thromboxane-a2 and fradafiban

We examined the contribution of cyclooxygenase (COX)-1 and -2 to the generation of prostacyclin, thromboxane (Tx) A(2), and 8-epi prostaglandin (PG) F(2alpha) during percutaneous transluminal coronary angioplasty (PTCA).. Both TxA(2) and 8-epi PGF(2alpha) activate platelets and are mitogenic, whereas prostacyclin is a platelet inhibitor, and therefore may influence the outcome of PTCA.. Twenty-one patients undergoing PTCA while receiving aspirin 300 mg daily or aspirin plus the selective COX-2 inhibitor nimesulide were compared with 13 patients treated only with fradafiban, a glycoprotein IIb/IIIa antagonist. Urine was analyzed for the metabolites of TxA(2) (Tx-M) and prostacyclin (PGI-M) and for the isoprostane, 8-epi PGF(2alpha).. In the fradafiban group, there was a marked increase in Tx-M during PTCA (mean, 1973; 95% confidence interval [CI] 112 to 3834 rising to mean 7645; 95% CI 2,009 to 13281 pg/mg creatinine, p = 0.018). The Tx-M excretion was similarly reduced by aspirin and the combination of aspirin and nimesulide. In contrast, the combination of nimesulide and aspirin inhibited PGI-M excretion to a greater extent than aspirin (p = 0.001). Urinary 8-epi PGF(2alpha) excretion was elevated following PTCA compared with normal subjects (p = 0.002) and appeared to be unaffected by any of the treatments.. The increase in TxA(2) during PTCA is primarily COX-1 dependent, and aspirin alone is effective in suppressing its formation. In contrast, prostacyclin generation is both COX-1 and COX-2 dependent. The inhibition of COX-1 and COX-2 did not prevent the production of 8-epi PGF(2alpha), suggesting that this is not enzymatically derived. The persistent generation of 8-epi PGF(2alpha) may contribute to the thrombosis and restenosis that complicate PTCA.

Topics: Angioplasty, Balloon, Coronary; Aspirin; Biphenyl Compounds; Cyclooxygenase 1; Cyclooxygenase 2; Dinoprost; Epoprostenol; Female; Humans; Isoenzymes; Male; Membrane Proteins; Middle Aged; Peroxidases; Platelet Aggregation Inhibitors; Platelet Glycoprotein GPIIb-IIIa Complex; Prostaglandin-Endoperoxide Synthases; Pyrrolidines; Sulfonamides; Thromboxane A2

Experimental data suggest that formation of thromboxane A2 may be suppressed during administration of a glycoprotein IIb/IIIa antagonist. We determined the dose of one such compound, fradafiban, required to provide > 80% occupancy of the platelet glycoprotein IIb/IIIa and examined its effects on thromboxane A2 formation in patients undergoing PTCA. The dose response to fradafiban and additional effects of aspirin were explored initially in patients with stable coronary artery disease. Fradafiban induced a dose-dependent inhibition of platelet aggregation that correlated with fibrinogen receptor occupancy and plasma drug concentration. Addition of aspirin 300 mg had no effect on these parameters. At the highest dose, mean fibrinogen receptor occupancy was 89.7 +/- 1.2% (n = 3) at 4 hours and platelet aggregation had decreased by 93.4 +/- 2.7%. Eighteen patients undergoing coronary angioplasty were randomized to receive either aspirin 330 mg or that dose of fradafiban producing > 80% fibrinogen receptor occupancy. Platelet aggregation was suppressed throughout the infusion of fradafiban to a greater extent than with aspirin. However, there was a marked increase in urinary excretion of 11-dehydrothromboxane B2 in patients treated with fradafiban: from 1973 +/- 889 to a peak of 9760 +/- 3509 pg/mg creatinine (P = .0046). Despite this evidence of continued platelet activation in vivo, there were no cases of coronary thrombosis. In conclusion, fradafiban suppresses platelet aggregation and may be a useful alternative to aspirin in the prevention of thrombotic events in patients undergoing PTCA. However, there is continued formation of thromboxane A2, which may continue to exert its effects as a potent vasoconstrictor and vascular smooth muscle mitogen.

Topics: Administration, Oral; Angioplasty, Balloon, Coronary; Anticoagulants; Aspirin; Biphenyl Compounds; Bleeding Time; Cell Division; Coronary Disease; Dose-Response Relationship, Drug; Double-Blind Method; Drug Therapy, Combination; Female; Fibrinogen; Heparin; Humans; Infusions, Intravenous; Male; Middle Aged; Muscle, Smooth, Vascular; P-Selectin; Pilot Projects; Platelet Aggregation; Platelet Aggregation Inhibitors; Platelet Glycoprotein GPIIb-IIIa Complex; Pyrrolidines; Thrombosis; Thromboxane A2; Thromboxane B2; Vasoconstriction