 4 h. Tirofiban produced a 2.5-fold increase in bleeding time and 97% inhibition of ADP-induced platelet aggregation. ^[3][4] 

References: 

[1] Egbertson MS, Chang CT, Duggan ME, et al. Non-peptide fibrinogen receptor antagonists. 2. Optimization of a tyrosine template as a mimic for Arg-Gly-Asp. J Med Chem. 1994 Aug 5; 37 (16):2537-51.

[2] Hofmann LV1, Razavi M, Arepally A, et al. GPIIb-IIIa receptor inhibitors: what the interventional radiologist needs to know. Cardiovasc Intervent Radiol. 2001 Nov-Dec; 24 (6):361-7.

[3] Barrett JS1, Murphy G, Peerlinck K, et al. Pharmacokinetics and pharmacodynamics of MK-383, a selective non-peptide platelet glycoprotein-IIb/IIIa receptor antagonist, in healthy men. Clin Pharmacol Ther. 1994 Oct; 56 (4):377-88.

[4] Peerlinck K1, De Lepeleire I, Goldberg M, et al. MK-383 (L-700,462), a selective nonpeptide platelet glycoprotein IIb/IIIa antagonist, is active in man. Circulation. 1993 Oct; 88 (4 Pt 1):1512-7.